Wigner's Friend Experiment

Foundations of physics and/or philosophy of physics, and in particular, posts on unresolved or controversial issues

Wigner's Friend Experiment

Postby FrediFizzx » Tue May 28, 2019 4:31 pm

"Experimental rejection of observer-independence in the quantum world"

https://arxiv.org/abs/1902.05080

More nonsense by experimenters based on the supposed violation of a CHSH inequality. Of course no such violation actually took place since they cheated and used an inequality with a higher bound.

There are probably more reasons why Wigner's friend thought experiment is faulty.
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Re: Wigner's Friend Experiment

Postby gill1109 » Tue May 28, 2019 8:59 pm

And what about the latest fashion in quantum mysterian circles: the Wigners' friend thought-experiment of Daniela Frauchiger and Renato Renner! You have the quantum system, observed by Mr. Wigner and also by Mrs. Wigner; and you have the Wigners' friend (ie, the friend of both of the two Wigners) who can observe both of them.

https://arxiv.org/abs/1604.07422 "Quantum theory cannot consistently describe the use of itself"

Abstract: Quantum theory provides an extremely accurate description of fundamental processes in physics. It thus seems likely that the theory is applicable beyond the, mostly microscopic, domain in which it has been tested experimentally. Here we propose a Gedankenexperiment to investigate the question of whether quantum theory can, in principle, have universal validity. The idea is that, if the answer was yes, it must be possible to employ quantum theory to model complex systems that include agents who are themselves using quantum theory. Analyzing the experiment under this presumption, we find that one agent, upon observing a particular measurement outcome, must conclude that another agent has predicted the opposite outcome with certainty. The agents' conclusions, although all derived within quantum theory, are thus inconsistent. This indicates that quantum theory cannot be extrapolated to complex systems, at least not in a straightforward manner.

Nature Communications 9, 3711 (2018); DOI: 10.1038/s41467-018-05739-8

I understand that Frauchiger and Renner end up with only the many-worlds theory, and qubism, as interpretations of quantum theory which are compatible with the predictions of quantum theory. However this is circular reasoning as by quantum theory, they mean explicitly "quantum theory with no collapse". So I think their thought experiment proves that we need collapse theories, such as the "eventum mechanics" of Slava Belavkin [RIP], or Joy Christian's theory. This leads us to quarrel about whether or not either is "local". I think we need a new definition of "local", or we need a new word instead of "spooky". Something benevolent and *not* scary, though obviously, something which is hard to understand. Maybe just "shut up and calculate" was the best answer, all along.

"Many worlds" means there is just the wave function of the universe which is evolving deterministically. So the only real thing in the universe is its wave function.

Qubism means that it is all in the mind (or minds) of observers. So there is nothing real in the universe at all except, I suppose, the minds of observers.
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Re: Wigner's Friend Experiment

Postby FrediFizzx » Tue May 28, 2019 9:20 pm

I have no problem with probability waves just disappearing. But I would imagine in some cases they get transformed into a different probability wave. And we don't have to worry about "spookiness". Nature is local as far as interaction events go. Of course a real wave can be somewhat non-local. Shake a 100 foot long rope attached at the other end up and down. Where is the wave? Of course it is along the whole 100 feet. But the interaction is at the loose end of the rope and that is completely local.
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