Joseph Polchinski explores the battle in physics: either quantum mechanics must break down, or our understanding of spacetime must be wrong. The latest is the 'firewall' paradox: if quantum mechanics is to be saved, then an astronaut falling into a black hole will have an experience very different from what Einstein's theory predicts. This has led to many new ideas that may lead to the unification of these two great theories. Recorded on 07/15/2015. (#30519)