Lessons on Physics

From Carlo Rovelli

Carlo Rovelli heads up the Quantum Gravity group at the Centre de Physique Théoretique at Aix-Marseille University. He’s also a lucid, poetic writer who makes the obscure concepts of contemporary physics accessible to laygrunts like me. His Seven Brief Lessons on Physics is indeed brief and, from what I can tell, covers large swathes of territory – relativity, quantum mechanics, cosmology, particles, “grains of space,” the uses of probability, the meaning of time, and the heat of black holes. For the better-informed, much of this is familiar. For the ill-informed, I summarize a few of Rovelli’s themes.

1. Einstein considered general relativity “the most beautiful of theories,” beautiful in part because of its “breathtaking simplicity” (6). Newton described gravity as a force, but how can a force be exerted over great distances, through the “great empty container” of space (as Newton conceived it)? Shortly before Einstein’s birth, Faraday and Maxwell discovered the electromagnetic field, “a real entity [that] can vibrate and oscillate like the surface of a lake and ‘transports’ the electrical force” (7). Einstein’s proposal: Gravity works through a “gravity field,” which is not diffused through space but is space (8). Space isn’t the shell where matter resides, but “is one of the ‘material’ components of the world” that “undulates, flexes, curves, twists.” Space curves and there’s matter. Large objects like the sun exert pressure on the gravitational field, bending space around themselves, so that Earth races along inclined space “like a marble that rolls in a funnel” (8).

The most beautiful theory seems to be true. Einstein’s predictions – that light curves around the sun, the existence of black holes, the big bang – now have experimental support.