Just when you thought quantum physics couldn’t get any weirder, it violates the pigeonhole principle.

No, it’s not about a pigeon in a hole that is simultaneously alive and dead. The pigeonhole principle is a basic tenet of mathematics. It illustrates what the very idea of numbers is all about. And it’s easy to state: If you put three pigeons in two pigeonholes, at least two of the pigeons end up in the same hole.

How can anybody, even a quantum physicist, argue with that? All you have to do is be able to count. Guess again, say quantum physicist Yakir Aharonov and collaborators in a new paper about the pigeonhole principle. “It seems … to be an abstract and immutable truth, beyond any doubt,” they write. “Yet … for quantum particles the principle does not hold.”

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