1:38:24General relativity from first principles – Adam Brown
Adam Brown, who taught general relativity at Stanford and now leads Blueshift at Google DeepMind, rebuilds Einstein's theory at a whiteboard from one coincidence: the mass that resists acceleration and the mass gravity pulls on are identical to one part in 10^15, for no reason Newton could give. Only fictitious forces are guaranteed to work that way, so Einstein leapt and declared gravity one of them, at the price of admitting we are wrong about which paths are straight. The second half is a black hole lecture built on a brick and a pulley: the Newtonian formula for extractable energy promises more than 100% of a brick's rest mass, and general relativity closes that free energy loophole by making gravity stronger rather than weaker, with the exact answer saturating at precisely 100% at the event horizon. Along the way: three Schwarzschild formulas that are secretly one, what falling in looks like from both sides, the three independent lines of evidence that black holes are real, and the 1919 eclipse whose two failed predecessors saved Einstein from publishing a wrong number. It closes on whether a civilization of language models could have found general relativity by thinking, and whether humans will follow what they find next.