Beyond Weird: Why Everything You Thought You Knew about Quantum Physics Is Different

by Philip Ball

What do we mean by ‘is’? Is an electron a particle or a wave? It can, in different circumstances, display the characteristics of either – or even a bit of both. But as for what an electron ‘is’, all we can talk about for sure is what we can see and measure, not what causes those observations. We must say that wave–particle duality is not a property of quantum objects but a feature often invoked (to questionable benefit) in our descriptions of them. They don’t have ‘split personalities’. The same applies to the much-vaunted notion that quantum particles can be in two places at once – or more generally, in two states at once. This, too, is not really true, but again I wouldn’t go so far as to say it is wrong. We are suspended in language. From the human perspective, it certainly looks as though quantum objects can possess two different, even contradictory, values of some property at once. But the human perspective is the wrong one for understanding quantum mechanics. Nonetheless, it’s all we have.