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crowded quantum information


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4 hours ago, bangstrom said:
17 hours ago, Eise said:

1. One of "Different observers seeing signals going into different directions" and how this is "a well understood phenomenon of SR".

That goes back to the old example where lightning strikes both ends a train simultaneously on both ends relative to an observer in the center.

Oh my. In the entanglement situation we are discussing that different inertial observers, in your interpretation where there is a FTL signal, must see one signal (between the measurements) going into opposite directions, but taking the same trajectory. And now you come with an example with two signals, taking two different trajectories, one of the front of the train to the middle, the other from rear to the middle.

4 hours ago, bangstrom said:

An observer at the front will say it struck the front first and an observer at the rear will say it struck the rear first.

And this has to do nothing with SR. SR is not about observers being at different locations. That can be handled just as well with Newtonian mechanics. Just take the signal velocity in account, and you are done. SR however is about the different observations by observers in different inertial frames of reference, i.e. observers that move (fast) relatively to each other. Do you know the difference between spacial distant events, and space-like separated events in SR at all?

4 hours ago, bangstrom said:

An example of a signal carrying information but not energy would be a signal involving entanglement. That is my answer and I have no other.

I thought so. Case closed.

3 hours ago, bangstrom said:

Some say that does violate SR but I say it only violates Einstein’s second postulate about nothing being faster than light. His second postulate was instrumental in formulating SR but it remains a provisional statement that is no longer supported by experimental evidence.

Ah. It only violates one of the two groundstones* of SR, without which SR would be thoroughly false. At the same time SR is essential to our understanding of QFT, it is the basis even of our classical understanding of electro-magnetism, it is practically essential for GPS and particle accelerators, it explains the colour of gold and the liquidness of mercury, etc, but yeah, the invariance of light speed is just a provisional conjecture.:blink: 

You have no idea how SR is one of the roots of our understanding of the physical world. Every fundamental law of nature must pass the criterion that it is Lorentz invariant, i.e. does not lead to inconsistencies when we apply SR.

* BTW the second postulate is not that nothing can go faster than light, it says that the speed of light is invariant. That  no material object can reach the speed of light is a conclusion of SR.

3 hours ago, iNow said:

Lather. Rinse. Repeat. 
 

I can’t wait to see what fun the next 21 pages of repeated thread will bring. 

He, 22 already! Do not eat too much popcorn...

popcorn-emoji.gif

 

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Let’s look at this whole quantum entanglement business systematically, because I really don’t think it requires 22 pages of discussion and argument to understand this. It may be counter-intuitive, but it really isn’t that complicated.

Suppose you have - to begin with - two completely separate particles, which aren’t part of a composite system; their states are thus entirely separate, and denoted by

\[|A\rangle ,|B\rangle\]

Don’t mind the precise meaning of this mathematical notation; it simply denotes two separate particles being in two separate states, where the outcome of measurements are probabilistic, and not in any way correlated at all. No mystery to this thus far.

Now let’s take the next step - we combine the two particles into a composite system. The state function of that composite system is then the tensor product of the states of the individual particles, like so:

\[ |\psi \rangle =|A \rangle \otimes |B \rangle \equiv |AB \rangle\]

Again, don’t mind the precise definition of these mathematical operations; the idea here is simply that our two particles A and B form a composite system. Let’s, for simplicity’s sake, assume that each particle can only have two states, ‘0’ and ‘1’ - the physical meaning of the tensor product above is then that it combines each possible state of one particle with each possible state of the other, so the overall combined system can have four possible states:

\[|00\rangle ,|01\rangle ,|10\rangle ,|11\rangle\]

Thus the overall combined state of the particle pair is (I will omit the coefficients here, as the precise probabilities aren’t important):

\[|\psi \rangle =|00\rangle +|01\rangle +|10\rangle +|11\rangle\]

This is an example of a system that is not entangled - the combined state function can be separated into the individual states of the constituents, and all combinations are possible (though not necessarily with equal probability). Non-entangled states are separable into combinations of states of the individual constituent particles - they are tensor products of individual states - which means physically that there are no correlations between outcomes of measurements performed at the constituent particles. If you get state ‘0’ for a measurement on particle A, then you can get either state ‘0’ or state ‘1’ for a measurement on B, and these outcomes are statistically independent from each other. Mathematically, the tensor product makes no reference to the separation of the particles, ie it is not a function of their position, hence neither is the overall combined state.

An entangled 2-particle state, on the other hand, looks like this:

\[|\psi \rangle  =\frac{1}{\sqrt{2}}\left(|01\rangle +|10\rangle \right)\]

Notice three things:

1. Compared to the non-entangled state, two of the possible measurement outcomes are missing; the set of possible outcomes is reduced

2. The combined state cannot be uniquely separated into tensor products of individual states; it is non-separable

3. The form of the combined state does not depend on the spatial (or temporal) position of the particles - it is purely a stochastic statement, not a function of spacetime coordinates.

What does this physically mean? Because the set of possible measurement outcomes in the overall state is reduced as compared to the unentangled case, there is now a statistical correlation between measurement outcomes - with emphasis being on the term statistical. There are now only two possible combinations, as opposed to four in the unentangled case. This is the defining characteristic of entanglement - it restricts the pool of possible combinations of measurement outcomes, because the overall state cannot be separated, due to there being extra correlations that weren’t present in the unentangled case. This is purely due to the form of the combined wave function - the outcome of individual measurements on each of the constituents is still purely stochastic, and not (!!!) a function of distant coordinates.

Because the outcome (statistical probability) of local measurements is not a function of coordinates or any distant states, it is completely meaningless to say that this situation is somehow non-local, or requires any kind of interaction, be it FTL or otherwise. The entire situation is fully about statistics and correlations, which is not the same as a causal interaction; in fact, any interaction between the constituents (including FTL ones) would change the combined wave function and preclude the possibility of there being a statistical correlation while at the same time maintaining the stochastic nature of the outcomes of individual measurements. This is evident in the fact that the entanglement property of the above state function isn’t encoded in any kind of coordinate dependence, but rather in a reduction of terms, ie in a reduced pool of possible outcomes. This hasn’t got anything to do with locality at all, but is purely a statistical phenomenon.

Hopefully the either helps, or possibly it might spark off another 22 pages of discussion :)

Edited by Markus Hanke
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15 hours ago, bangstrom said:

This is impossible for the sender. They can’t know what they sent or describe it. A person on the sending end can generate a pair of entangled particles and send one off but they can’t know the identity of which one they sent or which one they retain. If they observe the identity of their own particle, they break the entanglement.

On 11/20/2022 at 4:06 PM, joigus said:

So that the distant observer knows immediately it's either "0" or "1"

The receiver instantly knows if it is “0” or “1” but they can’t know what it means because even the sender can't know what they sent.

In other words. You're saying that somehow, what you say is true, just because you say so, but nobody can ascertain experimentally, or even in principle, that it's true.

Your simulation of an explanation is more or less the same in all your posts: You somehow know you're right, but you can't quite put your finger on why it's right, or even what exactly it is that you're right about.

At this point I'm only just curious about your convictions from a purely psychological point of view. There's certainly no science to be learnt from anything you say here.

And again, quantum particles have no identity:

https://en.wikipedia.org/wiki/Identical_particles#:~:text=In quantum mechanics%2C identical particles,one another%2C even in principle.

Quote

In quantum mechanics, identical particles (also called indistinguishable or indiscernible particles) are particles that cannot be distinguished from one another, even in principle. Species of identical particles include, but are not limited to, elementary particles (such as electrons), composite subatomic particles (such as atomic nuclei), as well as atoms and molecules. Quasiparticles also behave in this way. Although all known indistinguishable particles only exist at the quantum scale, there is no exhaustive list of all possible sorts of particles nor a clear-cut limit of applicability, as explored in quantum statistics.

 

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9 hours ago, Markus Hanke said:

Hopefully the either helps, or possibly it might spark off another 22 pages of discussion :)

It helps those of us who wish to understand entanglement more clearly.

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4 hours ago, MigL said:

It helps those of us who wish to understand entanglement more clearly.

:lol: 

And of course a +1 for Markus. At least I understand it a little more clearly now.

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Yep. A big +1 to Hanke, as it was a very transparent account of the whole thing. Unfortunately, it's possible that this will not be the last word we hear from Bangstrom, and we get past Xmas still talking about it, to iNow's boredom and despair.

We've got now 2 local experts, plus a bunch of other members, plus a panel of distinguished and reputable physicists, who've made their case against a standalone opinion.

Can we call it a day?

Edited by joigus
minor correction
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On 11/21/2022 at 9:46 AM, Markus Hanke said:

Hopefully the either helps, or possibly it might spark off another 22 pages of discussion

Hopefully, yes. I appreciate your efforts and support the accuracy of your description.

The majority of the 22 pages were not about entanglement but they veered off into circular discussions of unrelated topics such as fine points of SR sprinkled with many comments of a personal nature so little was accomplished. We should be able to do better.

 

On 11/21/2022 at 2:13 PM, joigus said:

Quantum particles have no identity in the sense of Dirac's observation that a an electron on Earth is no different from other electrons in the cosmos. It is as if there is only one electron that appears to be popping up everywhere at once.

But electrons do take on individual properties.

The disagreement de jour centers around my reply to your statement,

“OK, @bangstrom. Enough is enough. Take a code "0" and "1."

Describe a protocol that sends either "0" or "1" to a distant observer by using an entangled state.

Describe it clearly.”

To which I replied,”This is impossible for the sender. They can’t know what they sent or describe it. A person on the sending end can generate a pair of entangled particles and send one off but they can’t know the identity of which one they sent or which one they retain. If they observe the identity of their own particle, they break the entanglement.”

To which you replied, “In other words. You're saying that somehow, what you say is true, just because you say so, but nobody can ascertain experimentally, or even in principle, that it's true.”

I don’t find this to be my opinion alone and I try never to make a statement that I can’t support so here is a quote from Wikipedia in support of my claim that, “If they observe the identity of their own particle, they break the entanglement.”

https://en.wikipedia.org/wiki/Quantum_entanglement

“The paradox is that a measurement made on either of the particles apparently collapses the state of the entire entangled system—and does so instantaneously, before any information about the measurement result could have been communicated to the other particle (assuming that information cannot travel faster than light) and hence assured the "proper" outcome of the measurement of the other part of the entangled pair. In the Copenhagen interpretation, the result of a spin measurement on one of the particles is a collapse into a state in which each particle has a definite spin (either up or down) along the axis of measurement. The outcome is taken to be random, with each possibility having a probability of 50%. However, if both spins are measured along the same axis, they are found to be anti-correlated. This means that the random outcome of the measurement made on one particle seems to have been transmitted to the other, so that it can make the "right choice" when it too is measured.[34]

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2 hours ago, bangstrom said:

The majority of the 22 pages were not about entanglement but they veered off into circular discussions of unrelated topics such as fine points of SR sprinkled with many comments of a personal nature so little was accomplished. We should be able to do better.

The discussion was actually about FTL signals. More in particular, it assumed that FTL signals are actually implied by quantum entanglement. From that as a premise, it proposed the possibility that this "entangled information," whatever that means, can be somehow amplified, or "crowded."

It was I who first challenged the premise that FTL signals are possible from the mere basis of QM. @uncool then proposed whether it could be the breaking of quantum coherence --or, if you will, the collapse of the wave function-- that could be used as a signal. Here:

That was a very interesting point. I think I basically answered this with a clear resounding "no." But at this point the debate was getting, IMO, very interesting.

Then you intervened by entering into a dynamics of a dog chasing his own tail, by repeatedly denying matters of principle and experimental evidence that nobody else here has any significant doubt about. As long as you do not agree on these matters of principle, it will be impossible to further understand why this illusion of non-locality --that's implied, eg, in the last paragraph you quoted-- occurs when one thinks of QM in the terms of Copenhagen's interpretation of the theory. I did try to steer the debate in that direction, because I think it explains the confusion as close as effortlessly as it's possible to do.

You stubbornly repeated asking me for a criterion of non-locality after, many posts before, I had already given you one:

That you either didn't understand or didn't bother to read. For a theory to actually be non-local, it would have to be a system that, once cast in a Lagrangian form, would have an infinite sensitivity to spatial inhomogeneities. This would reflect in the Lagrangian as having arbitrarily-high order of spatial derivatives. That's why I know quantum mechanics cannot be non-local in any fundamental way, and the whole illusion must come from some kind of basic misunderstanding of the concepts.

So it is you who's stalling any progress by repeating over and over some kind of half-diggested undestanding that is not correct and leads anyone who reads it --and believes what you say-- in the wrong direction.

Your attitude, from a purely scientific POV, is obnoxious. At one point, it even reached that level from a civil POV, when you indulged in calling people names, when pressed for arguments you were unable to find.

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3 hours ago, bangstrom said:

Hopefully, yes. I appreciate your efforts and support the accuracy of your description.

Now it would be interesting to know if you agree with Markus' descriptions. 

3 hours ago, bangstrom said:

The majority of the 22 pages were not about entanglement but they veered off into circular discussions of unrelated topics such as fine points of SR

'Unrelated'? You simply do not see what the relation is. 

One could call SR a 'meta-theory': it describes how space and time transform when seen by different inertial observers. As we all observe physical phenomena in space and time, all fundamental laws of physics must pass the test if they are Lorentz invariant. If they are not, then they are not correct.

An FTL signal does not pass the test, so an entanglement explanation that contains an FTL signal cannot work. That is the whole argument in a nutshell. Even QM must 'obey' special relativity, which it does, as QFT.

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20 hours ago, joigus said:

The discussion was actually about FTL signals. More in particular, it assumed that FTL signals are actually implied by quantum entanglement.

Agreed, that was the primary topic.

20 hours ago, joigus said:

That you either didn't understand or didn't bother to read. For a theory to actually be non-local, it would have to be a system that, once cast in a Lagrangian form, would have an infinite sensitivity to spatial inhomogeneities. This would reflect in the Lagrangian as having arbitrarily-high order of spatial derivatives. That's why I know quantum mechanics cannot be non-local in any fundamental way, and the whole illusion must come from some kind of basic misunderstanding of the concepts.

And I still don't understand your explanations, which is why I can’t tell if yours is valid observation or a mathematical obfuscation. What is called "local" in Hermitian space is not what is called "local" outside the Hermitian, and as long as the terms are defined, I see no problem with calling entanglement non-local.

I understand how entanglement is a sort of hybrid state where two remote particles act locally as if side-by-side so entanglement has a local component but the instant decoherence of entanglement across, possibly extra galactic distances, is non-local by conventional definitions as is the apparent signal, if there really is a signal.

And is the Lagrangian of the wave function of entanglement not a non-local Lagrangian? Not that I am qualified to judge. I will leave that up to you. 

https://en.wikipedia.org/wiki/Nonlocal_Lagrangian

In field theory, a nonlocal Lagrangian is a Lagrangian, a type of functional L [ ϕ ( x ) ] {\displaystyle {\mathcal {L}}[\phi (x)]} containing terms that are nonlocal in the fields ϕ ( x ) {\displaystyle \phi (x)} , i.e. not polynomials or functions of the fields or their derivatives evaluated at a single point in the space of dynamical parameters

20 hours ago, joigus said:

Then you intervened by entering into a dynamics of a dog chasing his own tail, by repeatedly denying matters of principle and experimental evidence that nobody else here has any significant doubt about. As long as you do not agree on these matters of principle, it will be impossible to further understand why this illusion of non-locality --that's implied, eg, in the last paragraph you quoted-- occurs when one thinks of QM in the terms of Copenhagen's interpretation of the theory. I did try to steer the debate in that direction, because I think it explains the confusion as close as effortlessly as it's possible to do.

  I disagree but I will let that pass as your opinion.

20 hours ago, joigus said:

It was I who first challenged the premise that FTL signals are possible from the mere basis of QM. @uncool then proposed whether it could be the breaking of quantum coherence --or, if you will, the collapse of the wave function-- that could be used as a signal.

I also agreed that entanglement could not be used as a FTL communication at the macro level.

That doesn't mean it is not superluminal at the particle level.

I understand how entanglement is a sort of hybrid state where two remote particles act locally as if side-by-side so entanglement is not totally non-local but the instant decoherence of entanglement is non-local by conventional definitions as is the apparent signal, if there really is a signal.

 

19 hours ago, Eise said:

One could call SR a 'meta-theory': it describes how space and time transform when seen by different inertial observers. As we all observe physical phenomena in space and time, all fundamental laws of physics must pass the test if they are Lorentz invariant. If they are not, then they are not correct.

An FTL signal does not pass the test, so an entanglement explanation that contains an FTL signal cannot work. That is the whole argument in a nutshell. Even QM must 'obey' special relativity, which it does, as QFT.

I said SR is “meta” to the topic of entanglement and how outside observers, with their varied observations, can not change the temporal order of events in an experiment. In other words, SR is irrelevant to the discussion of experiments involving entanglement.

I am not saying SR is not important. It just isn't relevant to understanding most experiments involving entanglement, their collection of data, or calculations of the results.

The experiments themselves are normally setup with SR in mind so they eliminate any possible SR related artifacts in the timing of events which is why SR is not found in the calculations or discussions of the results.

 Are you saying nothing that transpires between the entangled particles has been demonstrated to be FTL?

19 hours ago, Eise said:

Now it would be interesting to know if you agree with Markus' descriptions. 

Yes, that is what I said.

Edited by bangstrom
Added a paragraph.
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34 minutes ago, bangstrom said:

I said SR is “meta” to the topic of entanglement and how outside observers, with their varied observations, can not change the temporal order of events in an experiment.

Seems you have wax in your ears:

Nobody claims that observers that are in other inertial frames of reference affect the experiment.

38 minutes ago, bangstrom said:

I am not saying SR is not important. It just isn't relevant to understanding most experiments involving entanglement, their collection of data, or calculations of the results.

There you are right, for one time. To understand entanglement, one must understand QM. But as said, SR is a 'filter' for possible explanations. If an explanation is in conflict with SR, then it is wrong. 

41 minutes ago, bangstrom said:
19 hours ago, Eise said:

Now it would be interesting to know if you agree with Markus' descriptions. 

Yes, that is what I said.

(No, it wasn't, but I let that be.)

Then did you read it well? Or didn't you understand it (again)?

On 11/21/2022 at 4:46 PM, Markus Hanke said:

This is purely due to the form of the combined wave function - the outcome of individual measurements on each of the constituents is still purely stochastic, and not (!!!) a function of distant coordinates.

On 11/21/2022 at 4:46 PM, Markus Hanke said:

Because the outcome (statistical probability) of local measurements is not a function of coordinates or any distant states, it is completely meaningless to say that this situation is somehow non-local, or requires any kind of interaction, be it FTL or otherwise.

On 11/21/2022 at 4:46 PM, Markus Hanke said:

This hasn’t got anything to do with locality at all, but is purely a statistical phenomenon.

 

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2 hours ago, bangstrom said:

I see no problem with calling entanglement non-local.

Non-locality means that the outcome of an experiment/measurement performed at a specific point (be that in spacetime, or in some abstract state space) depend explicitly on what happens at another point; so the outcome is not uniquely determined by physical conditions in a small local neighbourhood alone.

Consider again the example of the entangled wave function I gave earlier. The respective observable here is the probability of finding one of the particles in a specific state. For example, the local probability of finding particle A in the state ‘1’ is exactly ½; simultaneously, the local probability of finding particle B in state ‘1’ is also exactly ½. The global probability of finding state ‘10’ is 1/2, and the global probability for ‘01’ is 1/2. Neither of these probabilities is a function of coordinates - distant or otherwise -, or indeed a function of the state of the other particle. At the same time, the probability of the overall composite state to be ‘00’ or ‘11’ is exactly zero - again, without this being a function of any coordinates.

At no point is any of these probabilities a function of coordinates or distant states at all, so it is meaningless to speak of this situation as being non-local. It is, however, quite meaningful and natural to speak of the overall composite wave-function as being non-separable, which is purely a stochastic statement and has nothing to do with locality. It is also an example of the absence of local realism, which is a more general concept than locality.

2 hours ago, bangstrom said:

I understand how entanglement is a sort of hybrid state where two remote particles act locally as if side-by-side

No, that is not at all what entanglement means. Please refer back to my previous post - entanglement means that the overall wave-function of the composite system has a reduced set of possible composite states as compared to the same system sans entanglement relationships. At no point does this make any reference whatsoever to the spatial separation between these particles. Again, entanglement is purely a stochastic phenomenon to do with the form of the overall wave function, it is entirely separate from any embedding of this situation into a particular spacetime.

Note also that you can entangle more than just two particles at a time, again irrespective of how far the constituents of such an ensemble are from each other.

2 hours ago, bangstrom said:

the instant decoherence of entanglement across, possibly extra galactic distances, is non-local by conventional definitions

Also no. Decoherence is a purely local phenomenon - it means that local degrees of freedom of a wave function become coupled with local degrees of freedom of its immediate environment, e.g. as a result of performing a measurement. Note that the global situation - i.e. the original system plus the environment it came into contact with - remains completely coherent, and thus global unitarity remains conserved in this process, as of course it must be.

For example, if you perform a spin measurement on particle ‘A’ of our entangled pair, then its spin direction becomes coupled to the mechanism of the measurement apparatus. You now have a new statistical correlation - between particle A and the measurement apparatus which it comes into contact with it, as opposed to particle A with particle B. The exchange of information involved here is thus purely local, even if the entanglement between possibly distant particles is broken in the process.

2 hours ago, bangstrom said:

Are you saying nothing that transpires between the entangled particles has been demonstrated to be FTL?

Two particles being entangled fundamentally precludes the possibility of them interacting in any way after the point when the correlation has first been established, irrespective of the nature of such an interaction (FTL or not). Interacting particles cannot be entangled, since the composite wave function of such a system cannot have the form quoted earlier while still maintaining local probabilities of ½ during the measurement of the entangled property.

Edited by Markus Hanke
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5 hours ago, bangstrom said:

And is the Lagrangian of the wave function of entanglement not a non-local Lagrangian? Not that I am qualified to judge. I will leave that up to you. 

https://en.wikipedia.org/wiki/Nonlocal_Lagrangian

In field theory, a nonlocal Lagrangian is a Lagrangian, a type of functional L [ ϕ ( x ) ] {\displaystyle {\mathcal {L}}[\phi (x)]} containing terms that are nonlocal in the fields ϕ ( x ) {\displaystyle \phi (x)} , i.e. not polynomials or functions of the fields or their derivatives evaluated at a single point in the space of dynamical parameters

It absolutely is not a non-local Lagrangian. Let me rephrase without the double negative, which might be confusing: The Lagrangian is totally local.

Once the particles start flying apart, you can use free propagation to describe how the fly apart, and the initial entangled state as the initial condition of a so-called Cauchy problem. The Hamiltonian is separable, and contains only 2nd-order spatial derivatives, so local densities, fields, etc are only sensitive to nearby points. It is a 2nd-order polynomial in the spatial derivatives. Local as can be: Exactly the same sensitivity to spatial inhomogeneities as the equation for propagation of heat. And the state keeps entangled all the way. What the classical theory of heat doesn't have, that makes quantum mechanics so peculiar, is,

1) Superposition of several different "heat-radiating states"

2) A multi-system phase space

It is the initial condition that cannot be separated, which has consequences on the probabilities that are encapsulated in the state. As Markus said --with my emphasis,

On 11/21/2022 at 4:46 PM, Markus Hanke said:

Because the outcome (statistical probability) of local measurements is not a function of coordinates or any distant states, it is completely meaningless to say that this situation is somehow non-local, or requires any kind of interaction, be it FTL or otherwise. The entire situation is fully about statistics and correlations, which is not the same as a causal interaction; in fact, any interaction between the constituents (including FTL ones) would change the combined wave function and preclude the possibility of there being a statistical correlation while at the same time maintaining the stochastic nature of the outcomes of individual measurements. This is evident in the fact that the entanglement property of the above state function isn’t encoded in any kind of coordinate dependence, but rather in a reduction of terms, ie in a reduced pool of possible outcomes. This hasn’t got anything to do with locality at all, but is purely a statistical phenomenon.

Which is exactly what I was trying to say here,

On 9/13/2022 at 2:05 AM, joigus said:

The only thing that's physical is the whole vector. Then you obtain the expected value of spin along any direction you want and it always gives you zero for the sum.

Then you do some further quantum mechanical calculations and consider the evolution operator from, say, t=0 (when the singlet is prepared and the particles are next to each other) and a time T when the particles have come apart, and you will see that no expected value depends on the fact that the spatial factor of the states has taken them apart. It's all in the maths of QM.

As I said: The correlations are there when the singlet is prepared, they're there a minute later, they're there until you perform another measurement. And no experiment that I know of contradicts this.

This, by the way, you found either very surprising, or implying the opposite of what @Markus Hanke --and I too, many pages before-- is implying: As the probability distributions do not depend on spatial factors while the state is evolving, as it only depends on how the state is interwoven in its spin "tags," how could it encode anything having to do with local (space) properties? Or at least, that is, provided I've understood Markus correctly.

 

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8 hours ago, bangstrom said:

Are you saying nothing that transpires between the entangled particles has been demonstrated to be FTL?

Nothing has been shown to transpire between the particles.

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On 11/24/2022 at 4:28 AM, Eise said:

Seems you have wax in your ears:

Nobody claims that observers that are in other inertial frames of reference affect the experiment.

Yes, as I explained, outside observations, whether the observers are in motion or not, do not affect the results of the experiment which is why our circular discussion about SR and outside observations were irrelevant. That was my suggestion to get off the topic.

Perhaps I should have written it in red with a large font.

23 hours ago, Markus Hanke said:

Non-locality means that the outcome of an experiment/measurement performed at a specific point (be that in spacetime, or in some abstract state space) depend explicitly on what happens at another point; so the outcome is not uniquely determined by physical conditions in a small local neighbourhood alone.

With entanglement, the observation of one quantum property at one point instantly tells us something we can find expect to find about its entangled partner(s) at another point. We can expect to find that the same observed property will be anti-coordinated with the first observation. That appears to be contrary to local realism and the EPR effect.

In this case, the observation of the second particle depends on an observation at another point possibly a great distance away.

How is that not non-locality?

18 hours ago, swansont said:
On 11/24/2022 at 3:43 AM, bangstrom said:

Are you saying nothing that transpires between the entangled particles has been demonstrated to be FTL?

Nothing has been shown to transpire between the particles.

Right, "Nothing has been shown to transpire between the particles." That is why it is called, 'Instant action at a distance.'

There is nothing to see between the particles. The correlation is observed at the ends.

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19 minutes ago, bangstrom said:

How is that not non-locality?

18 hours ago, swansont said:

Same reason why the colour of my sclera, and the colour of yours are the same: Some event in the past determined both. In the example I'm offering you, the evolution of a family of primates.

Unless one of us is a possum who's learned to type. Let that be me. :D 

Oh, by the way, I've just received a message from next Christmas: Our future selves tell me we are still discussing this.

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2 hours ago, bangstrom said:

In this case, the observation of the second particle depends on an observation at another point possibly a great distance away.

No it doesn’t - the probability of measuring either state on any of the two particles is exactly ½, and that’s a fixed probability and not a function of some distant variable. It’s both constant and invariant. There’s no meaningful sense in which you can call this an example of non-locality, because the probability isn’t a function of anything, it’s simply constant.

To state this differently, there is no local experiment you can perform that will tell you whether or not a particle is entangled, because no local measurement you perform depends in any way on distant coordinates. You will always observe a probability of ½ for either local outcome of a binary state, regardless of whether the particle you perform the measurement on is entangled or not - and, more importantly, regardless of what happens anywhere else in the universe. It is only when you compare the outcomes - which you can only physically do in accord with the laws of SR - that you see the correlation. And of course, that correlation exists as the result of a purely local process in the past, which is how the entanglement came to be in the first place.

If the situation were non-local, then it wouldn’t be possible to get a statistical probability of exactly ½, because the outcome would explicitly depend on some distantly variable. This is evidently not so.

3 hours ago, bangstrom said:

We can expect to find that the same observed property will be anti-coordinated with the first observation.

No you can’t, unless you already know that the particle is entangled - which you can only do if you were either present in the past when the entanglement was created, or if you bring together and compare the outcomes of measurements in the present. Both cases ensure that your prediction/correlation remains a purely local process - if neither of these local cases apply, then the probability of the distant measurement coming out in any particular way remains ½.

IOW, if you don’t know whether or not a local particle is entangled, then you can’t predict the outcome of the distant measurement with certainty; and conversely, if you can predict the distant outcome with certainty, then that means the information about the pre-existing correlation is already available to you, thus ensuring that the prediction is a local process.

Not only is entanglement not an example of non-locality, but non-locality and entanglement are mutually exclusive concepts!

2 hours ago, bangstrom said:

That appears to be contrary to local realism

Yes, exactly - and that’s not the same as non-locality.

3 hours ago, bangstrom said:

How is that not non-locality?

See above, because none of the probabilities involved in the measurement outcomes is a function of distant coordinates - the correlation between outcomes exists because these particles underwent a local process in the past whereby they became entangled, and have remained that way ever since.

This whole thing is a good demonstration of counterfactual definiteness, the absence of local realism, and the non-separability of specific classes of wave functions - but not of non-locality.

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3 hours ago, bangstrom said:

Yes, as I explained, outside observations, whether the observers are in motion or not, do not affect the results of the experiment which is why our circular discussion about SR and outside observations were irrelevant.

And I explained that nobody was even saying this. So you were beating a dead horse. 

So let's try to explain it once again. As a starting point we take a Bell experiment, that closes the communication loophole. This means:

  • the measurements cannot influence each other with a light signal, or any slower signal
  • the decision which spin direction will be measured is taken after the particles left the entanglement source

So there can't be any causal connection between measurement device A, B, and the entanglement source. Said otherwise, no communication is possible between these 3 components.

To make the example as simple as possible we also assume that detectors and entanglement source do not move relative to each other, and the entanglement source is exactly in the middle, so the measurements are exactly at the same time in the rest frame of the experiment

Are you with me so far?

Maybe Joigus' drawing helps:

image.png

Just take Alice and Bob as other names for the detectors.

So now we ask ourselves what Carla and Daniel will see. Well, it is in the drawing: in Carla's frame of reference the measurement at Bob's side is first, for Daniel's FoR it was Alice's side. It is just a question of perspective, not of changing anything with the experiment of course. Got that too?

Now according SR observers can disagree on the timely order of events, when these events are space-like separated. But that is exactly what the closing of the communication loophole means. But SR also states that Carla and Daniel should at least agree on the physical process. But they don't:

  • according to Carla, Bob's measurement determined the outcome of Alice's
  • according to Daniel, Alice's measurement determined the outcome of Bob's

But these cannot both be true. So the conclusion is that there is no 'determination relation' between the measurements. So no signal, FTL or not. For Alice and Bob of course nothing changes. In their FoR the measurements are simultaneous, just as before. So Carla or Daniel have no influence at all on the experiment. But they should agree at least on the physics.

Edited by Eise
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21 hours ago, joigus said:

Same reason why the colour of my sclera, and the colour of yours are the same: Some event in the past determined both. In the example I'm offering you, the evolution of a family of primates.

Evolution is a long term series of local events. It is not entanglement.

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48 minutes ago, bangstrom said:

Evolution is a long term series of local events. It is not entanglement.

Quantum entanglement is also a series of local events, starting from the instant when the entanglement was first created - joigus was quite right in bringing up this (classical) analogy. The difference between them is simply counterfactual definiteness.

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19 hours ago, Markus Hanke said:

 See above, because none of the probabilities involved in the measurement outcomes is a function of distant coordinates - the correlation between outcomes exists because these particles underwent a local process in the past whereby they became entangled, and have remained that way ever since.

This whole thing is a good demonstration of counterfactual definiteness, the absence of local realism, and the non-separability of specific classes of wave functions - but not of non-locality.

Charged particles, especially electrons, can spontaneously entangle with any other similar charged particle on the same light cone so entanglement need not begin as local.

The initiation of entanglement, in this case, is instant as is the loss of entanglement and decoherence can span any distance which makes it a non-local action at a distance.

Two independent particles need not be anti-coordinated before entanglement, but upon entanglement, their individual quantum properties become indeterminate (superimposed). Later when the first particle is observed, the same quantum property for both is found to be anti-coordinated.

It is logical to say that their properties became anti-coordinated and have remained so from the start but this is one of the several ‘hidden variables’ that was eliminated as invalid by experiments involving the violation of Bell’s inequalities.

Independent of this, Anton Zeilinger, with his quantum teleportation, has demonstrated that an entire cascade of quantum properties can be instantly reversed to conform to a later entanglement no matter what the unobserved outcome of the first entanglement may have been.

If 0’s and 1’s are considered as the observations, their values can be instantly reversed to 1’s and 0’s indicating that the observed outcome of an experiment need not be fixed from the start but still they are anti-coordinated at the end.

It could be that the first observation ends the entanglement and begins the anti-coordination. This suggests some kind of signal from the first observation to the second indicating a signal sent and a signal received.

On 11/24/2022 at 6:34 AM, Markus Hanke said:

Non-locality means that the outcome of an experiment/measurement performed at a specific point (be that in spacetime, or in some abstract state space) depend explicitly on what happens at another point; so the outcome is not uniquely determined by physical conditions in a small local neighbourhood alone.

 If you exclude entanglement as an example of non-locality, what could be considered as non-local?

 

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1 hour ago, bangstrom said:

 If you exclude entanglement as an example of non-locality, what could be considered as non-local?

Entanglement may be an example of non-locality.
It hasn't been proven to be an example of non-locality.

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2 hours ago, bangstrom said:

Charged particles, especially electrons, can spontaneously entangle with any other similar charged particle on the same light cone so entanglement need not begin as local.

 

(Emphasis mine.)

What do you mean???

Here's a visual aid:

image.thumb.png.bce7733f6a0eb84184481301f8473dff.png

Same particles, same events for time-like separated particles.

And,

image.thumb.png.61774e0362375c73f0951a623aa90deb.png

 

Same particles, same events for space-like separated particles.

What light cone are you talking about? Same light cone of what exactly?

Will you make a smidgen of sense at some point in this simulation of a discussion?

I'm ignoring the rest of your nonsense. Let's start with the basics. Otherwise, you're gonna turn everyone crazy here.

"Especially electrons..." :doh: Yeah, that makes sense too!

Edited by joigus
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7 hours ago, bangstrom said:

 If you exclude entanglement as an example of non-locality, what could be considered as non-local?

5 hours ago, Lorentz Jr said:

Entanglement may be an example of non-locality.
It hasn't been proven to be an example of non-locality.

No I cannot think of any other example of non-locality.
As far as I know, no other effects require that the outcome of an event at a specific point is determined  explicitly on what happens at another point, unless there is a transfer of information.
And relativity explicitly states that information is constrained to transfer at speeds not exceeding c .

So non-locality is not just unproven yet, it is actually not needed; not even for entanglement.

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1 hour ago, MigL said:

No I cannot think of any other example of non-locality.

Objective collapse of individual particle wave functions.
With the same caveat that it's possible but not proven.

Quote

So non-locality is not just unproven yet, it is actually not needed

Non-locality is needed if one wants to retain realism.
Non-realism is needed if one wants to retain locality.

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