Is the cat alive, dead, both or unknown

[Nick666]

Just please look at the link, you'll see why I can't post the link here.

 

[bhobba]

Just please look at the link, you'll see why I can't post the link here.

There is no reason you can't post it here. Simply do what I said - give a precis of the argument. If you can't follow it simply say so and ask what others think. I have had a quick glance and as far as I can see its crank rot - claiming Bell was sloppy - and in such a way that hardly anyone else spotted it - I mean - really - is that creditable? Its not impossible and has happened before - in fact Bell picked up that exact issue with Von-Neumann - but its very very unlikely. However if you have concerns state them clearly. And if you can't follow it just say so - myself and/or others will get to the bottom of it.

Thanks
Bill

 

[Nick666]

In this website that you gave me http://drchinese.com/David/Bell_Theorem_Easy_Math.htm

Dr Chinese says that you can't measure angle A and angle B at the same time for a photon.

But then at the end, Dr.Chinese says that you can do the measurement with entangled particles.

But anti-Bell folks say that the measurement is only possible if somehow you would do the measurement for the entangled particles at precisely precisely precisely the exact same time for entangled particle a and for entangled particle b, cause if its done at a later time for one of the entangled particles the result is meaningless because obviously the measurements were done at different times. They think that the Bell experiment is useless because the measurements can't be practically made at the same time on the two entangled particles.I don't want to start with the math they use cause its too advanced for me.

 

[bhobba]

Dr Chinese says that you can't measure angle A and angle B at the same time for a photon.

Of course you cant.

But then at the end, Dr.Chinese says that you can do the measurement with entangled particles.

I can't find that. Like I said I have had problems with people claiming such and such shows this or that when in fact it does nothing of the sort. Can you please post the bit you think says that.

Added Later:
Is it the following:
'do A, B and C correspond to SIMULTANEOUS elements of reality?'

That's not saying it can be measured simultaneously.

Thanks
Bill

 

[Nick666]

 

[Nick666]

Just please don't think of me as anti-Bell. I really don't care about Bell or anti-Bell, I care about the discussions because they seem to be interesting, they are interesting at least to me.

 

[bhobba]

They are not measuring them simultaneously - Dr Chinese specifically states that's not it. What he is saying is by measuring a second particle with the same attributes you can infer it. But that has a flaw - well you can read the flaw.

Again so?

Thanks
Bill

 

[bhobba]

Just please don't think of me as anti-Bell. I really don't care about Bell or anti-Bell, I care about the discussions because they seem to be interesting, they are interesting at least to me.

That's Ok. That's what this forum is about. But to discuss it we need to be clear what is being discussed.

Thanks
Bill

 

[Nick666]

Before going further, I want to get this outta my way.

That makes no sense at all.

But why can't I assume that at the beginning of the universe, certain universal properties were created that still linger to these day? Like entanglement . What if entanglement its a property of spacetime/matter/whatever that goes somehow all they way back to the big bang ?

 

[bhobba]

But why can't I assume that at the beginning of the universe, certain universal properties were created that still linger to these day? Like entanglement . What if entanglement its a property of spacetime/matter/whatever that goes somehow all they way back to the big bang ?

I explained what entanglement was. It has nothing to do with anything you suggest. Its like saying what if the cause of nuclear fusion is that fire engines are red.

Please read my explanation of what entanglement is and you should see its got nothing to do with what you wrote.

If you think otherwise explain, in full detail, how that systems can be entangled, which follows from the principle of superposition, has anything to do with photons from the big bang?

Thanks
Bill

 

[Feeble Wonk]

All systems of the same type are entangled - Asher Peres made this clear in a book which I don't have the title to hand. I will do some searching and come back.

It's been a very interesting thread. But I've been hoping that Steve would come back with his source, and further expand on this point.

What does "All systems of the same type" refer to, and in what way are they entangled?

 

[StevieTNZ]

It's been a very interesting thread. But I've been hoping that Steve would come back with his source, and further expand on this point.

What does "All systems of the same type" refer to, and in what way are they entangled?

I'm here -- just woke up. Haven't had a chance to look for the copies I made from his book I got out of my uni library, but all systems of the same type I mean photons, electrons etc. I have two other references about all systems being entangled -- I also need to look those up from my books. Please bare with me.

 

[Feeble Wonk]

Thanks for effort. But, for now, do understand you to be saying that ALL particles (bosons and fermions) of any specific type are entangled on a cosmological scale?

 

[Feeble Wonk]

*...do "I" understand you to be saying...?

 

[StevieTNZ]

Some references:
"Quantum Mechanics: A New Introduction"(https://www.amazon.com/dp/0199560277/?tag=pfamazon01-20) pgs 512-513, section 18.4 Factorisation versus Entanglement

Entanglement is a very general feature of quantum mechanics, as all sub-systems in the universe do interact, or have interacted with each other in the past, to various degrees.

"Sneaking a Look at God's Cards" (https://www.amazon.com/dp/069113037X/?tag=pfamazon01-20) pgs 339-343
"Entangled World" (https://www.amazon.com/dp/3527404708/?tag=pfamazon01-20) Chapter 10

I have yet to find the Asher Peres photocopy.

 

[BiGyElLoWhAt]

...Its like saying what if the cause of nuclear fusion is that fire engines are red.Thanks
Bill

I really don't think that's what nick is saying. Correct me if I'm wrong here nick, but I'm going to try to elaborate on what I think you're trying to say.

At the big bang, it is reasonable to view all particles as being created from a common source, i.e. the big bang. So by "watching" 2 photons evolve throughout time from some "god frame" that was there before the big bang (not saying that it's reasonable to have an observer before the big bang, but bear with me), you can sum the quantum states and statistically determine the state of particle b by measuring the state of particle a. This can be increased in statistical accuracy up to 100% by assuming a 2 particle universe.

 

[StevieTNZ]

I have my Asher Peres photocopy, which I believe came from this book: https://www.amazon.com/dp/0792336321/?tag=pfamazon01-20 (pages 126-131):

An immediate consequence of Eqs (5.37) and (5.38) [given on page 127] is that two particles of the same type are always entangled, even if they are prepared independently, far away from each other, in different laboratories. We must now convince ourselves that this entanglement is not a matter of concern: No quantum prediction, referring to an atom located in our laboratory, is affected by the mere presence of similar atoms in remote parts of the universe.

 

[atyy]

I have my Asher Peres photocopy, which I believe came from this book: [URL='https://www.amazon.com/dp/0792336321/?tag=pfamazon01-20
Concepts-Fundamental-Theories/dp/0792336321[/URL] (pages 126-131):

An immediate consequence of Eqs (5.37) and (5.38) [given on page 127] is that two particles of the same type are always entangled, even if they are prepared independently, far away from each other, in different laboratories. We must now convince ourselves that this entanglement is not a matter of concern: No quantum prediction, referring to an atom located in our laboratory, is affected by the mere presence of similar atoms in remote parts of the universe.

I think Peres is referring to the symmetrization/anti-symmetrization of the wave function for identical particles that Haelfix and I discussed in posts #112-113 about whether a local interaction is needed for two particles to become entangled.

 

[StevieTNZ]

This thread has become so long I probably missed those posts. But yes, it is about idential particles.

 

[bhobba]

So by "watching" 2 photons evolve throughout time from some "god frame" that was there before the big bang (not saying that it's reasonable to have an observer before the big bang, but bear with me), you can sum the quantum states and statistically determine the state of particle b by measuring the state of particle a. This can be increased in statistical accuracy up to 100% by assuming a 2 particle universe.

Before the big bang? Its the birth of space-time - there is no before. And watching photons - you can't watch photons - that makes no sense at all - photons are what you use to watch with and they interact very very weakly - beams of light pass through each other.

Entanglement has nothing to do with anything like that - its simply applying the principle of superposition to systems. I gave a very careful explanation before - its really all there is to it. Nothing weird in the sense of being mystical etc etc is going on - it simply leads to a different type of correlation than occurs classically. The difference is classically you know it has properties all the time ie the green and red slips of paper are always green and red. In QM its more subtle as Bells theorem shows - but it's still just a correlation - its not some phenomena that needs further explanation. We know its explanation - systems can be in superposition and hence are correlated in a way different to classical correlations.

Thanks
Bill

 

[zonde]

Rather it is as Bhobba states, that Bells setup merely forces you into a choice.

This seems to be popular misconception so I will reiterate my argument but I hope more clearly.

Bell’s theorem can be phrased as “quantum mechanics cannot be both local and counterfactual”.

Yes, this is basically correct. We can check this by converting Bell's theorem into logical statement:
L and CD => BI (1)
transposition is valid rule of replacement, so we get:
not BI => not (L and CD) (2)
and if we add that QM can violate Bell inequality we get original statement.

A logically equivalent way of stating it is “quantum mechanics is either non-local or non-counterfactual”.

Yes, we get this by rewriting consequent in statement (2):
not BI => not L or not CD (3)

Now you can keep locality if you give up realism, you can keep realism if you give up locality, or you can give up both.

Let's rephrase this statement to make it more clear:
Model that gives up counterfactual definiteness or locality can violate Bell inequality (I suppose that realism in this context was meant as counterfactual definiteness).

Now it is clear that this statement is converse of (3):
not L or not CD => not BI (4)
and the truth of converse does not follow from truth of original statement i.e. it's possible that it's false.

 

[bhobba]

The logic is simple and doesn't require formal logic. You can give up locality or counter-factual definiteness or both. There is also another out not generally talked about and my personal view. Locality in QFT does not apply to correlated systems so locality may not even be a valid concept in this case.

Thanks
Bill

 

[zonde]

There is also another out not generally talked about and my personal view. Locality in QFT does not apply to correlated systems so locality may not even be a valid concept in this case.

Please specify in what sense you use "locality" here? Because it seems that your references for this statement might have used "locality" in different sense than any of the two used in discussions about Bell theorem.

 

[bhobba]

Please specify in what sense you use "locality" here? Because it seems that your references for this statement might have used "locality" in different sense than any of the two used in discussions about Bell theorem.

I have mentioned it a number of times. Its the cluster decomposition property which is the statement of locality in QFT:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

It does not apply to correlated systems and entangled systems are correlated. Hence the concept of locality is not relevant. And inherent in the discussion of Bell is the idea locality is a relevant concept - but that's precisely what I don't agree with. If you think it's relevant then Bell is airtight. But if its of no relevance then its of no concern at all.

Note also, as I have mentioned before, standard QM is based on the Galilean transformations so is inherently non-local at it very foundations.

This leads to the view this EPR stuff is not an issue - its just some interesting correlations.

Its not a common view - but some hold to it eg Brian Green:


Thanks
Bill

 

[zonde]

I have mentioned it a number of times. Its the cluster decomposition property which is the statement of locality in QFT:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

In your link I found this statement:
Here Weinberg introduces the concept of Cluster Decomposition: “It is one of the fundamental principles of physics (indeed, of all science) that experiments that are sufficiently separated in space have unrelated results…”

So it seems that "locality" here means that distant experiments have unrelated results. Is this right?

 

[bhobba]

In your link I found this statement:
Here Weinberg introduces the concept of Cluster Decomposition: “It is one of the fundamental principles of physics (indeed, of all science) that experiments that are sufficiently separated in space have unrelated results…” So it seems that "locality" here means that distant experiments have unrelated results. Is this right?

I will be more concise:
Uncorrelated experiments that are sufficiently separated in space have unrelated results.

There is a bit more to it at a technical level but basically that's the statement of locality in QM. And in that form its easy to see why you need the caveat uncorrelated.

EPR type experiments, and entanglement in general, are correlated so are not part of this definition of locality. Hence its meaningless, under this definition, to speak about locality in entangled systems. But of course you can have other definitions, and if you do that, then what Bell says comes into play - namely you can have counter-factual definiteness if some kind of instantaneous influence travels between entangled systems.

Thanks
Bill

 

[BiGyElLoWhAt]

I really don't think that's what nick is saying. Correct me if I'm wrong here nick, but I'm going to try to elaborate on what I think you're trying to say.

At the big bang, it is reasonable to view all particles as being created from a common source, i.e. the big bang. So by "watching" 2 photons evolve throughout time from some "god frame" that was there before the big bang (not saying that it's reasonable to have an observer before the big bang, but bear with me), you can sum the quantum states and statistically determine the state of particle b by measuring the state of particle a. This can be increased in statistical accuracy up to 100% by assuming a 2 particle universe.

Sigh... alright let me be more careful with my wording.
[Mentor's note: An extended speculation based on a misunderstanding of the Big Bang has been removed from this post]

I read through this thread, by the way, I have also worked somewhat with entanglement, if this is not how it works, then would you please bear with me and give me a dumbed down version of what entanglement actually means in a modern context? Because I was apparently unable to grasp it from what you've said...

If this is, in fact, how it works, then why are not ALL particles from the time of the big bang entangled, as nick666 has said?

 

[Nugatory]

If this is, in fact, how it works, then why are not ALL particles from the time of the big bang entangled, as nick666 has said?

The big bang is indeed in the causal past of everything, but any residual entanglement between two particles that have not interacted since then is near as no never mind zero. That is, the wave function of the two-particle system is for all practical purposes completely factorizable and the two particles can be treated separately.

(This might, however, be a good time to suggest googling for "quantum superdeterminism", as long as everyone promises not to prolong this thread based on what they find).

 

[Feeble Wonk]

I think Peres is referring to the symmetrization/anti-symmetrization of the wave function for identical particles that Haelfix and I discussed in posts #112-113 about whether a local interaction is needed for two particles to become entangled.

Can you elaborate more about this type of entanglement in conceptual language rather than mathematical? And how would this type of entanglement contribute, if at all, to decoherence effects?

 

[atyy]

Can you elaborate more about this type of entanglement in conceptual language rather than mathematical? And how would this type of entanglement contribute, if at all, to decoherence effects?

Good question! Actually, I don't know whether everyone counts this as "true" entanglement.

In the old sense, this is for electrons and protons, simply the Pauli exclusion principle, which is key to chemistry and the solids and liquids you see in everyday life.

I think the debate as to whether this constitutes "true" entanglement continues. There are recent papers trying to address the issue, eg.:

http://arxiv.org/abs/1312.4311
Phys. Rev. Lett. 112, 150501 (2014)
Extracting entanglement from identical particles
N. Killoran, M. Cramer, M. B. Plenio
(Submitted on 16 Dec 2013 (v1), last revised 22 Apr 2014 (this version, v2))
Identical particles and entanglement are both fundamental components of quantum mechanics. However, when identical particles are condensed in a single spatial mode, the standard notions of entanglement, based on clearly identifiable subsystems, break down. This has led many to conclude that such systems have limited value for quantum information tasks, compared to distinguishable particle systems. To the contrary, we show that any entanglement formally appearing amongst the identical particles, including entanglement due purely to symmetrization, can be extracted into an entangled state of independent modes, which can then be applied to any task. In fact, the entanglement of the mode system is in one-to-one correspondence with the entanglement between the inaccessible identical particles. This settles the long-standing debate about the resource capabilities of such states, in particular spin-squeezed states of Bose-Einstein condensates, while also revealing a new perspective on how and when entanglement is generated in passive optical networks. Our results thus reveal new fundamental connections between entanglement, squeezing, and indistinguishability.