Science and Discovery
Events · 240
- First Intermediate Period, c. 2181-2040 BCEHistory of Astronomy
Egyptians Divide the Night Sky Into 36 Decans
Egyptian astronomers charted the night sky as a 360-degree circle and divided it into 36 decans, small groups of stars that rose in sequence roughly every ten days across the year. Decans first appeared as star charts painted on coffin lids in the First Intermediate Period, and Egyptian priests used their staggered risings as a sidereal clock: a set of 12 decans visible on a given night changed gradually as the year went on, letting observers mark the passage of night hours by which decan had just appeared on the horizon. The system was tied to the Egyptian calendar's most important astronomical marker, the heliacal rising of the star Sopdet, known to the Greeks as Sothis and to modern astronomers as Sirius, which after roughly 70 days of invisibility reappeared in the pre-dawn sky each year at almost exactly the time the Nile's life-giving flood began.
Reputable source · 2 sources - c. 2000-1600 BCEHistory of Mathematics
Babylonian Scribes Solve Quadratic Equations on Clay Tablets
Babylonian mathematics, which replaced Sumerian mathematics in Mesopotamia from around 2000 BCE, used a positional number system with base 60 rather than base 10, the same system that survives today in 60 minutes to an hour and 360 degrees in a circle. Two tablets found at Senkerah on the Euphrates in 1854 date from 2000 BCE and list squares and cubes of integers up to 60. Babylonian scribes went further than arithmetic tables: to solve a quadratic equation they used essentially the standard formula still taught today, working through problems where, for example, a rectangle's area and the amount by which its length exceeds its breadth were both given, leaving the breadth to satisfy a quadratic. A separate tablet catalogued as BM 85200+, containing 36 problems of this type, is the earliest known attempt to set up and solve cubic equations.
Reputable source · 2 sources - c. 1900-1600 BCE (Old Babylonian period)History of Mathematics
The Babylonians Use the Pythagorean Relationship a Millennium Before Pythagoras
Four surviving Babylonian tablets from the Old Babylonian period, which flourished between 1900 and 1600 BCE, demonstrate a working knowledge of the relationship between the sides of a right triangle that would later be named Pythagoras's theorem. One tablet preserved in the British Museum poses and solves the problem directly: 4 is the length and 5 the diagonal, what is the breadth. Its worked solution runs, 4 times 4 is 16, 5 times 5 is 25, you take 16 from 25 and there remains 9, 3 times 3 is 9, 3 is the breadth. A second tablet, the Yale Babylonian Collection's YBC 7289, carries a diagram of a square with a diagonal drawn in and the value 1,24,51,10 written beside it, a sexagesimal approximation of the square root of 2 accurate to several decimal places. A third, known as Plimpton 322, lists number triples in which, in every row, the square of one number minus the square of a second is itself a perfect square, the defining property of Pythagorean triples.
Reputable source · 2 sources - c. 1650 BCEHistory of Mathematics
Egyptian Scribes Write the Rhind and Moscow Papyri
The Rhind Mathematical Papyrus, now in the British Museum, was written around 1650 BCE by a scribe named Ahmes, who states in the text that he is copying a document roughly 200 years older. It contains 87 problems, 81 of which involve operating with fractions, alongside a table expressing the fractions 2 divided by n, for every odd n from 3 to 101, as sums of fractions with a numerator of 1. A companion document, the Moscow Papyrus, dates from the same period, was written by a scribe whose name was not recorded, and contains 25 problems including geometric ones, among them a calculation of the volume of a truncated pyramid. Because Egyptian arithmetic had no convenient way to write general fractions, scribes built up quantities from sums of distinct unit fractions, a system practical enough for the trade, land-measurement, and bread- and beer-division problems that make up most of both papyri.
Reputable source · 2 sources - c. 1600 BCE (surviving copies; older originals)History of Medicine
Egyptian Physicians Write Down Surgery and Spells
Two surviving Egyptian papyri capture how medicine worked along the Nile more than 3,500 years ago. The Edwin Smith Papyrus, a copy dating to about 1600 BCE, is the oldest known work on surgical technique: it walks through case after case of traumatic injury with examination, treatment, and prognosis, and several of its cases describe the brain, its coverings, and cerebrospinal fluid for the first time in recorded history. The Ebers Papyrus of about 1550 BCE is a different kind of book, a compendium of some 876 prescriptions built from hundreds of ingredients, treating conditions from heart disease and diabetes to a despondency that reads like depression. It also records more than 700 magical formulas. Egyptian medicine did not separate the empirical from the magical; both were understood as legitimate ways to heal.
Peer-reviewed · 2 sources - c. 1050 BCE (Diagnostic Handbook)History of Medicine
Mesopotamia Splits Healing Between the Physician and the Exorcist
In ancient Mesopotamia a sick person could turn to one of two healers: the asu, a doctor who treated illness or injury empirically with drugs and dressings, or the asipu, who relied on what we would call magic. There is no sign in the ancient texts that one path was considered more legitimate than the other. The Babylonian physician Esagil-kin-apli made additions to the Diagnostic Handbook, a medical treatise compiled by various authors, and organized it around a logical idea: that one should inspect a patient's symptoms to arrive at a diagnosis, and could use those symptoms to judge cause and likely outcome. Alongside symptom reading, diagnosis leaned heavily on omens; one entry warns that if the healer sees a black dog or black pig on the way to a patient, the sick man will die.
Reputable source · 2 sources - c. 1000 BCEHistory of Astronomy
Babylonian Priests Use Ziggurats to Track the Stars
Babylonian priests observed the sky from the tiered temple towers called ziggurats that rose above every major Mesopotamian city. The Greek historian Diodorus Siculus, writing centuries later, recorded that Babylonian astronomers used the height of these structures to make their observations of the stars, whose risings and settings could be accurately observed by reason of the height of the structure. Ziggurats were built primarily as religious monuments to the city's patron god, but their height made them a natural platform for tracking celestial bodies against the horizon, work that fed directly into the astronomical omen texts and star catalogs Babylonian scribes kept on clay tablets for centuries.
Reputable source · 2 sources - before the 8th century BCEHistory of Astronomy
MUL.APIN Compiles Babylonia's Star Catalog
Babylonian scribes compiled MUL.APIN, a two-tablet cuneiform compendium that became the most widely copied astronomical text in ancient Mesopotamia. It lists the names of 66 stars and constellations and gives rising, setting, and culmination dates for them, organizing the sky into three celestial paths assigned to the gods Enlil, Anu, and Ea. Alongside the star list, MUL.APIN records planetary phases, mathematical schemes for the changing length of day and night across the year, rules for the luni-solar calendar, and a short collection of celestial omens linking sky events to predictions for the king and the state. The text survives in roughly 40 to 60 manuscript copies spanning from the Neo-Assyrian period through the Seleucid era, a span of some seven centuries.
Reputable source · 2 sources - c. 585 BCEHistory of Western Philosophy
Thales Declares That Everything Is Water
Thales of Miletus, active in the early 6th century BCE, was the first thinker on record to ask what the natural world is fundamentally made of and to answer with a single material principle rather than a myth. Aristotle later credited him with declaring water to be the arche, the originating substance behind change, nutrition, and growth. Thales left no writings; everything attributed to him comes through later writers, chiefly Aristotle, more than two centuries afterward. Ancient tradition also credits him with predicting a solar eclipse, usually dated to 585 BCE, though modern scholars who have examined the claim conclude the specific mechanism ancient sources describe almost certainly could not have worked, even if Thales did have some general basis for anticipating the event.
Reputable source · 2 sources - 28 May 585 BCEHistory of Astronomy
Thales Predicts a Solar Eclipse and Stops a War
According to the Greek historian Herodotus, the philosopher Thales of Miletus predicted a solar eclipse that occurred on 28 May 585 BCE, in the middle of a long war between the Medes and the Lydians. Herodotus wrote that day was all of a sudden changed into night, an event that had been foretold by Thales, who forewarned the Ionians of it, fixing for it the very year in which it took place. The Medes and Lydians, watching the sky darken mid-battle, ceased fighting and moved to negotiate peace. Modern historians are skeptical that Thales could have genuinely predicted the eclipse's timing using the astronomical knowledge available in early sixth-century BCE Greece, and suggest his later reputation as a predictor may rest on having simply been the recognized wise man present when a dramatic, independently occurring eclipse happened to fall near a date he had floated.
Reputable source · 2 sources - c. 530 BCEHistory of Mathematics
Pythagoras Founds a Brotherhood Built on Number
Pythagoras, born around 570 BCE and dead by around 490 BCE, left no writings of his own, and the secrecy code followed by the society he founded at Croton in southern Italy means historians today treat him as a genuinely mysterious figure, with early biographers attributing divine powers to him that make separating fact from legend difficult. The Pythagorean society had two tiers of membership: an inner circle called the mathematikoi, who lived communally, held no personal possessions, and were vegetarians taught directly by Pythagoras, and an outer circle called the akousmatics, who kept their own homes and property. Both men and women were permitted to join. The society held that whole numbers and their ratios were the key to understanding the universe, a belief the discovery of irrational numbers, certainly attributed to the Pythagoreans though unlikely to be due to Pythagoras himself, directly contradicted, since a number like the square root of 2 cannot be written as any ratio of whole numbers at all.
Reputable source · 2 sources - c. early-to-mid 5th century BCEHistory of Western Philosophy
Heraclitus and Parmenides Split Philosophy Over Change
Heraclitus of Ephesus, active around 500 BCE, argued that the world is defined by constant change, a doctrine later summarized as panta rhei, everything flows. His surviving fragment on rivers puts it directly: stepping into the same river, one encounters different waters flowing past each time. He also described a rational structure underlying that flux, the logos, which most people fail to grasp even though it is common to all. Parmenides of Elea, active in the early 5th century BCE, argued the opposite in his poem On Nature: what fully is cannot come from what is not, and what is cannot cease to be, so genuine change and motion are illusions produced by the senses rather than features of reality itself. Neither philosopher's work survives complete; both are known only through fragments quoted by later writers.
Reputable source · 2 sources - c. mid-5th century BCE onwardHistory of Western Philosophy
Socrates Practices the Elenchus in the Athenian Agora
Socrates of Athens, born around 469 BCE, spent his adult life questioning fellow citizens in the Agora about virtue, justice, and knowledge, using a method now called the elenchus: cross-examining a stated position or definition until its holder's own commitments contradict it. Socrates wrote nothing himself. Everything known about his views comes secondhand, chiefly through the dialogues of his student Plato and the memoirs of Xenophon, and the two portraits do not always agree, a problem scholars call the Socratic problem. His method aimed less at teaching answers than at exposing unrecognized ignorance in people who assumed they already understood concepts like courage or piety.
Reputable source · 2 sources - 430-426 BCEPandemics Through History
The Plague of Athens Strikes a City at War
In 430 BCE, the second year of the Peloponnesian War, an epidemic broke out in Athens, crowded far beyond its normal population because the countryside had emptied into the city walls for protection from Spartan raids. The historian Thucydides, who caught the disease and survived, recorded its course in detail: victims suffered sudden head fever, red and inflamed eyes, a bloody, foul-smelling throat, violent coughing, vomiting, pustules and ulcers over the skin, and unquenchable thirst, with death typically arriving seven to nine days in. Survivors often lost fingers, toes, eyesight, or their memory entirely. The outbreak recurred over roughly four years and, by ancient estimate, killed upwards of a third of the city's 250,000 to 300,000 residents, including the statesman Pericles.
Peer-reviewed · 2 sources - c. 460-370 BCE (life of Hippocrates)History of Medicine
Hippocrates Moves Illness From the Gods to the Body
Hippocrates was born on the Greek island of Kos in the 5th century BCE and became the most famous physician of antiquity. Historians credit him with turning medicine away from the supernatural and religious framework tied to the healing god Asclepius, toward observation, classification, and the tracing of causes and effects. Central to this approach was the humoral theory of health: the idea that four bodily fluids, blood, phlegm, yellow bile, and black bile, had to be kept in balance for a person to stay well. The Hippocratic Corpus, the collected writings attributed to him, contains about sixty works spanning diagnosis, epidemics, obstetrics, pediatrics, nutrition, and surgery. Whether Hippocrates himself wrote any of it is genuinely uncertain. Modern scholars conclude on stylistic grounds that the texts came from multiple authors, and note that no source from his own lifetime records him writing anything at all.
Reputable source · 2 sources Athens Tries and Executes Socrates
In 399 BCE an Athenian jury tried Socrates on formal charges that he failed to recognize the gods the city recognized, introduced new divinities of his own, and corrupted the young through his teaching and questioning. He was convicted and sentenced to death. Rather than accept exile or escape, an option his friends offered him, Socrates accepted the sentence and was executed by drinking hemlock, choosing to honor what he took to be his obligations to the laws of Athens over his own survival.
Reputable source · 2 sources- c. 387 BCEHistory of Western Philosophy
Plato Founds the Academy
Plato, born around 428/427 BCE, gathered a circle of fellow philosophers in Athens that gradually developed into the institution known as the Academy, named for the sacred grove of the hero Academus where it met, just outside the city walls. Scholars place the founding anywhere from 387 to 383 BCE, depending on how they date Plato's return from his first trip to Syracuse, and the school appears to have grown gradually rather than opening on a fixed date. The Academy remained Plato's base for the rest of his life and continued after his death in 347 BCE, surviving as an institution until the Roman general Sulla destroyed its grove and gymnasium in 86 BCE, though thinkers identifying as Platonists carried on in Athens for centuries after that.
Reputable source · 2 sources - c. 375 BCE (Republic)History of Western Philosophy
Plato Sets Out the Theory of Forms
In dialogues including the Republic, Plato argued that the physical world perceived by the senses is defective and changeable, while a separate, more real realm of Forms, eternal and unchanging entities such as Equality, Beauty, and the Good, provides the true objects of knowledge and the standard the visible world only imperfectly resembles. In the Republic, Plato used this framework to argue that the ideally just city would be ruled by philosopher-kings, people equipped by education and temperament to grasp the Forms directly, and that justice in an individual soul consists of each part of the soul, reason, spirit, and appetite, performing its proper role rather than overriding the others.
Reputable source · 2 sources - 4th century BCEHistory of Astronomy
Eudoxus Builds the First Geometric Model of the Heavens
In the fourth century BCE, the mathematician Eudoxus of Cnidus, a student of Archytas who had also studied under Plato, developed the earliest known geometric model of the cosmos in the Greek tradition. He proposed that the stars were fixed on a celestial sphere that rotated about a spherical, stationary Earth once every 24 hours, while the planets, Sun, and Moon each moved through their own systems of nested, rotating spheres set between the Earth and the outer sphere of stars. Eudoxus adopted Plato's assumption of a fixed, central Earth and expanded it into a working mathematical mechanism, arguing for planetary rotation on axes carried within these spheres, an approach that could reproduce the basic pattern of planetary motion even though it struggled with the observed changes in planetary brightness that a purely circular, Earth-centered model could not easily explain.
Reputable source · 2 sources - c. 350 BCEHistory of Physics
Aristotle Writes the Physics
Aristotle set out the first systematic theory of motion and matter in his treatise Physics, likely composed as lecture notes for his school in Athens around 350 BCE. He held that all terrestrial matter was made of four elements, earth, water, air, and fire, each defined by a pair of qualities such as hot, cold, wet, or dry, and each with a natural place in a cosmos centered on the stationary Earth. Earth and water had a natural tendency to fall toward the center, while air and fire had a natural tendency to rise, and objects displaced from their natural place moved back toward it in straight lines until they arrived and stopped. Celestial bodies, made of a separate fifth element, moved instead in perfect, eternal circles. Aristotle held that heavier objects fell faster than lighter ones, and that a moving object required a continuous mover in contact with it, since motion without a sustaining cause was, to him, unnatural.
Reputable source · 2 sources Aristotle Founds the Lyceum
Aristotle arrived in Athens at age seventeen and studied at Plato's Academy for twenty years, remaining until Plato's death in 347 BCE. After years away, including time tutoring the young Alexander of Macedon, Aristotle returned to Athens in 335 BCE and founded his own school in a public exercise ground dedicated to Apollo Lykeios, which gave the school its name, the Lyceum. Aristotle rejected Plato's theory of Forms as a separate realm, arguing instead that forms exist embedded in particular things, and he built the first formal system of logic, an account of four kinds of causes (material, formal, efficient, and final), and an empirical program that extended into biology, drawing on direct observation rather than argument from first principles alone.
Reputable source · 2 sources- c. 306 BCEHistory of Western Philosophy
Epicurus Founds the Garden
Epicurus, born in 341 BCE, founded philosophical schools in Mytilene and Lampsacus before moving to Athens around 306 BCE, where he purchased a property that became known as the Garden, a name that later applied to his school as a whole. Epicurus taught that pleasure is the highest good, but defined the goal of life not as active sensory indulgence but as ataraxia, freedom from mental disturbance, paired with freedom from bodily pain. Achieving this state, in his view, required banishing needless fears, particularly fear of the gods and of death, through a materialist physics that explained the world without divine intervention in human affairs.
Reputable source · 2 sources - c. 300 BCEHistory of Mathematics
Euclid Compiles the Elements
Euclid, who taught at Alexandria in Egypt and about whom almost nothing else biographical is known, compiled the Elements around 300 BCE, a work of 13 books that organizes existing Greek and Near Eastern mathematical knowledge into a single logical structure. Books 1 through 6 cover plane geometry, Books 7 through 9 cover number theory, Book 10 covers irrational numbers, and Books 11 through 13 cover three-dimensional geometry. The entire structure rests on five postulates, including that a straight line can be drawn between any two points and that all right angles are equal, plus a short list of common notions, and every subsequent proposition is derived from these through strict deductive proof rather than asserted from authority or measurement. A manuscript of the complete work, copied by Stephen the Clerk for Arethas of Patras in Constantinople in 888 CE, survives today in Oxford's Bodleian Library.
Primary source · 2 sources - c. 300 BCEHistory of Western Philosophy
Zeno of Citium Founds Stoicism at the Painted Porch
Zeno of Citium, a voracious reader of Socratic dialogues who had studied under the Cynic philosopher Crates and been influenced by Plato's Academy and the Megarian school, founded the Stoic school in Athens around 300 BCE. It took its name from the Stoa Poikile, the painted porch in the Athenian agora where Zeno and his followers met and lectured. Stoic ethics held that virtue, prudence, justice, courage, and moderation, is the only true good, and that external things like health, wealth, and reputation are properly indifferent to a person's happiness. The Stoic aim, later summarized by the successor Cleanthes, was living in agreement with nature: aligning human reason with the rational order the Stoics believed structured the cosmos.
Reputable source · 2 sources - c. 270 BCEHistory of Astronomy
Aristarchus Proposes a Sun-Centered Universe, 1,700 Years Too Early
Aristarchus of Samos, working in the third century BCE, proposed that the earth revolves about the sun on the circumference of a circle, with the sun lying in the middle of the orbit, making him the first known Greek astronomer to argue for a heliocentric universe rather than an Earth-centered one. In his one surviving work, On the Sizes and Distances of the Sun and Moon, Aristarchus used geometric reasoning based on the angle between the Sun and Moon at half-moon to estimate that the sun was between 18 to 20 times as far away as the moon, an estimate far too small by modern measurement but methodologically sound in its approach. His heliocentric idea itself does not survive in his own writing and is known only through references by later authors, including Archimedes.
Reputable source · 2 sources - c. 250 BCEHistory of Physics
Archimedes Formulates the Law of the Lever and the Principle of Buoyancy
Archimedes of Syracuse (c. 287-212 BCE) put mechanics on a mathematical footing. In his treatise On the Equilibrium of Planes he proved the law of the lever, that magnitudes balance at distances inversely proportional to their weights, turning a tool already in common use into a provable geometric relationship. In On Floating Bodies he laid down what is now called Archimedes' principle: an object immersed in a fluid experiences an upward force equal to the weight of the fluid it displaces. World History Encyclopedia is careful to separate the physics from the famous legend attached to it: the story that Archimedes discovered buoyancy in his bathtub and ran through the streets of Syracuse shouting Eureka comes from the Roman writer Vitruvius, writing around two centuries after Archimedes' death, and a McGill University analysis notes that even Vitruvius's account describes a cruder volume-displacement test for a suspected fraudulent crown, not the buoyancy principle itself.
Reputable source · 2 sources - 212 BCEHistory of Mathematics
Archimedes Calculates Pi and Dies Defending Syracuse
Archimedes, born around 287 BCE, perfected a method of integration, now called the method of exhaustion, that let him calculate areas, volumes, and surface areas of curved shapes long before calculus existed as a formal discipline. In Measurement of the Circle he showed that pi lies strictly between 3 10/71 and 3 1/7, a bound tight enough to be useful for engineering for the next 1,800 years. He also proved that the volume of a sphere is two-thirds the volume of its circumscribing cylinder, and that the sphere's surface area holds the same two-thirds ratio to the cylinder's surface area, a result he considered his most significant accomplishment and asked to have inscribed, alongside a diagram of a sphere and cylinder, on his own tomb. Archimedes was killed in 212 BCE during the Roman capture of Syracuse in the Second Punic War.
Reputable source · 2 sources - c. 200 BCE (later commentary 263 CE)History of Mathematics
China's Nine Chapters Solves Linear Systems and Names Negative Numbers
The Nine Chapters on the Mathematical Art, the most famous Chinese mathematics book of all time, most historians believe originated around 200 BCE, after the burning of books ordered by Shih Huang Ti destroyed much earlier material, though the mathematician Liu Hui, who wrote an influential commentary on it in 263 CE, believed the core text dated back a thousand years earlier and had simply absorbed material from later eras. The book poses 246 practical problems covering engineering, surveying, trade, and taxation, unlike Greek mathematics, it develops no axiomatic system of proof, working instead from problems toward methods. Its eighth chapter solves systems of simultaneous linear equations by arranging coefficients in an augmented matrix and reducing it to triangular form using column operations, the same procedure now called Gaussian elimination, seventeen centuries before Gauss. Solving these systems required working with negative quantities partway through the calculation, and the chapter includes explicit rules for computing with negative numbers, one of the earliest formal treatments of negative numbers anywhere in the historical record.
Reputable source · 2 sources - c. 150 CEHistory of Astronomy
Ptolemy Publishes the Almagest
Working in Alexandria, the astronomer Claudius Ptolemy completed the Almagest around 150 CE, drawing on astronomical observations he made between 127 and 141 CE, with his first precisely dated observation recorded on 26 March 127 and his last on 2 February 141. The work's original Greek title translates as The Mathematical Compilation, later shortened to The Greatest Compilation, a phrase that entered Arabic as al-majisti and passed into Latin, and then English, as Almagest. Across thirteen books, Ptolemy laid out in detail the mathematical theory of the motions of the Sun, Moon, and planets around a fixed, central Earth, and Books 7 and 8 contain a star catalog of over one thousand stars, whose observational originality relative to the earlier work of Hipparchus remains disputed among historians. Ptolemy's system described the sphere of the fixed stars rotating around a stationary Earth once daily, carrying with it the spheres of the sun, moon, and planets.
Reputable source · 2 sources - c. 129-216 CE (life of Galen)History of Medicine
Galen Dissects Animals and Rules European Medicine for a Millennium
Galen was a Greek physician who worked in Rome and built the most complete system of anatomy and physiology in the ancient world. In 157 CE he returned to Pergamon to serve as physician to a troupe of gladiators, a post that let him study the body through their wounds, and in Rome he gave public anatomical demonstrations using pigs, monkeys, sheep, and goats. Roman law and custom forbade human dissection, so Galen inferred human anatomy from animals, which introduced errors that would go uncorrected for centuries. He became court physician to the emperors Marcus Aurelius, Commodus, and Septimius Severus. For more than a thousand years after his death, Galen's treatises were read and studied across Europe as the authoritative account of how the body worked, so thoroughly that later physicians tended to trust his texts over their own eyes.
Reputable source · 2 sources - 165-180 CEPandemics Through History
The Antonine Plague Follows Roman Legions Home
Roman troops besieging the city of Seleucia on the Tigris in 165 CE brought a new disease back with them, and it spread north and west along military supply lines to Gaul and the Rhine frontier. The Greek physician Galen, who treated cases in Rome and left the fullest surviving account, described fever, diarrhea, vomiting, an inflamed throat, and a skin eruption that appeared around the ninth day of illness, a symptom pattern that has led most modern researchers to conclude the disease was smallpox, though measles remains a competing candidate. Roman citizens had no prior exposure to either virus, so the outbreak moved through a fully susceptible population for fifteen years, killing at a rate estimated at up to 2,000 people daily in Rome at its worst.
Reputable source · 2 sources - 249-262 CEPandemics Through History
The Plague of Cyprian Spreads Through a Crumbling Empire
A new epidemic appeared around Easter of 249 or 250 CE, first recorded in Egypt in the letters of Bishop Dionysius of Alexandria, then spreading across the Mediterranean and reaching Rome by 251. At its height the disease reportedly killed as many as 5,000 people a day in the city. Cyprian, the bishop of Carthage, recorded the symptoms in his treatise On Mortality: diarrhea, continuous vomiting, fever, deafness, blindness, paralysis of the legs and feet, swollen throats, and eyes filled with blood. Two emperors, Hostilian in 251 and Claudius II Gothicus in 270, are recorded as having died of it. The outbreak recurred in waves for roughly two decades.
Reputable source · 2 sources - c. 200-284 CEHistory of Mathematics
Diophantus Writes the Arithmetica and Gives Algebra Its Name
Almost nothing is known about Diophantus as an individual; historians place him in Alexandria, Egypt, sometime in the 3rd century CE, with dates of roughly 200 to 284 CE most often quoted, and even this range rests on indirect evidence rather than firm biographical record. His major surviving work, the Arithmetica, originally comprised 13 books of which only 6 survive in the original Greek, with others surviving in Arabic translation, and it collects 189 problems in algebra and number theory along with their solutions. Unlike earlier Greek mathematics, which had expressed problems in words, Diophantus introduced algebraic symbols to represent unknowns and operations, solving determinate and indeterminate equations by genuinely algebraic rather than purely geometric means, a method later called Diophantine analysis, from which the modern term Diophantine equation derives.
Reputable source · 2 sources - c. 397-400 CEHistory of Western Philosophy
Augustine Writes the Confessions
Augustine, born in 354 CE in Roman North Africa and later bishop of Hippo, wrote the Confessions around 397 to 400 CE, a work that scholars describe as philosophy conducted in the form of autobiography rather than autobiography in the modern sense. In it Augustine wove Christian theology together with ideas drawn from Platonism, examining memory, time, the nature of evil, and the will, which he defined in relation to sin as the will to pursue or keep something unjustly. Augustine's broader philosophical position held that everything that exists is good insofar as God created it, with evil understood not as a positive substance but as a privation, a lack or corruption of a good that should be present.
Reputable source · 2 sources - 499 CEHistory of Mathematics
Aryabhata Writes the Aryabhatiya and Approximates Pi
Aryabhata, born in 476 CE probably near modern Patna, finished the Aryabhatiya in 499 CE at the age of 23, a treatise of 118 verses summarizing Indian mathematics and astronomy up to that point. In it he gave a rule for the circumference of a circle that reduces to pi equal to 3.1416, a value scholars consider the most accurate approximation among the ancients and very close to the modern figure. Aryabhata also gave a table of sine values at intervals of 90 degrees divided by 24, introduced the versine into trigonometry, and, according to later scholarly assessment, extremely likely knew both the symbol for zero and the numerals of the place-value system that his work depended on for its calculations.
Reputable source · 2 sources - 541-549 CEPandemics Through History
The Plague of Justinian Opens the First Yersinia Pestis Pandemic
In 541 CE an epidemic began in the Byzantine Empire, reported first at the Egyptian port of Pelusium and reaching the capital Constantinople in 542, where the historian Procopius recorded it striking as many as 10,000 people a day at its worst under Emperor Justinian I, who caught the disease himself and survived. What became known as the First Pandemic recurred in waves across the Mediterranean and Europe for roughly two centuries, until about 750. For most of history the pathogen was inferred only from written symptoms; that changed when ancient DNA studies recovered Yersinia pestis genetic material from human teeth in a mass grave beneath the Roman hippodrome at Jerash, Jordan, near the outbreak's likely epicenter, and from burial sites across Britain, France, Germany, and Spain, directly confirming the bacterium responsible.
Peer-reviewed · 2 sources - 628 CEHistory of Mathematics
Brahmagupta Defines Zero as a Number
Zero had two distinct roles to fill: as an empty-place indicator in a positional number system, a use with earlier precedents, and as a number in its own right that could be added, subtracted, and multiplied like any other. Brahmagupta, born in 598 CE and head of the astronomical observatory at Ujjain, then India's foremost mathematical center, closed the second gap in his 628 CE treatise the Brahmasphutasiddhanta. He defined zero as the result of subtracting a number from itself and gave explicit rules: when zero is added to a number or subtracted from a number, the number remains unchanged, and a number multiplied by zero becomes zero. He phrased other rules in terms of fortunes, positive numbers, and debts, negative numbers, stating that a debt minus zero is a debt and a fortune minus zero is a fortune. He also attempted rules for dividing by zero, though this was the one operation his framework could not correctly resolve.
Reputable source · 2 sources - early 9th century CEHistory of Astronomy
Al-Ma'mun Founds Baghdad's House of Wisdom and Its Observatories
After becoming caliph around 813 CE, al-Ma'mun founded an academy in Baghdad called the House of Wisdom, where scholars translated Greek philosophical and scientific works, including astronomical texts, into Arabic. Astronomers and mathematicians such as al-Khwarizmi worked there, with tasks that involved the translation of Greek scientific manuscripts alongside original study and writing on algebra, geometry, and astronomy. Al-Ma'mun did not stop at translation: beyond the House of Wisdom, he set up observatories in which Muslim astronomers could build on the knowledge acquired by earlier peoples, giving Baghdad's scholars the instruments to test Ptolemy's Greek astronomy against fresh observation rather than simply reproducing it.
Reputable source · 2 sources - c. 820 CEHistory of Mathematics
Al-Khwarizmi Writes the Book That Names Algebra
Muhammad ibn Musa al-Khwarizmi, born around 780 CE and dead around 850 CE, worked alongside the Banu Musa brothers as a scholar associated with the House of Wisdom under the patronage of the Caliph al-Mamun in Baghdad. There he wrote a treatise titled Hisab al-jabr w'al-muqabala, the calculation of restoring and balancing, whose two key Arabic operations, al-jabr, moving negative terms to the other side of an equation, and al-muqabala, combining like terms, gave systematic methods for solving linear and quadratic equations. The word algebra comes directly from al-jabr in this title. Al-Khwarizmi also wrote a treatise expounding the Hindu decimal place-value system, which had arrived in the Islamic world from India only recently at that point, and its 12th-century Latin translation, titled Algoritmi de numero Indorum, is the source of the modern word algorithm, a Latinization of his own name.
Reputable source · 2 sources - observations 877-918 CE, catalog based on 880 CEHistory of Astronomy
Al-Battani Refines Ptolemy's Astronomy With a New Star Catalog
Al-Battani, born near Harran and active between 877 and 918 CE, made highly precise astronomical observations at Antioch and ar-Raqqah in Syria, producing a star catalog based on the year 880 CE that recorded 489 stars. He refined the existing values for the length of the year, which he gave as 365 days, 5 hours, 46 minutes, and 24 seconds, and for the length of the seasons, and he calculated the annual precession of the equinoxes at 54.5 arc-seconds per year while obtaining a value of 23 degrees 35 minutes for the inclination of the ecliptic. Rather than relying purely on Ptolemy's geometric constructions, al-Battani applied trigonometric methods to astronomical calculation, an important advance in how positions and motions were computed. His major compendium of astronomical tables was later translated into Latin around 1116 and into Spanish in the 13th century, with a printed edition appearing in 1537.
Reputable source · 2 sources - c. 865-925 CE (life of al-Razi)History of Medicine
Al-Razi Separates Smallpox From Measles
Abu Bakr Muhammad ibn Zakariya al-Razi, known to Europeans as Rhazes, was one of the most influential physicians of the medieval Islamic world. Working in and around the Persian city of Rayy, near modern Tehran, he left behind over a thousand recorded case histories that document his working life as a clinician. In his treatise On Smallpox and Measles he differentiated between the two diseases for the first time, giving detailed clinical descriptions of each and suggesting treatments matched to the severity of the symptoms. This mattered because the two illnesses, which look superficially similar in their early rashes and fevers, had long been treated as a single condition. His birth and death years vary across sources; the most frequently cited dates are 865 to 925 CE.
Peer-reviewed · 2 sources - c. 1025 CE (Canon compiled)History of Medicine
Ibn Sina Writes the Canon of Medicine
Ibn Sina, known in the West as Avicenna, was born around 980 near Bukhara in Central Asia and died in 1037, by which time he was regarded as one of the greatest philosophers of Islam and compared in medicine to Galen himself. His Canon of Medicine, compiled around 1025, was a comprehensive medical encyclopedia that synthesized Greek, Roman, and Persian knowledge with his own clinical observations. It was not merely influential in its own time and place: the Canon remained the most popular medical textbook in the world over the following six centuries, and it was still being used in medical schools until 1674, especially in Italian universities such as Padua and Bologna. Its opening book, covering medical philosophy and physiology, long served as the standard introduction to medical theory for new students.
Peer-reviewed · 2 sources - 11th-14th centuriesPandemics Through History
Leprosy Peaks in Medieval Europe, Then Mysteriously Recedes
Leprosy, caused by the slow-growing bacterium Mycobacterium leprae, had been present in Britain since at least the 4th century CE, but it became far more common between the 11th and 14th centuries, tracked by a surge in dedicated leprosy hospitals called leprosaria built to isolate the afflicted. Researchers sequenced M. leprae genomes from two skeletons, radiocarbon dated to 955-1033 CE and 1020-1162 CE, excavated at the St Mary Magdalen leprosarium near Winchester, England; both carried a lineage still found in modern leprosy cases, and both individuals showed the bone damage to the face and limbs characteristic of advanced infection. From the 14th century onward the disease declined sharply across Europe, and leprosaria were abandoned or repurposed; the last recorded case in Britain died in an Edinburgh hospital in 1798.
Peer-reviewed · 2 sources - c. 1070 CEHistory of Mathematics
Omar Khayyam Solves Cubic Equations With Conic Sections
Omar Khayyam, born in 1048 in Nishapur, Persia, is remembered today largely for the Rubaiyat, the collection of nearly 600 four-line verses made famous in the West by Edward Fitzgerald's 1859 translation, but his mathematical work was substantial in its own right. In a treatise on algebra, Khayyam gave a complete classification of cubic equations and, for each type, a geometric method of solving it by intersecting conic sections, such as a parabola with a circle, results Greek mathematicians had never achieved for cubics despite mastering conics themselves. He stated his ambition directly: if the opportunity arose he intended to give all fourteen forms of cubic equations with their branches and cases, and how to distinguish whatever is possible or impossible in each. Separately, in 1079, Khayyam was one of eight scholars commissioned to reform the Persian calendar, producing the Jalali calendar based on a year length of 365.24219858156 days, a figure very close to the modern measurement.
Reputable source · 2 sources - 9th-13th centuries CE (bimaristan tradition)History of Medicine
Islamic Hospitals Treat Everyone, Free of Charge
Across the medieval Islamic world, hospitals called bimaristans developed into organized public institutions unlike anything before them. They were established as charities and provided free services: patients seen as outpatients or admitted for inpatient care were given free medication, and their meals, heating, and lighting were covered as well. The wards were separated by disease and by sex, with distinct halls for internal illness, for trauma and fractures, and for communicable disease, plus sections for recovering patients. A psychiatric bimaristan operated in Baghdad in the 9th century, Ibn Tulun founded a hospital in Egypt in 872, and the later Bimaristan al-Mansuri in Cairo ran on a charter promising to keep every patient, man or woman, until fully recovered, with all costs borne by the hospital. Funding came from endowments, the income from shops, inns, baths, bridges, and fields dedicated to sustain the institutions for the long term.
Peer-reviewed · 2 sources - 12th-13th centuries CEHistory of Western Philosophy
The Latin West Recovers Aristotle Through Arabic Translation
Through the 12th and 13th centuries, scholars working especially in Toledo and Sicily translated a large body of Aristotle's works into Latin, in many cases by way of Arabic versions rather than directly from the original Greek, giving philosophers in the Christian West access to far more of Aristotle's corpus than had been available since antiquity. The Andalusian philosopher Averroes (Ibn Rushd, 1126-1198) wrote extensive commentaries on Aristotle that were themselves translated into Latin and became indispensable guides for Christian scholars trying to understand the newly available texts. By around 1270 nearly all of Aristotle's genuine works, along with some spurious ones attributed to him, were available for study, and the recovery transformed the university curricula that were then taking shape across Europe.
Reputable source · 2 sources - 1202 CEHistory of Mathematics
Fibonacci Publishes Liber Abaci and Brings Hindu-Arabic Numerals to Europe
Leonardo of Pisa, known as Fibonacci, was born around 1170 in Pisa but educated in North Africa, where his father Guilielmo held a diplomatic post representing Pisan merchants in Bugia, in modern Algeria. There Fibonacci learned mathematics and traveled widely with his father, encountering the Hindu-Arabic numeral system already established across the Islamic world since al-Khwarizmi's time. In 1202 Fibonacci published Liber Abaci, which introduced the Hindu-Arabic place-valued decimal system and Arabic numerals to a European audience still using Roman numerals for calculation. The book also poses a problem about a pair of rabbits that produces a new breeding pair every month starting from their second month, generating the sequence 1, 1, 2, 3, 5, 8, 13, 21, 34, 55 and onward, which later became known as the Fibonacci sequence.
Reputable source · 2 sources - 1265-1274 CEHistory of Western Philosophy
Aquinas Synthesizes Aristotle and Christian Theology in the Summa Theologiae
Thomas Aquinas, born around 1225 and a Dominican friar, composed the Summa Theologiae between 1265 and his death in 1274, a comprehensive work that draws on the newly recovered Aristotle to address nearly the whole of Aquinas's philosophical and theological concerns. Aquinas held that sound theology presupposes sound philosophical argument, and in the Summa's first part he offered five arguments, the Five Ways, for God's existence, three of them cosmological arguments resting on the claim that an infinite regress of causes is impossible. Each of the five ends with a version of the same formula: this is what everyone calls God.
Reputable source · 2 sources - 1347-1351Pandemics Through History
The Black Death Kills a Third of Europe in Four Years
The Black Death began in Central Asia and reached Europe in October 1347, when Genoese ships fleeing the besieged Black Sea port of Caffa docked at Messina, Sicily, carrying Yersinia pestis-infected fleas on the black rats that traveled aboard merchant vessels. Within three years the disease had spread to nearly every part of the continent, moving through both the bubonic form, marked by swollen, blackened lymph nodes in the groin and armpits, and the more lethal pneumonic form that spread person to person through the air. Contemporary chroniclers describe fever, joint pain, and death within days in untreated cases; the disease killed an estimated 25 to 30 million people in Europe, between 30 and 50 percent of the population in the hardest-hit regions, and Europe's population did not recover to its pre-1347 level until around 1550.
Peer-reviewed · 2 sources - c. 1320-1360 CEHistory of Physics
Medieval Scholars Break With Aristotle on Motion
In 14th-century Paris, the philosopher Jean Buridan proposed that a thrown object keeps moving not because it needs a continuous outside mover, as Aristotle held, but because the thrower impresses on it a quantity he called impetus, which the object retains until air resistance and its own weight wear it down. The MacTutor History of Mathematics archive credits Buridan with adding to Aristotle's theory of motion by recognizing that motion was retarded by resistance from the air, a genuine break from strict Aristotelian doctrine. Buridan's student Nicole Oresme went further mathematically: he became the first to prove the Merton College mean speed theorem, that a body moving under uniform acceleration for a fixed time covers the same distance as a body moving at a constant speed equal to its velocity at the midpoint of that time, a rule first stated by Oxford's Merton College scholars and later central to Galileo's own law of falling bodies.
Primary source · 2 sources - 1347-1352 CE (plague); 1377 quarantine at RagusaHistory of Medicine
The Black Death Breaks Galenic Medicine and Forces Quarantine
The plague epidemic that ravaged Europe between 1347 and 1352 killed an estimated 30 million people there and many more elsewhere. Physicians trained in the Galenic and humoral tradition were nearly helpless against it. That failure, historians note, came largely from strict adherence to ancient authorities and a reluctance to change the model of the body the ancients had handed down. The one measure that actually slowed the disease was not a cure but separation: keeping the sick apart from the well. In 1377 the Great Council of Ragusa, modern Dubrovnik, established a 30-day isolation period, the trentino, for arrivals from plague-stricken areas. In the following decades other cities adopted the practice and extended it from 30 to 40 days, the quarantino, from the Italian for forty, which is where the word quarantine comes from.
Peer-reviewed · 2 sources - construction begun 1428, catalog published 1437History of Astronomy
Ulugh Beg Builds the Samarkand Observatory
Ulugh Beg, grandson of Timur and ruler of the Timurid realm centered on Samarkand, built a major astronomical observatory there, with construction beginning in 1428. The observatory was circular in shape, had three levels, and measured over 50 metres in diameter and 35 metres high, designed to house enormous fixed astronomical instruments for precise measurement. Ulugh Beg invited roughly sixty scientists to work at his adjoining madrasah and observatory, including the astronomer and mathematician al-Kashi and the scholar Qadi Zada, and he personally led scientific meetings where astronomical problems were freely discussed among the staff. The combined effort of Ulugh Beg, al-Kashi, and Qadi Zada produced the Zij-i Sultani, a star catalog published in 1437 giving the positions of 992 stars. The observatory itself survived the Uzbek conquest of Samarkand in 1500 before eventually falling into ruin.
Reputable source · 2 sources - c. 1440s CEHistory of Western Philosophy
Lorenzo Valla and the Humanists Break With Scholasticism
Lorenzo Valla, one of the most important humanists of the 15th century, attacked scholastic-Aristotelian philosophy from a linguistic standpoint in his Repastinatio dialectice et philosophie, arguing that scholastic logic had grown barren and needed to be re-cultivated with the tools of rhetoric and grammar instead. Around the same period Valla used philological analysis, comparing the Latin text against known Latin usage of different eras, to demonstrate that the Donation of Constantine, a document long used to justify papal claims to temporal rule, was a medieval forgery rather than a genuine 4th-century imperial grant. He also compared Jerome's Latin Vulgate translation of the New Testament against the original Greek text, laying groundwork for critical biblical scholarship. Civic humanists more broadly, including Leonardo Bruni, who produced fresh Latin translations of Aristotle and other Greek texts directly from Greek rather than through medieval intermediary translations, championed a return to classical sources and rhetoric, the studia humanitatis, over the technical logic of the scholastic universities.
Reputable source · 2 sources - 1520-1521Pandemics Through History
Smallpox Devastates Tenochtitlan and the Population of the Americas
Smallpox reached the Valley of Mexico in September 1520 during the fighting between Hernan Cortes's forces and the Aztec Empire, and the outbreak lasted at least seventy days. Residents of Tenochtitlan identified the disease in Nahuatl as hueyzahuatl, great leprosy, and totomonaliztli, pustules; survivors quoted in the Florentine Codex described being covered in agonizing sores from head to foot, unable to move their limbs, and many who could not forage for food died of starvation rather than the disease itself because caregivers were incapacitated too. Current estimates put deaths at five to eight million across Mesoamerica in this single outbreak, with mortality rates in unexposed populations ranging from 30 to 100 percent of those infected. It was the first of repeated epidemics, smallpox followed by measles, typhus, and other Old World diseases, that struck Indigenous populations across the Americas in the following century.
Reputable source · 2 sources - 1543 CEHistory of Astronomy
Copernicus Publishes De Revolutionibus
Around 1514, Nicolaus Copernicus circulated a short handwritten manuscript, later called the Little Commentary, among friends, laying out an early version of a heliocentric theory built on principles including that the center of the universe is near the sun and that the Earth's own revolution around it accounts for the sun's apparent annual motion. Copernicus spent decades developing the full mathematical case in his major work, De revolutionibus orbium coelestium, which was published in Nuremberg in 1543, the year of his death; tradition holds he received a copy of the printed book for the first time on his deathbed. Copernicus anticipated hostile criticism from what he called babblers who, although completely ignorant of mathematics, would dare find fault with his undertaking, and the mathematician Georg Joachim Rheticus, who had lived with Copernicus for roughly two years from May 1539, helped get the manuscript to press.
Reputable source · 2 sources - before 1543The Scientific Revolution
Aristotle and Ptolemy's Earth-Centered Universe Rules Unchallenged
Before 1543, European astronomy and physics rested on a system built from Aristotle's cosmology and refined mathematically by the Alexandrian astronomer Claudius Ptolemy in his 13-book Almagest, written around 150 CE. In this model the Earth sat motionless at the center of the universe while the Sun, Moon, planets, and stars were carried around it on nested crystalline spheres. Aristotle held that the heavens were made of a perfect, unchanging fifth element, distinct from the four earthly elements of earth, air, fire, and water, so the celestial realm could not change or decay the way the sublunary world did. Because the planets sometimes appeared to loop backward against the stars, Ptolemy added epicycles, circles riding on circles, so the math could still predict their positions even though the underlying picture of a static Earth remained fixed. Aristotle also reasoned that if the Earth moved, a ball thrown straight up would land behind the thrower and a constant wind would blow across its surface, neither of which anyone observed.
Reputable source · 2 sources - 1543 CEHistory of Medicine
Vesalius Publishes the Fabrica and Corrects the Ancients
In 1543 Andreas Vesalius published De humani corporis fabrica, seven books on the fabric of the human body, printed in Basel and illustrated with detailed anatomical figures. What set the work apart was its method. Vesalius performed his own careful dissections of human cadavers and observed the body in great detail, confirming some of Galen's claims and refuting many others. Because Galen had inferred human anatomy from animals, his errors were baked into the texts European physicians had trusted for over a thousand years, and Vesalius, dissecting actual humans, could see where the master had been wrong. The Fabrica paired precise description with woodcut illustrations that let readers see the structures for themselves rather than take them on authority.
Reputable source · 2 sources Copernicus Publishes De Revolutionibus on His Deathbed
Nicolaus Copernicus, a Polish canon who had studied astronomy at Padua, spent much of his adult life quietly working out a mathematical model in which the Sun sits near the center of the universe and the Earth both orbits it and spins on its own axis. He kept the manuscript back for decades, and it took a visiting Wittenberg mathematician, Georg Joachim Rheticus, arriving in 1539 and spending two years pressing him, to get Copernicus to release it. The finished book, De Revolutionibus Orbium Coelestium, went to press in Nuremberg in 1543, the year Copernicus died. Without his knowledge, the Lutheran theologian Andreas Osiander, who oversaw the printing, added an unsigned preface telling readers the Sun-centered model was only a calculating convenience, not a claim about physical reality, softening the book's reception for decades. Because Copernicus still assumed the planets moved on perfect circles, he had to keep Ptolemy's epicycles to make the math fit the observations.
Reputable source · 2 sourcesVesalius Corrects Two Centuries of Galen From His Own Dissections
Andreas Vesalius, a Brussels-born anatomist teaching at the University of Padua, published De Humani Corporis Fabrica in 1543, the same year as Copernicus's book. Medical teaching at the time still followed the second-century Greek physician Galen, whose anatomical descriptions came largely from dissecting Barbary macaques, dogs, and sheep because Roman law barred human dissection in his time. Vesalius performed the cutting himself in front of students, breaking from the custom of an instructor reading Galen aloud while a barber-surgeon opened the body. Doing his own dissections, he found the human liver has two lobes, not five as Galen described, that the lumbar vertebrae differ from Galen's account, and that humans lack the rete mirabilis, a network of blood vessels at the base of the brain that Galen had observed in sheep and built into his theory of how vital fluid reaches the brain. Vesalius backed every claim in the Fabrica's seven volumes with his own dissections rather than citing older texts, and paired the text with detailed woodcut illustrations.
Reputable source · 2 sources- 1535-1545 CEHistory of Mathematics
Tartaglia Solves the Cubic, Then Cardano Breaks His Oath and Publishes It
Scipione del Ferro, who held the chair of arithmetic and geometry at the University of Bologna, worked out how to solve cubic equations of the form x cubed plus mx equals n sometime around 1515, but kept the method secret until just before his death in 1526, when he revealed it only to his student Antonio Fior. In 1535 Fior challenged Niccolo Fontana, known as Tartaglia, the stammerer, to a public problem-solving contest, but Tartaglia had independently worked out how to solve a wider class of cubics and, with only eight days left before the deadline, found a general method covering all of Fior's problem types, winning the contest outright. The mathematician and physician Gerolamo Cardano later persuaded Tartaglia to share the method, swearing by God's holy Gospels never to publish it and promising to record it only in code so no one could read it after his death. In 1543 Cardano learned that del Ferro had solved the same problem years earlier, and used that prior claim as justification to break his oath: in 1545 he published Ars Magna, the first major Latin treatise on algebra, disclosing the cubic solution along with his student Lodovico Ferrari's method for solving the quartic equation.
Reputable source · 2 sources - 1572 CEHistory of Astronomy
Tycho Brahe Observes a New Star and Builds Europe's Most Precise Observatory
On 11 November 1572, Tycho Brahe stepped outside after an evening of alchemical work and noticed an extra star that had not been there before, blazing in the constellation Cassiopeia. His published observations of the object, now recognized as a supernova, in 1574 helped establish that new stars could appear in the supposedly unchanging celestial realm, contradicting inherited Aristotelian cosmology. Brahe went on to build the observatory Uraniborg and equipped it with a mural quadrant, revolving quadrants, an astronomical sextant, and an equatorial armillary, all built with exceptional care during the mid-1580s; modern analysis of his data shows errors in his stellar and planetary position measurements falling mostly between about 0.5 and 1.0 arcminutes, an accuracy far beyond earlier pre-telescopic instruments. After Brahe's death in 1601, his enormous, precise dataset of planetary positions passed to his assistant Johannes Kepler, whose Rudolphine Tables, drawing on that data, were eventually published in 1627.
Reputable source · 2 sources Tycho Brahe Builds Uraniborg and Redefines Precision
In 1572, the Danish astronomer Tycho Brahe spotted a new star in the constellation Cassiopeia, bright enough to see in daylight, and spent over a year tracking it with a sextant to see if it shifted position against the background stars the way a nearby object like the Moon would. It did not move, meaning it belonged to the supposedly changeless celestial realm, directly contradicting the Aristotelian claim that the heavens were eternal and unchanging. King Frederick II of Denmark, wanting to keep his prized astronomer from leaving the country, granted Tycho the island of Hven in 1576 and funded a purpose-built observatory there called Uraniborg, later supplemented by a second observatory, Stjerneborg, built partly underground to stabilize its instruments against wind. Over roughly twenty years at Uraniborg, using large custom-built quadrants and sextants but no telescope, since none yet existed, Tycho recorded planetary positions with a precision of about one arcminute, several times better than anything available before him.
Reputable source · 2 sources- 17 February 1600The Scientific Revolution
Giordano Bruno Is Burned for Heresy in Rome
Giordano Bruno, a former Dominican friar who had left his order and traveled across Europe, argued that the universe was infinite, that stars were distant suns each potentially circled by their own planets, and that Copernicus's Sun-centered model was literally true rather than a mathematical convenience. Bruno mixed these cosmological claims with other doctrines the Roman Inquisition judged heretical, including denials of the Trinity and of the divinity of Christ. Arrested in Venice in 1592 and extradited to Rome, he spent roughly eight years in the custody of the Inquisition before being condemned and burned at the stake in the Campo de' Fiori on 17 February 1600.
Reputable source · 2 sources - 1609-1619 CEHistory of Physics
Kepler States His Laws of Planetary Motion
Working from Tycho Brahe's precise decades of naked-eye observations of Mars, Johannes Kepler published two laws of planetary motion in 1609 and a third a decade later. MacTutor's history of the laws describes the first as the Ellipse Law, that the curve or path of a planet is an ellipse whose radius vector is measured from the Sun which is fixed at one focus, discarding the circular orbits that Aristotle, Ptolemy, and even Copernicus had all assumed. The second, the Area Law, states that the time taken by a planet to reach a particular position is represented by the area swept out by the radius vector drawn from the fixed Sun, meaning planets move faster when nearer the Sun and slower when farther away. A third law, published in 1619, related a planet's orbital period to its average distance from the Sun by a fixed mathematical ratio, valid for every planet then known.
Primary source · 2 sources - 1609 and 1619 CEHistory of Astronomy
Kepler Publishes His Three Laws of Planetary Motion
Using Tycho Brahe's precise observational data on the planet Mars, Johannes Kepler discovered that its orbit was an ellipse with the Sun at one focus, a result he later extended to all the planets as what is now called Kepler's First Law, and that a line joining a planet to the Sun sweeps out equal areas in equal times as the planet moves along its orbit, known as Kepler's Second Law. Kepler published both laws in Astronomia Nova, printed in Heidelberg in 1609, after an intensive multi-year study of Mars's orbit. A decade later, in Harmonices Mundi, published in Linz in 1619, Kepler added a third relationship: for any two planets, the ratio of the squares of their orbital periods equals the ratio of the cubes of the mean radii of their orbits, now known as Kepler's Third Law.
Reputable source · 2 sources Kepler Breaks the Circle and Finds the Ellipse
Johannes Kepler, a German mathematician who became Tycho Brahe's assistant in 1600 and inherited his observational data after Tycho's death in 1601, was assigned the notoriously difficult problem of calculating the orbit of Mars. Kepler, like nearly every astronomer before him, initially assumed planetary orbits had to be built from perfect circles, since Renaissance thinkers still held the circle as the universe's divinely ordained shape. He struggled for years trying to reconcile Tycho's precise observations with a circular path for Mars and could not make them agree. Abandoning the circle, Kepler found that an ellipse, a stretched-out oval, with the Sun positioned at one focus rather than the center, fit the data. In Astronomia Nova, published in 1609, Kepler set out what became his first law, that planets move in ellipses with the Sun at one focus, and his second law, that a line from the planet to the Sun sweeps out equal areas in equal times, meaning a planet moves faster when nearer the Sun. A decade later, in Harmonices Mundi (1619), he added a third law relating each planet's orbital period to its distance from the Sun.
Reputable source · 2 sources- March 1610The Scientific Revolution
Galileo Turns His Telescope to the Sky
In 1609, Galileo Galilei, a mathematics professor in Padua, heard reports of a Dutch spyglass and built his own improved version, reaching about 20-power magnification through his own lens-grinding refinements. Turning it skyward, he found the Moon's surface was rough, mountainous, and shadowed like the Earth's rather than a smooth, perfect sphere as Aristotelian cosmology required of celestial bodies. He also discovered four moons orbiting Jupiter, which he named the Medicean Stars after his patrons the Medici family, proving that not every heavenly body circled the Earth. Galileo rushed these findings into print as Sidereus Nuncius, the Starry Messenger, in March 1610. Later that year he observed that Venus goes through a full cycle of phases like the Moon, which is only possible if Venus orbits the Sun rather than the Earth, and he saw Saturn's rings, though his telescope could not resolve them clearly enough for him to understand what he was seeing.
Reputable source · 2 sources - 1609-1610 CEHistory of Astronomy
Galileo Turns a Telescope on the Sky
By late 1609, Galileo Galilei had built his own telescopes and began making discoveries with them, observing mountains on the Moon's surface and determining that the Milky Way was made up of countless individual stars rather than a smooth band of light. His most significant find was four small bodies orbiting Jupiter, which he named the Medicean Stars to flatter the Grand Duke of Tuscany, and by 1612 he had worked out accurate orbital periods for each. Galileo published these findings in Sidereus Nuncius, or Starry Messenger, in May 1610, a book that caused a sensation and established his reputation as a leading astronomer. Decades later, his 1632 book Dialogue Concerning the Two Chief World Systems, which openly favored Copernican heliocentrism, brought him before the Roman Inquisition; the book was banned from sale, Galileo was found guilty and initially condemned to lifelong imprisonment, a sentence commuted to house arrest, under which he remained, watched by the Inquisition, until his death on 8 January 1642.
Reputable source · 2 sources Bacon Argues for Induction in the Novum Organum
Francis Bacon, born in 1561, published the Novum Organum in October 1620 as the second part of his larger Instauratio Magna, a planned six-part program for reforming human knowledge. Against what he considered the sterile deductive logic and reliance on syllogisms inherited from Aristotle and the medieval schoolmen, Bacon argued for building knowledge inductively, moving step by step from particular observations toward general axioms rather than starting from the most general principles and reasoning downward. He diagnosed four systematic sources of error that distort human reasoning, which he called idols of the mind: the Idols of the Tribe, the Cave, the Marketplace, and the Theatre, covering biases built into human nature, individual temperament, language, and inherited philosophical systems respectively.
Reputable source · 2 sources- October 1620The Scientific Revolution
Bacon's Novum Organum Argues for Knowledge Built From Observation
Francis Bacon, an English lawyer and former Lord Chancellor, published the Novum Organum in 1620 as the second part of a planned larger project called the Instauratio Magna, the Great Instauration. The title deliberately echoed and answered Aristotle's Organon, the body of logical works that had structured university teaching on reasoning for nearly two thousand years. Where Aristotle's logic proceeded from general premises to particular conclusions through syllogism, Bacon argued for what he called eliminative induction: gathering large, organized collections of specific observations, called natural histories, and working upward from them toward general conclusions, systematically ruling out false explanations as the evidence accumulated. Bacon also catalogued the mental habits, which he called the idols of the mind, that he believed distorted human judgment and had to be guarded against before reliable knowledge was possible.
Reputable source · 2 sources - 1628 CEHistory of Medicine
Harvey Shows the Blood Circulates
In 1628 William Harvey published his account of the movement of the heart and blood, a slim 72-page, poorly bound paper edition riddled with printing errors, known by its short Latin title De Motu Cordis. In it Harvey argued that the blood is driven round in a circular motion and moves perpetually, and that the heart performs this circulation by its pulsation, acting as a pump. This overturned the Galenic picture, which held that blood was continuously made in the liver and consumed by the body, and that some seeped through invisible pores in the wall between the heart's chambers. Harvey used measurement and experiment to show that the sheer volume of blood the heart moves could only be explained if the same blood circulated again and again through a closed system.
Peer-reviewed · 2 sources Harvey Demonstrates the Circulation of the Blood
William Harvey, physician to King James I and King Charles I and a graduate of the University of Padua's medical school, published Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, On the Motion of the Heart and Blood, in Frankfurt in 1628. Galenic medicine had held that blood was continuously produced by the liver and consumed by the body's tissues, ebbing and flowing rather than circulating in a fixed loop. Harvey combined observation of comparative anatomy across animal species with mechanical reasoning: he estimated the volume of blood the heart pumps in an hour and showed it far exceeds what the body could plausibly manufacture and use up in that time, and he used tight ligatures on arms and vessels to demonstrate that blood flows outward from the heart through arteries and returns through veins, moving in one direction through valves that prevent backflow. Harvey had first presented these findings in the 1616 Lumleian lectures at the Royal College of Physicians, refining the argument for over a decade before publishing.
Primary source · 2 sources- 22 June 1633The Scientific Revolution
The Inquisition Tries Galileo Over the Dialogue
In 1616, Galileo had already been privately warned by Cardinal Robert Bellarmine, a leading theologian on the Roman Inquisition, not to hold or defend Copernican astronomy as physically true. When his friend Cardinal Maffeo Barberini became Pope Urban VIII in 1623, Galileo felt freer to write, and completed the Dialogue Concerning the Two Chief World Systems, printed in Florence in February 1632. The book stages a conversation between defenders of the Ptolemaic and Copernican systems, and while it never explicitly declares one true, it structures its arguments so the Copernican side clearly wins. The Inquisition banned the book's sale shortly after publication and summoned Galileo, then 68 and in poor health, to Rome. After hearings running from April to June 1633, on 22 June Galileo was taken to the church of Santa Maria sopra Minerva, made to kneel, and found guilty of vehement suspicion of heresy. He was forced to read aloud and sign a formal abjuration renouncing the belief that the Sun is motionless at the universe's center and that the Earth moves, and his prison sentence was immediately commuted to house arrest for the remainder of his life.
Reputable source · 2 sources - 1637 CEHistory of Mathematics
Descartes Unites Algebra and Geometry
Rene Descartes, born in 1596 in La Haye, France, published La Geometrie in 1637 as an appendix to his Discourse on Method. The work introduced innovative algebraic techniques for analyzing geometric problems and a systematic way of connecting a curve's construction to its algebraic equation, letting any legitimately geometric curve be represented as an equation in what became known as coordinate, or Cartesian, geometry. Descartes considered the approach powerful enough to solve a problem that, according to the ancient mathematician Pappus, none of the Greeks had managed to solve, and he said so directly in his own text. Descartes held that mathematics alone offered certain knowledge, writing in his earlier Regulae that he was convinced it was a more powerful instrument of knowledge than any other human beings possess.
Reputable source · 2 sources Descartes Fuses Algebra and Geometry
Rene Descartes published Discours de la Methode in Leiden in 1637, a treatise on properly conducting reason, with three scientific appendices attached: Dioptrics, Meteorology, and La Geometrie. In La Geometrie, Descartes showed that a geometric curve could be represented by an algebraic equation relating two variable distances, what became known as coordinates, and conversely that any such equation could be plotted as a curve. This let mathematicians translate difficult geometric construction problems, which the Greeks had solved case by case with compass and straightedge, into algebraic manipulations that could be solved by a single general method. Descartes argued that this approach let questions of what could and could not be geometrically constructed be settled quickly through algebra where pure geometric reasoning alone might never resolve them.
Reputable source · 2 sources- 1638 CEHistory of Physics
Galileo Times Falling Bodies and Founds the Experimental Method
Unable to time free fall directly with the clocks of his day, Galileo Galilei slowed the motion down by rolling a bronze ball along a grooved, inclined wooden plank and measuring elapsed time with a water clock, a vessel that released a thin jet of water he could weigh at each interval. In his own account, reproduced by the University of Virginia's physics history archive, he ran the trial a full hundred times and always found that the spaces traversed were to each other as the squares of the times. This confirmed his law that a uniformly accelerating body picks up equal amounts of speed in equal time intervals, and that distance from rest grows with the square of elapsed time. Galileo published the result in 1638 in Discourses and Mathematical Demonstrations Relating to Two New Sciences, his final book, written after Church authorities had already placed him under house arrest for his defense of a Sun-centered cosmos.
Primary source · 2 sources Descartes Publishes the Meditations and the Cogito
Rene Descartes, born in 1596, published the Meditations on First Philosophy in Latin in 1641, with six sets of objections from other thinkers and his own replies included in the same volume. Descartes's method was to treat as false any belief that admitted even the slightest doubt, stripping away sensory belief, mathematical belief, and even the belief that he had a body, until he reached one claim that survived the doubt itself: that the very act of thinking proved his own existence, summarized in the phrase cogito, ergo sum, I think, therefore I am. From that foundation Descartes argued that mind and body are really distinct substances, the mind essentially a thinking thing and the body essentially an extended, divisible thing, a position that created what is still called the mind-body problem.
Reputable source · 2 sourcesHobbes Argues the State of Nature Is a War of All Against All
Thomas Hobbes, born in 1588, published Leviathan in English in 1651, arguing that without a common power to keep people in order, human life would exist in a state of war, in his words a war of every man against every man, in which nothing could count as unjust because no shared authority defined justice. Hobbes concluded that the only way out of this condition was for individuals to covenant together and transfer their rights to an absolute sovereign, an arrangement he called sovereignty by institution, in exchange for the peace and security that only such an authority could guarantee. Without that authority, Hobbes argued, life would be, in his famous phrase, solitary, poor, nasty, brutish, and short.
Reputable source · 2 sources- Summer 1654History of Mathematics
Pascal and Fermat Found the Theory of Probability
In the summer of 1654, Blaise Pascal exchanged a series of five letters with Pierre de Fermat that laid the foundation for the theory of probability. The correspondence addressed two problems already studied in less general form by earlier mathematicians including Cardano, Pacioli, and Tartaglia: the dice problem, asking how many times a pair of dice must be thrown before a double six can be expected, and the problem of points, asking how to fairly divide the stakes of a game of chance that is interrupted before it finishes. Pascal used a method of backward induction to work out each player's expected winnings at each possible stopping point, while Fermat provided an explicit formula using the same triangle of binomial coefficients now called Pascal's triangle, and the two independently arrived at consistent solutions. They fully solved the problem of points for two players but, as Pascal's biography notes, did not develop mathematical methods powerful enough to solve the same problem for three or more players.
Reputable source · 2 sources Huygens Patents the Pendulum Clock and Explains Saturn's Rings
Christiaan Huygens, a Dutch mathematician and astronomer, ground his own telescope lenses using an improved technique he developed around 1654, and in 1655 used one of his instruments to discover Titan, the first known moon of Saturn. The following year he worked out that Saturn's strange, changing appearance, which had puzzled Galileo, was caused by a thin ring encircling the planet at an angle, publishing the full argument in Systema Saturnium in 1659 after facing skepticism from other astronomers whose weaker telescopes could not confirm it. Because precise astronomical timekeeping mattered for tracking these observations, Huygens turned to the pendulum, patenting the first pendulum clock in 1656, and worked out the mathematics of pendulum motion in Horologium Oscillatorium in 1673, including a design meant to keep accurate time at sea for calculating longitude. His work with Robert Hooke and others on the physics of circular motion and elastic collision fed into the era's developing understanding of centrifugal force and, eventually, the inverse-square law of gravity that Newton would generalize.
Reputable source · 2 sources- 28 November 1660The Scientific Revolution
The Royal Society Is Founded on 'Nullius in Verba'
On 28 November 1660, following a lecture on astronomy by Christopher Wren at Gresham College in London, a group of informally meeting natural philosophers agreed to form a permanent society devoted to what they called natural knowledge, chartered soon after as the Royal Society of London for Improving Natural Knowledge. By 1662 the Society had appointed Henry Oldenburg as Secretary, who in 1665 launched the Philosophical Transactions, one of the first scientific journals, and Robert Hooke as Curator of Experiments, responsible for demonstrating experiments at weekly meetings. The Society adopted the motto Nullius in verba, take nobody's word for it, formally in its first charter of 1662, expressing a commitment to verifying claims by experiment rather than by appeal to ancient authority. Early Fellows included Robert Boyle, John Evelyn, and John Locke, and by 1672 Isaac Newton; foreign members elected over the following decades included Christiaan Huygens and Antonie van Leeuwenhoek.
Reputable source · 2 sources Boyle Publishes The Sceptical Chymist and Questions the Four Elements
Robert Boyle, the fourteenth child of the Earl of Cork who spent the Civil War years at Oxford experimenting with a circle of natural philosophers, published The Sceptical Chymist in London in 1661. Written as a dialogue among several debaters, the book challenged both the ancient Aristotelian claim that all matter is built from four elements, earth, air, fire, and water, and the alchemical claim, following Paracelsus, that three principles, sulfur, mercury, and salt, underlie all substances. Boyle argued that neither camp had ever actually demonstrated these building blocks through experiment; they had merely inherited the claims. He proposed defining an element as a body that cannot be broken down into anything simpler by any known chemical operation, and argued matter was built from corpuscles, tiny particles in motion, whose combinations produced the different substances observed. The year before, in 1660, Boyle had already published New Experiments Physico-Mechanicall, Touching the Spring of the Air, describing air-pump experiments that created a partial vacuum and studied the physical behavior of air.
Reputable source · 2 sources- 1665-1666Pandemics Through History
The Great Plague of London Kills a Quarter of the City
Plague cases first appeared in the parish of St Giles-in-the-Fields, just outside London's city walls, in the spring of 1665, and mortality rose through the summer heat to peak in September, when 7,165 Londoners died of plague in a single week according to parish Bills of Mortality. Officially recorded deaths reached 68,596, but the true toll is thought to have exceeded 100,000, roughly 15 percent of the city's population of about 460,000, since the bills excluded Quakers, Anabaptists, and Jews and often misattributed cause of death. Victims suffered fever, headache, vomiting, and the swollen, blackened lymph nodes known as buboes; untreated bubonic plague killed roughly 30 percent of those infected within about two weeks, while the rarer pneumonic and septicemic forms were nearly always fatal.
Primary source · 2 sources Hooke's Micrographia Names the Cell
Robert Hooke, the Royal Society's Curator of Experiments, published Micrographia in 1665, a large-format book of his own drawings made from what he saw through a compound microscope he built himself. The book presented around 60 magnified observations, moving from the point of a needle through silk fibers, frost patterns, and insects, and included spectacular fold-out engravings, most famously a flea rendered in intricate, life-sized detail. Examining a thin slice of cork under magnification, Hooke saw a honeycomb of small, regular compartments, and, because the boxy shapes reminded him of the small rooms monks lived in, he called them cells, the first recorded use of that word in its biological sense. Samuel Pepys recorded staying up until two in the morning reading it, calling it the most ingenious book he had ever read.
Reputable source · 2 sources- 1665 to 1666The Scientific Revolution
Newton's Plague-Year Annus Mirabilis
Isaac Newton earned his bachelor's degree from Trinity College, Cambridge, in April 1665, just as an outbreak of plague forced the university to close. Newton returned to his family's farm at Woolsthorpe in Lincolnshire, and over roughly two years there, still under 25, he made foundational advances across four fields at once. He worked out early versions of his three laws of motion and the law of centrifugal force for circular motion, and in 1666 had the insight that the same force pulling an apple to the ground might extend far enough to hold the Moon in orbit around the Earth, counterbalancing its centrifugal tendency to fly outward. Combining this idea with Kepler's third law, he deduced that this force must weaken with the square of the distance, the inverse-square law. In the same period he developed his method of fluxions, his version of calculus, and began the experiments on light and prisms that would become his later work on optics.
Reputable source · 2 sources - 9 October 1676The Scientific Revolution
Leeuwenhoek Reports 'Animalcules' to the Royal Society
Antonie van Leeuwenhoek, a cloth merchant in Delft with no university training, taught himself to grind single-lensed microscopes far more powerful than the compound instruments used by Hooke and others, reaching magnifications high enough to see individual cells and smaller. Beginning a correspondence with the Royal Society in 1673 that continued for the rest of his life, he sent detailed letters, over 300 in total, describing what he observed. In a letter dated 9 October 1676, he reported finding living creatures, which he called animalcules, in water infused with pepper, along with observations in rainwater, well water, and other samples, describing organisms he estimated at a scale thousands of times smaller than anything Dutch naturalist Jan Swammerdam had previously drawn. The Royal Society, skeptical at first that single-celled life existed at all, eventually had the observations verified by other witnesses using Leeuwenhoek's own instruments.
Primary source · 2 sources - 1666-1716 CE (development and dispute)History of Mathematics
Newton and Leibniz Both Invent Calculus, Then Fight Over Who Was First
Isaac Newton wrote a tract on fluxions, his term for what would become calculus, in October 1666, but the work was not published at the time, though it circulated privately among mathematicians, and his fuller treatments written in 1669 and 1671 were not formally published until 1711 and 1736. Gottfried Wilhelm Leibniz developed his own version independently, working out the core ideas during a period in Paris starting in 1672 and publishing his results in 1684 and 1686, using the integral symbol and differential notation still standard today. In 1711 the mathematician John Keill publicly accused Leibniz of deriving his calculus from letters Newton had sent years earlier, prompting Leibniz to demand a retraction and insist he had never even heard of Newton's fluxions until reading the work of John Wallis. The Royal Society convened a committee in 1713 that, in a report actually written by Newton himself, the Commercium Epistolicum, ruled in Newton's favor without properly hearing Leibniz's side.
Reputable source · 2 sources - August 1684The Scientific Revolution
Halley Persuades Newton to Write the Principia
In January 1684, three Fellows of the Royal Society, Christopher Wren, Robert Hooke, and Edmond Halley, discussed at a coffeehouse meeting whether an inverse-square law of gravitational attraction between the Sun and planets would necessarily produce elliptical orbits, the shape Kepler had described decades earlier. Hooke claimed he could prove it but never produced a demonstration. Halley, unsatisfied, traveled to Cambridge in August 1684 and put the question directly to Isaac Newton, who told him he had already worked out the proof years before but had misplaced the calculation. Halley pressed Newton to write it up properly, and over roughly three years, with Halley personally funding the printing and editing the text, Newton expanded a short answer into the full Philosophiae Naturalis Principia Mathematica, published in 1687 under the Royal Society's imprimatur.
Reputable source · 2 sources - 1687 CEHistory of Physics
Newton Publishes the Principia and the Laws of Motion and Gravity
In July 1687 Isaac Newton published Philosophiae Naturalis Principia Mathematica, a work MacTutor calls the greatest scientific book ever written. In it Newton set out three laws of motion, that a body stays at rest or in uniform motion unless acted on by a force, that force equals mass times acceleration, and that every action has an equal and opposite reaction, versions of which he already had in early form by 1666. He then proposed universal gravitation: every two masses in the universe attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. From this single law Newton deduced Kepler's three empirical laws of planetary motion and showed that a stone falling to Earth was subject to precisely the same force which kept the Moon in its orbit about the Earth and the planets in their orbits around the Sun, unifying terrestrial and celestial mechanics under one mathematical framework for the first time.
Primary source · 2 sources - 1687 CEHistory of Astronomy
Newton Publishes the Principia and Explains Why the Planets Orbit
Isaac Newton published Philosophiae Naturalis Principia Mathematica in 1687, after Edmond Halley persuaded him in 1684 to write up and formalize work Newton had developed piecemeal since the 1660s. The Principia's central law states that all matter attracts all other matter with a force proportional to the product of their masses and inversely proportional to the square of the distance between them, universal gravitation. Newton used this single law to show that the planets were attracted toward the Sun by a force varying as the inverse square of the distance, deriving Kepler's previously empirical laws of planetary motion as mathematical consequences of gravity rather than as independent rules, and he extended the same force to explain the orbits of comets, the tides, and the motion of the Moon as perturbed by the Sun's gravity.
Reputable source · 2 sources - 5 July 1687The Scientific Revolution
Newton Publishes the Principia Mathematica
Isaac Newton's Philosophiae Naturalis Principia Mathematica was published on 5 July 1687 under the Royal Society's imprimatur, with Edmond Halley funding the printing. The book set out three laws of motion: that a body at rest or in motion continues that way unless acted on by a force, that a force produces an acceleration proportional to its size and in its direction, and that every action has an equal and opposite reaction. Building on these, Newton stated the law of universal gravitation: every object attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Newton showed mathematically that this single law explained Kepler's three laws of planetary motion as consequences rather than separate rules, and that the same force governing a falling apple also governs the Moon's orbit and the ocean tides, which he showed result from the Moon's and Sun's gravitational pull on Earth's water.
Reputable source · 2 sources Locke Grounds Government in Consent and Natural Rights
John Locke, born in 1632, published his Two Treatises of Government anonymously in 1689, arguing against Hobbes's absolutism that people possess natural rights, to life, liberty, and property, that exist independently of any particular society's laws. Locke argued that legitimate government arises only through a social contract in which people in the state of nature conditionally transfer some of their rights to a government in exchange for protection of the rest, and that a government which fails to protect those rights, or actively violates them, can be resisted and replaced, a position that became his defense of the right of revolution.
Reputable source · 2 sources- 1699 to 1716The Scientific Revolution
The Newton-Leibniz Calculus Priority Dispute Turns Bitter
Gottfried Wilhelm Leibniz developed his own version of calculus while working in Paris in the mid-1670s, arriving at a working notation, including the integral sign, by November 1675, independently of Newton's earlier but unpublished fluxions. Newton wrote to Leibniz through the Royal Society's secretary Henry Oldenburg describing some of his own results without revealing his methods; by the time Leibniz replied, Newton believed his letter had been answered too quickly to be an honest independent response and grew suspicious that Leibniz had learned his methods secondhand. The dispute escalated into open accusations of plagiarism by 1699 and came to a head in 1711, when Leibniz appealed to the Royal Society to settle the matter. Newton, who was the Society's president at the time, appointed the investigating committee himself, wrote its supposedly impartial 1713 report, Commercium Epistolicum, anonymously, and then anonymously reviewed his own report favorably in the Philosophical Transactions.
Reputable source · 2 sources Variolation Spreads From Asia to Europe as Smallpox Prevention
Variolation, deliberately infecting a healthy person with material from a smallpox pustule or scab to trigger a mild, controlled case of the disease, had been practiced in Asia for centuries before it reached Europe. China's Golden Mirror of Medicine, a 1742 text, described inoculation methods used there since at least 1695, typically by drying smallpox scabs and blowing the powder into a patient's nostril, while practitioners in 16th-century India worked pus from pustules directly into the skin. By 1700 the practice had also spread to the Ottoman Empire and parts of Africa. Lady Mary Wortley Montagu, wife of the British ambassador to the Ottoman court, observed variolation in Constantinople in 1717 and had her own son inoculated there. After returning to England, she pushed for a public trial: in 1721, at her urging and that of the Princess of Wales, condemned prisoners and orphaned children were inoculated as a test, and when they survived subsequent exposure to smallpox, members of the British royal family adopted the procedure themselves. Variolation cut smallpox mortality to an estimated 1 to 2 percent of those inoculated, against roughly 30 percent for people who caught the disease naturally.
Reputable source · 2 sources- 1739-1740History of Western Philosophy
Hume Argues Reason Cannot Justify Induction
David Hume, born in 1711, published the first two books of A Treatise of Human Nature anonymously in 1739, with the third book following in 1740, before he was thirty years old. In it Hume argued that reasoning from past experience to future events, induction, has no rational foundation: we cannot prove that the future will resemble the past without already assuming the very principle we are trying to establish. Hume concluded that our confidence in cause and effect rests not on reasoned demonstration but on custom or habit, a psychological tendency to expect repetition based on past regularity. He also drew a sharp division, now called Hume's Fork, between relations of ideas, truths knowable through pure thought alone such as mathematics, and matters of fact, claims about the world that depend on experience and can always be coherently denied.
Reputable source · 2 sources - c. 1727-1783 CEHistory of Mathematics
Euler Reshapes Mathematical Notation While Going Blind
Leonhard Euler, born in 1707 in Basel, Switzerland, worked at the St Petersburg Academy of Sciences, then in Berlin for 25 years starting in 1741, then back in St Petersburg from 1766 until his death in 1783. During his 25 years in Berlin, Euler wrote around 380 articles, and after his return to St Petersburg, despite total blindness, he produced almost half of his entire lifetime output. He had already lost the use of one eye by 1740 and became almost completely blind after an illness soon after returning to Russia. Euler introduced or standardized much of the mathematical notation still in everyday use: the symbol e for the base of natural logarithms in 1727, the notation f(x) for a function in 1734, pi for the ratio of a circle's circumference to its diameter, the summation symbol sigma in 1755, and i for the square root of negative one in 1777.
Reputable source · 2 sources - 13 March 1781History of Astronomy
William Herschel Discovers Uranus and Doubles the Solar System
On 13 March 1781, William Herschel, using a telescope he had built himself after finding a commercial Gregorian instrument's performance inadequate, discovered the planet Uranus, the first planet to be discovered in historic times. Herschel had been surveying double stars from Bath, England, when he noticed an object near Eta Geminorum that showed a visible disk rather than the point of light typical of a star; three days later he observed that it had moved, but was initially unsure whether it was a planet or a comet. Even the Astronomer Royal shared the uncertainty at first, writing that it was as likely to be a regular planet moving in an orbit nearly circular round the sun as a comet moving in a very eccentric ellipse. Herschel received the Copley Medal in November 1781 and was elected to the Royal Society that December; the discovery's fame brought him a royal pension of 200 pounds a year, letting him give up his career as a professional musician by May 1782 to become a full-time astronomer.
Reputable source · 2 sources Kant Attempts a Copernican Revolution in Philosophy
Immanuel Kant, born in 1724, published the Critique of Pure Reason in 1781, revising it for a second edition in 1787, attempting to answer Hume's skepticism about induction and causation while preserving the possibility of necessary, universal knowledge. Kant proposed treating the problem the way Copernicus had treated planetary motion: rather than assuming all cognition must conform to objects as they are in themselves, he proposed that objects, as we experience them, must conform to the basic structures of the human mind. This produced Kant's distinction between phenomena, things as they appear to us, structured by space, time, and the categories of the understanding, and noumena, things as they are in themselves, which Kant held are permanently outside the reach of human knowledge.
Reputable source · 2 sources- 1789-1861History of Western Philosophy
Bentham and Mill Build the Case for Utilitarianism
Jeremy Bentham, born in 1748, set out classical utilitarian theory in An Introduction to the Principles of Morals and Legislation, printed in 1780 and published with additions in 1789, arguing that the principle of utility approves or disapproves of every action according to whether it tends to increase or decrease the happiness of those affected, a standard he summarized as the greatest happiness of the greatest number. Bentham proposed a felicific calculus for measuring pleasure and pain by dimensions including intensity, duration, and certainty. John Stuart Mill, born in 1806, revised and defended the theory in his 1861 essay Utilitarianism, arguing against Bentham's purely quantitative approach that pleasures differ in quality as well as amount, famously concluding that it is better to be a human being dissatisfied than a pig satisfied, since intellectual and moral pleasures rank higher than merely bodily ones. In On Liberty, published in 1859, Mill separately argued for the harm principle, that the only justification for restricting a person's liberty is to prevent harm to others, not to protect the person from themselves.
Reputable source · 2 sources - c. 1796 (construction); 1801 (Disquisitiones Arithmeticae)History of Mathematics
Gauss Constructs the 17-Gon and Reshapes Number Theory
Carl Friedrich Gauss, born in 1777 in Brunswick, stunned his teacher Buttner and his assistant Martin Bartels as a schoolboy by instantly summing the integers from 1 to 100, spotting that the sum equals 50 pairs each totaling 101. As a teenage student at Gottingen, Gauss proved that a regular 17-sided polygon, the heptadecagon, can be constructed using only a straightedge and compass, by showing that a primitive 17th root of unity can be found by solving a sequence of quadratic equations over the rational numbers, a construction problem that had stood unsolved since Euclid. Gauss left Gottingen in 1798 without a diploma, but by then he had made this discovery, which he later published as Section 17 of his Disquisitiones Arithmeticae in the summer of 1801, a book of seven sections, all but the last devoted to number theory.
Reputable source · 2 sources - 1721 (inoculation in Britain); 1796 (Jenner's vaccination)History of Medicine
From Inoculation to Vaccine: Montagu and Jenner Against Smallpox
Long before germs were understood, people fought smallpox by deliberately giving a mild case to build immunity. Lady Mary Wortley Montagu, wife of the British ambassador to Turkey, observed the scratch method of inoculation at seasonal inoculation gatherings in Constantinople, and on returning to Britain she had her own children inoculated during a smallpox outbreak in 1721, introducing the practice to London society. Inoculation used real smallpox and carried real risk. Edward Jenner made it far safer. Noticing that dairymaids who caught the milder cowpox seemed immune to smallpox, in 1796 he took matter from a cowpox pustule on the hand of milkmaid Sarah Nelmes and injected it into the arm of a young boy called James Phipps, then later exposed the boy to smallpox to test the protection. Phipps did not fall ill.
Reputable source · 2 sources - May-July 1796Pandemics Through History
Edward Jenner Tests Cowpox Against Smallpox and Creates the First Vaccine
By the late 18th century, variolation, deliberately infecting a healthy person with material from a mild smallpox case to induce immunity, was an established but risky practice; between 0.5 and 3 percent of variolated patients still died, and they could spread full-strength smallpox to others while infectious. Edward Jenner, a physician in rural Gloucestershire, had heard rural dairy workers claim that catching cowpox, a much milder disease, protected them from smallpox for life. In May 1796 he tested this directly: he took matter from a cowpox sore on the hand of milkmaid Sarah Nelmes and used it to inoculate an eight-year-old boy, James Phipps, who developed a mild, short illness and recovered fully. Two months later, in July 1796, Jenner deliberately exposed Phipps to material from an active smallpox sore. Phipps did not develop the disease, direct evidence that cowpox exposure had conferred protection.
Reputable source · 2 sources Hegel Traces the Development of Spirit Through History
Georg Wilhelm Friedrich Hegel, born in 1770, published the Phenomenology of Spirit in 1807, tracing how consciousness develops through successive stages of experience, each one exposed as incomplete and superseded, or in Hegel's term aufgehoben, negated yet preserved, by the next. Hegel's account, contrary to the popular shorthand of thesis-antithesis-synthesis, which is not his own terminology, works through what he called determinate negation. Applied to world history, Hegel argued that history is the necessary development, arising out of the concept of freedom, of successive stages of reason realizing itself through the actions of peoples, states, and individual historical actors, a teleological account of history later adapted, with the idealism stripped out, by Karl Marx.
Reputable source · 2 sources- 1823-1840 CEHistory of Mathematics
Bolyai and Lobachevsky Discover Geometry Without Euclid's Fifth Postulate
Euclid's fifth postulate, the claim that exactly one line parallel to a given line can be drawn through a point not on it, had frustrated mathematicians for two thousand years; the mathematician d'Alembert called the state of the problem in 1767 the scandal of elementary geometry. Carl Friedrich Gauss privately concluded by 1817 that the fifth postulate was logically independent of Euclid's other assumptions and worked out consequences of a geometry with multiple parallels, but never published this work, keeping it a secret, writing in 1813 that in the theory of parallels we are even now not further than Euclid and calling it a shameful part of mathematics. Janos Bolyai, working independently in Hungary, wrote to his father in 1823 that he had discovered things so wonderful that he was astounded, and that out of nothing he had created a strange new world, publishing his results in 1825 as a 24-page appendix to his father's book. Nikolai Lobachevsky in Russia published the same essential idea, that more than one line parallel to a given line can pass through a point not on it, in Russian in 1829 and in French, reaching a wider audience, in 1837.
Reputable source · 2 sources - 1831 CEHistory of Physics
Faraday Discovers Electromagnetic Induction
Michael Faraday, working at the Royal Institution in London, found in 1831 that a changing magnetic field could induce an electric current in a nearby wire, a phenomenon now called electromagnetic induction. MacTutor's account of Faraday's career notes that his experiments showed a magnet could induce an electrical current in a wire, letting him convert mechanical energy into electrical energy and build what is recognized as the first dynamo, since his apparatus recorded the first conversion of electrical into mechanical energy as well. Faraday, who lacked advanced mathematical training, explained his results using a physical picture rather than equations: he described lines of force filling the space around magnets and charges, a concept MacTutor identifies as central to his thinking throughout his career and the ancestor of the modern idea of a field.
Primary source · 2 sources - 1838 CEHistory of Astronomy
Bessel Measures the First Stellar Distance
Friedrich Bessel used the astronomical technique of parallax, measuring the tiny apparent shift in a star's position against more distant background stars as Earth orbits the Sun, to determine the distance to the star 61 Cygni, announcing his result in 1838. Bessel selected 61 Cygni deliberately: it had the greatest proper motion of all the stars he had studied, and he correctly deduced that this large apparent motion across the sky meant the star was relatively nearby. Using a Fraunhofer heliometer to make the measurements, Bessel announced a parallax value of 0.314 arcseconds, which, combined with the known diameter of Earth's orbit, gave a distance of about 10 light years; the modern accepted parallax value for 61 Cygni is 0.292 arcseconds. The astronomer John Herschel called Bessel's achievement the greatest and most glorious triumph which practical astronomy has ever witnessed, and the Royal Astronomical Society awarded Bessel its gold medal for the result.
Reputable source · 2 sources - 1843-1850 CEHistory of Physics
Joule Measures the Mechanical Equivalent of Heat
Between 1843 and 1850, the English brewer and physicist James Prescott Joule ran a series of experiments to show that heat and mechanical work were the same physical quantity in different forms. His best-known apparatus used a falling weight, connected by a string and pulleys, to turn a paddle wheel inside an insulated container of water; a PMC-hosted historical analysis of his work notes that each method gave more or less the same value for the mechanical equivalent of heat, and that by 1850 Joule had an accurate value for that conversion factor. The German physicist Hermann von Helmholtz, citing Joule's experiments directly, showed analytically in 1847 that when heat is included in the accounting, the total energy of a system is conserved, a conclusion that, alongside contributions from Julius Robert Mayer and Ludvig Colding working independently, established energy conservation as a general law rather than a special case confined to mechanics.
Primary source · 2 sources - October 16, 1846History of Medicine
Ether Makes Surgery Painless
On October 16, 1846, in the surgical amphitheater on the fourth floor of the Bulfinch Building at Massachusetts General Hospital, the first successful public demonstration of ether for surgical anesthesia was performed. William T. G. Morton, a dentist, administered ether to the patient Edward Gilbert Abbott through an apparatus of a tube connected to a glass globe, so that the surgeon John Collins Warren could remove a tumor from Abbott's neck. During the operation the patient did not shrink or cry out from pain; afterward he reported feeling only something like scraping with a blunt instrument. A plaque in the room, now called the Ether Dome, records that this was the first public demonstration of anesthesia to the extent of producing insensibility to pain during a serious surgical operation.
Peer-reviewed · 2 sources - 1847 CEHistory of Medicine
Semmelweis Asks Doctors to Wash Their Hands
At the Vienna General Hospital in the 1840s there were two obstetrics clinics: one staffed by physicians and medical students, the other by midwives. The doctors' clinic had a far higher rate of fatal childbed fever. Ignaz Semmelweis noticed that medical students and physicians often moved directly from performing autopsies to delivering babies without washing their hands. In 1847 the puzzle sharpened when his colleague Jakob Kolletschka died after his hand was cut with a scalpel during an autopsy, showing symptoms like those of the dying mothers. Semmelweis required all doctors and medical students to disinfect their hands with chlorinated lime before examining pregnant women. The mortality rate in his ward fell dramatically, from 18.27 percent to 1.27 percent, in 1848. His findings were met with skepticism and hostility from colleagues who could not accept that their own hands carried death, and the fight to have his ideas accepted took a severe toll on him.
Peer-reviewed · 2 sources - 1848-1867History of Western Philosophy
Marx and Engels Recast Philosophy as the Critique of Capital
Karl Marx, born in 1818, and Friedrich Engels published The Communist Manifesto in 1848, and Marx published the first volume of Capital (Das Kapital) in 1867, laying out a theory of historical materialism in which the primary direction of social explanation runs from a society's material conditions of production to its social forms and, in turn, to its forms of consciousness, reversing Hegel's idealist account of history as driven by the development of Spirit. Marx's analysis in Capital begins from the commodity and builds an account of capitalism in which workers experience alienated labor, work that could in principle be creative and fulfilling but is instead organized in ways that estrange workers from what they produce.
Reputable source · 2 sources - August-September 1854Pandemics Through History
John Snow Traces Cholera to the Broad Street Pump
On August 31, 1854, a cholera outbreak began in the Soho district of London, and within ten days about 600 people had died, with roughly 500 deaths concentrated in the first ten days near Broad Street. John Snow, a London physician, rejected the dominant miasma theory that blamed foul air, and instead mapped every death by household address. The map showed deaths clustering tightly around a single water pump on Broad Street, and Snow's door-to-door interviews found that nearly all the victims had drunk water from that pump, either regularly or occasionally, while workers at a nearby brewery who drank beer instead of pump water were largely unaffected. On September 7, 1854, Snow presented his findings to local officials and persuaded them to remove the pump's handle; new cases in the area dropped sharply afterward, though the outbreak was already waning as residents fled the area.
Peer-reviewed · 2 sources - 1859-1861 CEHistory of Astronomy
Kirchhoff and Bunsen Read the Sun's Chemistry From Its Spectrum
In 1859, the physicist Gustav Kirchhoff, building on decades of earlier work by Joseph von Fraunhofer identifying dark lines within the sun's spectrum, determined that each chemical element had a uniquely characteristic spectrum, establishing that for a given atom or molecule, the emission and absorption frequencies are the same. Kirchhoff explained the dark lines in the sun's spectrum as caused by absorption of particular wavelengths as light passes through gases in the sun's atmosphere, a finding that started a new era in astronomy. Working with the chemist Robert Bunsen, Kirchhoff went on to examine the spectrum of the sun directly in 1861 and identify the chemical elements present in the sun's atmosphere; in the course of the same investigations the pair also discovered two previously unknown elements, caesium and rubidium, by their distinctive spectral signatures.
Reputable source · 2 sources Louis Pasteur Traces Disease to Living Microorganisms
In the 1860s Louis Pasteur, a French chemist, investigated why batches of wine, beer, and vinegar sometimes spoiled or fermented incorrectly, and traced the problem to microorganisms contaminating the liquid rather than a defect in the liquid itself. His swan-neck flask experiments, in which broth exposed to air through a curved tube stayed sterile because airborne dust and microbes settled in the bend before reaching the liquid, directly disproved the long-held theory of spontaneous generation, the idea that living organisms could arise spontaneously from non-living matter. From this Pasteur proposed what came to be called the germ theory of disease: that many illnesses, like the fermentation problems he had studied, are caused by specific living microorganisms rather than bad air, imbalanced bodily humors, or spontaneous corruption. He presented the theory formally to the French Academy of Medicine in 1878.
Peer-reviewed · 2 sources- 1865 CE (final form 1873)History of Physics
Maxwell Unifies Electricity, Magnetism, and Light
James Clerk Maxwell took Michael Faraday's qualitative picture of electric and magnetic lines of force and translated it into rigorous mathematics. In his 1865 paper A Dynamical Theory of the Electromagnetic Field, and in final form in his 1873 book Electricity and Magnetism, Maxwell set out four partial differential equations, now called Maxwell's equations, describing how electric and magnetic fields interact and propagate. Around 1862 he calculated that the speed of propagation of an electromagnetic field matched the known speed of light and concluded, in his own words preserved by MacTutor, that we can scarcely avoid the conclusion that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena. Maxwell had shown that light, electricity, and magnetism were the same underlying phenomenon.
Primary source · 2 sources - 1867 CEHistory of Medicine
Lister Brings Antisepsis to the Operating Room
Joseph Lister took Pasteur's insight that microorganisms cause putrefaction and applied it to surgery, where wound infection and gangrene killed a large share of patients who survived the operation itself. In 1867 he adjusted his method, applying carbolic acid as a lotion directly to the raw wound, and published his results in six articles in The Lancet between March and July of that year. He also introduced weak carbolic hand washes for surgical staff and carbolic acid baths for instruments; the chemical, he found, killed germs on contact. His approach reduced the incidence of wound sepsis and gangrene, which in turn reduced the need for amputation. As the number of surgery-related infections fell, the evidence that antisepsis worked became irrefutable and it was adopted by surgeons around the world.
Peer-reviewed · 2 sources - 1874-1891 CEHistory of Mathematics
Cantor Proves Infinities Come in Different Sizes
Georg Cantor, born in 1845 in St Petersburg, developed set theory in the 1870s and 1880s and proved that infinite sets can differ in size, showing that the real numbers cannot be placed in one-to-one correspondence with the whole numbers even though both sets are infinite. Cantor was startled by his own results: writing to fellow mathematician Richard Dedekind in 1877 about a related discovery, a one-to-one correspondence between spaces of different dimensions, he wrote I see it, but I don't believe it, and elsewhere acknowledged he was placing himself in a certain opposition to views widely held concerning the mathematical infinite. His former teacher Leopold Kronecker rejected the entire approach, and the resulting bitter antagonism between the two men became public at a Mathematical Association meeting in 1891. Cantor spent much of his later career trying and repeatedly failing to resolve the continuum hypothesis, the question of whether any infinite set exists with a size strictly between that of the integers and that of the real numbers, at times believing he had solved it only to discover an error the next day.
Reputable source · 2 sources - 1876-1884Pandemics Through History
Koch's Postulates Prove Which Germs Cause Which Diseases
Building on Pasteur's germ theory, the German physician Robert Koch set out to prove that specific germs caused specific diseases, rather than merely correlating with them. In 1876 he isolated Bacillus anthracis from the blood of anthrax-infected cattle, cultured it in the lab, and showed that injecting the pure culture into healthy mice reproduced the disease, establishing what became known as Koch's postulates: the organism must be found in every case of the disease, isolated in pure culture, shown to reproduce the disease when introduced into a healthy host, and re-isolated from that host. On March 24, 1882, Koch announced to the Berlin Physiological Society that he had identified Mycobacterium tuberculosis as the cause of tuberculosis, then the leading cause of death in Europe, after nearly six months of daily work isolating and culturing the slow-growing bacillus. In 1883 and early 1884 he traveled to Egypt and then Calcutta during a cholera epidemic, examined roughly 100 autopsies, and on January 7, 1884 isolated Vibrio cholerae in pure culture from contaminated water tanks, identifying its distinctive comma shape.
Peer-reviewed · 2 sources - 1879-1922History of Western Philosophy
Frege, Russell, and Wittgenstein Turn Philosophy Toward Logic and Language
Gottlob Frege, born in 1848, published the Begriffsschrift in 1879, constructing the first fully axiomatic system of what would become modern predicate logic and developing an influential distinction between the sense and reference of linguistic expressions. Bertrand Russell, born in 1872, built on this foundation with Alfred North Whitehead in the three-volume Principia Mathematica, published between 1910 and 1913, attempting to derive mathematics from logic, and developed a theory of logical atomism holding that the world consists of a complex of simple logical facts that an ideal language could describe directly. Ludwig Wittgenstein, born in 1889, studied under Russell and published the Tractatus Logico-Philosophicus in German in 1921 and English in 1922, arguing that language works by picturing facts about the world and that many traditional philosophical problems arise from language misused beyond the limits where it can picture anything meaningful.
Reputable source · 2 sources - 1860s-1880s (Pasteur); 1882 (Koch's tubercle bacillus)History of Medicine
Pasteur and Koch Prove Germs Cause Disease
Over the second half of the 19th century, two researchers turned the germ theory of disease from a minority idea into established science. Louis Pasteur showed that microorganisms caused both fermentation and disease, that heating could kill the spoiling microbes in wine, an insight that became pasteurization, and on July 6, 1885 he treated his first human rabies patient, nine-year-old Joseph Meister, with a vaccine, saving him. Robert Koch supplied the rigor. On March 24, 1882 he presented his discovery of the bacterium that causes tuberculosis, and he set out the standard, later called Koch's postulates, for proving a specific microbe causes a specific disease: it must be present in every case, absent in other conditions, and able to reproduce the disease when isolated, cultured, and introduced into a healthy animal. Koch received the Nobel Prize in 1905 for this work.
Peer-reviewed · 2 sources - 1883-1887History of Western Philosophy
Nietzsche Declares the Death of God
Friedrich Nietzsche, born in 1844, wrote Thus Spoke Zarathustra in four parts between 1883 and 1885 and developed his critique of morality further in works including On the Genealogy of Morals in 1887. Nietzsche's pronouncement that God is dead argued that belief in the Christian God had become unbelievable in modern European culture, and that the whole of European morality built on that faith faced collapse as a result, whether or not people recognized it yet. In the Genealogy, Nietzsche traced what he called a slave revolt in morality, arguing that the priestly class, resentful of the power held by a noble warrior class, inverted the noble evaluation of good and bad into a new opposition between good and evil that redefined weakness as virtue. Nietzsche opposed both moral systems with his concept of the will to power, describing it in one late formulation as what is good: everything that heightens the feeling of power in man.
Reputable source · 2 sources - June 1894Pandemics Through History
Alexandre Yersin Identifies the Plague Bacterium During the Third Pandemic
A bubonic plague outbreak began in Hong Kong in early May 1894, part of what became the Third Plague Pandemic as infected rats spread the disease along steamship routes from southern China to port cities worldwide over the following decades. In June 1894, Alexandre Yersin, a Swiss-born French bacteriologist with the Pasteur Institute, traveled to Hong Kong and isolated a gram-negative bacillus from the buboes of plague victims, publishing his findings in the Annales de l'Institut Pasteur. His experiments met Koch's postulates for proving causation, and his description of the bacterium's staining properties proved more accurate than a competing claim published around the same time by the Japanese bacteriologist Kitasato Shibasaburo. The organism was later named Yersinia pestis in Yersin's honor. Researchers in the following years established that the bacterium was transmitted between rats and humans by fleas, completing the transmission picture.
Peer-reviewed · 2 sources - November 8, 1895History of Physics
Rontgen Discovers X-Rays
On the evening of November 8, 1895, the German physicist Wilhelm Rontgen was experimenting with cathode ray tubes in his darkened laboratory at the University of Wurzburg when, as HISTORY's account describes it, he caught a glimpse of a glow, not within the glass tube itself, but rather on a chemically coated screen he had placed nearby. World History Encyclopedia adds the physical detail: a board coated with barium platinocyanide glowed a faint yellow-green and Rontgen understood that rays from the tube had a luminescent effect, even though the tube itself was wrapped in black cardboard that should have blocked ordinary light. Rontgen spent seven weeks investigating the phenomenon virtually alone before going public, and named the unknown radiation X, for unknown. He produced an image of the bones inside his wife's hand, wedding ring included, as proof of the discovery.
Reputable source · 2 sources - November 1895History of Medicine
Rontgen Discovers X-Rays and Doctors See Inside the Living Body
Working with a completely shielded Crookes cathode tube in November 1895, Wilhelm Rontgen noticed that rays emitted from the tube somehow passed through the shielding and cast a shadow-like image on a light-sensitive screen nearby. Following up on the observation, on November 8, 1895 he produced an image of the bones of his wife's hand as evidence of his discovery, and one of the famous early radiographs, taken on December 22, 1895, shows her left hand with her ring visible on a finger. He called the unknown rays X-rays. The discovery saw immediate and widespread integration in the medical field; X-rays were quickly taken up by physicians to look inside the body without resorting to surgery. Rontgen received the first Nobel Prize in Physics, in 1901.
General source · 2 sources - 1897 CEHistory of Physics
J.J. Thomson Discovers the Electron
At Cambridge University's Cavendish Laboratory in 1897, J.J. Thomson showed that cathode rays, streams given off inside evacuated glass tubes, were deflected by electric fields, proving they were composed of charged particles rather than a wave phenomenon. By balancing the deflection from electric and magnetic fields against each other, Thomson measured the particles' charge-to-mass ratio. A Purdue University chemistry history page notes he found the same charge-to-mass ratio regardless of the metal used for the electrodes and regardless of the gas filling the tube, and concluded that the particles were a universal component of matter. A Le Moyne College historical chemistry archive adds that the small mass indicated that pieces of matter existed which were smaller, lighter, than the smallest atom yet known by a factor of 1000, and that this and the particles' universal presence together implied that even the smallest atoms have component parts, that they are not structureless or indivisible.
Reputable source · 2 sources - 1898 CEHistory of Physics
Marie and Pierre Curie Discover Radioactivity
Building on Henri Becquerel's 1896 discovery that uranium salts emitted radiation on their own, Marie Curie set out to measure this radiation systematically in ores containing uranium and thorium. She and her husband Pierre found that pitchblende, a uranium ore, was far more radioactive than its uranium content alone could explain, and the U.S. National Park Service records that this discovery led her to deduce that radiation emitted directly from atoms, not from how they are arranged within molecules, a genuinely new idea at the time. Pursuing that extra radioactivity through the arduous chemical separation of tons of ore, the Curies isolated two previously unknown elements in 1898: polonium, named for Marie's native Poland, and radium. In the course of this work Marie Curie coined the term radioactivity itself.
Primary source · 2 sources - 1900 CEHistory of Physics
Planck Introduces the Quantum
Trying to explain the spectrum of light emitted by a heated black body, a problem classical physics could not solve without predicting infinite energy at short wavelengths, Max Planck announced a new radiation formula in October 1900 that matched experimental data. He then had to find a physical justification for it. On 14 December 1900, at a meeting of the Physikalische Gesellschaft in Berlin, Planck presented his theoretical explanation: energy could only be emitted or absorbed in discrete packets, or quanta, whose size depended on a new constant he called, in his own words as recorded by MacTutor, the elementary quantum of action, now known as Planck's constant. Planck himself later admitted, in a remark MacTutor also preserves, that the whole procedure was an act of despair because a theoretical interpretation had to be found at any price, no matter how high that might be.
Primary source · 2 sources - c. 1900-1913History of Western Philosophy
Husserl Founds Phenomenology
Edmund Husserl, born in 1859, developed phenomenology as a rigorous method for describing the structures of conscious experience directly, rather than beginning from inherited metaphysical or scientific assumptions about the mind. Central to his method was intentionality, the claim that consciousness is always consciousness of something, directed toward objects, so that an experience cannot be fully described without describing what it is an experience of. Husserl summarized his method's demand with the phrase back to the things themselves, insisting that philosophy could not rest content with inherited concepts or vague, secondhand intuitions but had to return to direct experience as its evidence base.
Reputable source · 2 sources - 1905 CEHistory of Physics
Einstein Publishes His Annus Mirabilis Papers, Including Special Relativity
In 1905, while working as a patent examiner in Bern, Albert Einstein published four papers in Annalen der Physik that transformed physics. The first, examining the phenomenon Max Planck had discovered, treated light itself as arriving in discrete quanta, an idea that explained the photoelectric effect and would later win Einstein the 1921 Nobel Prize in Physics, awarded not for relativity but for this work. A third paper addressed statistical mechanics and Brownian motion, the erratic jostling of small particles suspended in a fluid, in a field previously studied by Ludwig Boltzmann and Josiah Gibbs. His second 1905 paper proposed what MacTutor calls his most consequential result: the special theory of relativity, built on the idea that the introduction of a light-ether will prove to be superfluous, that the laws of physics look the same in every uniformly moving reference frame, and that the speed of light in a vacuum is constant for every observer. Later that same year, in a short separate paper, Einstein showed how mass and energy were equivalent, the relationship expressed as E=mc^2.
Primary source · 2 sources - 1911 CEHistory of Physics
Rutherford Discovers the Atomic Nucleus
In 1911, Ernest Rutherford, working with Hans Geiger and Ernest Marsden at the University of Manchester, fired alpha particles at a thin sheet of gold foil expecting them to pass through with only slight deflection, as predicted by J.J. Thomson's plum-pudding model, in which negative electrons sat scattered through a diffuse cloud of positive charge. Instead, a small fraction of the alpha particles bounced almost straight back. A Purdue University history page records Rutherford's own astonished reaction to the result: “It was quite the most incredible event that has ever happened to me in my life.” Rutherford concluded that all of the positive charge and essentially all of the mass of the atom is concentrated in an infinitesimally small fraction of the total volume of the atom, which he called the nucleus, with his calculations putting the nucleus at least 10,000 times smaller than the atom itself, meaning the vast majority of the volume of an atom is therefore empty space.
Reputable source · 2 sources - 1908-1912 CEHistory of Astronomy
Henrietta Leavitt Finds the Key to Measuring the Universe
Working at the Harvard College Observatory, Henrietta Swan Leavitt published a catalog of over 1,777 variable stars in 1908, and by 1912 had confirmed a clear pattern across 25 Cepheid variable stars in the Small Magellanic Cloud: the brighter a Cepheid's true luminosity, the longer its pulsation period. Because all the stars in that cloud were effectively at the same distance from Earth, Leavitt could be confident that the differences she measured in apparent brightness were caused by real differences in luminosity rather than by some stars simply being closer, letting her isolate the clean relationship between a Cepheid's period and its intrinsic brightness. Leavitt's period-luminosity law lacked a zero point, meaning it could compare Cepheids to each other but could not yet convert a measured period directly into an actual distance in light-years, a gap the astronomer Harlow Shapley closed in 1918 by calibrating the relationship using Cepheids in globular clusters.
Reputable source · 2 sources - 1913 CEHistory of Physics
Bohr Proposes a Quantized Model of the Atom
In 1913 the Danish physicist Niels Bohr wrote a paper on the hydrogen atom that broke with classical theory, the first of three papers that year, discovering the major laws governing hydrogen's spectral lines, the specific colors of light hydrogen atoms absorb and emit. Bohr's model combined aspects of classical physics with Max Planck's concept of the quantum of action: electrons could only occupy certain fixed orbits around the nucleus, each with a specific quantized energy, and light was emitted or absorbed only when an electron jumped between these fixed orbits. The model successfully predicted the exact wavelengths of hydrogen's spectral lines, a result classical physics could not explain at all.
Primary source · 2 sources - 1913-1920 CEHistory of Mathematics
Ramanujan Sends Hardy a Letter Full of Unproven Theorems
Srinivasa Ramanujan, born in 1887 in Erode, India, had no university education and was largely self-taught from a single 1886 textbook of results, G.S. Carr's Synopsis of Pure Mathematics. In January 1913 he wrote to the Cambridge mathematician G.H. Hardy, introducing himself plainly, stating he had no university education but had undergone the ordinary school course, and enclosing pages of original theorems without proof. Hardy, initially suspicious the letter might be a hoax, spent hours working through the results with his colleague Littlewood and concluded the theorems must be genuine, since, as he put it, great mathematicians are commoner than thieves or humbugs of such extraordinary skill. Hardy replied on 8 February 1913 expressing keen interest and soon arranged for Ramanujan to come to Cambridge, where the two collaborated and wrote five joint papers. Hardy later said the limitations of Ramanujan's formal knowledge were as startling as its profundity, and that introducing him to new material typically produced an avalanche of original ideas rather than the standard textbook response. Ramanujan was elected a Fellow of the Royal Society in 1918 before returning to India in February 1919 in poor health; he died the following year, in 1920, at age 32.
Reputable source · 2 sources - 1915 CEHistory of Physics
Einstein Publishes the General Theory of Relativity
On 25 November 1915, Albert Einstein submitted his paper The Field Equations of Gravitation, giving the correct field equations of general relativity, a theory describing gravity not as a force acting across space but as the curvature of spacetime caused by mass and energy. Earlier that November, Einstein had already corrected an error in his own 1911 calculation of how much starlight passing near the Sun should bend, revising his predicted deflection upward. The theory also explained a long-standing puzzle in Mercury's orbit: MacTutor records that Einstein applied his theory of gravitation and discovered that the advance of 43 arcseconds per century in Mercury's perihelion, a discrepancy astronomers had been unable to explain for decades, was exactly accounted for without any need to postulate invisible moons or any other special hypothesis. The theory's prediction for starlight deflection was tested directly in 1919, when two British expeditions measured the bending of light during a solar eclipse and obtained results of 1.98 plus or minus 0.30 arcseconds and 1.61 plus or minus 0.30 arcseconds, confirming Einstein's prediction after many earlier failed attempts due to cloud, war, and other setbacks.
Primary source · 2 sources - 1918-1919Pandemics Through History
The 1918 Influenza Pandemic Kills More People Than the War It Followed
The influenza pandemic of 1918-1919, caused by a novel H1N1 strain with genetic material derived from birds, spread in three waves across nearly every populated region of the world within about a year. Wartime censorship in the combatant nations of the First World War suppressed early reporting, while neutral Spain's uncensored press covered it freely, creating the lasting but misleading label Spanish flu, even though the earliest documented cases appeared in Haskell County, Kansas in March 1918. The pandemic infected an estimated one-third of the global population and killed at least 50 million people worldwide, with some estimates reaching 100 million, a case fatality rate above 2.5 percent compared with less than 0.1 percent for typical seasonal flu, and it killed unusually large numbers of healthy young adults rather than only the very old or very young.
Peer-reviewed · 2 sources - 1921 CEHistory of Mathematics
Emmy Noether Founds Modern Abstract Algebra Without a Paid Position
Emmy Noether, born in 1882 in Erlangen, Germany, completed her doctorate in 1907, but the standard academic path toward a professorship, the habilitation, was not open to women in Germany at the time. At Gottingen, David Hilbert worked around the restriction by advertising her lecture course under his own name during 1916 and 1917, and Noether was not granted habilitation, and with it the unpaid teaching rank of Privatdozent, until 1919. In 1921 she published Idealtheorie in Ringbereichen, ideal theory in rings, a paper of fundamental importance in the development of modern algebra that established how ideals decompose into primary ideals within commutative rings, work that helped found the field now known as abstract algebra. Earlier, in relation to Einstein's general relativity, she had proved what became known as Noether's theorem, that to every continuous symmetry of a physical system there corresponds a conservation law, a result Einstein praised directly. In April 1933 Nazi policy caused her dismissal from Gottingen because she was Jewish, and she emigrated that October to a visiting position at Bryn Mawr College in the United States, where she died in 1935.
Primary source · 2 sources - 1925-1926 CEHistory of Physics
Heisenberg and Schrodinger Complete Quantum Mechanics
In 1925, Werner Heisenberg wrote his first paper on quantum mechanics, developing what became known as matrix mechanics, an abstract mathematical formulation built entirely from measurable quantities rather than pictures of electron orbits. Two years later he stated his uncertainty principle, that the position and momentum of a particle cannot both be measured with arbitrary precision at once, expressed as the relation Delta x times Delta p is greater than or equal to h-bar. In 1926, working independently, Erwin Schrodinger published a series of papers introducing an entirely different approach, wave mechanics, in which each particle is described by a wave function governed by what is now called the Schrodinger equation. MacTutor's history of the period records that mathematicians quickly showed the two theories were equivalent: to each function of the position and momentum coordinates in wave mechanics there may be related a matrix in such a way that these matrices, in every case, satisfy the formal calculation rules of Born and Heisenberg, meaning Schrodinger's differential equation and Heisenberg's matrix algebra described exactly the same physics from two different mathematical directions.
Primary source · 2 sources - 16 March 1926Space Exploration
Robert Goddard launches the first liquid-fueled rocket
On 16 March 1926, Robert H. Goddard, a physics professor at Clark University, launched the world's first liquid-propellant rocket from his Aunt Effie's farm in Auburn, Massachusetts. The rocket, later nicknamed Nell, burned gasoline and liquid oxygen. It climbed 41 feet in the air during a flight that lasted 2.5 seconds, then came down 184 feet away in a cabbage field. Goddard's wife Esther and a couple of assistants from Clark were the only witnesses. The rocket itself was unimpressive to look at: a combustion chamber and nozzle mounted on top of the fuel tanks, the reverse of a modern rocket's layout. Goddard had already spent years working on solid-fuel designs and had published a 1919 paper, 'A Method of Reaching Extreme Altitudes,' that proposed liquid propellants as the way to reach real altitude, a claim newspapers mocked at the time.
Primary source · 2 sources Heidegger Reopens the Question of Being, Then Joins the Nazi Party
Martin Heidegger, born in 1889, published Being and Time in 1927, an unfinished but hugely influential treatise whose declared aim was the concrete working out of the question of the meaning of Being, a question Heidegger argued Western philosophy had asked at its outset and then largely forgotten. Heidegger's central analysis focused on Dasein, his term for the distinctively human way of existing, whose basic structure he described as being-in-the-world, always already involved with a surrounding world and with other people rather than standing apart from it as a detached observer. In May 1933, several years after the book's publication, Heidegger joined the Nazi Party, a decision one biographer describes as a matter of conviction rather than opportunism, and one that has permanently complicated how his philosophical legacy is read.
Reputable source · 2 sources- September 1928Pandemics Through History
Alexander Fleming Discovers Penicillin in a Contaminated Petri Dish
In September 1928, Alexander Fleming, a bacteriologist at St Mary's Hospital in London, returned from a two-week vacation to find that a petri dish of Staphylococcus bacteria he had left uncovered on his bench had been contaminated by a mold, likely drifting up from another lab in the building or in through a window. The temperature conditions during his absence had allowed both the bacteria and the mold to grow side by side, and Fleming noticed a clear zone around the mold where the surrounding bacterial colonies had been killed or stopped from growing. He identified the mold as Penicillium notatum and named the antibacterial substance it produced penicillin. Fleming published the finding in 1929, but it drew little scientific attention at the time and he did not pursue it as a treatment. The breakthrough into a usable drug came over a decade later, when Oxford researchers Howard Florey and Ernst Chain isolated and purified enough penicillin to demonstrate its therapeutic effect in 1940.
General source · 2 sources - 1928 (Fleming); early 1940s (Florey and Chain)History of Medicine
Fleming's Mold and the Antibiotic Age
A chance event in a London laboratory in 1928 changed the course of medicine. Alexander Fleming, a bacteriologist at St. Mary's Hospital, returned from a vacation and noticed a zone around an invading fungus on an agar plate where the bacteria did not grow. The mold, a Penicillium, was producing something that killed bacteria. Fleming did not take the next steps to purify it or test it as a treatment. That work fell to Howard Florey and Ernst Chain at Oxford: Florey directed that penicillin's antibacterial properties be tested in mice, the decisive step Fleming had not taken, and on August 24, 1940 Florey and Chain reported their findings in The Lancet, describing how to produce and purify penicillin with enough potency to protect infected animals. Penicillin's effects led to the Nobel Prize in Physiology or Medicine in 1945, shared by Fleming, Chain, and Florey.
Peer-reviewed · 2 sources - 1929 CEHistory of Astronomy
Hubble Shows the Universe Is Expanding
By 1929, Edwin Hubble had shown that the universe was home to millions of galaxies beyond the Milky Way, and that the universe itself was expanding. Studying the light from distant galaxies, Hubble found that it appeared displaced toward the red end of the spectrum, a redshift indicating that those galaxies were receding from Earth. Hubble demonstrated that galaxies farther away recede faster than those nearby, a relationship now known as Hubble's Law, using measurements of Cepheid variable stars to establish galaxy distances and comparing those distances against each galaxy's measured redshift. His 1929 paper, A relation between distance and radial velocity among extra-galactic nebulae, laid out the observational evidence for cosmic expansion.
Reputable source · 2 sources - 1931 CEHistory of Mathematics
Godel Proves Mathematics Cannot Prove Its Own Completeness
Kurt Godel, born in 1906 in Brunn, Austria-Hungary, published his incompleteness theorems in 1931 under the title Uber formal unentscheidbare Satze der Principia Mathematica und verwandter Systeme, on formally undecidable propositions of Principia Mathematica and related systems. The theorems demonstrated that in any axiomatic mathematical system powerful enough to describe basic arithmetic, there exist propositions that can be neither proved nor disproved within the axioms of that system, and further that such a system cannot prove its own consistency from within itself. The result dealt a severe blow to the formalist program associated with the mathematician David Hilbert, which had aimed to place all of mathematics on a complete and self-verifying logical foundation, though it did not destroy the fundamental idea of formalism outright, since it demonstrated only that any adequate system would have to be more comprehensive than Hilbert had envisaged.
Reputable source · 2 sources - 1932 CEHistory of Astronomy
Karl Jansky Detects Radio Waves From the Milky Way
In 1932, Karl Jansky, an engineer at Bell Telephone Laboratories in New Jersey, revealed that stars and other objects in space radiated radio waves, a discovery he made while investigating the sources of static interference plaguing transatlantic radiotelephone communications. Jansky built a large directional antenna to track down the interference and eventually linked the source of a persistent, unexplained hiss to something in the sky rather than to any terrestrial cause, identifying the source as the center of the Milky Way galaxy in the constellation Sagittarius. Jansky's finding was announced on the front page of the New York Times in May 1933 and marked the beginning of radio astronomy as a field distinct from traditional optical observation of the night sky.
Reputable source · 2 sources - 1932-1972History of Medicine
The Tuskegee Study: Forty Years of Deliberate Non-Treatment
From 1932 to 1972 the U.S. Public Health Service ran a study of untreated syphilis involving 600 Black men in Macon County, Alabama, centered on the Tuskegee Institute. For 40 years the researchers intentionally withheld effective therapy from these men in order to observe the natural course of the disease. Informed consent was never sought; instead the men were deceived into believing they were being treated for what was called bad blood. When penicillin became available and, by the late 1940s, the standard cure for syphilis, the researchers chose to withhold it from the study's participants rather than treat them. Even after the Public Health Service set up rapid treatment centers across the country in 1947, there was no discussion of treating the men in the study. It continued until 1972, when press coverage exposed it and the government shut it down.
Peer-reviewed · 2 sources - 1936 CEHistory of Mathematics
Turing Defines Computability and the Limits of Machines
Alan Turing, born in 1912 in London, published On Computable Numbers, with an Application to the Entscheidungsproblem in 1936, defining a computable number as a real number whose decimal expansion could be produced by an abstract machine, later called a Turing machine, starting from a blank tape. Turing had come to the problem after attending a course by Max Newman covering Godel's incompleteness results and Hilbert's Entscheidungsproblem, the decision problem asking whether an algorithm could determine the truth of any mathematical statement, and his 1936 paper showed that no such general algorithm can exist, since some well-defined computational questions are simply undecidable. During the Second World War, Turing's codebreaking work at Bletchley Park, including machines built to help break German ciphers, is credited with saving lives by shortening the war. Turing died in 1954 of cyanide poisoning; an inquest ruled it self-administered, though his mother maintained it was accidental.
Reputable source · 2 sources - December 1938 - February 1939History of Physics
Meitner and Frisch Explain Nuclear Fission
In December 1938 in Berlin, chemists Otto Hahn and Fritz Strassmann bombarded uranium with neutrons and found what looked like barium among the products, a baffling result since barium is roughly half the mass of uranium. The U.S. National Park Service's account of the discovery notes that Hahn achieved nuclear fission during an experiment but did not realize it, and asked Meitner for help in explaining his puzzling results. Lise Meitner, a physicist who had fled Nazi Germany for Sweden earlier that year because she was Jewish, worked out the answer with her nephew, physicist Otto Frisch: the uranium nucleus was splitting into two lighter nuclei, releasing enormous energy in the process. The National Park Service credits the pair directly: Meitner and Frisch were the first to call the process fission, and in 1939 they published a scientific paper explaining the process, appearing in the journal Nature in February 1939.
Primary source · 2 sources - 1942-1945 CEHistory of Physics
The Manhattan Project Builds the Atomic Bomb
Within three years of the discovery of nuclear fission, the United States turned the physics into a weapon. The Manhattan Project, described by the National Park Service as an unprecedented, top-secret World War II government program in which the United States rushed to develop and deploy the world's first atomic weapons before Nazi Germany, employed hundreds of thousands of workers across three primary sites: a uranium enrichment complex at Oak Ridge, Tennessee, a plutonium production complex at Hanford, Washington, and a bomb design laboratory at Los Alamos, New Mexico, led by J. Robert Oppenheimer under General Leslie Groves. On 16 July 1945 the project successfully tested a plutonium device, code-named Gadget, at the Trinity site in New Mexico, an event the National Park Service says ushered in the nuclear age. On 6 August 1945 a uranium bomb called Little Boy was dropped on Hiroshima, Japan; a HISTORY-hosted account puts the immediate death toll at an estimated 80,000 people, with tens of thousands more dying later of radiation exposure. Three days later a plutonium bomb called Fat Man was dropped on Nagasaki, killing an estimated 40,000 people immediately, with combined estimates for both cities, counting later deaths from radiation, ranging from roughly 130,000 to 215,000.
Primary source · 2 sources - 3 October 1942Space Exploration
Germany develops the V-2 at Peenemunde
After 1937, Wernher von Braun and a German army rocket team worked at a secret research station at Peenemunde on the Baltic coast, developing the A-4 missile, later known as the V-2. On 3 October 1942, the fourth test vehicle became the first A-4 to fly successfully, reaching an altitude of about 60 miles and a range of 125 miles. Hitler ordered mass production that November. Production later moved to the underground Mittelwerk factory, where roughly 20,000 prisoners from the Mittelbau-Dora concentration camp built the missiles under brutal conditions; about half of the camp's deaths are attributed to the V-2 program. The V-2 was first used operationally against targets in Western Europe, including London, Paris, and Antwerp, starting in September 1944. It was a 46-foot liquid-propellant missile weighing 29,000 pounds, the first long-range ballistic missile in history.
Primary source · 2 sources McCulloch and Pitts model the neuron as a logic gate
Warren McCulloch, a neurophysiologist at the University of Illinois, and Walter Pitts, a largely self-taught logician, published 'A Logical Calculus of the Ideas Immanent in Nervous Activity' in the Bulletin of Mathematical Biophysics. They argued that because a neuron either fires or does not, its all-or-none behavior can be treated with propositional logic. They showed that a network of these simplified neurons, wired together with weighted connections, could compute any expression that logic itself could express, and that for any such logical statement a net could be built to match its behavior. There was no learning rule and no hardware; it was a mathematical proof that logic and neural wiring could be made equivalent.
Primary source · 2 sources- 1943-1949History of Western Philosophy
Sartre and de Beauvoir Build an Existentialist Ethics of Freedom
Jean-Paul Sartre, born in 1905, published Being and Nothingness in 1943, arguing that for human beings existence precedes essence, meaning people are not born with a fixed nature to fulfill but must create their own meaning through free choices, a freedom Sartre described as inescapable: people are condemned to be free, bearing full responsibility and anguish for their situation. Sartre illustrated the alternative, bad faith, through the example of a waiter who plays at being a waiter as though it were a fixed identity rather than a role he has chosen. Simone de Beauvoir, born in 1908, published The Second Sex in 1949, applying and extending existentialist method to argue that one is not born, but rather becomes, a woman, meaning femininity is a social and historical construction rather than a biological destiny, and developing an ethics in which willing one's own freedom requires willing the freedom of others as well.
Reputable source · 2 sources - 1941-1945Pandemics Through History
A Moldy Cantaloupe Makes Penicillin a Wartime Mass-Produced Drug
After Howard Florey and Ernst Chain proved penicillin worked as a treatment in 1940, the drug still existed only in tiny, painstakingly extracted quantities. Florey traveled to the United States in 1941 to secure help mass-producing it, and the U.S. War Production Board coordinated 21 companies, government agencies, and universities into what researchers later called a unified scientific workforce of mycologists, chemists, and engineers. The key breakthrough came from an unglamorous source: scientists at the Northern Regional Research Laboratory in Peoria, Illinois were collecting mold samples from wherever they could find them, including fruit brought in from local markets, when a moldy cantaloupe yielded a strain, later designated NRRL 1951, that produced far more penicillin than Fleming's original mold and proved ideal for large tank fermentation. Seven major firms, Merck, Squibb, Pfizer, Eli Lilly, Abbott, Upjohn, and Parke-Davis, scaled up production using this strain and deep-tank fermentation techniques, and by the end of 1943 there was enough penicillin to treat all Allied armed forces; monthly production increased more than 250-fold between May and June of 1944 alone, in time to treat wounded troops after the Normandy invasion.
Peer-reviewed · 2 sources Turing proposes the Imitation Game
In 'Computing Machinery and Intelligence,' published in the philosophy journal Mind, Alan Turing set aside the question 'Can machines think?' as too bound up in ambiguous definitions, and replaced it with the imitation game. An interrogator exchanges typewritten messages with two hidden respondents, one human and one machine, and must decide which is which. Turing proposed that if a machine could make the interrogator guess wrong about as often as a human competitor would, that performance should count as thinking, regardless of what is happening inside the machine. He devoted much of the paper to answering objections to this standard, including arguments from consciousness, mathematical limits, and the claim that machines could never do anything genuinely new.
Primary source · 2 sources- 1951 CEHistory of Medicine
Henrietta Lacks and the Cells Taken Without Consent
In 1951 Henrietta Lacks, a 31-year-old African American woman, went to Baltimore's Johns Hopkins Hospital to be treated for cervical cancer. When she arrived, she did not know that her cervical cells would be used for future scientific experiments; there was no informed consent detailing that use. Cells taken from her tumor turned out to grow indefinitely in the laboratory, the first immortal human cell line, named HeLa. After her death in 1952, HeLa cells became a vital tool in biomedical research, used in tens of thousands of studies, from testing the polio vaccine to work on cancer and countless other questions. Her family learned of the use of these cells only decades later, long after the line had become foundational to research, and they later sought legal action but for many years received no compensation.
Peer-reviewed · 2 sources - 1953 CEHistory of Medicine
The Double Helix and the Data Behind It
The discovery in 1953 of the double helix, the twisted-ladder structure of DNA, by James Watson and Francis Crick marked a turning point in biology. Their model showed how the molecule that carries heredity could store information and copy itself. The discovery rested substantially on the experimental work of Rosalind Franklin at King's College London. Her X-ray evidence demonstrated that the two sugar-phosphate backbones lay on the outside of the molecule, confirmed that the backbones formed a double helix, and revealed to Crick that they ran in opposite directions. Her superb experimental work proved essential to the discovery, yet Watson and Crick gave her scant acknowledgment, and her data was shared with them, without her knowledge, through her colleague Maurice Wilkins and Max Perutz. How to weigh her role remains actively debated; recent scholarship argues she is best remembered as an equal contributor rather than only as a wronged figure.
Reputable source · 2 sources - December 23, 1954History of Medicine
Murray Performs the First Successful Organ Transplant
In late 1954 Richard Herrick, just 23, was dying of kidney failure. He had an identical twin brother, Ronald, which meant a transplanted kidney would be genetically matched and would not be rejected as foreign tissue, the obstacle that had defeated earlier attempts. On December 23, 1954, at Peter Bent Brigham Hospital in Boston, a surgical team led by Joseph Murray transplanted one of Ronald's kidneys into Richard, with a separate team led by J. Hartwell Harrison operating on the donor. The operation gave Richard a new lease on life and ushered in the era of organ transplantation. Richard survived eight years before dying of heart failure; Ronald, the donor, lived more than fifty years after giving up a kidney. Murray received the Nobel Prize in Physiology or Medicine in 1990, together with Edward Donnall Thomas.
Peer-reviewed · 2 sources - April 12, 1955 (results announced)History of Medicine
The Polio Vaccine Ends a Terror
Polio was one of the most feared diseases of the early 20th century, paralyzing and killing children in seasonal epidemics. Jonas Salk developed a vaccine made from killed virus, and in 1954 a massive controlled field trial was launched, sponsored by the National Foundation for Infantile Paralysis, in which almost two million U.S. children between six and nine took part; more than 600,000 were injected with vaccine or placebo and the rest served as observed controls. On April 12, 1955, Thomas Francis, the trial's director and Salk's mentor, reported that the vaccine was safe, potent, and about 90 percent effective against paralytic polio. Salk became a national hero, and famously did not patent the vaccine. Soon after, Albert Sabin's live-virus oral polio vaccine, given in drops or on a sugar cube, replaced Salk's injectable vaccine in many parts of the world.
Peer-reviewed · 2 sources The Logic Theorist proves theorems by search
Allen Newell, Herbert Simon, and Cliff Shaw, working at the RAND Corporation, built the Logic Theorist to prove theorems from Whitehead and Russell's Principia Mathematica. Before any code ran on a machine, the team simulated the program by hand, with Simon's family members acting out the roles of individual program components using index cards. Once running on the JOHNNIAC computer, the program worked backward from a theorem to be proved, searching through chains of logical rules and past results to find a valid derivation, an approach the team called heuristic search rather than exhaustive checking. It went on to prove 38 of the first 52 theorems in chapter two of Principia Mathematica, including one for which its proof was shorter and more elegant than the original by Russell and Whitehead.
Reputable source · 2 sources- 18 June 1956Artificial Intelligence
The Dartmouth Workshop names 'artificial intelligence'
John McCarthy of Dartmouth College, Marvin Minsky of Harvard, Nathaniel Rochester of IBM, and Claude Shannon of Bell Telephone Laboratories submitted a proposal dated August 31, 1955 for a two-month, ten-person study to be held at Dartmouth College in the summer of 1956. The proposal stated the founding conjecture of the field: that every aspect of learning or intelligence could in principle be described precisely enough that a machine could be made to simulate it. It listed specific problems to attack, including how to make a computer use language, form abstractions, and improve itself, and it used the phrase 'artificial intelligence' to describe the whole undertaking, the term's first recorded appearance. The workshop itself ran through the summer with a rotating cast of attendees rather than the full ten researchers working continuously.
Primary source · 2 sources - 4 October 1957Space Exploration
The Soviet Union launches Sputnik 1
On 4 October 1957, the Soviet Union launched Sputnik 1 from what is now the Baikonur Cosmodrome in Kazakhstan, placing the first artificial satellite into orbit. The satellite weighed 184 pounds and was about the size of a beach ball, orbiting Earth roughly every 90 to 98 minutes on an elliptical path with an apogee of 584 miles and a perigee of 143 miles. It carried no scientific instruments, only a radio transmitter that sent out a continuous 'beep-beep' signal on frequencies amateur radio operators around the world could pick up. Visible with binoculars near dawn or dusk, Sputnik passed over the United States several times a day, and Americans tuned their radios to listen to the signal of a Soviet machine crossing their own sky.
Primary source · 2 sources - 3 November 1957Space Exploration
Laika becomes the first animal to orbit Earth
Less than a month after Sputnik 1, the Soviet Union launched Sputnik 2 on 3 November 1957, carrying a dog named Laika, a stray picked up off the streets of Moscow. Sputnik 2 weighed about 508 kilograms, far more than its predecessor, and remained attached to its booster rocket after reaching orbit. Soviet engineers built the mission in under a month at Premier Nikita Khrushchev's request, timed to mark the fortieth anniversary of the Bolshevik Revolution. Because the schedule left no time to design a recovery system, no provisions were made to bring Laika home alive; the mission was never meant to be survivable. Soviet media claimed for years that she survived for days in orbit. In October 2002, however, Russian scientist Dimitri Malashenkov revealed that Laika's capsule had overheated and she had died within a few hours of launch, not days as officially reported at the time.
Primary source · 2 sources Rosenblatt builds the Perceptron
Frank Rosenblatt, working at the Cornell Aeronautical Laboratory under Office of Naval Research funding, published 'The Perceptron: A Probabilistic Model for Information Storage and Organization in the Brain' in Psychological Review. Unlike McCulloch and Pitts' fixed logical networks, the perceptron adjusted the weights on its connections automatically based on whether its output was right or wrong, so it learned to classify simple patterns, such as letters, from labeled examples rather than from a programmer's rules. The device drew heavy press attention, with some coverage suggesting it might one day walk, talk, and reproduce itself. In 1969, Marvin Minsky and Seymour Papert's book 'Perceptrons' proved mathematically that a single-layer perceptron could not compute certain simple functions, including logical XOR, a limitation that was true of that specific architecture but was widely read as a verdict on neural networks in general.
Primary source · 2 sources- 31 January 1958Space Exploration
Explorer 1 discovers the Van Allen radiation belt
Explorer 1, the first American satellite, launched from Cape Canaveral at 10:48 p.m. EST on 31 January 1958, atop a Jupiter-C rocket built by Wernher von Braun's Army Ballistic Missile Agency team, with the Jet Propulsion Laboratory managing the spacecraft and mission. Weighing just 30.66 pounds, 18.35 pounds of which was instrumentation, Explorer 1 carried a cosmic-ray detector designed by University of Iowa physicist James Van Allen. Unlike Sputnik, the American satellite returned real scientific data. Van Allen's instrument registered a far lower cosmic-ray count than expected in some parts of the orbit; he theorized the detector had been saturated by intense radiation from a belt of charged particles trapped by Earth's magnetic field. A second satellite two months later confirmed the belt existed, and it was named after him.
Primary source · 2 sources - 29 July 1958Space Exploration
Congress creates NASA
Sputnik's launch in October 1957 and the appearance of Soviet superiority in missile and satellite technology pushed the US government to act. On 2 April 1958, President Dwight Eisenhower asked Congress in a letter to create a civilian National Aeronautics and Space Agency, built around the existing National Advisory Committee for Aeronautics, which had been running wind-tunnel and flight research since 1915. Congress passed the resulting legislation, and Eisenhower signed the National Aeronautics and Space Act of 1958 into law on 29 July 1958. The act abolished NACA and transferred its people, labs, and resources to the new agency. NASA formally opened for business on 1 October 1958, absorbing NACA's roughly 8,000 employees and four research centers as its founding workforce.
Primary source · 2 sources - 12 April 1961Space Exploration
Yuri Gagarin becomes the first human in space
On 12 April 1961, Soviet cosmonaut Yuri Gagarin launched aboard Vostok 1 from a site in what is now Kazakhstan, becoming the first human to fly in space. His spacecraft completed a single orbit of Earth, traveling at roughly 27,400 kilometers per hour, with the whole flight lasting 108 minutes. Unlike later American capsules, Vostok 1 was not designed for Gagarin to land inside it: at low altitude he ejected from the descending capsule and parachuted to the ground separately, a detail the Soviet Union did not initially disclose. During the flight Gagarin famously radioed, 'I see Earth! It is so beautiful.' He was 27 years old and became an instant international hero.
Primary source · 2 sources - 5 May 1961Space Exploration
Alan Shepard becomes the first American in space
On 5 May 1961, less than a month after Gagarin's orbital flight, Alan Shepard became the first American in space, riding a Redstone rocket in a Mercury capsule he named Freedom 7. The launch came from Cape Canaveral, Florida, and reached a peak altitude of 116 miles and a downrange distance of 302 miles before Freedom 7 parachuted into the Atlantic Ocean after 15 minutes and 22 seconds, having hit a top speed of 5,180 miles per hour. Unlike Gagarin's mission, Shepard's flight was suborbital: the capsule never achieved a full orbit of Earth, a far less demanding trajectory than the Soviet flight. NASA had selected Shepard three weeks earlier from the Mercury Seven, the agency's first group of astronauts chosen in 1959.
Primary source · 2 sources - 25 May 1961Space Exploration
Kennedy commits the United States to landing on the Moon
On 25 May 1961, in a Special Message to Congress on Urgent National Needs, President John F. Kennedy declared, 'I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth.' The 46-minute address came just three weeks after Alan Shepard's suborbital flight and was framed around competing with the Soviet Union across a range of fields, not space alone. Kennedy reaffirmed the commitment on 12 September 1962 in a speech at Rice University in Houston, telling the crowd, 'We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard,' a line largely written by his speechwriter Ted Sorensen.
Primary source · 2 sources - 16 June 1963Space Exploration
Valentina Tereshkova becomes the first woman in space
Valentina Tereshkova, a 26-year-old former textile-factory worker and amateur parachutist, launched aboard Vostok 6 on 16 June 1963, becoming the first woman in space. She had been selected in February 1962 from more than 400 applicants as part of a Soviet program specifically created to ensure the first woman in space would be a Soviet citizen. Using the radio call sign 'Chaika,' meaning seagull, she flew solo for just under three days, two days, 23 hours, and 12 minutes, completing 48 orbits of Earth. During the mission Vostok 5, launched two days earlier with cosmonaut Valery Bykovsky aboard, came within 4.5 kilometers of Tereshkova's capsule, marking the second time two crewed spacecraft were in orbit simultaneously. Both spacecraft landed on 19 June 1963, and Tereshkova was awarded the title Hero of the Soviet Union.
Primary source · 2 sources - 18 March 1965Space Exploration
Alexei Leonov performs the first spacewalk
On 18 March 1965, Soviet cosmonaut Alexei Leonov left the Voskhod 2 spacecraft to perform the first spacewalk in history, floating free for about 12 minutes while tethered to the capsule. The spacewalk went as planned until Leonov tried to return: his spacesuit had ballooned so severely in the vacuum of space that he could no longer fit through the airlock hatch. In a decision not part of the mission plan, he bled air out of his suit through a valve to shrink it enough to squeeze back inside, working alone with no way to consult ground control in real time about the fix. He and fellow cosmonaut Pavel Belyayev returned safely, though later in the mission a guidance failure forced them to land hundreds of kilometers off course in a forest, where they spent a night surrounded by wolves before rescue.
Reputable source · 2 sources - 3 June 1965Space Exploration
Ed White makes the first American spacewalk
During the Gemini 4 mission, astronaut Ed White became the first American to leave a spacecraft in orbit, exiting the capsule on 3 June 1965 while commander James McDivitt remained inside and photographed him. White was secured to the spacecraft by a 25-foot umbilical line wrapped in gold tape and maneuvered himself using a hand-held oxygen-jet gun, nicknamed the 'zip gun,' that expelled pressurized gas to push him around outside the capsule. The extravehicular activity started over the Pacific Ocean near Hawaii and lasted 23 minutes before ending over the Gulf of Mexico. Gemini 4 as a whole lasted just under four days and 62 orbits, a length NASA chose specifically to approach the endurance record the Soviets had already set.
Primary source · 2 sources - 1947-1965 CEHistory of Physics
Feynman, Schwinger, and Tomonaga Complete Quantum Electrodynamics
After the Second World War, physicists trying to apply quantum theory to the interaction of light and charged particles kept running into equations that predicted infinite, meaningless results. Working independently, Julian Schwinger in the United States, Sin-Itiro Tomonaga in Japan, and Richard Feynman, also in the United States, each solved the problem in a different mathematical style between the late 1940s and the mid-1950s. Schwinger used a technique called renormalization, which, according to a National MagLab history of the period, rid the quantum field theory developed by Paul Dirac of serious incongruities with experimental observations that had nearly prompted the scientific community to abandon it. Feynman's approach used intuitive diagrams, now called Feynman diagrams, which MacTutor describes as graphic analogues of the mathematical expressions needed to describe the behaviour of systems of interacting particles. All three approaches were later shown to be mathematically equivalent, together forming quantum electrodynamics, or QED.
Primary source · 2 sources - 1964-1965 CEHistory of Astronomy
Penzias and Wilson Detect the Cosmic Microwave Background
Arno Penzias and Robert Wilson, two radio astronomers at Bell Telephone Laboratories, were using a large horn antenna in Holmdel, New Jersey, originally built to test communications with NASA's Echo satellite, when they encountered a faint, persistent microwave signal they could not eliminate no matter where in the sky they pointed the instrument. The signal matched a temperature of about 3.5 degrees Kelvin and appeared uniformly across the entire sky regardless of time or season, leading the pair to conclude it originated from beyond the galaxy rather than from any local source of interference. Their result coincided with theoretical predictions made by physicists including George Gamow, Ralph Alpher, and Robert Herman back in the late 1940s, who had argued that if the universe began in a hot Big Bang, its residual heat should still be faintly detectable today; Penzias and Wilson's team and a group at Princeton University announced the discovery together in a pair of letters published in the Astrophysical Journal in July 1965.
Reputable source · 2 sources - 14 July 1965Space Exploration
Mariner 4 sends back the first close-up images of Mars
Mariner 4, launched by NASA's Jet Propulsion Laboratory on 28 November 1964, flew past Mars on 14 July 1965 at a distance of 6,118 miles, completing the first successful mission to another planet. Its onboard camera captured 22 photographs during the flyby, covering less than 1 percent of the Martian surface, which took days to transmit back to Earth over the spacecraft's slow radio link. The images showed a heavily cratered terrain resembling the Moon rather than the canals and vegetation some scientists had speculated might exist, a result that reshaped assumptions about the planet almost overnight.
Primary source · 2 sources Weizenbaum's ELIZA imitates a therapist
Joseph Weizenbaum at MIT published 'ELIZA, A Computer Program for the Study of Natural Language Communication Between Man and Machine' in Communications of the ACM. ELIZA worked by scanning a user's typed sentence for a keyword, applying a scripted transformation rule tied to that keyword, and printing the result back as a question, in the manner of a Rogerian psychotherapist reflecting a patient's own words. If no keyword matched, it fell back on a content-free prompt like 'please go on.' There was no understanding of meaning anywhere in the program, only string matching and substitution. Weizenbaum became alarmed when he found that people, including his own secretary, treated their sessions with ELIZA as genuinely private and confided in it as they would a real therapist, and asked him to leave the room.
Primary source · 2 sources- 27 January 1967Space Exploration
The Apollo 1 fire kills three astronauts
On 27 January 1967, astronauts Virgil 'Gus' Grissom, Ed White, and Roger Chaffee died when a fire swept through their Apollo command module during a launch pad test at Cape Kennedy. The test was a 'plugs-out' rehearsal, meant to check whether the spacecraft could run on internal power alone; because neither the rocket nor the capsule held fuel or cryogenics and its pyrotechnics were disabled, engineers had classified the test as non-hazardous. The capsule's atmosphere was pure oxygen at higher than normal pressure, and a spark, later traced to frayed wiring near Grissom's seat, ignited flammable material inside the sealed cabin. The crew could not escape in time; a NASA investigation board led by Langley Research Center director Floyd Thompson later found the primary cause of death was cardiac arrest from carbon monoxide, with the astronauts' suits and oxygen lines melted by the fire.
Primary source · 2 sources - 21 December 1968Space Exploration
Apollo 8 becomes the first crewed flight to the Moon
Apollo 8 launched on 21 December 1968 carrying Frank Borman, Jim Lovell, and William Anders, becoming the first crewed spacecraft to leave Earth's orbit entirely and travel to the Moon. It was also the first crewed launch of the massive Saturn V rocket. The crew orbited the Moon ten times without landing, becoming the first humans to see the Moon's far side directly and the first to see and photograph an Earthrise, Earth appearing to rise over the lunar horizon, on 24 December 1968. The mission splashed down in the Pacific Ocean on 27 December. Nature photographer Galen Rowell later called the Earthrise photograph, taken by Anders, the most influential environmental photograph ever taken; some historians credit it with helping spark the modern environmental movement.
Primary source · 2 sources - 1966-1972Artificial Intelligence
Shakey becomes the first robot that reasons about its actions
Researchers at the Stanford Research Institute, led by Charles Rosen, Nils Nilsson, and Peter Hart, built Shakey, a wheeled robot that operated in a set of rooms containing blocks and ramps. Shakey used a camera and bump sensors to perceive its surroundings, and a planning program called STRIPS (Stanford Research Institute Problem Solver) to break a goal such as 'push block 9 to doorway 4' into a sequence of achievable actions. If an action failed partway through, Shakey could re-plan around the failure rather than simply stopping. Its control software was organized into layers, from low-level motor control up to high-level planning, an architecture that later became a template for other robots. It was not fast or practical: a single task could take Shakey hours to complete.
Peer-reviewed · 2 sources - 20 July 1969Space Exploration
Apollo 11 lands the first humans on the Moon
On 20 July 1969, the lunar module Eagle, carrying commander Neil Armstrong and pilot Buzz Aldrin, separated from the Apollo 11 command module and touched down on the Sea of Tranquility at 4:17 p.m. EDT, while Michael Collins orbited overhead in the command module. At 10:56 p.m. EDT, with more than half a billion people watching on television, Armstrong climbed down the ladder and became the first human to set foot on another world, saying, 'That's one small step for a man, one giant leap for mankind.' Aldrin joined him roughly twenty minutes later, and together they spent about two and a half hours on the surface, collecting rock and soil samples, taking photographs, and setting up scientific instruments before returning to the lunar module. The crew splashed down in the Pacific Ocean off Hawaii on 24 July 1969.
Primary source · 2 sources - 13 April 1970Space Exploration
Apollo 13's oxygen tank explodes en route to the Moon
Apollo 13 launched on 11 April 1970 as the third planned Moon landing, but at 55 hours and 46 minutes into the mission, just after the crew finished a television broadcast, an oxygen tank in the service module exploded, disabling a second tank as well. Crewmember Jack Swigert radioed, 'Houston, we've had a problem here,' as the spacecraft lost two of its three fuel cells and the power, oxygen, and water they generated. Commander Jim Lovell, Swigert, and Fred Haise abandoned the planned landing and moved into the lunar module Aquarius, using it as a lifeboat for the trip around the Moon and back, conserving power and water while ground controllers worked out emergency return procedures. They splashed down safely in the Pacific Ocean near Samoa on 17 April 1970, five days, 22 hours after launch. A later investigation traced the explosion to damaged wiring insulation inside the tank, degraded years earlier when its internal heater voltage was upgraded without updating the thermostatic switches meant to protect it.
Primary source · 2 sources - 19 April 1971Space Exploration
The Soviet Union launches Salyut 1, the first space station
On 19 April 1971, the Soviet Union launched Salyut 1, the world's first space station, beating the American Skylab into orbit by roughly two years. The Soyuz 10 crew attempted to dock with the station but could not achieve a hard dock and had to abort. The Soyuz 11 crew, cosmonauts Georgi Dobrovolski, Vladislav Volkov, and Viktor Patsayev, successfully docked and spent a record-setting 24 days aboard Salyut 1 conducting experiments. On their return to Earth, however, a valve on their Soyuz capsule opened prematurely during separation, causing the cabin to depressurize; all three cosmonauts died before the capsule reached the ground. Following the tragedy, Salyut 1's mission was terminated and the station was deliberately deorbited, burning up on 11 October 1971.
Primary source · 2 sources Rawls Reimagines Justice From Behind a Veil of Ignorance
John Rawls, born in 1921, published A Theory of Justice in 1971, reviving the social contract tradition that had lain largely dormant in political philosophy since the 18th century. Rawls proposed a thought experiment, the original position, in which representatives of real citizens agree on principles of justice from behind a veil of ignorance that deprives them of knowledge of the race, class, gender, and social position of the people they represent, forcing them to choose principles that would be acceptable no matter which position in society they personally ended up occupying. From this position, Rawls argued, rational representatives would choose two principles: an equal claim to the fullest possible scheme of basic liberties for all, and a rule, the difference principle, permitting social and economic inequalities only when they work to the greatest benefit of society's least advantaged members.
Reputable source · 2 sources- 7 December 1972Space Exploration
Apollo 17 makes the last crewed Moon landing
Apollo 17 launched on 7 December 1972, the eleventh and final crewed mission of the Apollo program. Commander Eugene Cernan and lunar module pilot Harrison Schmitt, a professional geologist selected in place of astronaut Joe Engle specifically so a trained scientist would walk on the Moon, landed in the Taurus-Littrow valley while command module pilot Ronald Evans orbited above. Using a lunar rover, Cernan and Schmitt covered ground including a point 7.4 kilometers from the lunar module, the farthest any Apollo crew traveled from their spacecraft, and conducted three moonwalks totaling just over 22 hours, a program record. The mission splashed down on 19 December 1972. When Cernan climbed back into the lunar module to leave the surface, he became, and remains, the last person to have walked on the Moon.
Primary source · 2 sources The Lighthill Report triggers the first AI winter
The UK Science Research Council commissioned applied mathematician James Lighthill, who was not an AI researcher, to assess the field's progress. His 1973 report, 'Artificial Intelligence: A General Survey,' concluded that AI research had produced a pronounced sense of disappointment relative to the hopes raised since 1950, singling out the failure of general-purpose problem solvers to scale beyond toy problems, what Lighthill called the 'combinatorial explosion.' The report split AI research into categories and judged some, like robotics research under Donald Michie at Edinburgh, more harshly than others. Following the report and a televised debate between Lighthill and AI researchers including Michie, British funding for AI research outside a few select programs was sharply reduced.
Primary source · 2 sources- 3 December 1973Space Exploration
Pioneer 10 becomes the first spacecraft to reach Jupiter
Pioneer 10 launched on 2 March 1972 and became the first spacecraft to cross the asteroid belt, entering it on 15 July 1972 and emerging unscathed on 15 February 1973. On 3 December 1973, it flew past Jupiter at a distance of 82,178 miles, traveling at roughly 78,000 miles per hour, the first close encounter any spacecraft had with the solar system's largest planet. Pioneer 10 carried a gold anodized plaque designed by Carl Sagan and Frank Drake, showing a man and woman and the Sun's position relative to nearby pulsars, intended as a message in case the spacecraft were ever found by another civilization after leaving the solar system. On 13 June 1983, Pioneer 10 passed the orbit of Neptune and became the first human-made object to leave the solar system entirely.
Primary source · 2 sources - c. 1961-1974 CEHistory of Physics
Physicists Complete the Standard Model
Over roughly a decade and a half, particle physicists assembled the Standard Model, the theory that, in CERN's own words, explains how the basic building blocks of matter interact, governed by four fundamental forces. Developed in stages, including the 1964 proposal of quarks by Murray Gell-Mann and George Zweig and the incorporation of the Higgs mechanism into the electroweak theory by Steven Weinberg and Abdus Salam in 1967, CERN describes the theory as developed in the early 1970s, stating it has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. The finished model organizes matter into six quarks and six leptons, including the electron and its heavier relatives, and describes three of the four fundamental forces, electromagnetic, weak, and strong, through the exchange of force-carrying bosons: the photon, the W and Z bosons, and the gluon.
Primary source · 2 sources - 20 July 1976Space Exploration
Viking 1 makes the first successful landing on Mars
Viking 1's lander separated from its orbiter and touched down on Mars on 20 July 1976, exactly seven years after the Apollo 11 Moon landing, becoming the first American spacecraft to land successfully on another planet. It set down on the western slopes of Chryse Planitia, or Golden Plain, and began transmitting the first photograph of its landing site within five minutes. Viking 1 carried three biology experiments built to search for signs of microbial life in Martian soil, along with a gas chromatograph mass spectrometer to analyze samples for organic compounds. The lander went on to operate on the surface for more than 2,300 days, over six years, the longest extraterrestrial surface mission until Opportunity's rover broke the record in 2010.
Primary source · 2 sources - 5 September 1977Space Exploration
Voyager 1 and 2 launch carrying the Golden Record
Voyager 2 launched on 20 August 1977, followed by Voyager 1 on 5 September 1977, taking advantage of a rare alignment of the outer planets, occurring roughly every 175 years, that allowed a single spacecraft to visit Jupiter, Saturn, Uranus, and Neptune using gravity assists between each flyby. Each spacecraft carries an identical Golden Record, a 12-inch gold-plated copper disc holding sounds and images meant to portray life on Earth. NASA's Jet Propulsion Laboratory manager John Casani appointed astronomer Carl Sagan to lead the committee that assembled its contents: 115 photographs, greetings spoken in 55 languages, natural sounds like thunder and whale song, and 90 minutes of music spanning Bach, Chuck Berry, and traditional recordings from cultures around the world.
Primary source · 2 sources - 1970s-1980sArtificial Intelligence
Expert systems drive AI's 1980s commercial boom
Researchers at Stanford, led by Edward Shortliffe and Bruce Buchanan, built MYCIN in the mid-1970s to diagnose bacterial blood infections and recommend antibiotic treatment. MYCIN encoded roughly 500 rules describing an infectious-disease specialist's reasoning as if-then statements, and used backward chaining, starting from a hypothesis such as a specific bacterial infection and asking what facts would need to be true for the hypothesis to hold, then querying the physician for those facts. It could also explain its own reasoning chain when asked. MYCIN itself was never deployed clinically, largely over liability and integration concerns, but the rule-based approach it demonstrated was commercialized widely through the 1980s across finance, manufacturing, and computer configuration, at one point rules-based systems like Digital Equipment Corporation's XCON handling thousands of production rules.
Primary source · 2 sources - May 8, 1980Pandemics Through History
The World Declares Smallpox Eradicated
The World Health Organization launched an Intensified Eradication Program for smallpox in 1967, deploying a strategy called ring vaccination, developed by epidemiologist William Foege, that focused vaccination on people surrounding each new case rather than trying to vaccinate entire populations. The thirteen-year campaign cost about $300 million and involved roughly half a billion individual vaccinations delivered by thousands of health workers worldwide. The last known case of naturally occurring smallpox was Ali Maow Maalin, a hospital cook in Merca, Somalia, diagnosed with the milder Variola minor strain on October 26, 1977; none of his many contacts developed the disease, and aggressive containment stopped any further spread. On May 8, 1980, the 33rd World Health Assembly formally declared: "The world and all its peoples have won freedom from smallpox."
Reputable source · 2 sources - 12 April 1981Space Exploration
The Space Shuttle Columbia flies for the first time
On 12 April 1981, commander John Young and pilot Robert Crippen launched aboard the space shuttle Columbia on STS-1, the first orbital flight of NASA's Space Shuttle program and the first crewed American launch since the Apollo-Soyuz Test Project in 1975. The two-day test flight checked the orbiter's systems in space for the first time; the mission carried no other payload since the entire spacecraft itself was the experiment. Roughly 70 anomalies were noted during and after the flight, reflecting how many new components had never been tested together in this configuration before. The launch fell, by design, on the twentieth anniversary of Yuri Gagarin's first human spaceflight in 1961.
Primary source · 2 sources - June 5, 1981Pandemics Through History
The First AIDS Cases Are Reported and a New Pandemic Begins
On June 5, 1981, the CDC's Morbidity and Mortality Weekly Report published a short article titled "Pneumocystis Pneumonia, Los Angeles," describing five previously healthy young gay men treated at three Los Angeles hospitals between October 1980 and May 1981 for Pneumocystis carinii pneumonia, a form of lung infection almost never seen outside people with severely compromised immune systems. Two of the five had already died by the time of publication, and the remaining three died soon after. Michael Gottlieb, the immunologist who first noticed the pattern, worked with CDC officials to rush the report into print because case numbers were rising too fast for a standard scientific paper. Similar clusters of rare infections and cancers were soon reported from other cities, and the CDC formed a task force just three days after publication. HIV, the virus responsible, is now understood to have jumped from chimpanzees to humans earlier in the 20th century, decades before it was recognized.
Primary source · 2 sources Japan launches the Fifth Generation Computer Project
Japan's Ministry of International Trade and Industry started the Fifth Generation Computer Project in 1982, establishing the Institute for New Generation Computer Technology (ICOT) to run it. The goal was a new kind of computer built for knowledge-based information processing rather than conventional arithmetic, using massively parallel hardware and the logic-programming language Prolog instead of standard procedural code. ICOT built a series of prototype parallel inference machines, including the PIM/p with 512 processing elements and the PIM/m with 256, aiming for hundreds of millions of logical inferences per second. The project ran for its full planned decade and consumed about 54 billion yen before concluding in 1992 without producing commercially competitive machines, as conventional workstations and the desktop computing revolution overtook its specialized hardware.
General source · 2 sources- 28 January 1986Space Exploration
Space Shuttle Challenger breaks apart after launch
On 28 January 1986, Space Shuttle Challenger broke apart 73 seconds into the flight of mission STS-51L, killing all seven crew members: Dick Scobee, Michael Smith, Ellison Onizuka, Judith Resnik, Ronald McNair, Gregory Jarvis, and Christa McAuliffe, a New Hampshire schoolteacher who would have been the first private citizen in space. The Rogers Commission, which investigated the disaster, found that a rubber O-ring seal in the right solid rocket booster had failed after becoming brittle in unusually cold weather at the launch pad. Engineers at Morton Thiokol, the booster's manufacturer, had explicitly warned the night before that O-rings should not be flown below 53 degrees Fahrenheit; the temperature at launch was 36 degrees. The Commission's report concluded plainly that had decisionmakers known all the facts, 'it is highly unlikely that they would have decided to launch.'
Primary source · 2 sources - 19 February 1986Space Exploration
The Soviet Union launches the Mir space station
The Soviet Union launched the core module of the Mir space station on 19 February 1986. Designed with a planned lifespan of about five years, Mir stayed in orbit for fifteen, roughly three times its intended life, as additional modules were added over the following decade. During 13 years of continuous or near-continuous human occupancy, Mir hosted 125 cosmonauts and astronauts from 12 countries, including cosmonaut-physician Valery Polyakov, who set an endurance record of 438 consecutive days in space between January 1994 and March 1995 that still stands. Mir held the record for the longest continuous human presence in space, 3,644 days, until the International Space Station surpassed it in 2010. The station was deliberately deorbited in March 2001 after funding for its upkeep was cut.
Primary source · 2 sources - 1987-1993Artificial Intelligence
The Lisp machine crash brings a second AI winter
Through the mid-1980s, companies including Symbolics and Lisp Machines Inc. sold specialized workstations, known as Lisp machines, built to run the AI programming language Lisp efficiently, priced from tens of thousands to over $100,000. By 1987, general-purpose workstations from vendors like Sun Microsystems had closed the performance gap at a fraction of the cost, and the dedicated Lisp-hardware market collapsed within about a year; Lisp Machines Inc. filed for bankruptcy in 1987 and Symbolics followed in 1993. At the same time, expert systems such as DEC's XCON, despite genuine early success managing tens of thousands of rules, proved brittle and expensive to maintain as their rule sets grew, a problem researchers called the knowledge acquisition bottleneck. DARPA, which had funded AI heavily through its Strategic Computing Initiative since 1983, cut funding sharply after concluding the initiative would not deliver on its original goals.
Primary source · 3 sources - 24 April 1990Space Exploration
The Hubble Space Telescope launches with a flawed mirror
The Hubble Space Telescope launched aboard the space shuttle Discovery on mission STS-31 on 24 April 1990. Soon after it began returning data, astronomers found that instead of the sharp, point-like star images they expected, Hubble produced stars surrounded by fuzzy halos of light. The main mirror had been ground with a flaw at its edge, off by roughly a fiftieth the width of a human hair, too small to see by eye but large enough to blur every image the telescope produced, a defect called spherical aberration. NASA corrected the problem with a servicing mission, STS-61, in December 1993, installing an instrument called COSTAR along with a corrective optics package built into a replacement camera, WFPC2. On 18 December 1993, astronomers at the Space Telescope Science Institute watched the first corrected image appear on a monitor, free of the blur that had defined Hubble's first three and a half years.
Primary source · 2 sources - 1990-1993 CEHistory of Astronomy
Hubble Space Telescope Launches, Then Gets Fixed in Orbit
The Hubble Space Telescope launched on 24 April 1990 aboard the space shuttle Discovery, the culmination of decades of planning that began when the project was first conceived in the 1940s under the name Large Space Telescope and was built through the 1970s by NASA with contributions from the European Space Agency, after delays including the 1986 Challenger disaster pushed the launch back from an originally planned 1983 date. Soon after reaching orbit, astronomers found that Hubble's images were not the crisp, point-like star images they had expected but were instead surrounded by large, fuzzy halos of light, caused by the edges of the telescope's primary mirror having been ground too flat by a fraction of the width of a human hair. NASA sent astronauts to fix the flaw on the Servicing Mission 1 shuttle flight, and on 18 December 1993 scientists at the Space Telescope Science Institute watched and cheered as the first corrected image, free of the earlier blurriness, appeared on their monitor. Over its operating lifetime Hubble has taken more than 1.7 million observations, which astronomers have used to publish more than 23,000 peer-reviewed scientific papers.
Reputable source · 2 sources - 1993-1995 CEHistory of Mathematics
Fermat's Margin Note Waits 358 Years for Andrew Wiles
Pierre de Fermat wrote in the margin of his copy of Diophantus's Arithmetica around 1630 that no three positive integers a, b, and c can satisfy a to the power n plus b to the power n equals c to the power n for any integer n greater than 2, adding, in his own words, that he had discovered a truly marvelous proof which this margin is too small to contain. No such proof by Fermat has ever been found, and the claim, known as Fermat's Last Theorem, went unproved for over 350 years. Andrew Wiles, born in 1953, announced a proof in a lecture at Cambridge's Isaac Newton Institute in June 1993, ending simply, I will stop here. By December 1993 a gap had emerged in the argument, centered on bounding a mathematical structure called the Selmer group, and Wiles spent nearly a year trying to fix it. On 19 September 1994, working with his former student Richard Taylor, Wiles found the fix using an approach tied to Barry Mazur's and Victor Flach's earlier methods, later describing the moment as the most important of his working life. The completed proof, Modular Elliptic Curves and Fermat's Last Theorem, was published in the Annals of Mathematics in 1995. Wiles received the Abel Prize in 2016, with the official citation praising his proof of Fermat's Last Theorem by way of the modularity conjecture for semistable elliptic curves as opening a new era in number theory.
Primary source · 3 sources - October 1995History of Astronomy
Mayor and Queloz Find the First Exoplanet Around a Sun-Like Star
In October 1995, the Swiss astronomers Michel Mayor and Didier Queloz announced the first detection of a planet orbiting a star like our Sun, using the ELODIE spectrograph on a 1.9-meter telescope at the Observatoire de Haute-Provence in France. They found the planet, 51 Pegasi b, by measuring the Doppler shift in its host star's light as the star wobbled around the center of mass it shared with the orbiting planet, a technique known as the radial velocity method. The planet turned out to be a hot Jupiter, a gas giant with a surface temperature between roughly 1,000 and 1,800 degrees Fahrenheit that completes an orbit around its star in just four days, an arrangement unlike anything in our own solar system. Mayor and Queloz shared the 2019 Nobel Prize in Physics for the discovery.
Reputable source · 2 sources - 11 May 1997Artificial Intelligence
Deep Blue defeats a reigning world chess champion
IBM's Deep Blue, a chess computer using 32 processors and 216 custom chess chips, played a six-game rematch against reigning world champion Garry Kasparov at the Equitable Center in New York in May 1997, a year after Kasparov had beaten an earlier version of the machine. Deep Blue searched up to 200 million chess positions per second, evaluating moves through brute-force lookahead rather than any learned strategic sense, aided by hand-tuned evaluation functions built with input from chess grandmasters. Kasparov won game one, Deep Blue took game two, three games were drawn, and Deep Blue won the decisive sixth game, taking the match 3.5 to 2.5. Kasparov later said the loss unsettled him enough that he suspected human interference, an accusation IBM denied and that has never been substantiated.
Primary source · 2 sources - 4 July 1997Space Exploration
Sojourner becomes the first wheeled rover on another planet
NASA's Mars Pathfinder mission, launched 4 December 1996, landed on Mars on 4 July 1997 using an entry, descent, and landing sequence that relied on airbags rather than retro-rockets, the first American spacecraft to land this way. The mission deployed the Sojourner rover, a 23-pound, six-wheeled robot that rolled off the lander onto the Martian surface, becoming the first wheeled vehicle to operate on another planet. Designed to last about 30 days, Sojourner instead worked for nearly three months, sending back more than 550 images and analyzing the chemical composition of 16 locations near the landing site in Ares Vallis. Pathfinder as a whole returned more than 1.2 gigabits of data and over 10,000 pictures before the mission ended.
Primary source · 2 sources - 20 November 1998Space Exploration
Zarya launches, beginning construction of the International Space Station
The Zarya module, whose name means 'sunrise,' launched on 20 November 1998 aboard a Russian Proton rocket, becoming the first component of the International Space Station placed in orbit. Zarya was built by the Khrunichev State Research and Production Space Center in Moscow under a NASA contract, making it a Russian-built module that counted as a US contribution to the station. On 4 December 1998, the space shuttle Endeavour launched carrying Unity, the first American-built module, and on 6 December the crew of mission STS-88 connected Unity to Zarya in orbit, formally beginning ISS assembly. Zarya's job in these early years was to provide the station's initial power, propulsion, and guidance while later modules were added.
Primary source · 2 sources - 1 February 2003Space Exploration
Space Shuttle Columbia breaks apart during reentry
Space Shuttle Columbia launched on 16 January 2003 for STS-107, a 17-day science mission. During ascent, a piece of foam insulation broke off the external fuel tank and struck the reinforced carbon-carbon panels on the leading edge of the orbiter's left wing, an event caught on launch video but not seen as an immediate threat by mission managers at the time. On 1 February 2003, as Columbia reentered the atmosphere for a scheduled landing at Kennedy Space Center, the damaged wing allowed superheated atmospheric gases to penetrate the wing structure. The orbiter broke apart over Texas, killing all seven crew members: Rick Husband, William McCool, Michael Anderson, David Brown, Kalpana Chawla, Laurel Clark, and Ilan Ramon, Israel's first astronaut.
Primary source · 2 sources - 1990-2003History of Medicine
The Human Genome Project Reads the Full Sequence
The Human Genome Project was a large, well-organized, and highly collaborative international effort to generate the first sequence of the human genome, the full set of genetic instructions for a human being. It officially began on October 1, 1990, when the NIH allocated the first funds toward developing the approaches, technologies, and resources needed to map and sequence the genome. On June 26, 2000, the International Human Genome Sequencing Consortium announced that it had completed a working draft of the sequence. On April 14, 2003, the consortium announced the successful completion of the project, more than two years ahead of schedule, and by a coincidence of timing the finished sequence arrived essentially fifty years after the double helix was described.
Reputable source · 2 sources - 3 January 2004Space Exploration
Spirit and Opportunity find evidence of ancient water on Mars
NASA's twin Mars Exploration Rovers landed three weeks apart in January 2004: Spirit on 3 January in Gusev Crater, chosen because geologists suspected it once held a lake, and Opportunity on 24 January on the opposite side of the planet at Meridiani Planum, an area with mineral signs of a wet history. Designed to operate for just 90 days, both rovers vastly outlasted their planned missions. Soon after landing, Opportunity found small spherical mineral grains nicknamed 'blueberries,' rich in hematite, that had formed in acidic water. Spirit later found evidence of ancient hot springs that could have supported microbial life. Spirit's mission ended in 2010 after it became stuck in soft soil; Opportunity kept operating until a planet-wide dust storm cut off its solar power in June 2018, having traveled nearly 30 miles over almost 15 years.
Primary source · 2 sources - 14 January 2005Space Exploration
The Huygens probe lands on Titan
The joint NASA/ESA/ASI Cassini-Huygens spacecraft launched on 15 October 1997 and reached Saturn's system in 2004. On Christmas Day 2004 the European-built Huygens probe separated from the Cassini orbiter and began a 22-day coast toward Titan, Saturn's largest moon. On 14 January 2005, Huygens entered Titan's atmosphere and descended by parachute for about two hours and 28 minutes before landing on a frigid floodplain surrounded by icy cobblestones. The touchdown marked the farthest a human-made spacecraft had ever landed from Earth and the first landing ever achieved anywhere in the outer solar system.
Primary source · 2 sources - 28 September 2008Space Exploration
SpaceX reaches orbit with Falcon 1, on its fourth attempt
On 28 September 2008, SpaceX's Falcon 1 rocket reached Earth orbit on its fourth launch attempt, becoming the first privately developed, liquid-fueled rocket to do so. The rocket launched from Omelek Island in the Kwajalein Atoll carrying a 165-kilogram non-functional payload mass simulator built by SpaceX specifically for the test. The company's first three attempts, in 2006, 2007, and August 2008, had all failed for different reasons: a fuel leak and fire shortly after the first launch, an early engine shutdown on the second, and a stage-separation collision on the third. By the time of the fourth flight, SpaceX was nearly out of money and founder Elon Musk had put most of his personal fortune into the company; a fourth failure would very likely have ended it.
Reputable source · 2 sources - 20 June 2009Artificial Intelligence
ImageNet gives computer vision a dataset at internet scale
Jia Deng, Wei Dong, Richard Socher, Li-Jia Li, Kai Li, and Li Fei-Fei presented 'ImageNet: A Large-Scale Hierarchical Image Database' at the IEEE Conference on Computer Vision and Pattern Recognition in Miami. The dataset organized images according to WordNet, a lexical database that groups roughly 80,000 English nouns into hierarchical concepts, or synsets, such as mammal, then dog, then golden retriever. Using Amazon Mechanical Turk to crowdsource human verification of image labels at scale, the initial 2009 release already contained 3.2 million images across 5,247 synsets, with the stated goal of eventually reaching tens of millions of images covering the majority of WordNet's noun concepts. The team's founding insight was that computer vision progress had been limited less by algorithms than by the small size of existing training sets, some containing only a few thousand images.
Primary source · 2 sources A Decade-Old Pig Virus Becomes the First 21st-Century Flu Pandemic
In 2009 a new influenza strain, a reassortment of bird, swine, and human flu genes combined with a Eurasian pig flu virus, began spreading among people after first being identified in La Gloria, a rural town in Veracruz, Mexico. On June 11, 2009 the World Health Organization raised its pandemic alert to Phase 6, its highest level, indicating sustained community transmission on at least two continents, making this the first influenza pandemic of the 21st century. Genomic research published years later established that the parent virus had circulated undetected in pig populations in a small region of central Mexico for roughly a decade before a version emerged capable of jumping into humans, and that the original swine strains were still present in those pig populations at the time of the research.
Peer-reviewed · 2 sources- 16 February 2011Artificial Intelligence
Watson beats Jeopardy!'s greatest champions
IBM's Watson, a question-answering system built on a room-sized cluster of 90 servers and 2,880 processor cores, competed on Jeopardy! against the show's two most successful all-time champions, Brad Rutter and Ken Jennings, in a televised match broadcast over three episodes in February 2011. Watson's DeepQA software decomposed each clue's wordplay and phrasing, generated multiple candidate answers, then scored each candidate against evidence gathered from a large corpus of text using natural language processing techniques, all without a live internet connection. Watson won decisively, finishing with $77,147 against Jennings' $24,000 and Rutter's $21,600; in his closing answer on the show, Jennings wrote 'I for one welcome our new computer overlords.'
Primary source · 2 sources - 2012 (key paper); 2020 (Nobel Prize)History of Medicine
CRISPR Turns the Genome Into Something You Can Edit
CRISPR began as a bacterial immune system, a way microbes cut up the DNA of invading viruses. In a 2012 paper, Jennifer Doudna, Emmanuelle Charpentier, and colleagues showed that this system could be repurposed as a general gene-editing tool. They demonstrated that a mature guide RNA paired with a second RNA forms a structure that directs the protein Cas9 to make double-stranded cuts in target DNA, and that the Cas9 enzyme could be programmed with a single engineered RNA to target and cut essentially any DNA sequence a researcher chose. That made precise, low-cost editing of genomes broadly possible. In 2020 Doudna and Charpentier won the Nobel Prize in Chemistry for the co-development of CRISPR-Cas9, becoming the first women to share a science Nobel together.
Primary source · 2 sources - July 4, 2012History of Physics
CERN Discovers the Higgs Boson
On 4 July 2012, the ATLAS and CMS collaborations at CERN's Large Hadron Collider announced they had independently observed a new particle in the mass region of around 125 GeV, a particle consistent with the long-sought Higgs boson. CERN's own physics pages describe the particle's key confirming properties: it had no electrical charge, it was short-lived, and it decayed in ways that the Higgs boson should, according to theory. Physicists had spent nearly five decades searching for the particle since its existence was first proposed in 1964 by theorists including Peter Higgs and Francois Englert, who argued that an invisible field permeating all of space gives elementary particles their mass. By examining two and a half times more data than they had at the July announcement, CERN reports, the two teams concluded in March 2013 that some kind of Higgs boson had indeed been discovered, confirming the mechanism directly.
Primary source · 2 sources - 6 August 2012Space Exploration
Curiosity lands on Mars using a rocket-powered sky crane
NASA's Curiosity rover landed in Gale Crater on 6 August 2012 (5 August Pacific time), using a landing method never before attempted because the rover, at roughly the size of a small car, was too large and heavy for the airbag system used by earlier Mars rovers. After a heat shield and a 51-foot supersonic parachute slowed its descent, a rocket-powered descent stage took over and lowered Curiosity on nylon tethers in a maneuver NASA called the 'sky crane,' setting the rover down at about 1.7 miles per hour before explosive bolts cut the tethers and the descent stage flew off to crash safely at a distance. Gale Crater, an impact basin estimated at 3.5 to 3.8 billion years old, was chosen because scientists suspected it once held a lake. Curiosity's mission is to determine whether Mars ever had conditions that could support microbial life, and the rover remains operational years past its original planned lifetime.
Primary source · 2 sources - 30 September 2012Artificial Intelligence
AlexNet wins ImageNet and starts the deep learning boom
Alex Krizhevsky, Ilya Sutskever, and Geoffrey Hinton, at the University of Toronto, entered a convolutional neural network in the 2012 ImageNet Large Scale Visual Recognition Challenge. The network, later called AlexNet, had 60 million parameters across five convolutional layers and three fully connected layers, and was trained on two consumer-grade Nvidia GeForce GPUs rather than specialized research hardware. It used ReLU activations to train faster than the standard sigmoid function of the time, and a regularization technique called dropout, which randomly disables neurons during training, to reduce overfitting. AlexNet achieved a top-5 error rate of 15.3 percent, beating the second-place entry's 26.2 percent by nearly 11 percentage points, a margin far larger than the field's usual year-over-year gains.
Primary source · 2 sources - 16 January 2013Artificial Intelligence
word2vec turns words into vectors that capture meaning
Tomas Mikolov, Kai Chen, Greg Corrado, and Jeffrey Dean at Google published 'Efficient Estimation of Word Representations in Vector Space' on arXiv, introducing what became known as word2vec. The method trained a shallow neural network on the simple task of predicting a word from its surrounding context, or vice versa, across a text corpus of 1.6 billion words. Once trained, each word was represented as a dense vector of a few hundred numbers, and words used in similar contexts ended up with similar vectors, so that arithmetic on the vectors captured relationships, the canonical example being that the vector for 'king' minus 'man' plus 'woman' lands near the vector for 'queen.' The whole training process took under a day on a single CPU, far cheaper than the more complex neural language models it outperformed.
Primary source · 2 sources - 10 June 2014Artificial Intelligence
Goodfellow invents Generative Adversarial Networks
Ian Goodfellow, then a PhD student at the University of Montreal, conceived Generative Adversarial Networks after a late-night conversation with friends at a Montreal bar, Les 3 Brasseurs, about whether a computer could generate photos on its own; he went home and coded a working version that night. The paper, co-authored with Jean Pouget-Abadie, Mehdi Mirza, and others including Yoshua Bengio, described a framework pitting two neural networks against each other: a generator that produces fake data, and a discriminator that tries to tell the fakes from real training examples. Goodfellow compared it to a counterfeiter trying to produce undetectable fake currency against a police force trying to catch the fakes; as training proceeds, both networks improve until the generator's output is statistically indistinguishable from real data. The framework required no explicit description of the data's structure, only the adversarial contest between the two networks.
Primary source · 2 sources - 2014-2016Pandemics Through History
West Africa's Ebola Outbreak Becomes the Largest in History
An Ebola virus outbreak began in the forested rural region of southeastern Guinea, confirmed by the World Health Organization in March 2014, and spread to the capital cities of Guinea, Liberia, and Sierra Leone within months, making this the largest Ebola outbreak since the virus was first identified in 1976. In August 2014, WHO declared it a Public Health Emergency of International Concern. By the time the outbreak was declared over in June 2016, more than 28,600 people had been infected and over 11,300 had died, a toll more than eleven times larger than all previously known Ebola outbreaks combined. The disease also spread to Mali, Nigeria, Senegal, and, through travel, to Italy, Spain, the United Kingdom, and the United States, with limited secondary transmission in several of those countries. Healthcare workers were hit especially hard: by July 2015, WHO reported 874 infected and 509 dead among health workers alone.
Peer-reviewed · 2 sources - 26 February 2015Artificial Intelligence
DeepMind's DQN learns Atari games from raw pixels
DeepMind researchers led by Volodymyr Mnih, Koray Kavukcuoglu, and David Silver published 'Human-level control through deep reinforcement learning' in Nature. Their deep Q-network, or DQN, combined a convolutional neural network with reinforcement learning to play Atari 2600 games, receiving only the raw pixels on screen and the game's score as input, with no hand-coded knowledge of any game's rules. DQN used a technique called experience replay, storing past game transitions and randomly sampling from that memory during training rather than learning strictly in the order actions occurred, which stabilized the learning process. Using the same algorithm, network architecture, and hyperparameters across all games, DQN matched or exceeded the level of a professional human game tester on a majority of the 49 Atari games tested.
Primary source · 2 sources - 14 September 2015 (announced 11 February 2016)History of Astronomy
LIGO Detects Gravitational Waves From Colliding Black Holes
On 14 September 2015, at 5:51 a.m. Eastern Daylight Time, both twin detectors of the Laser Interferometer Gravitational-Wave Observatory, in Livingston, Louisiana, and Hanford, Washington, registered a gravitational wave signal, the first direct detection of ripples in spacetime ever recorded. Physicists concluded that the waves were produced during the final fraction of a second of the merger of two black holes, with masses of about 29 and 36 times the mass of the Sun, an event that took place roughly 1.3 billion years ago; about three solar masses of matter were converted directly into gravitational wave energy in that instant, with a peak power output about 50 times that of the entire visible universe. The National Science Foundation formally announced the detection on 11 February 2016, confirming a phenomenon Albert Einstein had predicted a century earlier in his general theory of relativity, one that scientists had been trying to detect directly for roughly 50 years.
Reputable source · 2 sources - September 14, 2015 (announced February 11, 2016)History of Physics
LIGO Detects Gravitational Waves for the First Time
At 5:51 a.m. Eastern time on September 14, 2015, both detectors of the Laser Interferometer Gravitational-wave Observatory, LIGO, one in Livingston, Louisiana, and one in Hanford, Washington, simultaneously registered a signal lasting a fraction of a second. Caltech's LIGO Laboratory identified the source: physicists concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole, an event roughly 1.3 billion light-years away that came to be called GW150914. NASA's own announcement of the result called it the first time scientists had observed ripples in the fabric of spacetime called gravitational waves arriving at Earth from a cataclysmic event in the distant universe, confirming a major prediction of Albert Einstein's 1915 general theory of relativity a full century after Einstein made it. The discovery was formally announced on 11 February 2016, after months of analysis to rule out instrumental error.
Primary source · 2 sources - 21 December 2015Space Exploration
SpaceX lands an orbital rocket booster for the first time
On 21 December 2015, the first stage of a SpaceX Falcon 9 rocket returned from orbital launch velocity and landed upright at Landing Zone 1, Cape Canaveral Air Force Station, after delivering a batch of Orbcomm satellites to orbit. It was the first time any company had recovered a rocket stage that had actually reached the speed and altitude of an orbital launch, as opposed to the shorter, lower suborbital hops other companies had landed previously. The booster used its engines to perform a boostback burn, reenter the atmosphere, and land vertically on legs at a pad near its original launch site, rather than expending itself in the ocean as every prior orbital rocket stage had done.
Reputable source · 2 sources - 9-15 March 2016Artificial Intelligence
AlphaGo defeats Lee Sedol at Go
DeepMind's AlphaGo, developed under David Silver, played a five-game match against Lee Sedol, winner of 18 world Go titles and widely regarded as one of the greatest players of his generation, in Seoul, South Korea. AlphaGo combined a 'policy network,' trained first on human expert games and then refined through self-play, to propose promising moves, with a 'value network' to judge how good a board position was, both guiding a Monte Carlo tree search rather than exhaustively searching Go's roughly 10 to the 170th power possible positions. AlphaGo won the match 4 games to 1, watched by an estimated 200 million people worldwide. In game two, AlphaGo played a move, later called 'Move 37,' that professional commentators initially thought was a mistake because it violated centuries of accumulated Go strategy, and Lee Sedol needed nearly fifteen minutes to respond to it.
Primary source · 2 sources - 30 March 2017Space Exploration
SpaceX reflies a Falcon 9 booster for the first time
On 30 March 2017, SpaceX launched the SES-10 communications satellite aboard a Falcon 9 whose first stage had already flown once before, on the CRS-8 cargo mission to the International Space Station on 8 April 2016. It was the first time an orbital-class rocket first stage had been recovered, refurbished, and successfully launched a second time, achieved in just under a year of turnaround between flights. The booster launched from Kennedy Space Center's Launch Complex 39A and, after separating from the second stage, landed again on a drone ship positioned in the Atlantic Ocean. SpaceX president Gwynne Shotwell called the flight the demonstration that the company's reuse technology genuinely worked, not just as a landing exercise but as a complete reflight.
Reputable source · 2 sources - 12 June 2017Artificial Intelligence
'Attention Is All You Need' introduces the Transformer
Ashish Vaswani and seven co-authors at Google Brain and Google Research published 'Attention Is All You Need,' introducing the Transformer architecture. Earlier sequence models processed text word by word in order, using recurrent connections that made long-range relationships hard to learn and training difficult to parallelize. The Transformer replaced recurrence entirely with a self-attention mechanism, which lets the model weigh every word in a sentence against every other word simultaneously to build a representation informed by the whole context at once, rather than only what came before. Because self-attention can be computed for all words in parallel rather than one step at a time, Transformers trained dramatically faster on modern GPU hardware. The model achieved a new state-of-the-art BLEU score of 41.8 on an English-to-French translation benchmark after training for just 3.5 days on eight GPUs, far less compute than prior best results required.
Primary source · 2 sources - 11 October 2018Artificial Intelligence
BERT makes language models read in both directions
Jacob Devlin, Ming-Wei Chang, Kenton Lee, and Kristina Toutanova at Google AI Language published 'BERT: Pre-training of Deep Bidirectional Transformers for Language Understanding.' Earlier Transformer-based language models, including OpenAI's original GPT, read text strictly left to right, so each word could only be informed by the words before it. BERT instead trained using a 'masked language model' objective, randomly hiding some words in a sentence and training the model to predict them using context from both the left and the right simultaneously, giving it a genuinely bidirectional understanding of a sentence. The pretrained model could then be fine-tuned with just one additional output layer for a specific task, and it set new state-of-the-art results across eleven different natural language processing benchmarks, pushing the GLUE benchmark score up by 7.7 percentage points over the prior best. Google open-sourced the model and pretrained weights the following month.
Primary source · 2 sources - 14 February 2019Artificial Intelligence
OpenAI withholds GPT-2 over misuse concerns
Alec Radford and colleagues at OpenAI published 'Language Models are Unsupervised Multitask Learners,' describing GPT-2, a 1.5-billion-parameter Transformer trained purely to predict the next word across a 40-gigabyte scrape of internet text called WebText. Without any task-specific training, GPT-2 could perform reading comprehension, translation, and summarization simply by being prompted in the right format, a capability the paper called zero-shot task transfer, and it achieved state-of-the-art results on seven of eight tested language modeling benchmarks. Rather than releasing the full trained model as it had with prior research, OpenAI announced it was withholding GPT-2's largest version, citing concern about malicious uses such as generating fake news or impersonating people online, and instead released progressively larger versions over the following months as what it called a staged release, an experiment in responsible disclosure.
Primary source · 3 sources - 28 May 2020Artificial Intelligence
GPT-3 shows scale alone unlocks few-shot learning
Tom Brown and over thirty co-authors at OpenAI published 'Language Models are Few-Shot Learners,' introducing GPT-3, an autoregressive Transformer with 175 billion parameters, ten times larger than any earlier non-sparse language model. Rather than fine-tuning the model's weights for each new task, the paper showed that simply describing a task in the prompt and providing a small number of examples, so-called few-shot learning, let GPT-3 perform competitively on many benchmarks with no gradient updates at all. Performance on these tasks improved smoothly as the model scaled up, without any architectural changes, suggesting scale itself was driving the new capability. In September 2020, Microsoft announced an exclusive license to GPT-3's underlying model for its own products, while OpenAI continued to offer the model to others through an API.
Primary source · 2 sources - 30 May 2020Space Exploration
SpaceX launches NASA astronauts on Crew Dragon
On 30 May 2020, NASA astronauts Robert Behnken and Douglas Hurley launched aboard SpaceX's Crew Dragon spacecraft, named Endeavour, from Launch Complex 39A at Kennedy Space Center, riding a Falcon 9 rocket to the International Space Station. The Demo-2 mission was the first time NASA astronauts had launched from American soil since the Space Shuttle program ended in 2011, during which time the US had relied on Russian Soyuz spacecraft for crew transport, and the first time any commercially built and operated spacecraft had carried NASA astronauts into orbit. The mission served as a full end-to-end test of SpaceX's crew transportation system before it entered regular operational service, with Behnken and Hurley staying aboard the ISS for roughly two months before returning to Earth.
Primary source · 2 sources - 2020-2021Artificial Intelligence
AlphaFold effectively solves protein structure prediction
DeepMind's AlphaFold 2 competed in CASP14 (the 14th Critical Assessment of protein Structure Prediction), a biennial blind test in which independent judges compare predicted protein structures against ones solved experimentally but not yet published. AlphaFold produced models for about two-thirds of the CASP14 target proteins with accuracy indistinguishable from experimental methods, measured by a global distance test score above 90 out of 100, a level most competing methods had never reached even once. CASP's assessors, who are not affiliated with DeepMind, stated that AlphaFold had effectively solved the fifty-year-old protein structure prediction problem, predicting a protein's three-dimensional folded shape from its amino acid sequence alone. DeepMind published the full method in Nature in July 2021 and released the AlphaFold source code and, in partnership with EMBL's European Bioinformatics Institute, predicted structures for hundreds of millions of proteins.
Primary source · 2 sources - 5 January 2021Artificial Intelligence
DALL-E generates images directly from text captions
OpenAI announced DALL-E, a 12-billion-parameter version of the GPT-3 Transformer architecture trained to generate images from text descriptions rather than text from text. Aditya Ramesh and co-authors described the underlying method in 'Zero-Shot Text-to-Image Generation': the model treated both text and image patches as tokens in a single stream, using a discrete variational autoencoder to compress images into a manageable vocabulary of visual tokens the Transformer could then predict autoregressively, one token at a time, conditioned on the caption. DALL-E could generate plausible images for captions describing combinations that had likely never co-occurred in its training data, such as anthropomorphized objects or animals rendered in specific artistic styles, and it could also apply requested edits or transformations to existing images.
Primary source · 2 sources - 18 February 2021Space Exploration
Perseverance lands in Jezero Crater and Ingenuity makes the first powered flight on another planet
NASA's Perseverance rover launched on 30 July 2020 and landed in Jezero Crater on 18 February 2021, targeting a site scientists believe once held a river delta feeding an ancient lake, chosen specifically because such deltas can preserve evidence of past microbial life. Perseverance carried the experimental helicopter Ingenuity attached to its belly; the small aircraft was deployed to the surface on 3 April 2021 as a technology demonstration meant to attempt up to five flights in thirty days. On 19 April 2021, Ingenuity lifted off, climbing to a hover of about 3 meters and staying airborne for just over 39 seconds, becoming the first aircraft in history to make a powered, controlled flight on another planet. Ingenuity far outlasted its planned test run, eventually completing 72 flights over nearly three years before its final flight on 18 January 2024.
Primary source · 2 sources - 25 December 2021Space Exploration
The James Webb Space Telescope launches and reveals its first images
The James Webb Space Telescope, a joint project of NASA, the European Space Agency, and the Canadian Space Agency, launched on 25 December 2021 aboard an Ariane 5 rocket from Europe's spaceport in French Guiana. After a month-long journey to its observing position near the Sun-Earth L2 Lagrange point, about 1.5 million kilometers from Earth, the telescope spent months unfolding its segmented mirror and cooling its infrared instruments to operating temperature. On 11 and 12 July 2022, NASA revealed the telescope's first full-color science images, including a view of the galaxy cluster SMACS 0723 that the agency described as the deepest and sharpest infrared image of the distant universe taken to date, gathered in just 12.5 hours of observing time.
Primary source · 2 sources - launched 25 December 2021, first images 12 July 2022History of Astronomy
The James Webb Space Telescope Reveals Its First Images
The James Webb Space Telescope launched on 25 December 2021 aboard an Ariane 5 rocket from Europe's Spaceport in French Guiana, a joint mission of NASA, the European Space Agency, and the Canadian Space Agency. After a 29-day journey of roughly a million miles to reach the second Lagrange point, followed by months of mirror alignment and instrument calibration, NASA released the telescope's first full set of full-color images and spectroscopic data on 12 July 2022, at a live event streamed from Goddard Space Flight Center. Built to solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe, Webb's early observations demonstrated its reach across exoplanet atmospheres, distant galaxies, stellar birth regions, and supermassive black holes.
Reputable source · 2 sources - 22 August 2022Artificial Intelligence
Stable Diffusion open-sources text-to-image generation
Robin Rombach, Andreas Blattmann, Dominik Lorenz, Patrick Esser, and Bjorn Ommer, working across LMU Munich, Heidelberg University, and Runway, published 'High-Resolution Image Synthesis with Latent Diffusion Models,' describing a diffusion model that generates images by learning to reverse a process of gradually adding noise to an image, but crucially performing that denoising in a compressed latent space produced by a pretrained autoencoder rather than on full-resolution pixels directly. That compression cut the computational cost enough to make training and running the model practical on far more modest hardware than earlier diffusion approaches required. Stability AI, in collaboration with the original research groups, EleutherAI, and LAION, publicly released the resulting model, called Stable Diffusion, on August 22, 2022, under a license permitting commercial use, after an earlier restricted release to about 1,000 researchers. It could generate 512-by-512 pixel images using under 7 gigabytes of GPU memory, putting it within reach of a single consumer graphics card.
Primary source · 2 sources - 30 November 2022Artificial Intelligence
ChatGPT brings conversational AI to the mainstream
OpenAI released ChatGPT as a free research preview, describing it as a sibling model to GPT-3.5 fine-tuned specifically for dialogue using reinforcement learning from human feedback, in which human trainers ranked candidate responses to steer the model toward answers people preferred. Unlike the raw text-completion interface of earlier GPT models, ChatGPT's dialogue format let it answer follow-up questions, acknowledge and correct its own mistakes, challenge premises it judged incorrect, and decline requests it was trained to treat as inappropriate. According to OpenAI co-founder Sam Altman, ChatGPT reached one million users within five days of launch with essentially no marketing push, and analysts at UBS estimated it reached 100 million monthly users by January 2023, a pace of adoption faster than either TikTok or Instagram achieved in their early growth.
Primary source · 2 sources - 14 March 2023Artificial Intelligence
GPT-4 adds multimodal, human-level exam performance
OpenAI released GPT-4, described in its technical report as a large-scale, multimodal Transformer that accepts both image and text inputs and produces text outputs, a departure from earlier GPT models that handled text only. OpenAI reported that GPT-4 achieved human-level performance on a range of professional and academic benchmarks originally designed for people, including a simulated bar exam on which it scored around the top 10 percent of test takers, compared with GPT-3.5's bottom-10-percent score on the same test. A significant part of the underlying engineering effort, according to the report, went into building training infrastructure that behaved predictably across scales, letting OpenAI forecast aspects of GPT-4's eventual performance using much smaller models trained with a tiny fraction of GPT-4's total compute. OpenAI did not disclose GPT-4's parameter count, architecture details, or training data in the technical report, a departure from the fuller disclosures of earlier GPT papers.
Primary source · 2 sources - 12 September 2024Artificial Intelligence
OpenAI's o1 introduces visible chain-of-thought reasoning
OpenAI released o1-preview and o1-mini, describing them as a new series of models trained with reinforcement learning to work through a chain of thought before producing a final answer, rather than generating a response immediately as prior GPT models did. Through this training process, the model learned to break difficult problems into smaller steps, try alternative approaches when one path stalled, and recognize and correct its own errors, spending more computation at answer time on harder problems. On a qualifying exam for the International Mathematical Olympiad, OpenAI reported that its existing GPT-4o model correctly solved only 13 percent of problems, while the new reasoning model scored 83 percent. OpenAI deliberately kept the model's internal chain of thought hidden from users, citing both safety monitoring and competitive concerns, and reset its model-naming scheme to '1' to mark what it described as a new level of capability distinct from the GPT series.
Primary source · 2 sources - 8-9 October 2024Artificial Intelligence
Neural network pioneers win the 2024 Nobel Prizes
The Royal Swedish Academy of Sciences awarded the 2024 Nobel Prize in Physics jointly to John Hopfield and Geoffrey Hinton for foundational discoveries and inventions enabling machine learning with artificial neural networks. Hopfield had created an associative memory network, modeled mathematically on the physics of atomic spin systems, that could store and reconstruct patterns by settling into low-energy states; Hinton built on such networks to develop methods letting machines autonomously find properties in data, work that underlies later deep learning. The following day, the Academy awarded the 2024 Nobel Prize in Chemistry half to David Baker for computational protein design and jointly to Demis Hassabis and John Jumper of Google DeepMind for AlphaFold's protein structure predictions. It was the first time Nobel Prizes across two categories in the same year recognized artificial intelligence research directly.
Primary source · 2 sources