Re: non-separability of 2 particle systems in quantum mechanics
From: John Sefton (john_at_petcom.com)
Date: 10/13/04
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Date: Wed, 13 Oct 2004 17:52:08 -0600
richardconers@yahoo.com wrote:
> I'm reading "Quantum mechanics and experience". It's starting to sink
> in, and I hope I can use this formum to clarify some points as I go
> along (I finished reading it, but I'm reading it a second time because
> there's no way I get it entirely in the first round <g>.)
>
> My big hang-up so far is understanding non-locality/non-separability
> of 2 particle states. Albert doesn't explain how such a state comes
> about in the first place. Can I assume that all combinations of 2
> particles at a time are NOT in a non-separable state? Then what puts
> them into that state? And what causes the end of non-separability
> (i.e., separate reactions of the particles independent of the changes
> going on in the other particle)?
>
> I raise the questions because I don't understand why Albert makes such
> a big deal out of non-locality. If two particles are in a
> "non-separable state" where the color of A is opposite the color of B
> (A+B = 0) is the quantum state of the two particle system, then
> non-locality seems to follow logically.
>
> In this state neither A's color nor B's color is determined, just the
> state of the two particle system. So if A is then measured, A-B is
> still undetermined because B has not been measured yet. When B is
> finally measured, it will turn out to be "minus A or the opposite of
> A", unless something is done to change the two particle system, which
> meausring alone won't do, since A-B is already in a determined state.
> So B, at the time of measuring of A, is still undetermined, but there
> is no way (I assume) to confirm that B is undetermined without
> measuring it. As soon as you measure B, it must be "minus A" per the
> 2 particle system state.
>
> If the above is true, nothing in that description calls for any
> "direct, physical" contact between A and B, so non-locality is
> inherent in having something called a "non-separable" state. You
> don't even need Bell's theorem to conclude this, do you?
>
> I raise this question because this non-separability seems to me to be
> very, very much different from incompatible properties of a one
> particle system. It seems like quantum mechanics is asserting right
> from the start that there are pairs of properties of a single particle
> which are 100% incompatible. This seems to be inherent in the
> physical makeup of the universe.
>
> In contrast, I don't think Albert makes explicit under what
> circumstances non-separability of two particle systems obtains. Is he
> saying that non-separability is inherent in all two particle pairs,
> just like incompatibility is inherent in pairs of properties of one
> particle systems? Even so, that wouldn't mean that all 2 particle
> pairs are in a non-separable state, since only specific pairs of
> properties of a one particle state are incompatible, not all pairs of
> properties.
>
> So that leads me back to the question of what generates
> non-separability of two particle systems--and which properties become
> non-separable under those circumstances (hopefully it doesn't mean
> that all properties are non-separable in that state)?
>
> Thank you for your explanation(s)!!!
Particles don't exist.
Everything is energy.
John
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