I Is the fork in the Einstein Podolsky Rosen argument correct?

[sahashmi]

Not in the sense in which "communication" is used in the theorem. Or the term "signaling"--since the "no signaling theorem" is a common alternate name for it. "Communication" and "signaling" in the theorem are perfectly objective notions that do not even require humans at all to happen.


If two events are spacelike separated, their time ordering is frame dependent. On the usual understanding of "causality", where the "cause" must precede the "effect", this means neither of the two events can possibly be the cause, or the effect, of the other, since their time ordering is not invariant.


Whether Bohmian mechanics is even compatible with relativity is an open question. There are other PF threads on this topic.

The point is that one measurement outcome can affect another measurement outcome where we still can’t signal. This is because even though each measurement outcome may be not predictable (atleast as of now), as soon as one measurement outcome is measured, it can influence the other, even if we can’t use this for signalling. The no signalling comes from the unpredictability, not necessarily because one measurement isn’t influencing the other.

In regards to the space like separation comment, yes, the time ordering can change. But this assumes relativity and if the EPR argument in regards to the fork is correct, and local hidden variables are wrong, and if there are non local influences, it might be an indication that relativity needs work or is not fundamental and rather emergent (as Bell seemed to suspect but not necessarily assert, and others like Maudlin or others believing that relativity has to go).

 

[sahashmi]

The "communication" in the no-communication theorem isn't anthropomorphic, it is any form of information transfer. The theorem is significant precisely because it shows that correlated measurements do not and cannot violate causality.

Most presentations of Bohmian mechanics consider only the non-relativistic form of the theory so the question of compatibility with relativity never comes up (or maybe I should say that incompatibility with relativity has already been conceded). I won't speak to the relativistic formulations of Bohmian mechanics because we have people here who are far more qualified than I to do so, and because the topic is not altogether free of controversy.

Again, the point is that regardless of how you define it, no informational transfer is not the same as “one measurement outcome does not influence the other.” In other words, no communication != no influences.

The traditional version of Bohmian mechanics as an example posits that one measurement outcome influences the other even with no signalling. John Bell was a believer of non local theories like this even though he himself had a proof of the no signalling theorem.

 

[PeterDonis]

relativity needs work...is not fundamental and rather emergent

PF regular @Demystifier has published at least one paper discussing this hypothesis, which IIRC has been referenced in some PF threads.

 

[PeterDonis]

In regards to MWI, that’s why I wrote “unless you believe in many worlds” in my post

Yes, but allowing that possibility concedes that there are more possibilities than the ones described in the "fork".

 

[sahashmi]

Yes, but allowing that possibility concedes that there are more possibilities than the ones described in the "fork".

Yes fair enough, if outcomes are not just one outcome, then the fork is incorrect. I was just confused as to how “local non realism” can result in the correlations

 

[Morbert]

But if there is local “non realism” and indeterminism where Alice’s measurement outcome does not affect Bob’s, then they cannot be perfectly correlated. This is because if I can predict X with certainty, X must be determined (this is the Einsteinian argument). For if X was not determined, it makes no sense to be able to predict it.

Perfect correlations in appropriately executed tests are expected by both realists and antirealists alike, as both accept the operational validity of quantum mechanics.

What the antirealist rejects is an ontological model of quantum mechanics. A realist might remark that an antirealist has no ontological model to explain the operational validity of quantum mechanics, and an antirealist would respond by saying nature is not obliged to be understood in terms of such models.

So Alice's outcome X lets her predict with certainty Bob's outcome without entailing some underlying model of reality cryptically determining all outcomes.

 

[sahashmi]

Perfect correlations in appropriately executed tests are expected by both realists and antirealists alike, as both accept the operational validity of quantum mechanics.

What the antirealist rejects is an ontological model of quantum mechanics. A realist might remark that an antirealist has no ontological model to explain the operational validity of quantum mechanics, and an antirealist would respond by saying nature is not obliged to be understood in terms of such models.

So Alice's outcome X lets her predict with certainty Bob's outcome without entailing some underlying model of reality cryptically determining all outcomes.

It’s not really cryptic any more than it’s cryptic that when you put your phone in a room, leave, and come back, you find your phone still in there.

Every time you enter the room, you will predict that the phone is there, and find out that it’s there. A realist would say this is occurring because something in reality causes it to be there every time. An antirealist would say “we don’t need an ontological model to explain the fact that something in reality caused the phone to be there”.

If reality is not objective and mind independent (note, not observation independent), then what are we measuring, and why are we having a 100% prediction rate of X being a value, if X was not determined to be that value?

 

[PeroK]

It’s not really cryptic any more than it’s cryptic that when you put your phone in a room, leave, and come back, you find your phone still in there.

That's the sort of reasoning that works for a phone, but does not work for a photon (or an electron).

For example, the UP (Uncertainty Principle) applies to a phone, but is quantitatively negligible. Your phone is in one sense bound to be precisely where you left it and in a state of rest relative to the room, say. The UP applies to an electron in ways that are significant. You won't find an electron precisely where you left it. And you cannot simply describe its state of motion in classical terms.

Moreover, you know it's your phone as there are ways to uniquely identify it. Electrons, however, are indistingishable. Technically, there is no way to know that it is "your" electron. There is a serious physics and philosphy of physics issue here that electrons do fundamentally have a different sort of "reality" from a phone.

In fact, I would argue that electrons are part of a mathematical model and don't exist in the same way that a phone exists. That, however, is a side issue.

Any argument about QM that draws a direct analogy with macroscopic objects is fundamentally flawed. This is something that Einstein never really accepted. Hence the EPR paper.

At the very least, the dynamic quantities associated with an electron (position, momentum, angular momentum, spin) do not have well-defined values in the way that the corresponding quantities for a phone do.

In fact, if you upgrade to QFT, then the electron is no longer an element of physical reality - whereas, the phone remains "real" independent of whatever fundamental theory of particle physics you adopt.

 

[sahashmi]

That's the sort of reasoning that works for a phone, but does not work for a photon (or an electron).

For example, the UP (Uncertainty Principle) applies to a phone, but is quantitatively negligible. Your phone is in one sense bound to be precisely where you left it and in a state of rest relative to the room, say. The UP applies to an electron in ways that are significant. You won't find an electron precisely where you left it. And you cannot simply describe its state of motion in classical terms.

Moreover, you know it's your phone as there are ways to uniquely identify it. Electrons, however, are indistingishable. Technically, there is no way to know that it is "your" electron. There is a serious physics and philosphy of physics issue here that electrons do fundamentally have a different sort of "reality" from a phone.

In fact, I would argue that electrons are part of a mathematical model and don't exist in the same way that a phone exists. That, however, is a side issue.

Any argument about QM that draws a direct analogy with macroscopic objects is fundamentally flawed. This is something that Einstein never really accepted. Hence the EPR paper.

At the very least, the dynamic quantities associated with an electron (position, momentum, angular momentum, spin) do not have well-defined values in the way that the corresponding quantities for a phone do.

In fact, if you upgrade to QFT, then the electron is no longer an element of physical reality - whereas, the phone remains "real" independent of whatever fundamental theory of particle physics you adopt.

It’s of course just an analogy but I think the antirealists when it comes to QM miss the point.

If I can determine a measurement outcome with 100% certainty, it doesn’t imply that the photon had a definite path before measurement, nor that it is exactly particle like or wave like, nor that it even exists! But what it does imply, using Einsteinian words, is that some element of reality determines or causes the measurement outcome which we all agree is real.

This difference is crucial. The antirealist thinks that the “realist” is making the former claim I just mentioned when it’s really the latter. As long as something determines it (it doesn’t actually matter what it is), the argument goes through. The only escape from this argument is to quite literally not beleive in a mind independent reality. But then this is a true antirealist and I would hope this person takes this argument to its full conclusion by being a solipsist, not believing in an external world at all, or not believing the world is real after one dies.

Note that even if you were a solipsist, you would still be making 100% predictions on measurement outcomes within the experience of your mind, and so something in your (now mind dependent reality) must still be determining the outcome!

 

[PeroK]

Well, of course, I think it's you that are entirely missing the point. QM is not a bad dream that you can wave away with a philosophical magic wand.

Part of the reason you miss the point is that you have never studied QM and are pretending that your understanding of phones and footballs will suffice to understand elementary, microscopic phenomena.

 

[sahashmi]

Well, of course, I think it's you that are entirely missing the point. QM is not a bad dream that you can wave away with a philosophical magic wand.

Part of the reason you miss the point is that you have never studied QM and are pretending that your understanding of phones and footballs will suffice to understand elementary, microscopic phenomena.

I just explained the argument and pointed out that as long as you believe the measurement outcome is real, the argument goes through, regardless of what you think exists before measurement.

You didn’t respond to the clarification whatsoever and instead re asserted that I don’t know what I’m talking about without saying anything substantial. This makes me think you would say the same to Einstein or Bell who have the same viewpoint despite them having studied QM more than you. Your assertions aren’t arguments so I have nothing else to add here

 

[PeroK]

You didn’t respond to the clarification whatsoever and instead re asserted that I don’t know what I’m talking about

I didn't recognise what you wrote as clarification. This is a physics forum, and I didn't recognise any physics in your response.

In a literal sense you don't know what your talking about. In the strict sense that you don't know the subject matter.

I may be wrong, but I'd bet you can't actually do any physics. You can only talk about it.

 

[sahashmi]

I didn't recognise what you wrote as clarification. This is a physics forum, and I didn't recognise any physics in your response.

In a literal sense you don't know what your talking about. In the strict sense that you don't know the subject matter.

I may be wrong, but I'd bet you can't actually do any physics. You can only talk about it.

In a literal sense you’re evading the argument and dodging. The subsection of this forum is called quantum interpretations and foundations. I clarified the simple Einsteinian argument of how a 100% prediction rate implies that something in reality is determining it.

You can either ignore it and admit you don’t have a response or focus on how much I know or don’t know about physics when tons of physicists including Einstein have made the same argument.

 

[PeroK]

In a literal sense you’re evading the argument and dodging. The subsection of this forum is called quantum interpretations and foundations. I clarified the simple Einsteinian argument of how a 100% prediction rate implies that something in reality is determining it.

You can either ignore it and admit you don’t have a response or focus on how much I know or don’t know about physics when tons of physicists including Einstein have made the same argument.

My answer is that Einstein, great physicist though he was, became hopelessly out of touch with quantum theory.

The EPR paper is extremely poor and doesn't deserve the attention it gets.

I think you would struggle to find a modern physicist who would support Einstein in this respect. And see the EPR paper as a viable starting point for a reworking of modern physics.

Another problem is that Einstein never provided any alternative to quantum theory. Just a quasi-religious belief that it must be incomplete. So, there is nothing to work on in any case.

Physics has moved on a long way since the EPR paper was published. You'd struggle to find any serious physicists who wants to turn the clock back to 1935 and abandon all the physics that has been developed since then on the basis of QM.

If Einstein was misguided in 1935, then perhaps that is forgivable. To promote the EPR paper in 2025 is something entirely different.

 

[sahashmi]

My answer is that Einstein, great physicist though he was, became hopelessly out of touch with quantum theory.

The EPR paper is extremely poor and doesn't deserve the attention it gets.

I think you would struggle to find a modern physicist who would support Einstein in this respect. And see the EPR paper as a viable starting point for a reworking of modern physics.

Another problem is that Einstein never provided any alternative to quantum theory. Just a quasi-religious belief that it must be incomplete. So, there is nothing to work on in any case.

Physics has moved on a long way since the EPR paper was published. You'd struggle to find any serious physicists who wants to turn the clock back to 1935 and abandon all the physics that has been developed since then on the basis of QM.

If Einstein was misguided in 1935, then perhaps that is forgivable. To promote the EPR paper in 2025 is something entirely different.

I think the EPR argument is a good one if it generates answers like this that merely re assert their opinionated conclusions without justifying it.

 

[Nugatory]

I clarified the simple Einsteinian argument of how a 100% prediction rate implies that something in reality is determining it.

That is a defensible proposition, and if we accept it then the EPR conclusion that quantum mechanics is incomplete (or that relativity is wrong) does follow.

However, what you've been doing in this thread and your previous threads is a proof by emphatic assertion that this proposition is incontrovertible truth. That is unproductive, so this thread has joined your earlier ones on the "closed" list.