1840s–1850sReputable sourceWell documented
Energy and the Laws of Thermodynamics
On the timeline · around 1840s–1850s ·
What happened
As steam power drove industry, physicists worked out the laws governing heat, work, and energy. James Joule showed that heat and mechanical work are interchangeable forms of energy; William Thomson (Lord Kelvin), Rudolf Clausius, and others established that energy is conserved — never created or destroyed — and that heat always flows from hot to cold, a one-way process captured by the new idea of entropy.
Why it matters
Thermodynamics is one of the most universal frameworks in all of science, governing engines, chemistry, living things, stars, and the ultimate fate of the universe. The conservation of energy became a bedrock principle of physics.