Superdeterminism and the Mermin Device

[PeterDonis]

I didn't mean that you are wrong but the statements by @RUTA . We had extended discussions about this repeatedly!

Can you give any links to threads/posts?

 

[Lord Jestocost]

"Impart quantum spin" is too narrow; it should be "exchange angular momentum". Quantum spin can be inter-converted with other forms of angular momentum.

I would be interested in seeing any references in the literature to analyses of measurement interactions that address this question.

To my mind, you find some thoughts on MathPages in the article “On Cumulative Results of Quantum Measurements”.
https://www.mathpages.com/home/kmath419/kmath419.htm

 

[vanhees71]

Here's the most detailed discussion about this misleading statements on angular-momentum conservation in QT of mine I could find, using the search function:

https://www.physicsforums.com/threa...elers-1986-paper-comments.952665/post-6056948

 

[RUTA]

How do you know? You're not measuring the exchange of angular momentum with the environment. That doesn't mean you can assume it doesn't happen. It means you don't know.

The Bell spin states are chosen to model conserved spin angular momentum. It's totally analogous to having an astronaut throw her flashlight in outer space so that conservation of momentum makes her move toward her spaceship. You write $\vec{P}_{astronaut} + \vec{P}_{flashlight} = 0$. Of course if you wanted to confirm this you'd have to make measurements and that would introduce experimental uncertainty because momentum would be lost relative to the equation. But, that is not conveyed in the equation itself.

 

[PeterDonis]

To my mind, you find some thoughts on MathPages in the article “On Cumulative Results of Quantum Measurements”.
https://www.mathpages.com/home/kmath419/kmath419.htm

This article doesn't talk at all about what I was talking about, namely, the exchange of conserved quantities (such as angular momentum) between measured systems and measuring devices (and environments).

 

[PeterDonis]

The Bell spin states are chosen to model conserved spin angular momentum if you ignore any exchange of angular momentum between the measured systems and measuring devices and environments, and if you ignore that spin angular momentum is not the same as total angular momentum.

See the bolded qualifier I added. My point is that you can't ignore what is being ignored in the definition of the Bell spin states, if you are going to make claims about conservation laws. Conservation laws don't apply to open systems in isolation. They also don't apply to particular pieces of a conserved quantity in isolation. Spin angular momentum is not conserved by itself; only total angular momentum is conserved. But only spin angular momentum of the measured particles is captured in the mathematical model using Bell states.

 

[RUTA]

I didn't mean that you are wrong but the statements by @RUTA . We had extended discussions about this repeatedly!

And as I explained to you in those discussions, everything I am saying follows mathematically from the Bell states. There is absolutely nothing wrong with my statements. That's why it's been published numerous times in various contexts now. I have no idea what confuses you about it, so I can't help you there. Sorry.

 

[PeterDonis]

everything I am saying follows mathematically from the Bell states

Only if you assume that angular momentum conservation can be applied to the combined spin angular momentum of the measured systems taken in isolation, even though they are open systems during measurement and even though spin angular momentum is not conserved separately. But that assumption is false.

 

[RUTA]

See the bolded qualifier I added. My point is that you can't ignore what is being ignored in the definition of the Bell spin states, if you are going to make claims about conservation laws. Conservation laws don't apply to open systems in isolation. They also don't apply to particular pieces of a conserved quantity in isolation. Spin angular momentum is not conserved by itself; only total angular momentum is conserved. But only spin angular momentum of the measured particles is captured in the mathematical model using Bell states.

The bolded statement is exactly correct, assuming no losses to the measurement device. Such losses would vary from situation to situation even though the source of spin-entangled particles was the same in every experimental arrangement. Therefore, the Bell spin states certainly do not attempt to capture such losses, as they are not written in a form where one can enter specific experimental details.

 

[RUTA]

Only if you assume that angular momentum conservation can be applied to the combined spin angular momentum of the measured systems taken in isolation, even though they are open systems during measurement and even though spin angular momentum is not conserved separately. But that assumption is false.

See post #114

 

[PeterDonis]

the Bell spin states certainly do not attempt to capture such losses

Which means you cannot use them as a basis for claims about conservation laws.

Such losses would vary from situation to situation

This is much too vague. I would say that the exchange of angular momentum between the measured particle and the measuring device would vary based on the orientation of the measuring device. Which is precisely the kind of variation that could maintain conservation of total angular momentum in cases where the two entangled particles have their spins measured in different orientations.

 

[RUTA]

Which means you cannot use them as a basis for claims about conservation laws.

Is that what you would say about the astronaut?

This is much too vague. I would say that the exchange of angular momentum between the measured particle and the measuring device would vary based on the orientation of the measuring device. Which is precisely the kind of variation that could maintain conservation of total angular momentum in cases where the two entangled particles have their spins measured in different orientations.

Now it looks like you want to invoke counterfactual definiteness for the particles' spins (like Alice and Bob in my story). The reason I do that is precisely to show how it differs from the QM prediction of $\pm 1$ at all angles. How would your explanation account for the $\pm 1$ prediction at all angles, given it is supposedly accounting for transfer to the environment, which would certainly vary with angle.

 

[PeterDonis]

Is that what you would say about the astronaut?

What astronaut?

Now it looks like you want to invoke counterfactual definiteness for the particles' spins

I don't know where you are getting that from. I am only talking about the spin measurement results that are actually observed, not about any counterfactual ones.

How would your explanation account for the $\pm 1$ prediction at all angles

The $\pm 1$ prediction at all angles means that the net angular momentum exchange between the measured particles and the measuring devices (i.e., the vector sum of the exchanges from both measurements) must vary by angle (more precisely, by the difference in angle between the two measurements) if total angular momentum is to be conserved. (Note that the angular momentum that is exchanged does not have to be spin; it can be orbital, since what needs to be conserved is total angular momentum, not spin alone.) And that is what we would expect since we expect the angular momentum vector describing the exchange in each individual measurement to vary with the orientation of the measuring device.

 

[DrChinese]

So we do need to find a valid theory that works. Sean Carrol advocates for the “many worlds” interpretation. ... But I have to believe that, since there are legitimate scientists who believe SD is a possible reality, that it is a least POSSIBLE a theory can be developed. It just seems odd that most of the arguments I have read by Physicists against SD are emotional opinionated arguments dealing with free will, and “many worlds” is considered over SD as a better alternative, but Bell recognizing SD as a possible loophole to his theorem. Did he just not think it through before he made that statement? Is there something in the points that you make above the John Bell was not aware of? Specifically something that has been discovered after Bell that invalidates his claim?

1. I won't defend MWI, you can see the reasoning in favor of it in papers about it. I think an honest assessment will admit it is viable, and as best I understand it there is no net creation of matter/energy involved regardless of the number of worlds. But I could be wrong.2. I am not sure what you mean about "emotional arguments", but for SD to work as a local realistic solution:

There must be a locally accessible "master plan" particle/field/property/object that instructs each quantum interaction how to act (i.e. to provide the outcome of every measurement). This master plan would have object copies in every region of space (to be local), and must provide "answers" (measurement outcomes) for at least 13.8 billion years of history of particles/energy being created/destroyed/transformed, etc. And it must do so in a manner so that the "true" quantum statistics (to explain Bell's result) are hidden from inquiring human experimentalists investigating Quantum Theory, which provides an accurate prediction of the observed statistics.

Really, I don't know where one starts to develop this from "handwaving speculation" to a credible hypothesis or theory. But I guess it is "possible" someone might do so in the future, in which case we would have something to critique (or perhaps test, although that is not really a requirement for an interpretation). As it is now, SD is impossible to critique precisely because its supporters give it such amazing elements/powers - of course constructed on the fly - that no criticism can topple it. This is no different than invoking the existence of an omniscient omnipotent deity, by the way. 3. Bell was not a believer in Superdeterminism. Like most, he threw that out to demonstrate how far you would need to go to keep local realism (post Bell's Theorem). He didn't need to come up with any details, leaving it to the audience to draw their own conclusions. (He could just as easily have invoked the above deity making the same decisions.)

Bell (1985ish): "There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be."

Unsaid: what created the original map (master plan); and how did it calculate, store and hide all of the future outcomes? How does an entangled particle know how to read the map so it can acquire the proper spin (when spin correlations are being studied in a lab)?

 

[StevieTNZ]

What astronaut?

https://www.physicsforums.com/threads/superdeterminism-and-the-mermin-device.1013414/post-6818631

 

[PeterDonis]

Is that what you would say about the astronaut?

In the case of the astronaut, the astronaut plus the flashlight is a closed system, at least as far as the astronaut throwing the flashlight is concerned. So I don't see the analogy with the case we are discussing.

 

[Jarvis323]

There must be a locally accessible "master plan" particle/field/property/object that instructs each quantum interaction how to act (i.e. to provide the outcome of every measurement). This master plan would have object copies in every region of space (to be local), and must provide "answers" (measurement outcomes) for at least 13.8 billion years of history of particles/energy being created/destroyed/transformed, etc. And it must do so in a manner so that the "true" quantum statistics (to explain Bell's result) are hidden from inquiring human experimentalists investigating Quantum Theory, which provides an accurate prediction of the observed statistics.

Do you have a more precise definition and argument that would clarify what you mean here?

 

[Jarvis323]

The issue, to me, seems to be a fundamental error in our conceptualization of the problem from the start.

We start with a classical picture and we use our intuition to derive settings which we assume QM ought or might be subject to. Then we wonder how our classical picture derives/emerges from QM.

Do quantum systems occupy the world that they create and then we observe? Or do they occupy a world that is unknown to us, and maybe we cannot obtain knowledge of? Or something else?

This issue, to me, makes the principle of locality suspect, or at least unclear to me, in the context of QM.

 

[gentzen]

The issue, to me, seems to be a fundamental error in our conceptualization of the problem from the start.

Which issue are you talking about? Superdeterminism?

Doesn't superdeterminism just repeat what happened with deBroglie-Bohm and MWI before? Both de Broglie's original proposal and Bohm's proposal had serious gaps or flaws, as did Everett's proposal. But the critics didn't bother to find the real flaws, or convince the proponents that those flaws should be fixed first. Instead, they tried to find reasons why they didn't need to spend time with those proposals in the first place. And the proponents were no better.

Even MWI is not yet sufficiently clarified, despite all the effort spent already. But at least Lev Vaidman is now making serious efforts to call the proponents to order, to explain the real flaws to them, and how (or why) he believes those can be fixed.

The proponents of deBroglie-Bohm started somewhat earlier trying to find and fix the real flaws, but they don't seem be finished yet. Of course, the critics believe that those flaws cannot be fixed anyway, and that the time spent trying to fix them is wasted, because who needs deBroglie-Bohm anyway?

On the positive side, the Copenhagen like (orthodox) interpretations are pretty well understood now. Things like consciousness-causes-collapse or superpositions between life-and-dead cats are no longer seriously discussed. So progress seems actually possible, but it goes incredibly slow.

As I showed in this Insight, the indeterminism we have in QM is unavoidable according to the relativity principle. And, yes, that means conservation of spin angular momentum is not exact when Alice and Bob are making different measurements. Conservation holds only on average (Bob saying Alice must average her results and Alice saying the same about Bob) when they make different measurements.

Maybe progress is also slow, because ... I don't know. A statement like "Conservation holds only on average" without further explanations is dangerous, and risks to create confusion. The consciousness-causes-collapse was also fueled by such dangerous statement, from London and Bauer, and maybe also from von Neumann. Their statements were not wrong, but only potentially misleading and dangerous first, before people like Henry Stapp turned them into actually wrong claims, and then charlatans exploited them to make money and spread even more confusion.

 

[RUTA]

The $\pm 1$ prediction at all angles means that the net angular momentum exchange between the measured particles and the measuring devices (i.e., the vector sum of the exchanges from both measurements) must vary by angle (more precisely, by the difference in angle between the two measurements) if total angular momentum is to be conserved. (Note that the angular momentum that is exchanged does not have to be spin; it can be orbital, since what needs to be conserved is total angular momentum, not spin alone.) And that is what we would expect since we expect the angular momentum vector describing the exchange in each individual measurement to vary with the orientation of the measuring device.

Alice and Bob obtain the same physical outcomes $\pm 1$ at all angles. When they happen to make a measurement at the same angle, they always get the same result, both get +1 or both get -1, per conservation of spin angular momentum. Now suppose in trial 1, Alice and Bob measured at the same angle and both obtained +1. In trial 2 Bob changed to $\theta$ wrt to Alice who got +1 and he got +1. In trial 3, they did the same measurements as in trial 2 with Alice getting +1 and Bob getting -1. How does conservation of spin angular momentum per the Bell states account for trials 2 and 3?

My answer to that question is just the standard understanding of QM. That is, classically speaking, if our source is producing a pair of particles with equal and aligned angular momenta in some direction (magnitude +1) and Alice measures +1 and Bob measures in the same direction as Alice, he will get +1. If Bob measures at $\theta$ relative to Alice when she gets +1, then of course Bob will measure $\cos{\theta}$. All of that is in accord with conservation of angular momentum. Since QM results typically average to what is expected from classical physics, it's no surprise at all (at least for me and the referees of our papers) that QM predicts Bob's $\pm 1$ outcomes will average to $\cos{\theta}$ in those trials when Alice measured +1, per conservation of angular momentum. Ditto in reverse.

What's your answer?

 

[PeterDonis]

What's your answer?

I've already given my answer several times: you are only evaluating conservation of angular momentum using the measured particles. But the measured particles are not a closed system. So you should not expect angular momentum to always be conserved if you only look at the measured particles. So the fact that you find that it isn't is not a problem.

The correlations between Bob's and Alice's measurements are explained by the entangled states that you prepared them in. I am not saying that the prepared states are not the states you use in your model. Of course they are. And those prepared states are sufficient to account for the measurement results. So I don't know what you are asking me to answer with regard to how the measurement results are to be explained. "Standard QM" of course explains them just fine, and I have not said otherwise.

The claim you are making, however, goes beyond using the prepared state to explain the measurement results. Your claim is basically this: the two-particle system is prepared in an eigenstate of total angular momentum (parallel spin and zero orbital angular momentum--the latter is not explicitly specified, but is implicit in your model). But conservation of angular momentum then requires that the two-particle system stays in that eigenstate after measurement--and this is not what we observe in cases where Alice's and Bob's measurement angles for spin are different. So conservation of angular momentum must be violated in those cases; all we have is "average conservation" over many trials.

My response to this is that your claim is based on a false premise. It is not true that the two-particle system must stay in the eigenstate of angular momentum in which it was prepared, after the measurement. The system interacts with measuring devices, and this interaction can exchange angular momentum between the system and the measuring devices (and their environments). So it is not valid to argue that angular momentum is not conserved on the basis that, when Alice's and Bob's measurement angles are different, the two-particle system does not end up in the same eigenstate of angular momentum in which it started.

Nothing you have said responds to this argument.

 

[RUTA]

I've already given my answer several times: you are only evaluating conservation of angular momentum using the measured particles. But the measured particles are not a closed system. So you should not expect angular momentum to always be conserved if you only look at the measured particles. So the fact that you find that it isn't is not a problem.

If it's not conserved, where is it going on a trial-by-trial basis? And why does it not disappear when they make the same measurement? Where is that information in the wave function? How could it possibly be in the wave function, since you're talking about any number of possible measurement techniques? You're being way too vague here. Again, the physical measurement outcome is always the same, there is no variation in the amplitude of the outcome as Bob and Alice rotate their SG magnets. You haven't addressed that issue at all.

You can do the same thing with polarizers and photons. When you send a single vertically polarized photon through a polarizer at 45 deg, either it passes or it doesn't, but classically we're supposed to get 1/2 a photon. It's quantum, so half photons don't exist. That's why we have average-only transfer of momentum. It has nothing to do measurement devices per se, average-only conservation (for entangled photon pairs) is all about discrete (average only) versus continuous (exact) outcomes.

The correlations between Bob's and Alice's measurements are explained by the entangled states that you prepared them in. I am not saying that the prepared states are not the states you use in your model. Of course they are. And those prepared states are sufficient to account for the measurement results. So I don't know what you are asking me to answer with regard to how the measurement results are to be explained. "Standard QM" of course explains them just fine, and I have not said otherwise.

Then you should have no concern at all with what I said. But, for some reason, you think what I'm saying is crazy or wrong. I'm simply pointing out the QM facts.

The claim you are making, however, goes beyond using the prepared state to explain the measurement results. Your claim is basically this: the two-particle system is prepared in an eigenstate of total angular momentum (parallel spin and zero orbital angular momentum--the latter is not explicitly specified, but is implicit in your model). But conservation of angular momentum then requires that the two-particle system stays in that eigenstate after measurement--and this is not what we observe in cases where Alice's and Bob's measurement angles for spin are different. So conservation of angular momentum must be violated in those cases; all we have is "average conservation" over many trials.

A measurement destroys the Bell state regardless of whether or not they measure at the same angle. I don't know what you're trying to say here.

My response to this is that your claim is based on a false premise. It is not true that the two-particle system must stay in the eigenstate of angular momentum in which it was prepared, after the measurement. The system interacts with measuring devices, and this interaction can exchange angular momentum between the system and the measuring devices (and their environments). So it is not valid to argue that angular momentum is not conserved on the basis that, when Alice's and Bob's measurement angles are different, the two-particle system does not end up in the same eigenstate of angular momentum in which it started.

Nothing you have said responds to this argument.

Again, what do you mean "stays in the eigenstate in which it was prepared"? The state refers to any direction in the symmetry plane because it's rotationally invariant. Therefore, I can let Alice's direction be the direction of the Bell state or I can let it be Bob's. Who is measuring the "right" direction in your explanation?

 

[PeterDonis]

If it's not conserved, where is it going on a trial-by-trial basis? And why does it not disappear when they make the same measurement?

My answers are already implicit in what I've said before. I don't see the point of belaboring it.

I would, however, point out that you are looking at this backwards. The one making an extraordinary claim in this discussion is you, not me. Consequently, the burden of proof is on you to demonstrate that angular momentum is not conserved in the processes you described; it is not on me to show how it is conserved. And to meet that burden, it should be obvious that you cannot rely on a model that does not include all interactions involved that can exchange angular momentum. If you want to claim that angular momentum is not conserved in these measurements, you need to build a model that includes all the relevant interactions and shows how angular momentum is not conserved when they are all taken into account. You have not done that.

A measurement destroys the Bell state regardless of whether or not they measure at the same angle.

Yes, that is true. But you are basing your claim of non-conservation of angular momentum only on what happens when the angles are not the same. As far as I can tell, you are saying that angular momentum is conserved when the angles are the same.

what do you mean "stays in the eigenstate in which it was prepared"? The state refers to any direction in the symmetry plane because it's rotationally invariant.

Yes; that rotationally invariant state is the state that is prepared. Are you saying this state is not an eigenstate of angular momentum? If so, how can you possibly make any claim about angular momentum being conserved or not conserved, when it doesn't even start out with a well-defined value?

 

[PeterDonis]

I'm simply pointing out the QM facts.

"The QM facts" do not include a claim that angular momentum is not conserved. Only you are making that claim, not "standard QM".

Indeed, when we pass to quantum field theory as the basis for "standard QM", we find that QFT asserts that angular momentum is conserved, by Noether's theorem, as long as the Lagrangian is rotationally invariant--which it is for the cases you are discussing.

 

[Lord Jestocost]

This article doesn't talk at all about what I was talking about, namely, the exchange of conserved quantities (such as angular momentum) between measured systems and measuring devices (and environments).

"To see how this enters into the general quantum process, recall that in every measurement there is a degree of uncertainty depending on the precise manner in which the measurement is taken, i.e., the "basis" onto which we project the state vector to give the probabilities of the various possible discrete outcomes. The issue of conservation arises when we consider the interaction of two or more subsystems. The crucial point is that we're free to select the bases for our measurements of these various subsystems independently, and therefore the bases are not, in general, parallel. As a result, the exhibited behaviors of the subsystems will not, in general, be equal and opposite, and so each set of measurements represents a step in a random walk around the point of strict conservation...

...The hypothesis (confirmed in the case of simple EPRB situations) is that if we evaluate the expected net "residual" un-balanced sum of the predicted results of measurements of the particular quantity (e.g., momentum) uniformly over the space of possible interactions, the quantum mechanical predictions (among all possible joint distributions) yield the minimum possible net un-balance."

https://www.mathpages.com/home/kmath419/kmath419.htm

 

[vanhees71]

And as I explained to you in those discussions, everything I am saying follows mathematically from the Bell states. There is absolutely nothing wrong with my statements. That's why it's been published numerous times in various contexts now. I have no idea what confuses you about it, so I can't help you there. Sorry.

It's a misconception about the meaning of conservation laws on your side. The point is, as I tried to explain to you several times, that if you have prepared the singlet state of two spin-1/2 spins and you measure the angular-momentum components in non-collinear directions, you cannot say more concerning angular-momentum conservation than the probabilities for getting each of the four possible outcomes since all that angular-momentum conservation tells you is that spin components when measured in the same direction are always opposite to each other, given the preparation of the two spins in the spin-singlet state. Analogous statements of course also hold when you have prepared the system in one of the three spin-1 states.

It's also clear that when the system interacts with something else ("the environment"), i.e., when you have the system as an open system, then angular momentum can be exchanged with the environment, and the angular momentum of the system under consideration needs not to be conserved. That's the same as in classical mechanics.

 

[akvadrako]

This article doesn't talk at all about what I was talking about, namely, the exchange of conserved quantities (such as angular momentum) between measured systems and measuring devices (and environments).

This seems relevant: https://arxiv.org/pdf/2108.08342.pdf

Because the apparatus has an enormous number of
degrees of freedom relative to the measured system, even a very tiny difference
between the apparatus states that are correlated with the orthogonal states of
the measured system can be sufficient to account for the perceived deviation
from strict conservation of the quantity in question. Hence measurements need
not violate conservation laws.

 

[RUTA]

No one here has shown me how the Bell states account for the missing conserved quantities per this "open system" explanation of entanglement (via classical thinking) only when Alice and Bob make different measurements. On the other hand, I can explain exactly how the Bell states map to conventional quantum-classical thinking when viewing them as pertaining to just the particles involved. PeterDonis said it is incumbent upon me to provide my explanation, but he has no such requirement to provide the details for his "open system" explanation (which I cannot follow at all). Here are the publications, posts, and videos containing or using our explanation.

Publications and Paper​

“Why the Tsirelson Bound? Bub’s Question and Fuchs’ Desideratum,” W.M. Stuckey, Michael Silberstein, Timothy McDevitt, and Ian Kohler. Entropy 21(7), 692 (2019).

“Re-Thinking the World with Neutral Monism: Removing the Boundaries Between Mind, Matter, and Spacetime,” Michael Silberstein and W.M. Stuckey. Entropy 22(5), 551 (2020).

“Answering Mermin’s Challenge with Conservation per No Preferred Reference Frame,”
W.M. Stuckey, Michael Silberstein, Timothy McDevitt, and T.D. Le. Scientific Reports 10, 15771 (2020).

“The Completeness of Quantum Mechanics and the Determinateness and Consistency of Intersubjective Experience: Wigner’s Friend and Delayed Choice,” Michael Silberstein and W.M. Stuckey. In Consciousness and Quantum Mechanics, edited by Shan Gao (Oxford University Press, 2022) 198–259.

“Beyond Causal Explanation: Einstein’s Principle Not Reichenbach’s,” Michael Silberstein, W.M. Stuckey, and Timothy McDevitt. Entropy 23(1), 114 (2021).

“Introducing Quantum Entanglement to First-Year Students: Resolving the Trilemma,” W.M. Stuckey, Timothy McDevitt, and Michael Silberstein.

“No Preferred Reference Frame at the Foundation of Quantum Mechanics,” W.M. Stuckey, Timothy McDevitt, and Michael Silberstein. Entropy 24(1), 12 (2022).

Posts​

“Einstein’s Missed Opportunity to Rid Us of ‘Spooky Actions at a Distance’,” W.M. Stuckey. Science X Dialogs (12 October 2020).

“Quantum Information Theorists Produce New ‘Understanding’ of Quantum Mechanics,”
W.M. Stuckey. Science X Dialogs (6 January 2022).

How Quantum Information Theorists Revealed the Relativity Principle at the Foundation of Quantum Mechanics

A Principle Explanation of the “Mysteries” of Modern Physics

Answering Mermin’s Challenge with the Relativity Principle

Exploring Bell States and Conservation of Spin Angular Momentum

The Unreasonable Effectiveness of the Popescu-Rohrlich Correlations

Why the Quantum | A Response to Wheeler’s 1986 Paper

Videos​

Beyond Causal Explanation: Einstein's Principle Not Reichenbach's

No Preferred Reference Frame in Quantum Mechanics (Non-technical)

No Preferred Reference Frame in Quantum Mechanics (Technical)

Making Sense of Quantum Mechanics per Its Information-Theoretic Reconstructions (invited talk at the Institute for Quantum Optics and Quantum Information in Vienna, April 2022).

Again, this explanation is straightforward and in perfect accord with textbook QM. In the photon polarizer example, classical physics says half the vertically polarized photon should pass through a polarizer at 45 deg. Since QM says the photon either passes or it doesn't, it is impossible to satisfy our classical model of a polarizing filter in that case, but on average, half of all photons do pass. So we see that QM satisfies classical expectations via average-only transmission. When that photon is one of a pair in a Bell state, that leads to average-only conservation of spin angular momentum (spin-1 in this case) when Alice and Bob are making different measurements.

This also maps to the key difference between classical probability theory and quantum probability theory per Information Invariance & Continuity. A classical bit (e.g., opening one of a pair of boxes to find a ball or not) has only discrete measurement options while a quantum bit has continuous measurement options (pure states connected via continuously reversible transformations). There are only the two boxes to open for the classical bit example yielding a ball or no ball, but the polarizer can be rotated continuously in space yielding pass or no pass in every direction.

So, everything I'm sharing on PF has been thoroughly vetted in the foundations community and agrees perfectly with conventional QM thinking (which violates classical thinking in this case). I'm doing my best to explain that here, but the reader must set aside their classical prejudices when dealing with QM in order to follow what I'm saying.

If those who are trying to explain the Bell states via "open systems" ever publish, post or otherwise provide the details, please send me a link via a Physics Forums Conversation. Now I have to get back to work ... on our corresponding book :-)

 

[DrChinese]

Do you have a more precise definition and argument that would clarify what you mean here?

LOL, you tell me! All I can figure out is:

- It's got to be local, by definition (that's the point after all). So the predetermined "answer" for say, an electron having its spin measured today: it must be able to consult that local object (which conceivably could be hidden inside the electron, making the electron a composite particle).

- It must also have something that says what its spin will be when measured tomorrow. And if it has existed since the big bang, then it needed instructions for 13.8 billion years of measurements (interactions).

 

[vanhees71]

There is no "missing conserved quantities". I don't know, how I should explain this very basic properties of QT. One last try: You have 100% correlation between the outcomes of measurements of the single-particle spin components if you measure the spin components on both particles in the same transition, and that's why you can prove "angular-momentum conservation" for this component by measurement, i.e., you know that your entangled spins are measured on two particles from a decay of a scalar particle, i.e., you know that the total spin of the system is in the singlet, $S=0$, state.

Measuring the single-particle spins in different directions you only have probabilities for the possible outcomes, and of course some correlation between these outcomes, but you cannot proof or disprove angular-momentum conservation with those measurements, because the correlations are not 100% anymore. That's at the heart of the entire issue of entanglement and also with the content of the Bell inequalities for local realistic HV theories being in contradiction to the predictions of QT.

 

[PeterDonis]

No one here has shown me how the Bell states account for the missing conserved quantities per this "open system" explanation of entanglement (via classical thinking) only when Alice and Bob make different measurements.

The Bell states don't account for it because they only describe the measured particles, not the measurement apparatus and its environment. In other words, the mathematical model consisting of the Bell states is simply inadequate to even analyze the question of whether angular momentum is conserved in Alice's and Bob's measurements, because it does not capture all of the physical systems involved in those measurements.

To even analyze conservation laws during measurements, you need to build a model that includes all of the physical systems involved, since the interactions between them can exchange conserved quantities. Surely this is obvious?

"open system" explanation (which I cannot follow at all)

I find this statement astounding. You cannot follow the simple fact that, during the measurements, the particles being measured interact with the measuring devices and their environments, and therefore are open systems (open systems being systems that are not isolated and interact with other systems), and that these interactions can exchange angular momentum?

 

[PeterDonis]

@Lord Jestocost your post #130 just confirms what I said in what you quoted there: the article you reference only talks about the measured systems, not about the measuring devices or their environments. But, as I have pointed out repeatedly now, since conserved quantities can be exchanged between measured systems and measuring devices and their environments during measurements, you cannot analyze conservation laws during measurements if you only look at the measured systems. The article you reference simply does not discuss that at all. I was asking for references to anywhere in the literature that does discuss it.

 

[Lord Jestocost]

I find this statement astounding. You cannot follow the simple fact that, during the measurements, the particles being measured interact with the measuring devices and their environments, and therefore are open systems (open systems being systems that are not isolated and interact with other systems), and that these interactions can exchange angular momentum?

In negative-result measurements, the result is obtained not through the occurrence of a physical event, as for a normal measurement, but by the absence of such an event.

 

[PeterDonis]

In negative-result measurements

Which are irrelevant to this discussion since no such measurements are involved in the experiments being discussed.

 

[.Scott]

I watched the video by Sabine Hossenfelder
https://www.physicsforums.com/insights/superdeterminism-and-the-mermin-device/

She concludes that explaining quantum statistics with superdeterminism avoids non-locality.
However, one of her main points is that SD does not subvert the common notion of "free will".

Personally, I have no problem with any relegation of free will. The tasking of the brain to find strategies that enhance our well-being includes an inherent presumption that our well-beings are capable of being enhanced. The illusion of free will is inherent in the sense of being purposeful. Such an illusion may or may not directly align with the Physics.

That said, she has not described a situation where superdeterminism is both local and does not subvert "free will".
The Bell inequality demonstrates that the two measurement mechanisms are not fully isolated. The isolation failure can occur from non-locality or from sharing a light cone. If it's from sharing the light cone, you are limited to the choice of the particle state causing the measurement direction (Oh My!) or something much broader - like tracing the light cones all the way back to the Big Bang and positing that an undiscovered pattern in Physics as a whole is aligning the measurements with the particle states.

From post #13 by @Demystifier , Sabine seems to favor the latter:

In her "Guide for the Perplexed", Sabine Hossenfelder writes:
"What does it mean to violate Statistical Independence? It means that fundamentally everything in the universe is connected with everything else, if subtly so. You may be tempted to ask where these connections come from, but the whole point of superdeterminism is that this is just how nature is. It’s one of the fundamental assumptions of the theory, or rather, you could say one drops the usual assumption that such connections are absent. The question for scientists to address is not why nature might choose to violate Statistical Independence, but merely whether the hypothesis that it is violated helps us to better describe observations."

Sign on the Gates to Fate: You abandon free will and enter here. (with apologies to Dante)

As best I can tell, SD is not a theory or even a selection of theories - but an interpretation. The ultimate values of one interpretation over another is what new experiments and question each interpretation promotes. Does on interpretation make some part of Physics easier to understand or explore?