Genius (21 page)

Melville, Lucille, Richard, and Joan at the house they shared with Lucille's sister's family, at 14 New Broadway.

Richard and Arline : left , at Presbyterian Sanatorium.

At Los Alamos: “I opened the safes which contained behind them the entire secret of the atomic bomb…”

Slouching beside J. Robert Oppenheimer at a Los Alamos meeting: “He is by all odds the most brilliant young physicist here, and everyone knows this.”

Awaiting the Trinity test: “And we scientists are clever-too clever- care you not satisfied? Is four square miles in one bomb not enough? Men are still thinking. Just tell us how big you want it !”

I. I. Rabi (left) and Han s Bethe: Physicists are the Peter Pans of the human race, Rabi said.

At th e Shelter Island Conference , June 1947: Willis Lamb and John Wheeler , standing; Abraham Pais, Feynrnan, and Herman Feshbach, seated; Julian Schwinger, kneeling.

Jul ian Schwinger : “It seems to be the spirit of Macaulay which takes over, for he speaks in splendid periods, the carefully architected sentences rolling on, with every subordinate clause duly closing.”

Feynman and Hideki Yukawa in Kyoto, 1955 : Feynman presented his theory of superfluidity, the strange , frictionless behavior of liquid helium quantum mech anics writ large.

At Caltech , before a slide from his original presentation on antiparticles traveling backward through time.

Victor Weisskopf (left) and Freeman Dyson.

That was Feynman and Wheeler’s view. By insisting on the symmetry of past and future, they made the combination of retarded and advanced potentials seem a necessity. In the end, there was an asymmetry in the universe of their theory—the role of ordinary retarded fields far outweighs the backward advanced fields—but that asymmetry does not lie in the equations. It comes about because of the disordered, mixed-up nature of the surrounding absorber. A tendency toward disorder is the most universal manifestation of time’s arrow. A movie showing a drop of ink diffusing in a glass of water looks wrong when run backward. Yet a movie showing the microscopic motion of any one ink molecule would look the same backward or forward. The random motions of each ink molecule can be reversed, but the overall diffusion cannot be. The system is microscopically reversible, macroscopically irreversible. It is a matter of chaos and probability. It is not impossible for the ink molecules, randomly drifting about, someday to reorganize themselves into a droplet. It is just hopelessly improbable. In Feynman and Wheeler’s universe, the same kind of improbability guaranteed the direction of time by ensuring disorder in the absorber. Feynman took pains to spell out the distinction in the twenty-two-page manuscript he wrote early in 1941:

We must distinguish between two types of irreversibility. A sequence of natural phenomena will be said to be microscopically irreversible if the sequence of phenomena reversed in temporal order in every detail could not possibly occur in nature. If the original sequence and the reversed in time one have a vastly different order of probability of occurrence in the macroscopic sense, the phenomena are said to be macroscopically irreversible… . The present authors believe that all physical phenomena are microscopically reversible, and that, therefore, all apparently irreversible phenomena are solely macroscopically irreversible.