Einstein had looked at the numbers and dimensions that went into his equations for gravitational waves and said, essentially, 'This is so tiny that it will never have any influence on anything, and nobody can measure it.' And when you think about the times and the technology in 1916, he was probably right.

We've seen black holes, which is already wonderful. We also expect to see the merger of neutron stars, and that was a thing that actually gave this field a certain credibility when it was discovered that there were pairs of neutron stars in our galaxy, and people stopped laughing at us when that was found out.

By the time 1967 had rolled around, general relativity had been relegated to mathematics departments... in most people's minds, it bore no relation to physics. And that was mostly because experiments to prove it were so hard to do - all these effects that Einstein's theory had predicted were infinitesimally small.

It's a spectacular signal. It's a signal many of us have wanted to observe since the time LIGO was proposed. It shows the dynamics of objects in the strongest gravitational fields imaginable, a domain where Newton's gravity doesn't work at all, and one needs the fully non-linear Einstein field equations to explain the phenomena.

I said, suppose you take a light - I was thinking of just light bulbs because, in those days, lasers were not yet really there - and sent a light pulse between two masses. Then you do the same when there's a gravitational wave. Lo and behold, you see that the time it takes light to go from one mass to the other changes because of the wave.

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