Wednesday, November 7, 2012

New paper tries to disprove quantum mechanics

I commented in May on work supposedly Showing that the wavefunction is real. Now the theorists are trying experimental tests, and have posted this paper:
Can different quantum state vectors correspond to the same physical state? An experimental test

A century on from the development of quantum theory, the interpretation of a quantum state is still discussed. If a physicist claims to have produced a system with a particular wave function, does this represent directly a physical wave of some kind, or is the wave function merely a summary of knowledge, or information, about the system? A recent no-go theorem shows that models in which the wave function is not physical, but corresponds only to an experimenter's information about a hypothetical real state of the system, must make different predictions from quantum theory when a certain test is carried out. Here we report on an experimental implementation using trapped ions. Within experimental error, the results confirm quantum theory. We analyse which kinds of theories are ruled out. ...

The result of Ref. [3] can be considered as a no-go the-orem for interpretations of quantum theory, analogous to Bell's theorem. Each theorem states that a certain class of theories must make different predictions from quan-tum theory -- locally causal theories in the case of Bell's theorem and ψ-epistemic theories in the case of Ref. [3]. We have suggested that a natural threshold is defined by quantum state discrimination.
So they are claiming that they have disproved ψ-epistemic theories, just as Bell and Bell test experiments have disproved locally causal theories.

No, Bell did not disprove locally causal theories. He only disproved a type of hidden variable theories that no one believed anyway. Likewise, these guys are only trying to disprove ψ-epistemic theories that no one believes. I explain further here and here.

Quantum mechanics was discovered in the 1920s, and incorporated into physics textbooks in the 1930s. Ever since, the mainstream interpretation has been that it is a locally causal theory and a ψ-epistemic theory. So why are all these physicists, 80 years later, trying to do experiments that prove quantum mechanics correct but also disprove local causality and ψ-epistemic ontology?

Maybe this paper has some clever new way of testing quantum mechanics. I don't know. But it is not telling us anything except what was common knowledge 80 years ago.

I will be interested to see whether this paper gets publicized as some profound new result, and if the editors require that the claims be scaled back before publication. If I were the referee, I would require that the article say that it was only confirming what Bohr, Heisenberg, and the textbooks said 80 years ago. I doubt that the editor will require any such change.

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