What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics

by Adam Becker

Feynman himself had explained Bell’s theorem during his keynote speech at an MIT conference in 1981 (though strangely he did not actually mention Bell himself in the course of doing so). The conference was on a seemingly unrelated subject—the physics of computation—yet Feynman showed that Bell’s theorem held the answer to a crucial question in this field. “Can physics be simulated by a universal computer?” Feynman asked the conference. “[The] physical world is quantum mechanical, and therefore the proper problem is the simulation of quantum physics—which is what I really want to talk about,” he continued. The answer, for a normal computer operating under ordinary conditions, was no: using simple ones and zeros in the usual fashion, without strange long-range connections within the computer or some other kind of trick, limited the computer to simulating local physics, rendering it impossible to fully simulate quantum effects. But, Feynman speculated, there might be another way to get the job done. “Can you do it with a new kind of computer—a quantum computer?” Feynman wondered. “I’m not sure.… So I leave that open.” Several years later, a young physicist named David Deutsch took up where Feynman had left off. In 1985, Deutsch proved that a quantum computer—a computer taking full advantage of the difference between quantum physics and classical physics—could perform tasks more efficiently than an ordinary classical computer. Deutsch’s proof opened up the possibility of pract...