The “chirp” is bright and bird-like, its pitch rising at the end as though it’s asking a question. To an untrained ear, it resembles a sound effect from a video game more than the faint, billion-year-old echo of the collision of two black holes.But to the trained ear of experimental physicist, it is the opening note of a cosmic symphony. On Thursday, for the first time in history, scientists announced that they are able to hear the ripples in the space-time continuum that are produced by cosmic events — called gravitational waves. The discovery opens up a new field of scientific research, one in which physicists listen for the secrets of the universe rather than looking for them.
“Until this moment, we had our eyes on the sky and we couldn’t hear the music,” said Columbia University astrophysicist Szabolcs Márka, a member of the discovery team, according to the international Media . “The skies will never be the same.”
Thursday’s moment of revelation has its roots almost a century earlier, in 1916, when Albert Einstein predicted the existence of gravitational waves as part of his ground-breaking theory of general relativity. The intervening years included brush-offs and boondoggles, false hope, reversals of opinion, an unlikely decision to take a $272 million risk, and a flash of serendipity that seemed too miraculous to be real — but wasn’t.
Here’s how it all happened.
In 1915, Einstein gave a series of lectures on his theory of general relativity, asserting that space and time form a continuum that gets distorted by anything with mass. The effect of that warping is gravity — the force that compels everything, from light to planets to apples dropping from a tree, to follow a curved path through space.
Gravitational waves, which he proposed the following year, are something of a corollary to that theory. If spacetime is the fabric of the cosmos, then huge events in the cosmos — like a pair of black holes banging into each other — must send ripples through it, the way a the fabric of trampoline would vibrate if you bounced two bowling balls onto it. Those ripples are gravitational waves, and they’re all around us, causing time and space to minutely squeeze and expand without us ever noticing. They’re so weak as to be almost undetectable, and yet, according to Einstein’s math at least, they must be there.