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As one of the founders of arguably the most successful scientific idea, quantum theory, you’d expect Niels Bohr to be interested in the nature of reality. He studied what we think of as the fundamental building blocks of the universe: atoms, electrons, photons, etc.
But for Bohr, reality was not actually his business: “It is a mistake to think that the problem of physics is to discover how nature is,” he said, in a line often quoted in the early days of quantum theory, “physics is concerned with what can be said about nature.”
This distinction may sound pedantic, but when it comes to quantum physics, it’s impossible to ignore. The theory describes a world of subatomic particles that is baffling: particles can seemingly be in two places at once, time stands still, and there is no such thing as empty space. Is that really reality?
Some physicists ignore this question: like Bohr, they are not talking about reality, but only about our vague perception of it. But many are not at all convinced by this view and want to believe in a world made up of perceptible objects that exist independently of what we know about them. That is, they are realists. One of them is Robert Spekkens of the Perimeter Institute in Canada, who plans to…
