What are considered hidden variables in physics? Would dark matter be considered as a hidden variable? - by Viktor T. Toth - Quora Question Review

This document contains a review of the answer by Viktor T. Toth on the question in Quora: "What are considered hidden variables in physics? Would dark matter be considered as a hidden variable?"
To order to read all the answers select: https://www.quora.com/What-are-considered-hidden-variables-in-physics-Would-dark-matter-be-considered-as-a-hidden-variable

• The text in italics is copied from the article.
  
• Immediate followed by some comments
  

Contents

• 1. Answer Review

Reflection

• Reflection 1 - Question Review

1. Answer Review

No, dark matter has nothing to do with it. Hidden variables arise in the context of quantum physics, in particular the famous Bell’s Theorem according to which quantum physics is nonlocal. This is best illustrated by an example from Bell’s book, an example involving socks. Suppose you take a trip somewhere. Upon arrival in your hotel room, you notice that you have only half a pair of your favorite gray socks in your suitcase. From this you instantly infer that the other half must be left behind at home in your socks drawer. The variable representing half a pair of your gray socks was there all along, but it was “hidden” from you for whatever reason.

To explain any physical phenomena, has nothing to do with an observer. If there are exist 2 socks marked: #1 and #2 and if you observe #1 than somewhere else there must be #2.

Now take the analogy to the quantum realm. You have a pair of correlated particles isolated from the environment, say, a pair of electrons.

To make such a statement you have to perform 100 identical experiments. All these experiments should show the same results, when both spins are measured, there is always one electron which has direction +1 and one which has direction -1.

You measure the spin of one of the electrons and you immediately infer the outcome of a spin measurement that might be carried out on that other electron.

In the above case when you measure the spin of one electron and you measure +1 you can infer that the spin of the other one is a -1. This can be demonstrated when the spin of the second one is tested. The moment when the second one is tested is unimportant. That means when the second electron is measured before or after the first test (unknown to the observer). The reason is that the correlation is established, as part of the reaction that created both electrons.

Could it be that the spin value of the electron, just like the information about your socks, was there all along, as a “hidden variable”?

The concept "hidden variables" is not required to explain the correlation.

The answer is a no, for reasons that are mildly technical, but I think I can explain the essence. A spin measurement involves orienting the instrument with respect to which the spin is measured. This orientation need not be known in advance. Yet the spins of the two electrons will be correlated nonetheless. There is no classical physics analogue for this phenomenon. The point is, information in the form of “local hidden variables” that the electrons carried with themselves is not sufficient to account for the correlation between the two electrons under arbitrary orientations of the instruments used to measure them. Additional, “non-local” information is required to account for the observed correlation. Quantum physics is thus manifestly non-local, cannot be explained using hidden variables.

The explanation of the fact that the directions of the spins are correlated is part of the explanation why as part of the reaction there are two electrons created in the first place.

(What is absolutely fascinating that despite this nonlocality, quantum field theory is demonstrably and strictly causal, i.e., contrary to some fictionalized accounts or even some misguided popular science explanations, quantum entanglement cannot be used to circumvent the relativistic speed limit or create a time machine. It just does not work that way, which, incidentally, is actually a Good Thing, as an acausal universe would be chaotic and unpredictable, quite possibly unstable.)

In order to explain any physical reaction, specific quantum entanglement, no hidden parameters are required.
See also: Article_Review_Polarization_Correlation_of_Photons_Emitted_in_an_Atomic_Cascade.htm
Or: https://escholarship.org/uc/item/1kb7660q

Go Back to Quora Question Review
Back to my home page Index