Feynman Path Integral At a beer party at the Nassau Tavern in Princeton, a young Richard Feynman asked Herbert Jehle whether anyone had built Quantum Mechanics out of the action. The next day Jehle showed him a paper by Dirac in the library. That led to Feynman's idea that a particle takes every possible path at once, and each path adds a little spinning arrow. As more paths through these slits get added here, their arrows add up into the real interference pattern.

The Universe Humming With Gravitational Waves In 1983, Ron Hellings and George Downs worked out a simple curve: If space itself is rippling with slow gravitational waves, pairs of pulsars should drift early and late together in a way that depends only on how far apart they sit in the sky. In June 2023, after 15 years of timing 68 of these spinning stellar clocks, the NANOGrav team reported evidence for exactly that pattern. The whole universe appears to be humming with gravitational waves whose single ripple takes years to pass.