throughout cosmic historyReputable sourceWell documented
Gravitational Waves Ripple Through Spacetime
On the timeline · around throughout cosmic history · The Age of Galaxies
What happened
When massive objects such as black holes spiral together and merge, they send ripples through spacetime itself — gravitational waves — spreading outward at the speed of light. Albert Einstein predicted them in 1915; they were first directly detected in 2015.
Why it matters
Their detection opened an entirely new way to observe the universe, letting astronomers 'hear' cataclysms — like colliding black holes — that give off no light.
How we know
LIGO's first detection, on 14 September 2015, came from two black holes about 30 times the Sun's mass merging 1.3 billion light-years away — confirming Einstein's century-old prediction.