I The Great Rift In Physics: The Tension Between Relativity and QM

[sahashmi]

I reiterate, if Maudlin and you claim that GR and QM are incompatible it's not true, because QFT exists. (@Peter objected that it's more correct to say "SR is compatible with QM", but it's also true that SR is a subset of GR)

It's correct to say "SR and QM are compatible" and "GR and QM are partially compatible," unlike Maudlin and you, . I don't see the point in using Bell correlations to claim that.

Entanglement is the most important phenomenon of QM, since it’s the phenomenon that departs most strongly from our day to day intuitions. As I already wrote, QFT does not explain entanglement. So its existence, although useful, does not imply that a local theory can explain the nonlocal correlations in entanglement.

Bell already showed that no local theory, including QFT, can. Bell was well aware of QFT. He is unfortunately heavily and widely misunderstood or misinterpreted. This is the point of Maudlin’s paper.

Since locality is built into relativity, and since no local theory can explain entanglement, no relativistic theory can explain entanglement. This is not a “speculation”. It’s what the experiments show.

 

[javisot]

Since locality is built into relativity, and since no local theory can explain entanglement, no relativistic theory can explain entanglement. This is not a “speculation”. It’s what the experiments show.

With GR you can conjecture er=epr, I understand that Maudlin and you consider that path incorrect?

 

[sahashmi]

With GR you can conjecture er=epr, I understand that Maudlin and you consider that path incorrect?

The ER=EPR approach would arguably be a non local hidden variable theory. That is only if entanglement can, on a fundamental level, be mechanistically explained by wormholes in spacetime

Whatever connection the particles would have would involve some sort of superluminal influence

 

[martinbn]

You use locality as if there is only one notion with that name!

 

[mitchell porter]

As I already wrote, QFT does not explain entanglement.

Hopefully you're aware that entanglement does exist in QFT?

 

[sahashmi]

Hopefully you're aware that entanglement does exist in QFT?

It exists but it is not explained. An explanation of why non local correlations occur involves showing why they occur instead of not. There is no reason given for this in any local theory. Non local theories do give reasons for this: the measurement of one particle can influence the other

 

[Fra]

I agree the distinction between descriptive value and explanatory value is important.

The focus of the paper was conceptual inconsistencies; not descriptive inconsistencies.

But it's hard not to think that the lack of progress, is not related to our lack of understanding, and I think this is what Maudlin thinks as well, even if I don't share his confidence in the claims.

What became more clear after reading Maudlins various argument is the strong constraints on reasoning that I think are implicit in the paradigm it self. And then I mean the system dynamics paradigm.

How can a description ever offer an explanation beyond the obvious timeless picture: initial state + law => future state.

To answer, why that particular law? why this statespace? We can finetune it to match observations, but what does that "explain"?

And in the case of entanglment, we are asking questions about parts of the systems interacting with other parts. Then we at minimum need to explain how a more complex system are formed, from combining smaller systems, and how the dynamical law of the joint system is like? and why! We can't "explain" this in the paradigm. The law is just "input".

I see a big problem in the reasoning about this, that has to do with our preconception of that "theory" must fit into the system dynamics paradigm. I think this is inhibiting. This disturbed me the most as reading his paper, and it's why I don't share the sub-conclusions of the paper, except that last scentence:

"What sort of space-time structure should be used in place of the space-timme of Special Relativity or the
spacetimemes of General Relativity is not at all clear, and should be a queston given the highest
level of attention by anyone seeking to “reconcile” quantum theory with Relativity"

No matter how much time passed since, respect to Einstein for not letting the conceptual disturbances pass, when most people let it go when theory after all makes good predictions and avoid headache we don't get paid for having.

/Fredrik

 

[sahashmi]

I agree the distinction between descriptive value and explanatory value is important.

The focus of the paper was conceptual inconsistencies; not descriptive inconsistencies.

But it's hard not to think that the lack of progress, is not related to our lack of understanding, and I think this is what Maudlin thinks as well, even if I don't share his confidence in the claims.

What became more clear after reading Maudlins various argument is the strong constraints on reasoning that I think are implicit in the paradigm it self. And then I mean the system dynamics paradigm.

How can a description ever offer an explanation beyond the obvious timeless picture: initial state + law => future state.

To answer, why that particular law? why this statespace? We can finetune it to match observations, but what does that "explain"?

And in the case of entanglment, we are asking questions about parts of the systems interacting with other parts. Then we at minimum need to explain how a more complex system are formed, from combining smaller systems, and how the dynamical law of the joint system is like? and why! We can't "explain" this in the paradigm. The law is just "input".

I see a big problem in the reasoning about this, that has to do with our preconception of that "theory" must fit into the system dynamics paradigm. I think this is inhibiting. This disturbed me the most as reading his paper, and it's why I don't share the sub-conclusions of the paper, except that last scentence:

"What sort of space-time structure should be used in place of the space-timme of Special Relativity or the
spacetimemes of General Relativity is not at all clear, and should be a queston given the highest
level of attention by anyone seeking to “reconcile” quantum theory with Relativity"

No matter how much time passed since, respect to Einstein for not letting the conceptual disturbances pass, when most people let it go when theory after all makes good predictions and avoid headache we don't get paid for having.

/Fredrik

Here’s the issue with this.

You may be right that “explanation” in science does often come down to initial state, law, and future state. But not every law is the same.

For example, a future law that tells you why the (+,-) result occurs instead of a (-,+) in the case of entanglement is clearly superior to a “law” that says one of them will occur (current QM). The structure remains the same: you have an initial state, law, and future state. But one is deterministic and the other is indeterministic. Determinism is superior in the sense that it provides more explanatory power and we should get as close to that as possible.

As scientists, we must peer further and further into phenomenons as much as possible. Until QM, we never came across anything that did not have a cause. And the fact that there are statistical laws instead of deterministic ones in QM shouldn’t be seen as evidence that millions of uncaused things are happening every second. Rather, it should be seen as a signal that we have more to explore

 

[Nugatory]

It exists but it is not explained.

This is true, but then again quantum mechanics doesn't explain anything. It is a theory about measurement results and doesn't pretend to explain why the results are what they are.

An explanation of why non local correlations occur involves showing why they occur instead of not. There is no reason given for this in any local theory. Non local theories do give reasons for this: the measurement of one particle can influence the other

And which non-local theories make that claim? You look at the observed correlations and assert that the correlations can only arise from one measurement influencing the other. But QM makes no such claim, it doesn't say anything except that its mathematical formalism accurately predicts measurement results.

 

[sahashmi]

This is true, but then again quantum mechanics doesn't explain anything. It is a theory about measurement results and doesn't pretend to explain why the results are what they are.
And which non-local theories make that claim? You look at the observed correlations and assert that the correlations can only arise from one measurement influencing the other. But QM makes no such claim, it doesn't say anything except that its mathematical formalism accurately predicts measurement results.

Sure but then it’s not a complete theory. One can still make inferences on there being nonlocal influences without having a complete theory though. For example, one could have made a reasonable inference that there was unknown physical mechanism that can be represented as a theory to explain lightning, before we actually discovered this.

 

[Sambuco]

As I already wrote, QFT does not explain entanglement. So its existence, although useful, does not imply that a local theory can explain the nonlocal correlations in entanglement.

Just to clarify something, since two different notions of locality are being used. The statement "QFT is local" means that it is based on microcausality, i.e. space-like measurements commute. On the other hand, "nonlocal correlations" means Bell inequality violations. In that sense, QFT is nonlocal because it predicts entanglement.

Lucas.

 

[martinbn]

It exists but it is not explained. An explanation of why non local correlations occur involves showing why they occur instead of not. There is no reason given for this in any local theory. Non local theories do give reasons for this: the measurement of one particle can influence the other

Aha, here it is! You say explanation but you mean a classical explanation. This of course is your problem. Well, it is a problem for your and anyone else who cannot accept quantum mechanics.

 

[Fra]

Here’s the issue with this.

You may be right that “explanation” in science does often come down to initial state, law, and future state. But not every law is the same.

Of course, but the "form" or "paradigm" of these laws, constrains strongly what is mathematically possible and what isn't.

So lets not get confused that a "no-go theorem" proven in one paradigm, applies to every competing paradigm.

This is what made me frown when reading Maudlins paper. But I applaud not giving up the conceptual problems.

For example, a future law that tells you why the (+,-) result occurs instead of a (-,+) in the case of entanglement is clearly superior to a “law” that says one of them will occur (current QM). The structure remains the same: you have an initial state, law, and future state. But one is deterministic and the other is indeterministic. Determinism is superior in the sense that it provides more explanatory power and we should get as close to that as possible.

As scientists, we must peer further and further into phenomenons as much as possible. Until QM, we never came across anything that did not have a cause. And the fact that there are statistical laws instead of deterministic ones in QM shouldn’t be seen as evidence that millions of uncaused things are happening every second. Rather, it should be seen as a signal that we have more to explore

For me, I think determinism is not restorable, that's not what this is about fore me at all. That we should be able to predict the future with certainy, even "without disturbing it" to me even itself seems like a conceptual confused position (ie. from my preferred paradigm).

It's the inseparability that is the conceptual issue. And no matter what we say, and how great QM works, this issue persist since Einstein thought about it and I certainly don't thikn it should pass. But perhaps the resolution needs to take a differen "form" that Einstein and Bell originally was contemplating.

/Fredrik

 

[Fra]

Aha, here it is! You say explanation but you mean a classical explanation. This of course is your problem. Well, it is a problem for your and anyone else who cannot accept quantum mechanics.

I partly agree, because there are two issues here.

There is no explanation at all right now! Classical or not. There is only a description, a very successful one yes, but noone seems to really understand it conceptaully. And this is bad.

So what we could stop doing, is looking for the "old style" explanation, ie. the one that Bell's theorem rules out. But this class is not exhaustive.

So even if I do accept QFT as one of great achievments of science, describing alot of subatomic inteactions, I still have a problem The insight should be not that there is no problem, but that the solution to the problem may need a paradigm change.

/Fredrik

 

[sahashmi]

Aha, here it is! You say explanation but you mean a classical explanation. This of course is your problem. Well, it is a problem for your and anyone else who cannot accept quantum mechanics.

Again, this is just a common tactic used by some physicists who try to escape the conclusion that the bell experiments clearly show.

Allow me to use an analogy. Suppose every time I moved my finger, the sun moved. You ask “how? What’s the explanation?” and I say “well, it just does. Here is the formula describing this phenomenon. That’s all we need. You’re just assuming that there is a further classical explanation. This new, magical, phenomenon does not need the kind of classical explanation you seek.”

You’d call me ludicrous. Believe it or not, you’re doing the same here. Of course, the analogy isn’t the same, and this is a different situation, but your logic is fundamentally the same. Words like classical and quantum are categories that we have made up. The universe doesn’t care about these categories that we make up. Reality is reality.

An explanation, to anyone with a sound mind, must tell you why one outcome occurs instead of another and the mechanism by which it occurs. That is what has been meant by explanation in all sciences since the dawn of time. When a phenomenon is left unexplained by any local theory, such as the phenomenon of how particles remain correlated at large distances, and why/how a particular measurement outcome occurs instead of another, it means that there is no explanation, not “we have an explanation, it’s just not a classical explanation”.

These tactics by physicists to escape the conclusion of non locality don’t work anymore. It’s a cop out and Bell anticipated this. It’s unfortunate that many misinterpret him.

 

[javisot]

An explanation, to anyone with a sound mind, must tell you why one outcome occurs instead of another and the mechanism by which it occurs. That is what has been meant by explanation in all sciences since the dawn of time.

According to this logic, anyone who accepts non-locality would not be doing science, since they do not explain any mechanism, they simply accept it. it's like accepting that dark energy is an ad hoc parameter rather than a natural mechanism.

That's why one of the criticisms I raised: "Okay, you're right, now what?"

 

[weirdoguy]

Okay, you're right, now what?

Now physicists should adjust to what non-physicists think is the proper way to do physics and how to think about physics.

My opinion: unless some philosopher of physics is actively doing research in physics and can handle the math at handy, then they are not ready to do philosophy of physics. I did write reviews of a few philosophy of physics papers, at the request of a "true reviewer", professor of philosophy Piotr Bołtuć (Illinois University, he rented me an apartment at that time, that's how I got into this), and the level of misunderstanding and knowledge of physics only at the level of popular science books was overwhelming. Fortunately, professor Bołtuć saw what the level of these works was, he just had to have a "backing" in the form of a physicist's opinion.

 

[martinbn]

Allow me to use an analogy. Suppose every time I moved my finger, the sun moved. You ask “how? What’s the explanation?” and I say “well, it just does. Here is the formula describing this phenomenon. That’s all we need. You’re just assuming that there is a further classical explanation. This new, magical, phenomenon does not need the kind of classical explanation you seek.”

You’d call me ludicrous.

No, I would not. I would call you genius. You would have done what Newton did about the planets and their motion. That's good science.

An explanation, to anyone with a sound mind, must tell you why one outcome occurs instead of another and the mechanism by which it occurs.

It seems that you cannot accept the possibility that nature can have randomness. To quote Feynman, if you don't like it, go somewhere else. Go to a universe where the laws of nature conform with your philosophical prejudices.

That is what has been meant by explanation in all sciences since the dawn of time. When a phenomenon is left unexplained by any local theory, such as the phenomenon of how particles remain correlated at large distances, and why/how a particular measurement outcome occurs instead of another, it means that there is no explanation, not “we have an explanation, it’s just not a classical explanation”.

What is the explanation according to you? You just say the word "non-locality", but surely that is not an explanation. So, what is the explanation?

 

[weirdoguy]

to anyone with a sound mind

Again, sound mind can do nothing, if one doesn't know the physics. And by know the physics I mean knowing the math formalism and being able to do exercises and solve problems using math, not some vague words, at hand. Some general, non-math knowledge, in my opinion, give you no right to tell physicists how they should do physics. And for me it's clear that you "don't know the physics" in the above sense.

 

[Fra]

An explanation, to anyone with a sound mind, must tell you why one outcome occurs instead of another and the mechanism by which it occurs. That is what has been meant by explanation in all sciences since the dawn of time.

Only to the extent possible yes, but not further.

But when one is in a chronic situation of ALWAYS struggling with incomplete information, but have to take actions based on it, I would say then part of "reality" is dealing with this uncertainty. It is not unreasonable that there are actual irreducible unpredictability that we can no escape, and that this actually has observable effects on interactions.

This is why I deeply object to the association: explanation ~ determinism.

I do not share the idea that a local explanation of the apparently pre-determined correlations, requires determinism and predeterminism of the single outcomes. This conclusion IMO is related to constraints of the paradigm implicit in Bells reasoning; some may categorize it as "classical realism", whatever that means. I just know i don't adopt it, and I surely also reject the usual definition of realism as something you can determinied with certainty without distorting it. If THAT is the "definition" of realism, then I am apparentl as much anti-realist as you can be! Although for me "realism" can have another meaning as well, but it leads nowhere to discuss labels.

Quantum "explanations" are supposedly at best, of the form that it is the "dice" that evolves deterministically.

IF that is the case, the "explaination" should be rather than "why one outcome occurs instead of another", why this dice insted of another one?

QM does not reallyt "explain this", it DESCRIBES how the dice evoles, but not where it comes from. It is input, with hilbert spaces and hamiltonians.

/Fredrik

 

[javisot]

The ER=EPR approach would arguably be a non local hidden variable theory.

I understand (maybe I'm wrong) that this isn't correct. Why do you say it's like a nonlocal hidden variable theory?
Physicists working on this believe, by definition, that QM and GR are compatible.

 

[sahashmi]

According to this logic, anyone who accepts non-locality would not be doing science, since they do not explain any mechanism, they simply accept it. it's like accepting that dark energy is an ad hoc parameter rather than a natural mechanism.

That's why one of the criticisms I raised: "Okay, you're right, now what?"

No one who believes in non locality says “we’re done here.” So no, it is patently incorrect to suggest that people who accept non locality aren’t doing science.

Scientific theory discovery starts from insights. Those insights must be rational. One can believe that a non local explanation exists which can then lead one to discover non local theories.

People who say there is no non locality when it has been demonstrated that no local theory can explain the correlations are denying reality. They are the ones not doing science.

“Now what?” simple. Focus our efforts into searching for the mechanism that would explain the non local correlations instead of denying the clear experimental results that violate locality

 

[martinbn]

Here is an interesting paper.
https://research.tue.nl/en/publicat...s-and-their-irrelevance-to-the-problem-of-loc

A straightforward derivation of the Bell inequalities is given, without in any way appealing to locality. This demonstrates the incompatibility of both local and nonlocal hidden variables theories with quantum mechanics, and the irrelevance of the Bell inequalities to the problem of (non)locality in such theories.

 

[sahashmi]

Now physicists should adjust to what non-physicists think is the proper way to do physics and how to think about physics.

My opinion: unless some philosopher of physics is actively doing research in physics and can handle the math at handy, then they are not ready to do philosophy of physics. I did write reviews of a few philosophy of physics papers, at the request of a "true reviewer", professor of philosophy Piotr Bołtuć (Illinois University, he rented me an apartment at that time, that's how I got into this), and the level of misunderstanding and knowledge of physics only at the level of popular science books was overwhelming. Fortunately, professor Bołtuć saw what the level of these works was, he just had to have a "backing" in the form of a physicist's opinion.

It seems that you are more focused on repeating the claim that certain people don’t understand the physics rather than actually demonstrating this.

Consider that eminent scientists like Bell, who’ve probably spent 100x the amount of time in physics as you have, know what they’re talking about and their conclusions flatly contradict yours

 

[sahashmi]

No, I would not. I would call you genius. You would have done what Newton did about the planets and their motion. That's good science.

It seems that you cannot accept the possibility that nature can have randomness. To quote Feynman, if you don't like it, go somewhere else. Go to a universe where the laws of nature conform with your philosophical prejudices.

What is the explanation according to you? You just say the word "non-locality", but surely that is not an explanation. So, what is the explanation?

It seems that you are repeatedly misunderstanding points which leads me to believe you perhaps have not read Maudlin’s paper.

The debate is not over randomness. The debate is over whether there are influences that are non locality leading to non local correlations. Non locality is not the same as the denial of randomness.

As for the explanation? No one knows. We’re obviously working on it. But the first step is to accept the results of the Bell experiments so people are not misguided in their search. There is a reason why Bell looked for non local theories unlike many physicists who misinterpreted his results

 

[sahashmi]

Here is an interesting paper.
https://research.tue.nl/en/publicat...s-and-their-irrelevance-to-the-problem-of-loc

Here is the response to it: https://ui.adsabs.harvard.edu/abs/1986PhLA..117..433D/abstract

Anyone who claims that the bell inequalities have nothing to say about locality is simply misrepresenting the science

 

[martinbn]

It seems that you are repeatedly misunderstanding points which leads me to believe you perhaps have not read Maudlin’s paper.

Which points? I just don't agree with you. It seems that you are using tactics by accusing those who disagree with you of not understanding.

The debate is not over randomness. The debate is over whether there are influences that are non locality leading to non local correlations. Non locality is not the same as the denial of randomness.

You brought that up! You want a mechanism to tell you why an outcome occurs. Say why spin up and not spin down. You cannot accept that it is random.

As for the explanation? No one knows. We’re obviously working on it. But the first step is to accept the results of the Bell experiments so people are not misguided in their search. There is a reason why Bell looked for non local theories unlike many physicists who misinterpreted his results

But there is the possibility that there is no explanation of the type you are looking for. At some point people were convinced of the existence of the planet Vulcan. Should astronomers work on that rather on something else?

 

[martinbn]

Here is the response to it: https://ui.adsabs.harvard.edu/abs/1986PhLA..117..433D/abstract

Anyone who claims that the bell inequalities have nothing to say about locality is simply misrepresenting the science

This doesn't address the paper at all!

 

[Morbert]

@sahashmi According to Bell: "A theory will be said to be locally causal if the probabilities attached to values of local beables in a space-time region 1 are unaltered by specification of values of local beables in a space-like separated region 2, when what happens in the backward light cone of 1 is already sufficiently specified, for example by a full specification of local beables in a space-time region 3. [...] Ordinary quantum mechanics is not locally causal."

Quantum theory is straightforwardly nonlocal according to this condition. But is violation of this Bell locality a sufficient condition for Einstein nonlocality, where external influences on region 1 can immediately affect region 2?

Antirealist interpretations, or Oxford-Everettian interpretations, or superdeterministic interpretations, or interpretations drawing from Bohr toposes are said not to violate Einstein locality even if they violate Bell locality.

 

[Lord Jestocost]

This distinction between “realistic” and “non realistic” is a misnomer. Science is about explaining what we observe. What we observe is “real”. No one who believes in “non realism” has ever managed to explain what that even means

Maybe, it might help if the idea of realism is understood. In their paper “Reality without Realism: On the Ontological and Epistemological Architecture of Quantum Mechanics”, Arkady Plotnitsky and Andrei Khrennikov present the following definition:

“In other words, realism is defined by an assumption, which defined Kant’s philosophy, that the ultimate
constitution of nature possesses attributes that may be unknown or even unknowable, but that are thinkable, conceivable [14, p. 115]. In physics, this constitution is often deemed conceivable on the model of classical physics and its ideal of reality, possibly adjusted to accommodate new phenomena, such as electromagnetic or relativistic ones, and new concepts, such as field, classical or quantum, or more recently automata, including quantum automata [15,16]......."

And further on, with respect to non-realism:

"The nonrealist argumentation just outlined (now including that of Bohr) is not simply “an arbitrary
renunciation” of an analysis the ultimate constitution of nature [2, v. 2, p. 62]. It is an argument that, on the basis of its analysis of the nature of quantum phenomena and quantum theory, specifically quantum mechanics, is compelled to conclude that this constitution is beyond the reach of theoretical description or even thought itself, at least as things stand now. In this sense, one can speak of “reality without realism”: quantum objects may said to be real and, as such, have effects on the world we observe, and yet prevent us from representing them, specifically by the formalism of quantum theory, or possibly even from forming any conception concerning them.⁶”
[Bold in quote by LJ]

 

[Morbert]

Yes, "antirealism" is often instinctively misunderstood as a position like "nothing is real". In a quantum mechanics context, it means microscopic systems are understood in terms of responses they induce in macroscopic tests, rather than in terms of some primitive ontology.

 

[WernerQH]

Again, your belief that the experiments do not contradict relativity is a belief, not science.

Also experiments require interpretation. Whenever we discuss experiments we rely on some theoretical (or proto-theoretical) framework. If yours is different, it doesn't mean that somebody else's must be non-scientific.

Entanglement is the most important phenomenon of QM, since it’s the phenomenon that departs most strongly from our day to day intuitions.

It's curious that so many people believe that. Shouldn't we aim for a simpler description of the facts that doesn't rely on inappropriate (classical) concepts? A paradigm shift?

As I already wrote, QFT does not explain entanglement.

You are right, if you insist that an explanation should provide a "mechanism". Would you accept retrocausality as a mechanism? QFT has propagators that reach into the backward light cone and make sure that Nature's book-keeping is always correct.

Bell was well aware of QFT. He is unfortunately heavily and widely misunderstood or misinterpreted.

Bell wrote an essay "Against Measurement". Among the terms we wished to be banned in expositions of the foundations of QM was the word "system". I think it's the root of the problems with "entanglement". We are too constrained by thinking in terms of "systems" that evolve according to some fixed law.

For example, a future law that tells you why the (+,-) result occurs instead of a (-,+) in the case of entanglement is clearly superior to a “law” that says one of them will occur (current QM). The structure remains the same: you have an initial state, law, and future state. But one is deterministic and the other is indeterministic. Determinism is superior in the sense that it provides more explanatory power and we should get as close to that as possible.

Good luck searching for such a law!

Until QM, we never came across anything that did not have a cause.

Yes everything has always had a cause. The Greeks had many gods and could explain everything.

 

[mitchell porter]

The ER=EPR approach would arguably be a non local hidden variable theory.

I understand (maybe I'm wrong) that this isn't correct. Why do you say it's like a nonlocal hidden variable theory?

@sahashmi is saying what they think ER=EPR would have to be, to offer an explanation of quantum nonlocality.

However, as things stand, ER=EPR is indeed supposed to be quantum on both sides of the equation. The prototype is the construction of wormholes in AdS/CFT, and while sometimes one uses a classical approximation on the AdS side, ultimately this is supposed to be an equivalence between quantum gravity in AdS, and a non-gravitational QFT on the boundary.

 

[weirdoguy]

Anyone who claims that the bell inequalities have nothing to say about locality is simply misrepresenting the science

Oh stop with this arrogant accusations. You are the one that is against what most of scientist think, so you should stop and think why they are like that. Instead you think you know better than them.

 

[Sambuco]

As I already wrote, QFT does not explain entanglement. So its existence, although useful, does not imply that a local theory can explain the nonlocal correlations in entanglement.

Just to give an analogy that might be helpful. There is no "explanation" for time dilation/length contraction in special relativity. One reason for this is due to the principled formulation of the theory. When Einstein showed that Lorentz transformations are the only way to reconcile Galileo's relativity and Maxwell's electromagnetism, it was accepted that there is nothing that "causes" the length to contract when one observer moves relative to another.

In that sense, quantum mechanics lacks a formulation based on commonly accepted principles, although much progress has been made in the field of reconstruction programs.

Lucas.

 

[Fra]

Just to give an analogy that might be helpful. There is no "explanation" for time dilation/length contraction in special relativity.

Indeed, SR rests on some postualtes that are not explained. So SR is forged from the constraints the postulates impy.

Why or there is a max speed limite of communication/propagation, that all "observers" or "observer frames" agree upon, is something that likely might be EXPLAINED in the future, perhaps as emergent, from deeper principles in research programs that look at the foundations of quantum gravity.

So it is not only QM that begs for an improved understanding. And I don't think they should be forgotten either.

/Fredrik

 

[Sambuco]

I'd like to add something regarding local causality. In a sense, this is a discussion about continuity. At the risk of oversimplifying, we could say that QM is a theory that, given a past event, allows us to calculate the probability of another event occuring in the future. These two correlated events are obviously "real", we know they occur. For this calculation, we introduce the quantum state that unitarily evolves from the initial time to the final time. To relate one thing to another (the actual outcomes and the unitarily evolved quantum state), we use the Born's rule.

So, the questions are: (i) how to interpret what happens between these two events, i.e. the unitary evolution of the quantum state, and (ii) how to smoothly connect this unitary evolution with the appearance of the detector's clicks. Many people don't agree with the idea that nothing "real" happens between the two events, so they try to provide the theory with some ontology that "fills" that gap. In many-worlds, the quantum state is considered as the only thing that exists. In Bohmian mechanics, along with the unitary evolution of the quantum state, there are the particles that (continously) move from the first event to the second. In GRW-like spontaneous collapse, a sudden state reduction explains the transition from spacially distributed wave functions to well-localized detection events. On the other hand, some people try to interpret the theory in its minimal form, without adding anything to it. This is how some epistemic interpretations work. We could mention Copenhagen-like interpretations or information-based ones, such as relational quantum mechanics. In these kind of interpretations, as @Morbert said in post #81, reality is associated more to the interaction between systems than to systems themselves.

In my view, the above distinction allows to understand how each interpretation addresses nonlocality. For interpretations that attempt to fill the gap between two correlated events with something ontic, a non local mechanism is usually considered as an explanation for non local correlations, as in Bohmian mechanics. For the interpretations that consider interactions to be the only real things, there is no fundamental causation that propagates the cause in the past to the effect in the future in a smooth and continuous manner through spacetime. That is, the discreteness of the QM realm is accepted as fundamental.

Furthermore, for the second kind of interpretation, even when the mathematical tools employed to calculate probabilities for events' correlations are not considered "real", relativistic causality plays a fundamental role in this calculation, by evolving the state of the system between the spacetime points of the two "real" events. In other words, relativity is correct for calculate these transition probabilities, but it has nothing to do with possible outcomes becoming real outcomes.

Lucas.

 

[PeroK]

“Now what?” simple. Focus our efforts into searching for the mechanism that would explain the non local correlations instead of denying the clear experimental results that violate locality

What you mean is that all physicists should accept your philosophical worldview and devote their working lives to what they consider a pointless exercise, searching for something that they believe cannot possibly exist.

I.e. forget everything they have learned and follow the lead of someone who hasn't even bothered to learn the basics, let alone get a degree in physics?

Your arrogance is staggering. You really believe your powers of pure reason overrule every physicists who ever worked on QM? That they have precisely nothing to contribute to the debate other than accept a novice philosopher has the ultimate knowledge of physics?

Your arrogance is stupefying.

 

[sahashmi]

Which points? I just don't agree with you. It seems that you are using tactics by accusing those who disagree with you of not understanding.

You brought that up! You want a mechanism to tell you why an outcome occurs. Say why spin up and not spin down. You cannot accept that it is random.

But there is the possibility that there is no explanation of the type you are looking for. At some point people were convinced of the existence of the planet Vulcan. Should astronomers work on that rather on something else?

You are right that there is a possibility that there may be no explanation. However, we must assume that there is an explanation since that what is the whole point of science. Before we figured out the cause of lightning, we assumed there was a cause.

Secondly, the question is not about why a particle is spin up or down. That part to me still requires an explanation but it is atleast feasible there may be none. The more interesting part is why two particles very far away remain correlated to each other while having no pre defined properties. This is the spooky action at a distance that Einstein thought was happening. If he was alive, he would believe that the particles are influencing each other, since that was his alternative if his preferred theory of local hidden variables didn’t turn out to be true.

 

[sahashmi]

Yes, "antirealism" is often instinctively misunderstood as a position like "nothing is real". In a quantum mechanics context, it means microscopic systems are understood in terms of responses they induce in macroscopic tests, rather than in terms of some primitive ontology.

The whole point of Bell’s theorem is that an anti-realist interpretation still does not save nonlocality. Bell’s theorem has two assumptions: locality and statistical independence. You have to assume one of those is wrong if the inequalities are confirmed: not locality or realism. As I mentioned earlier, it doesn’t matter what you think is happening before measurement. You can choose to believe whatever. You can choose to believe that the relevant particles don’t even exist or fundamentally cannot be described in any way.

You don’t even have to believe in quantum mechanics! This is because the correlations of outcomes in the lab still remain, and these are macroscopic outcomes that we all agree on. And what Bell did is show that these correlations cannot be explained by any sort of local dynamics, regardless of your ontological beliefs of “reality” before measurement.

You would literally have to deny the experimental results in order to save yourself, but that would be ironic given that the majority of the anti-realist camp puts experiments on a pedestal

See this answer that deals with this in detail: https://physics.stackexchange.com/q...on-realism-alone-explain-quantum-entanglement

From the answer,

“I felt it was time to write up a long account on why there are no “local non-realist” theories which can explain Bell Correlations”

 

[sahashmi]

What you mean is that all physicists should accept your philosophical worldview and devote their working lives to what they consider a pointless exercise, searching for something that they believe cannot possibly exist.

I.e. forget everything they have learned and follow the lead of someone who hasn't even bothered to learn the basics, let alone get a degree in physics?

Your arrogance is staggering. You really believe your powers of pure reason overrule every physicists who ever worked on QM? That they have precisely nothing to contribute to the debate other than accept a novice philosopher has the ultimate knowledge of physics?

Your arrogance is stupefying.

You’re putting words in my mouth. I’m just pointing out that a lot of physicists are misled by Bell’s theorem and by what it proves. Bell would agree with me. This is my opinion. You can feel free to disagree with it.

I’m not forcing a physicist to do anything. They can do what they want. If the experiments rule out a certain kind of worldview, and I point that out, that doesn’t make me arrogant. It just means I’m stating the truth.

You might as well call Bell or Tim Maudlin or David Bohm or any of the other scientists and thinkers who do have physics degrees, and objectively possess more knowledge than most people arrogant too. Their views are aligned with mine.

 

[Sambuco]

This is the spooky action at a distance that Einstein thought was happening. If he was alive, he would believe that the particles are influencing each other, since that was his alternative if his preferred theory of local hidden variables didn’t turn out to be true.

Sorry, but that's not true. Einstein believed that locality (perhaps local causation would be a more accurate description) must be true, so the evidence for this "spooky action at a distance" was, in fact, the reason he argued that QM is incomplete. This is the point of the EPR paper!
As for his preference for a hidden-variables theory, he was still alive when Bohm presented his interpretation, and Einstein didn't like it.

Lucas.

 

[PeterDonis]

Einstein believed that locality (perhaps local causation would be a more accurate description) must be true, so the evidence for this "spooky action at a distance" was, in fact, the reason he argued that QM is incomplete. This is the point of the EPR paper!

But Einstein's belief in "locality" as he defined it was wrong. That's what Bell proved. Any theory that meets Einstein's requirement of "locality" cannot violate the Bell inequalities. But nature does violate them. So whatever theory accurately describes nature, it cannot meet Einstein's "locality" requirement.

Some physicists argue for other, different definitions of "locality" than the one Einstein used, and argue that nature (and QM) satisfies those definitions. But none of that changes the fact that Einstein's version of "locality" has been ruled out by Bell's theorem and the experiments that show Bell inequality violations.

 

[PeterDonis]

I’m just pointing out that a lot of physicists are misled by Bell’s theorem and by what it proves.

You're doing more than that. The claim of yours that @PeroK quoted is that a "mechanism" must exist and we should be searching for it. He didn't put any words in your mouth; he quoted your own words directly.

 

[sahashmi]

Sorry, but that's not true. Einstein believed that locality (perhaps local causation would be a more accurate description) must be true, so the evidence for this "spooky action at a distance" was, in fact, the reason he argued that QM is incomplete. This is the point of the EPR paper!
As for his preference for a hidden-variables theory, he was still alive when Bohm presented his interpretation, and Einstein didn't like it.

Lucas.

You misread what I wrote. I said the same thing. That Einstein believed in local hidden variables.

But his EPR paper said that if local hidden variables were not true, then there must be spooky action at a distance. His preference was proven wrong. Thus, if he was alive and saw Bell’s theorem, he would believe the particles were influencing each other (whether at a distance or through Superluminal speeds).

He scoffed at “antirealists” since that position according to him was incoherent. He did not think “antirealism” was a valid option whatsoever.

 

[sahashmi]

You're doing more than that. The claim of yours that @PeroK quoted is that a "mechanism" must exist and we should be searching for it. He didn't put any words in your mouth; he quoted your own words directly.

Sure, I do think a mechanism is there and that we must search for it. But I can’t force physicists who disagree with me to do anything nor am I implying that.

John Bell until his death complained about physicists misinterpreting his theorem, and unfortunately many still do to this day. Yet even he can’t force them to do anything. He can merely state his views which is what I’m doing.

 

[jedishrfu]

Thank you @sahashmi for opening this thread. It seems there a lot of good responses and discussion going on. However, it also appears that the thread has run its course and now its time to close it.

Thanks to all who contributed.

The thread is now closed.