Dead cats and the wow factor

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"NOBODY understands quantum mechanics!" has become a famous quote. Its author, popular Nobel Laureate Richard Feynman, expressed a frustration felt both by that handful of great minds who first conceived quantum theory in the early part of this century, and by younger physicists and their philosophical fellow travellers ever since. The stuff works, but nobody knows what it means.

One of the great paradoxes of quantum theory is highlighted in the parable of Schrdinger's cat. This cat, who is kept in an opaque box and is allegedly alive and dead at the same time, illustrates the capacity of quantum things to be in two or more contradictory states (or places or times), simultaneously. When we open the box and look at the cat, it is alive or dead. We can never catch quantum things in their double act.

John Gribbin's imaginatively titled new book concentrates on an even more thorny quantum paradox - the problem of "non-locality". This was an aspect of quantum theory that Einstein could never accept. He called it "ghostly and absurd", and argued that the very idea of it proved quantum mechanics was wrong-headed. Non-locality predicts that two quantum objects like photons (particles of light), once "introduced" at a common source, can be shot off to opposite ends of a room - or even to opposite ends of the universe - and yet remain linked in such a way that a change in one results instantaneously in an opposite change in the other. This appears to violate relativity, which argues that nothing can travel faster than the speed of light. How could any signal get from one photon to the other instantaneously?

Einstein said that that non-locality would have to depend upon some impossible "telepathy" between the distant photons. But telepathy or not, faster than light signals or not, non-locality became an experimentally proven fact in the 1980s. Just how it could happen remains a great mystery. John Gribbin illustrates the problem graphically by proposing that Schrdinger's cat has had two kittens, each of which is sent off in a different direction across the universe within an isolated space capsule. When intelligent aliens in some distant galaxy open one capsule and discover a live kitten, similar aliens in another galaxy open the other - at precisely the same moment - to discover a dead kitten.

Gribbin is a showman. He likes to surprise and excite his audience. This gives his writing a delightful vitality, and graphic imagery that makes difficult ideas accessible. The whole parable of "Schrdinger's kittens" is brilliant. But showmen also find it hard to resist adding a "wow!" factor. In the case of Schrdinger's Kittens, Gribbin's "wow" is that he promises to reconcile relativity theory and quantum theory (it's never been done) and "to solve all the mysteries of quantum mechanics", including especially that of non-locality. He then sets out to do this with a sleight of hand worthy of the best magicians.

Introducing the very post-modern, and highly contentious, view that quantum theory proves that "reality is in very large measure what you want it to be" (Gribbin calls this his "favorite science fiction," "a myth for our times"), he then goes on to put forward his own favorite interpretation of non-locality and how it can be explained. Asserting that any "message" between one distant "kitten" and another must involve some kind of feedback mechanism, he looks for a kind of signal that could pass from one to another without violating the speed of light. He finds a "likely candidate" in a paper published 55 years ago by John Archibald Wheeler and Richard Feynman, in which they propose that light can travel backwards in time. Abracadabra - we have it! A photon goes from the first kitten to the observer's eye and then travels backwards in time to let the other kitten in on its fate.

The problem with this, like that other great quantum sleight of hand "the many worlds theory", is that it saves conventional interpretation of one quantum mystery at the great expense of contorting our sense of reality in other directions. Photons going backwards in time as a solution requires, for example, that we live in a closed universe whose "edges" they can bounce back from, and there is no proof of that. Nor does this reconcile general relativity and quantum mechanics, where the problem is that one explains gravity with a curved space-time universe and the other seems only to function in conventional Euclidean space.

Gribbin, like many others, is trying to squeeze quantum mechanics into his familiar paradigm. He wants to understand it by means of the mental model he has already got (feedback, and signals, and so on). But the real challenge of this new science is that it calls upon us to think in a new way. It requires that we shift our paradigm. This has yet to happen.