Whenever you see the word “quantum”, if the topic under discussion is not physics, you can ignore it. Well in this case the topic is indeed Physics.

There is a controversial paper in *Nature Physics*, where some theorists claim that they can prove that wavefunctions — the entity that determines the probability of different outcomes of measurements on quantum-mechanical particles — are real states.

The paper is entitled … On the reality of the quantum state … the abstract reads …

Quantum states are the key mathematical objects in quantum theory. It is therefore surprising that physicists have been unable to agree on what a quantum state truly represents. One possibility is that a pure quantum state corresponds directly to reality. However, there is a long history of suggestions that a quantum state (even a pure state) represents only knowledge or information about some aspect of reality. Here we show that any model in which a quantum state represents mere information about an underlying physical state of the system, and in which systems that are prepared independently have independent physical states, must make predictions that contradict those of quantum theory.

Yawn … another dull paper … er no perhaps not, because it is thought by some to be one of the most important in quantum foundations in decades. The authors say that the mathematics leaves no doubt that the wavefunction is not just a statistical tool, but rather, a real, objective state of a quantum system.

Matt Leifer, a physicist at University College London who works on quantum information, says that the theorem tackles a big question in a simple and clean way. He also says that it could end up being as useful as Bell’s theorem, which turned out to have applications in quantum information theory and cryptography.

Now perhaps you might ponder the thought that this comes from a few fringe kooks, but no they have some heavyweights in their corner: their view was once shared by Austrian physicist and quantum-mechanics pioneer Erwin Schrödinger, who proposed in his famous thought experiment that a quantum-mechanical cat could be dead and alive at the same time.

But it’s incompatible with quantum mechanics, so the theorem also raises a deeper question: could quantum mechanics be wrong? Probably not because it is too well-confirmed, but lets see.

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