B Layman question about faster than light communication

[rede96]

If the process was local, the outcomes - random as you mention - would be independent (factorizable) even if they were correlated.

I’m not sure I understand your point. What do you mean exactly by independent or factorizable? I think this is the part I never quite grasp.

You can't use the EPR program for that, basically that's what we learned from Bell. Which is what you are trying to do, regardless of what you call it.

Just to reiterate, I’m not arguing against the physics. I just can’t for the life in me see how Bells theorem prohibits local variables and leads to the conclusion there must be instantaneous communication between the entangled pair.

EDIT: I can see why it prohibits pre existing states. But I don’t get why not having a pre existing state means nothing local going on.

 

[PeterDonis]

What do you mean exactly by independent or factorizable?

Have you read Bell's paper? You can find it here:

http://www.drchinese.com/David/Bell_Compact.pdf

Equation (2) in the paper describes a factorizable probability function.

I’m not arguing against the physics. I just can’t for the life in me see how Bells theorem prohibits local variables

This is a "B" level thread, and the question you are implicitly asking here really needs at least an "I" level discussion, if not "A" level. So you really need to start a separate thread. (I would strongly recommend reading the Bell paper first.)

and leads to the conclusion there must be instantaneous communication between the entangled pair.

It doesn't lead to that conclusion. It just says local hidden variable models can't reproduce the actual QM correlations. It doesn't make any claims about what other kind of model can reproduce the QM correlations, or whether such a model requires instantaneous (FTL) communication. Those are separate questions.

 

[DrChinese]

1. I’m not sure I understand your point. What do you mean exactly by independent or factorizable? I think this is the part I never quite grasp.

2. Just to reiterate, I’m not arguing against the physics. I just can’t for the life in me see how Bells theorem prohibits local variables and leads to the conclusion there must be instantaneous communication between the entangled pair.

1. Let's say that the action on each side is independent, no communication between them (which would need to be FTL, to match experiments in which the distance is too far to be c or less). Therefore if there is any random factor involved that is NOT like your scenario I ("pre-existing state"): there is a chance that the result on one side (which is random and independent) and the result on the other side (which is random and independent) will not match up.

2. This is NOT a conclusion or deduction from Bell. Bell excludes local realistic theories. It could be non-local or non-realistic (or both).

 

[rede96]

You say that the state of your card is unknown because you don't yet know how you will measure it, but once you choose a measurement angle, the result is inevitable. QM is not like that. Even when we know the measurement angle for a polarity measurement, the result can be random.

Sorry, that wasn’t what I was trying to demonstrate. In my card example both the card and measurement angle were random. So the result wasn’t inevitable once the measurement angle was selected.

It’s just that there was something additional going on that meant the two paired cards were random in a similar way which led to correlations.

 

[rede96]

1. Let's say that the action on each side is independent, no communication between them (which would need to be FTL, to match experiments in which the distance is too far to be c or less). Therefore if there is any random factor involved that is NOT like your scenario I ("pre-existing state"): there is a chance that the result on one side (which is random and independent) and the result on the other side (which is random and independent) will not match up.

Ok, thanks for explaining that. Again maybe it’s my understanding of what a pre-existing state.

Lets say the action on each side is independent. So I produce and measure a number of entangled particles. For the sake of argument I measure them all at the same angle. I find each pair may give a different result each time, (e.g. one pair up down and the next down up etc) but each pair are always correlated.

So I assume this is because they are exact copies of each other, it makes sense that their results always match at the same angle. I also assume as each pair appear to be random, albeit correlated, they don’t have a pre-existing state in those circumstances.

But what I think you are saying is that for each pair to be independent, random and exactly correlated, they must have a pre-existing state. As their correlation can’t be explained any other way using local variables. Is that correct?

And what Bells theorem says is they can’t have a pre-existing state, so something non local must be going on.

Is that sort of the gist of it?

 

[DrChinese]

Ok, thanks for explaining that. Again maybe it’s my understanding of what a pre-existing state.

Lets say the action on each side is independent. So I produce and measure a number of entangled particles. For the sake of argument I measure them all at the same angle. I find each pair may give a different result each time, (e.g. one pair up down and the next down up etc) but each pair are always correlated.

So I assume this is because they are exact copies of each other, it makes sense that their results always match at the same angle. I also assume as each pair appear to be random, albeit correlated, they don’t have a pre-existing state in those circumstances.

But what I think you are saying is that for each pair to be independent, random and exactly correlated, they must have a pre-existing state. As their correlation can’t be explained any other way using local variables. Is that correct?

And what Bells theorem says is they can’t have a pre-existing state, so something non local must be going on.

Is that sort of the gist of it?

Yes, I was showing you that if there are to be the proper stats at the same angles, and they are random and independent (no FTL communication), there cannot be anything depending on anything OTHER than the initial state (i.e. the measurement system). And yes, Bell would rule that out (the initial state a la EPR) when you check other angle settings.

There could be FTL communication. There could be retrocausal communication. There are some other hypothetical mechanisms. But nothing Local Realistic.

 

[rede96]

Have you read Bell's paper? You can find it here:

This is a "B" level thread, and the question you are implicitly asking here really needs at least an "I" level discussion, if not "A" level. So you really need to start a separate thread. (I would strongly recommend reading the Bell paper first.)

Thanks for the link. I have read Bell's paper but unfortunately the math is beyond me. Hence why I am trying to take the logic approach. It's also why I stay around the B level.

But the posts here have helped (thanks to everyone) so I'll reflect and go through the paper again and start a new thread as recommended.

Thanks again.