Cat-in-the-box
By Ivan Semeniuk
THE Universe is full of things that are difficult to locate: car keys, umbrellas, matching socks. Some eventually turn up unaided, others have a way of resisting even the most determined search. But everything we lose track of in everyday life is united by one solid physical fact: wherever it is, it can only be in one place at a time.
Until you bring quantum mechanics into the picture, that is. Weird as it seems, your car keys could be hiding in your coat pocket and under a pile of newspapers at the same time, while not fully existing in either place. It may run counter to intuition, but that's what standard quantum theory says. And because the theory does such a good job of describing how the Universe's most fundamental building blocks behave, most physicists feel they have no choice but to go along with it.
"It's one of these things you learn when you're an undergraduate," says Oxford University's Roger Penrose. "Initially students will say 'What the hell's going on?'. Then they find that the lecturer seems to know what he's talking about and so, after a while, they get used to it."
But some people, he says, still worry about it—and he counts himself among them. Penrose accepts that electrons, atoms and other particles on that tiny scale can be in more than one place at a time; there's simply too much evidence to believe otherwise. But he won't accept that this means a bunch of keys behaves the same way.
This unwillingness to follow the party line has led Penrose into proposing some new …
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