3    Half a Theory?

This reticence is unique to quantum mechanics. No other theory of physics is so reticent. Newton’s theory of gravitation speaks of the solar system as sort of a gigantic clock, a smoothly functioning machine. Statistical mechanics describes a gas as a swarm of particles, rapidly zooming about every which way. Electromagnetism tells of space filled with invisible fields. Each of these theories gives us a vivid picture of the world. But quantum theory tells us nothing of the sort: it leaves us no picture at all.

The refusal of the theory to give a picture of reality, to respond to certain questions, and its seeming inability to describe any mechanisms lying behind its predictions, deeply disturbed the theory’s creators. One of those creators was Albert Einstein. He was so disturbed that he decided that there was something wrong with the theory. To him no respectable theory of physics should be so speechless.

Is there something wrong with quantum mechanics? It seems so limited! Is it too limited? Is there something wrong with it? Maybe it is not a theory but half a theory.

For surely there must be some way to penetrate beyond the silence of the theory! Surely something is missing from quantum mechanics. Could it be that it is only a partial theory, that underlying it there is a deeper understanding, a fuller and more complete explanation of the workings of the microworld? In this view quantum mechanics is only a start, and we need to search for a better theory that will speak of all those things that the Predictor fails to address. This new theory, if we could find it, would clearly describe the invisible reality—the actual physical situation, the real state of affairs—of which we would dearly love to learn.

Figure 3.1

Albert Einstein. Although he was one of the creators of quantum mechanics, he never accepted it. Over and over again, Einstein argued that the theory was incomplete because it failed to describe subatomic reality. The arguments that Einstein advanced are the fertile soil from which grew the discoveries described in this book. Photo courtesy of the American Institute of Physics Emilio Segre Visual Archives.

Does this view make sense to you? If you feel that it does make sense, then you believe in hidden variables. And it made sense to many people before Bell’s Theorem and the experiments that it inspired came along.

In particular, it made sense to Albert Einstein. In his view quantum mechanics, successful though it may be, was incomplete. The theory was perfectly good so far as it went, he felt—but “so far as it went” was not good enough for him. Einstein wanted something more: a complete theory.

Is quantum theory incomplete? Or are there are reasons to think that it is all that we will ever get?

On the one hand, if we are going to revise quantum mechanics to make it into a complete theory, the task won’t be easy. It won’t be a matter of making a few tweaks here and there. The very structure of the theory, the way in which it is formulated, is antithetical to the goals of such a revision. If we are looking for a more talkative Predictor, it’s an utterly different person that we’re after. And if we do decide to go looking for a new one, we’d better remember that she’s got some pretty big shoes to fill. Quantum mechanics as it stands is that good.

Furthermore, it seems inconceivable that such a Predictor—a talkative Predictor, one who describes what is really going on—could ever be found. What sort of description could there be of a particle existing in many places at once, of an atom with a broad range of energies, of an object most definitely spinning on an axis but of that axis having no particular direction until it is observed? The more we probe the quantum world, the more we learn that its properties simply cannot be described in anything like the ordinary manner.

Many of the theory’s creators felt that the refusal of quantum theory to provide a detailed account of the workings of the microworld is not a problem but a discovery. It is not a limitation but an advance. In this view the theory is profoundly right in confining itself to doing only what can be done, and avoiding what cannot. These people insist that the question “What is the reality that the Predictor perceives so clearly?” is misguided—that there simply is no such thing. They insist that the idea of a reality that can be explained is a naive notion that we need to outgrow, on a par with another intuitively obvious concept that turned out to be wrong—that of a flat Earth beneath our feet.

Einstein, on the other hand, thought that these people were just spouting nonsense. He set out to prove them wrong. And it was the arguments that Einstein brought to bear that led in the long run to Bell’s famous theorem, a theorem that, in a supreme irony, almost certainly showed that Einstein had been wrong.