Einstein's theory of relativity predicted that waves of gravity can spread through space, just like light waves. Only these "gravitational waves" are ripples in space and time themselves, changing the shapes and sizes of objects as they pass through. Einstein himself didn't believe that these waves could exist, but in 2015 we detected a gravitational wave produced by two enormous black holes spiralling in and colliding with each other. To detect this wave, we had to measure a four kilometer tunnel alternately growing and shrinking by less than the width of an atomic nucleus! I'll explain in this talk what gravitational waves are, what produces them, how we detect them, and what they might be able to reveal to us about the universe.
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