It doesn't matter if you accept it or not. The notion of locality in local QFT is not strong enough to allow the deduction of indeterminism from the violation of Bell's inequality. You would also need to eliminate the non-local nature of the state space in addition to asserting the locality of the interactions that generate the state evolution.vanhees71 said:I don't accept to call a local QFT nonlocal, because that's a contradiction in itself, and this hast to be avoided in scientific discussions.
I have no idea what are you trying to say. For example, how does Bohmian mechanics imply non-determinism?DrChinese said:Contextual models don't need to be non-deterministic. For example: Bohmian Mechanics is both deterministic and contextual. However, contextual models *imply* non-determinism, as the quantum expectation is solely based on the context.
vanhees71 said:Of course Weinberg doesn't explain the EPR correlations with a local deterministic HV theory. The point is to show that it cannot be explained with such a model to begin with.
Arguments of this type require thinking in terms of real objects which are not measured/measurable. Standard/orthodox/Copenhagen school of thought rejects any arguments based on such objects, except when used in favor of standard/orthodox/Copenhagen school of thought.AndreiB said:This is why (if you, for some reason reject EPR's conclusion) I am asking for an explicitly local explanation of EPR perfect correlations by an explicitly indeterministic theory. I think this is impossible. How could you make two independent coin flips to always agree? They either are not independent (and since they are space-like you have non-locality) or they are predetermined (hidden variables).
Demystifier said:Arguments of this type require thinking in terms of real objects which are not measured/measurable. Standard/orthodox/Copenhagen school of thought rejects any arguments based on such objects, except when used in favor of standard/orthodox/Copenhagen school of thought.
If one accepts hiden variables, then one accepts objects which are not measured/measurable.AndreiB said:accept hidden variables
Demystifier said:If one accepts hiden variables, then one accepts objects which are not measured/measurable.
I don't know in which sense you mean the state space is local or non-local.Jazzdude said:It doesn't matter if you accept it or not. The notion of locality in local QFT is not strong enough to allow the deduction of indeterminism from the violation of Bell's inequality. You would also need to eliminate the non-local nature of the state space in addition to asserting the locality of the interactions that generate the state evolution.
EPR is based on only 2 premises:vanhees71 said:This is a typical "delayed-choice" situation. You can do the necessary coincidence measurements and just store them in corresponding protocols, one for each local measurement also noting the necessary "time stamps". Then you can share the information in the protocols to choose certain subensembles each of which corresponds to one of the four entangled states of the "new" pairs. That this really are the corresponding entangled states is certain, because you had two entangled (but not mutually entangled) pairs in the beginning. There is no retrocausation nor faster-than-light communication necessary to explain this.
I said measured/measurable. When they are measurable, they are called hidden because they are assumed to exist even when they are not measured.AndreiB said:The hidden variables are certainly measurable.
Delayed choice has of course nothing to do with it. This could be possible for local HV theories too. The point however is that Bell's inequality follows from such HV theories, and these are violated within QT, and all experiments with very high significance show that indeed Bell's inequalities are violated in perfect agreement with the predictions of QT.AndreiB said:EPR is based on only 2 premises:
1. locality (space-like events do not cause each other)
2. The predicted perfect correlations exist.
As far as I can tell, nothing you said here, about delayed choices, has anything to do with these two premises. So, the conclusion of the argument (hidden variables exist) necessary follows.
It seems to me there is a difference between a philosophical prejudice that predated subatomic experimental results: namely, determinism; and, a philosophical prejudice that is tailored to the experimental results of the 20th century.Demystifier said:I absolutely agree that it's complete FAPP. Bell himself (who coined the FAPP acronym) also often emphasized that. But the whole point of quantum foundations is to say something beyond FAPP. It's impossible to discuss quantum foundations and discard all aspects which are beyond FAPP, at the same time. A very dishonest thing to do is to accept only those beyond FAPP aspects which fit your own philosophical prejudices and discard all the others by claiming that you only care about FAPP.
PeroK said:If, for example, subatomic results were the only results we had and there was no preconception of determinism, would you still want a deterministic interpretation of QT?
vanhees71 said:Delayed choice has of course nothing to do with it.
vanhees71 said:The point however is that Bell's inequality follows from such HV theories, and these are violated within QT, and all experiments with very high significance show that indeed Bell's inequalities are violated in perfect agreement with the predictions of QT.
vanhees71 said:Within QT the values of these observables are objectively not predetermined but "really" random.
vanhees71 said:No! Locality (fulfilled in local relativistic QFT) does not imply determinism.
vanhees71 said:The EPR argument is disproven by observation!
vanhees71 said:We don't have a lack of knowledge about a state for system
vanhees71 said:The time at which a radioactive nucleus decays is "truely random" (with the known probability for survival being approximately ##\exp(-\Gamma t)##).
Absence of evidence is not evidence of absence.vanhees71 said:Well, according to our knowledge today QT is valid, and there is "true randomness".
He does not, because he does not agree with the EPR criterion of reality.AndreiB said:OK, do you agree with the conclusion that EPR proves that locality implies hidden variables?
No logical argument has ever been disproved by observation. An observation may disprove an assumption in the argument, but not the argument itself. A logical argument can only be disproved by logic (and its derivatives, such as math).vanhees71 said:The EPR argument is disproven by observation!
Bell makes no such assumption. A hidden variable model can have the hidden variables as measurable, but it is not required to.AndreiB said:The hidden variables are certainly measurable. It is what you actually measure.
AndreiB said:Fast Vacuum Fluctuations and the Emergence of Quantum Mechanics
Gerard 't Hooft
Found.Phys. 51 (2021) 3, 63
DOI: 10.1007/s10701-021-00464-7
"Fast moving classical variables can generate quantum mechanical behavior. We demonstrate how this can happen in a model. The key point is that in classically (ontologically) evolving systems one can still define a conserved quantum energy. ..."
It doesn't. Contextuality *implies* non-determinism... but not strictly so. After all, it is the measurement context that provides us the information about correlations, and nothing else. Surely it must seem odd that no one has ever been able to pinpoint experimentally any prior cause that explains the apparently random outcomes. Again, this is not a strict argument.Demystifier said:I have no idea what are you trying to say. For example, how does Bohmian mechanics imply non-determinism?
AndreiB said:EPR is based on only 2 premises:
1. locality (space-like events do not cause each other)
2. The predicted perfect correlations exist.
As far as I can tell, nothing you said here, about delayed choices, has anything to do with these two premises. So, the conclusion of the argument (hidden variables exist) necessary follows.
DrChinese said:No, it is based on more than these 2. You skipped the following crucial assumption (quoting from EPR):
"Indeed, one would not arrive at our conclusion if one insisted that two or more physical quantities can be regarded as simultaneous elements of reality only when they can be simultaneously measured or predicted. On this point of' view, since either one or the other, but not both simultaneously, of the quantities P and Q can be predicted, they are not simultaneously real. This makes the reality of P and Q depend upon the process of measurement carried out on the first system, which does, not disturb the second system in any way. No reasonable definition of reality could be expected to permit this."
DrChinese said:It was precisely this assumption, and no other, that Bell challenged - and it was found wanting. This assumption is essentially that reality is not subjective... i.e. is NOT contextual.
QM is not the same as classical mechanics! There never has been any viable classical model of the atom. QM didn't replace CM at the subatomic level, because CM was never successful in that case.AndreiB said:In order to predict Earth's future state it's not enough to know its present position and momentum, you also need "contextual" information, like what other massive objects are, where they are and where they are going. You need to know about the Sun, Moon, Jupiter, the rest of the galaxy and so on. QM is the same.
I strongly disagree with identification subjective=contextual. If something depends on the apparatus, but not on a conscious perception, then I would call it contextual but not subjective. It is only QBism that strictly identifies contextual with subjective.DrChinese said:This assumption is essentially that reality is not subjective... i.e. is NOT contextual.
No, 't Hooft's model is a cellular automaton, an array of cells, each cell updating at some time interval according to some local rule (the state of a cell changes based on its previous state and the states of the surrounding cells). At each "tick" all cells update. This implements a speed limit, so the theory is local.PhilDSP said:May I ask: what does 't Hooft mean by "fast moving classical variables"? Is he including or requiring or implying superluminal transportation of some form of information for his argument?
AndreiB said:So, if the X-spins are measured we can conclude that the X-spins existed before measurement. If the Y-spins are measured we can conclude that the Y-spins existed before measurement, and so on for any other orientation.
Have you tried to work out how this predetermination of the spin works in BM? Let me try myself ... how do I actually model the fact that the X-spins have been measured by both Alice and Bob?PeroK said:Forget about entanglement and the Bell theorem, and focus solely on electron spin. First, there must be a lot of hidden variables. You cannot model electron spin by specifying a single axis of rotation. There must be a hidden variable for every conceivable measurement angle.
Well, superdeterminism is both a label for an assumption (its absence) in Bell's theorem, and a label for some absurd mechanism people imagined how it could be used to produce the correlations predicted by QM. But there is a deeper issue, namely that our ignorance of initial conditions does not always come with a probability distribution (or improper Bayesian prior) for that unknow part. There is a probability distribution for the particle positions in BM, but note that we are also ignorant about most parts and details of the wavefunction. And there seems to be no canonical probability distribution for that part.PeroK said:Leaving aside BM, the battleground after the test of Bell's theorem has shifted to ever more bizarre reworking of determinism, such as superdeterminism.
EPR overlook that the entangled particles are one system. The very definition of entanglement is that, well, subsystems are entangled or, as Einstein said in a way better than the EPR paper in 1948, inseparable.DrChinese said:No, it is based on more than these 2. You skipped the following crucial assumption (quoting from EPR):
"Indeed, one would not arrive at our conclusion if one insisted that two or more physical quantities can be regarded as simultaneous elements of reality only when they can be simultaneously measured or predicted. On this point of' view, since either one or the other, but not both simultaneously, of the quantities P and Q can be predicted, they are not simultaneously real. This makes the reality of P and Q depend upon the process of measurement carried out on the first system, which does, not disturb the second system in any way. No reasonable definition of reality could be expected to permit this."
It was precisely this assumption, and no other, that Bell challenged - and it was found wanting. This assumption is essentially that reality is not subjective... i.e. is NOT contextual.
I didn't say that.PeroK said:QM is not the same as classical mechanics!
I guess you wanted to say "QM DID replace CM". Agreed.PeroK said:There never has been any viable classical model of the atom. QM didn't replace CM at the subatomic level, because CM was never successful in that case.
Indeed.PeroK said:Forget about entanglement and the Bell theorem, and focus solely on electron spin. First, there must be a lot of hidden variables. You cannot model electron spin by specifying a single axis of rotation. There must be a hidden variable for every conceivable measurement angle.
PeroK said:This is where Einstein was being slightly disingenuous IMHO. Of course, electron spin could theoretically be governed by hidden variables. But, it's incredibly messy to say how those variables are organised.
He proved QM incomplete or non-local. That result still stands. The mistake of EPR was that they insisted on the existence of HV for non-commuting properties, allowing Bohr to escape. But the argument works fine for only the measured values. Had Bohr been presented with this, simplified argument, he would have been defeated.PeroK said:The battleground shifted to entanglement because Einstein believed that would undermine QM.
What results? EPR assumed QM gives the right predictions, so QM's predictions being confirmed could not possibly undermine the argument. QM predicts perfect correlations. Local randomness would predict correlations 50% of the time. Local randomness is falsified, end of story.PeroK said:But of course, the results vindicated QM and further undermined hidden variables. Not the reverse.
This is not bizarre. Since EPR proved local indeterminism impossible, and Bell proved a type of local determinism impossible, the only local option remains superdeterminism. What I find even more bizarre is the belief in logically impossible fundamental theories, like local and non-deterministic ones.PeroK said:Leaving aside BM, the battleground after the test of Bell's theorem has shifted to ever more bizarre reworking of determinism, such as superdeterminism.
This is why the unification program along string theory is such a success. As long as the local/non-local character of QM is irrelevant (as in the case of optimising a superconductor), the theory works fine and one is free to ignore EPR. When locality matters, such is the case of unification program, nature hits the indeterminist hard, again and again.PeroK said:Whereas, those who broadly support orthodox QM have hardly had to modify their understanding in a century.
Yes, there is. Locality is very likely right, there is no evidence against it, all our theories accept it, including GR. We have a sound argument proving that locality implies determinism. I cannot think of any better evidence for determinism than that. 100% correlations between space-like measurements utterly falsify indeterminism.PeroK said:You have this whole debate back to front. There is no solid deterministic edifice.
You simply assume QM is fundamentally indeterministic, instead of a statistical theory. This assumption is unjustified. What's wrong with a solid statististical edifice?PeroK said:Instead, there is a solid QM edifice, which the determinists by hook or by crook are hoping to topple.
Indeed.PeroK said:But, again leaving BM aside, there is no solid deterministic edifice waiting to replace QM.
PeroK said:Only wishful thinking held together by a belief in unknown laws that result in almost magical correlations.
Demystifier said:He does not, because he does not agree with the EPR criterion of reality.
PeroK said:@AndreiB I'm not sure we've ever had anyone on here before who has argued that the 20th Century provided an unbroken and unassailable vindication of deterministic mechanics!
PeroK said:The QM model of the atom is the only viable model there has ever been. There's no other explanation for chemistry, nor has there ever been.
Be very careful with such comments. They might indicate a missing effort from your side to try to understand what your communication partner was saying.AndreiB said:I guess you wanted to say "QM DID replace CM". Agreed.
Even so the word "local" has a clear meaning, it is a property of something in some context. Asserting "locality is true" is a pretty meaningless statement, as long as no context is given, and even with context you should still try to clarify what it is that is asserted to be local.AndreiB said:The problem is that I have a sound logical argument that links the existence of those hidden variables to locality, and locality is very likely to be true.
I think there is a logical third way out. I can predict what will be the result of measuring B at the time when I measure B, but I can deny that B had any value at all before I measured it. That's indeed how Copenhagenish (non-realist) type of interpretations work.AndreiB said:i don't think the criterion can be denied. The criterion says that if you an element of reality exists if you can predict that quantity without disturbing the system. Now, if you don't disturb B by your A measurement, and QM says that your A measurement leaves B in well-defined spin state it logically follows that B was in a well-defined spin state before your A measurement. As Tim Maudlin said, the criterion is "analytic", it necessary follows from the meaning of the words. The only way out is to deny that A does not disturb B (and accept non-locality) or deny the QM prediction (that the state after the A measurement is a well-defined spin, opposite to the one found at A.
True.vanhees71 said:An important part we have learned about Nature is the atomistic structure of matter, which implies that it is impossible to measure the "atoms" without disturbing them, because we need at least one other "atom" to measure. There's no way to measure anything without interacting with it in such a way as to disturb the system.
vanhees71 said:That's also true in a way when measuring far distant entangled parts of a quantum system. Though there is no non-local interaction by measurement at A's position on the part at B's position, nevertheless the system as a whole is disturbed../
Let's say the A measurement was UP. QM says that the state of B is DOWN (regardless if B was measured or not). If the A measurement did not change B and B is DOWN what was the state of B before the A measurement? The only answer is DOWN. If it was UP before the A measurement, and DOWN after the measurement it means that the A measurement did change B. If it was in an undecided state before the A measurement, and DOWN after the measurement it means that the A measurement did change B. If it was a 6-dimentional pink rabbit before the A measurement, and DOWN after the measurement it means that the A measurement did change B. And so on. The only state B could have had before the A measurement that is consistent with the requirement that it was not changed by the A measurement is DOWN. So, for that particular experiment we proved that the DOWN state of B is predetermined.vanhees71 said:You can also gain information on the outcome of certain measurements at B having measured A, but this does not in any way justify EPR's conclusion that this measured value at B was predetermined before A's measurement.
vanhees71 said:To the contrary, for a maximally entangled system the observables of the parts are both usually maximally indetermined.
If two particles are entangled they do not have individual states before measurement: that is the definition of entangled. In QM you cannot talk about the state of each particle before measurement.AndreiB said:Let's say the A measurement was UP. QM says that the state of B is DOWN (regardless if B was measured or not). If the A measurement did not change B and B is DOWN what was the state of B before the A measurement? The only answer is DOWN.
I have a pair of new identical socks. I put one, let's call it A, on my left foot and it beomes a left sock. Instantaniously the other sock, let's call it B, becomes a right sock. Was B a right sock all along or did the sock A change it? Is there a cause and effect relationship? I personally don't have a problem with my socks to not have a predetermined value of their left/right-ness, and I don't need a spooky action at a distance to explain any of the above.AndreiB said:Let's say the A measurement was UP. QM says that the state of B is DOWN (regardless if B was measured or not). If the A measurement did not change B and B is DOWN what was the state of B before the A measurement? The only answer is DOWN. If it was UP before the A measurement, and DOWN after the measurement it means that the A measurement did change B. If it was in an undecided state before the A measurement, and DOWN after the measurement it means that the A measurement did change B. If it was a 6-dimentional pink rabbit before the A measurement, and DOWN after the measurement it means that the A measurement did change B. And so on. The only state B could have had before the A measurement that is consistent with the requirement that it was not changed by the A measurement is DOWN. So, for that particular experiment we proved that the DOWN state of B is predetermined.
Demystifier said:I think there is a logical third way out. I can predict what will be the result of measuring B at the time when I measure B, but I can deny that B had any value at all before I measured it. That's indeed how Copenhagenish (non-realist) type of interpretations work.
I've constructed an explicit hidden variable model in which those arguments are invalid.AndreiB said:This is not a way out. The A measurement leaves B in a spin DOWN state. If A measurement did not disturb B, B was in a spin DOWN before the A measurement, and also before the B measurement (in some reference frame).
What you are saying refers to the meaning of a spin DOWN state. Is there a "real" particle or it's just a propensity for the instrument to give a "DOWN" outcome? It does not matter. EPR proves that the DOWN propensity was there before both A and B measurements. Since a DOWN propensity is experimentally distinguishable from an UP propensity or no propensity at all, they cannot negate it.
In your example the correlation has nothing to do with the socks, but with the "instruments", your feet. The socks simply reveal a pre-existing correlation between the instruments. Since your "instruments" will always give you the same result, the left foot will only give "left" socks, and the right one only right socks the experiment fails to reproduce the EPR setup. Anyway, the explanation for the observed correlations is still in terms of deterministic "hidden variables". The left and right feet were there before the experiment, the results were predetermined.martinbn said:I have a pair of new identical socks. I put one, let's call it A, on my left foot and it beomes a left sock. Instantaniously the other sock, let's call it B, becomes a right sock. Was B a right sock all along or did the sock A change it? Is there a cause and effect relationship? I personally don't have a problem with my socks to not have a predetermined value of their left/right-ness, and I don't need a spooky action at a distance to explain any of the above.
You are missing the point. Suppose I have two new socks, neither has been molded by my left or right foot. One of the socks is white, the other is black. Sometimes the outcome of my experiment will be a white left and a black right, sometimes a black left and a white write.AndreiB said:In your example the correlation has nothing to do with the socks, but with the "instruments", your feet. The socks simply reveal a pre-existing correlation between the instruments. Since your "instruments" will always give you the same result, the left foot will only give "left" socks, and the right one only right socks the experiment fails to reproduce the EPR setup. Anyway, the explanation for the observed correlations is still in terms of deterministic "hidden variables". The left and right feet were there before the experiment, the results were predetermined.
Demystifier said:I've constructed an explicit hidden variable model in which those arguments are invalid.
https://arxiv.org/abs/1112.2034
The point is that the "measurement" results are predetermined. Your left foot was a left foot before the experiment, the right one was right before the experiment, the white sock was white, the black sock was black. The observed correlations are explained in terms of past causes that determine them. This is the conclusion of the EPR as well, I accept that conclusion, so I don't understand what you are arguing against.martinbn said:You are missing the point. Suppose I have two new socks, neither has been molded by my left or right foot. One of the socks is white, the other is black. Sometimes the outcome of my experiment will be a white left and a black right, sometimes a black left and a white write.
martinbn said:Also your complaint about the instruments applies to the EPR set up as well. You get 100% correlation only of you measure along the same axis.
Ok, here is a new pair of socks. Can you point to the left one, please! Oh, you cannot! Then what is predetermined about the leftness/rightness of the socks?!AndreiB said:The point is that the "measurement" results are predetermined. Your left foot was a left foot before the experiment, the right one was right before the experiment, the white sock was white, the black sock was black. The observed correlations are explained in terms of past causes that determine them. This is the conclusion of the EPR as well, I accept that conclusion, so I don't understand what you are arguing against.
A Stern Gerlach device does not always measure UP or always DOWN. Your left foot always "measures" left socks. This is my complain. But the conclusion of the argument stands anyway, only in this case the "element of reality" is not the color of the sock (which is always white, in your first example) but the shape of the foot.
In the second example the "elements of reality" are both the shape of the foot and the color of the sock.
