Sean Carroll: commitment

Transcript context

…What does greatness look like for a physicist? How difficult is it to take the leap from special relativity to general relativity? How difficult is it to imagine that, to consider spacetime together and to imagine that there’s a curvature to this whole thing? Yeah. That’s a great question. I think that if you want to make the case for Einstein’s greatness, which is not hard to do, there’s two things you point at. One is in 1905, his famous miracle year, he writes three different papers on three wildly different subjects, all of which would make you famous just for writing that one paper. Special relativity is one of them. Brownian motion is another one, which is just the little vibrations of tiny little dust specks in the air. But who cares about that? What matters is it proves the existence of atoms. He explains Brownian motion by imagining there are molecules in the air and deriving their properties. Brilliant. Then he basically starts the world on the road to quantum mechanics with his paper on, which again, is given a boring label of the photoelectric effect. What it really was is he invented photons. He showed that light should be thought of as particles as well as waves. He did all three of those very different things in one year. Okay. But the other thing that gets him genius status is, like you say, general relativity. This takes 10 years from 1905 to 1915. He wasn’t only doing general relativity. He was working on other things. He invented refrigerator. He did various interesting things. He wasn’t even the only one working on the problem. There were other people who suggested relativistic theories of gravity. But he really applied himself to it. I think as your question suggests, the solution was not a matter of turning a crank. It was something fundamentally creative. In his own telling of the story, his greatest moment, his happiest moment was when he realized that if the way that we would modern … say it in modern terms, if you were in a rocket ship accelerating at 1G, at acceleration due to gravity, if the rocket ship were very quiet, you wouldn’t be able to know the difference between being in a rocket ship and being on the surface of the earth. Gravity is not detectable or at least not distinguishable from acceleration. Number one, that’s a pretty clever thing to think. But number two, if you or I had had that thought, we would’ve gone, “Huh. We’re pretty clever.” He reasons from there to say, “Okay. If gravity is not detectable, then it can’t be like an ordinary force.” The electromagnetic force is detectable. We can put charged particles around. Positively charged particles and negatively charged particles respond differently to an electric field or to a magnetic field. He realizes that what his thought experiment showed, or at least suggested, is that gravity isn’t like that. Everything responds in the same way to gravity. How could that be the case? magnetic field. He realizes that what his thought experiment showed, or at least suggested, is that gravity isn’t like that. Everything responds in the same way to gravity. How could that be the case? Then this other leap he makes is, “Oh, it’s because it’s the curvature of spacetime.” It’s a feature of spacetime. It’s not a force on top of it. The feature that it is, is curvature. Then finally he says, “Okay. Clearly, I’m going to need the mathematical tools necessary to describe curvature. I don’t know them, so I will learn them.” They didn’t have MOOCs or AI helpers back in those days. He had to sit down and read the math papers, and he taught himself differential geometry and invented general relativity.…

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