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Almost all resources I've read about Quantum Entanglement speak about how 'amazing' it is that two entangled particles are bound over any distance, and that the state of one particle determines the state of the other.

I believe that there is possibly a profoundly wrong assumption here that doesn't get addressed properly. The assumption is that when the state of one particle is observed, it is then, and only then, determined, exiting it's super position state (and thus the state of the other particle also being determined, over any distance, instantly - which is where most of the focus lies when talking about entanglement).

But here is my problem - why is the assumption that the state of the first particle is being determined on observation so easily accepted ? It seems to me much more logical and absolutely free of unexplained voodoo that:

  1. the particles are entangled (have opposite symmetrical states).
  2. The state of the first and second particles is unknown and unknowable until observed, but is predetermined from the moment of the particle's inception.
  3. Upon observation, nothing in the particle changes, except that our knowledge of the first particle's state leaves a "super-positioned" state into a specific one.
  4. Basic logical consistency dictates that we "instantly" know the state of the second particle, without the need for "spooky action at a distance".

So I guess that my basic premise is - it seems much more reasonable that our (my?) understanding of superposition is wrong, rather than that particles exchange state information instantly across any space.

Please help me understand where I am wrong ?

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You should really read the following famous article by Mermin: web.pdx.edu/~pmoeck/pdf/Mermin%20short.pdf It essentially answers your question in a simple, elegant way. –  joshphysics Aug 21 '14 at 22:28
as Feynman said: "Noone understands quantum mechanics", "when expressed in copenhagen interpretation" (last mine) :) –  Nikos M. Aug 21 '14 at 23:13
This is a great question, by the way. Given the evidence that you were previously aware of, the hypothesis that the states of the particles are determined before observation is much better than the hypothesis that the states are determined upon observation. It happens, though, that we have additional evidence which contradicts the first hypothesis. –  Tanner Swett Aug 22 '14 at 1:13
There is no such thing as "state of the first and second particle". There is only one state, which describes both particles. What you call voodoo is merely the consequence to what happens, when we intuitively assume that physical distance somehow "separates" that one state. It doesn't. –  CuriousOne Aug 22 '14 at 1:14
@gpgemini: you are right and the answer has always been in plain sight. The particles do not turn out to be entangled. We know they are entangled at the onset of the experiment, so why should we expect they cease to be entangled at the end? –  bright magus Aug 22 '14 at 5:53

3 Answers 3

up vote 5 down vote accepted

What you are proposing is called a local hidden variable theory. Bell's theorem proves that any such local hidden variable theory is inconsistent with behavior predicted by quantum mechanics. Bell test experiments have been performed, which show that the predictions made by quantum mechanics are correct, in ways that cannot be explained by a local hidden variable theory.

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I've read Mermin's excellent article, Aspect_experiment, EPR paradox and Bell's theorem. This makes no sense. No one has any idea what is going on, except that some very odd experiments don't behave as we would expect them to. –  171 Aug 22 '14 at 20:57
explained by a "local, real and causal" theory. It is supposed to be choose any two. –  Nikos M. Aug 23 '14 at 0:08
@gpgemini Sort of. Some very odd experiments don't behave as classical intuition would predict, but there is a formalism which predicts their results perfectly (so far). After that, whether we understand it or not mostly depends on your definition of 'understand'. –  Emilio Pisanty Aug 23 '14 at 17:18
@gpgemini I'd say that we do know what's going on. If we assume that states are predetermined, then we end up with experiments whose outcomes don't make any sense. If we assume that states aren't predetermined, we have these theories which explain things perfectly. The logical conclusion is that states aren't predetermined. –  Tanner Swett Aug 24 '14 at 14:34
@TannerSwett, following this logic, if states aren't predetermined, how do you explain that measuring one particle determines it's state, and instantly also the state of it's entangled sibling, which was previously undetermined. The current theories don't explain how this happens, thus we do not know what is going on. –  171 Aug 25 '14 at 6:38

My understanding is that the Aspect experiment shows that your understanding is wrong. http://en.wikipedia.org/wiki/Aspect_experiment

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Here are my two cents on this.

In quantum mechanics, one, two,...many particles are described by a state function. The state function is gives a probability distribution that includes all the possible measurable values of the one,two...many particles.

Let us take two for simplicity and because here is where confusion arises. Because of conservation of quantum numbers the possible probability states of two spin a half particles to be created from a spin zero particle are two, either particle_1 can have spin up and the particle_2 spin down, or the particle_2 is up and particle_1 down. It is a limited outcome probability distribution, but a distribution never the less. In the same way that spinning a coin and getting heads gives you the knowledge that the other side is tails, if you measure one particle's spin you know the spin of the other even if it has gone off to infinity. There is nothing more esoteric than conservation of quantum numbers here.

In my opinion all this entanglement navel gazing is not worth the effort to think it through. Dealing with state functions and probabilities is the job of the physicist who measures.

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