Ethan Siegel in Forbes:
One of the oldest predictions of Einstein’s general theory of relativity — the gravitational theory that spacetime is a fabric that gets bent and curved by the presence of matter and energy — is that masses that accelerate in the Universe produce ripples in the fabric of space itself: gravitational waves. But Einstein’s conception of gravity is still a classical picture, as:
- space and time are continuous entities, not discrete ones,
- the predictions of the theory break down (give nonsense answers) at very small distances and in the presence of very large fields,
- and there’s no way to calculate the gravitational field for inherently quantum systems, like an electron confronted with a double slit.
We fully expect that at some level, gravity will turn out to be quantum in nature, although we don’t yet have any experimental evidence of that. But with LIGO’s recent direct detection of gravitational waves, we have every reason to believe that the existence of these waves hold the key to showing — for the first time — that gravity truly is a force that’s quantum in nature.