Superdeterminism

[Heinera]

Sabine Hossenfelder has a new post on her blog Backreaction about Bell's theorem.

It appears she is investigating superdeterminism together with her postdoc. My take on superdeterminism is that it's simply not a scientific approach in the sense of Popper, since it's an idea that can never be falsified. It is also an argument that can be used to explain anything, not just local realism. Any phenomenon can be "explained" by the idea that it was superdetermined at the start of the universe. It's like claiming God created the earth 6 000 years ago.

"But what about the fossils?"

"Well, God obviously created those, as well."

Any objection can be met with "that's the way it was created 6 000 years ago." It will be a hopeless discussion.

[gill1109]

Sabine Hossenfelder has a new post on her blog Backreaction about Bell's theorem.

It appears she is investigating superdeterminism together with her postdoc. My take on superdeterminism is that it's simply not a scientific approach in the sense of Popper, since it's an idea that can never be falsified. It is also an argument that can be used to explain anything, not just local realism. Any phenomenon can be "explained" by the idea that it was superdetermined at the start of the universe. It's like claiming God created the earth 6 000 years ago.

"But what about the fossils?"

"Well, God obviously created those, as well."

Any objection can be met with "that's the way it was created 6 000 years ago." It will be a hopeless discussion.

I tend to agree with you, Heinera. But Louis Vervoort, whom she cites, is an interesting "meta-physicist". And she has Gerard 't Hooft on her side too. And then there is our friend on this forum, Jarek Duda, who swears that physics is time-reversible and deterministic and that there is no measurement problem and everything is solved by maximum entropy random walk.

[Jarek]

What is the difference between superdeterminism and just determinism?
Like in Lagrangian mechanics we use from QFT to GR: values and derivatives in a given moment would, at least in theory, allow to evolve the solution as far as we want thanks to Euler-Lagrange equation - is e.g. general relativity superdeterministic or only deterministic?

[Heinera]

What is the difference between superdeterminism and just determinism?

In the context of Bell's theorem (which I guess is the only place where "superdeterminism" is used):

Determinism: Everything is determined by the initial conditions of the universe (much like a pseudorandom number generator)

Superdeterminism: The initial conditions are such that Bell's theorem will always appear to be violated in experiments. In other words, both the detector settings and the hidden variable are jointly determined in such a way that we always see the quantum correlations.

[Jarek]

So superdeterminism sounds like that the initial conditions were maliciously chosen having in mind all these human physicists testing Bell inequality?

I disagree with such anthropocentric view, this violation is more intrinsic - there is Born rule at heart of all wavefunction collapses (e.g. ions choosing parallel or anti-parallel alignment in strong magnetic field of pulsar like in Stern-Gerlach) , which has squares disagreeing with standard probabilitsitcs used to derive given inequality. And this square is already there in "just determinism" - if only accepting time/CPT symmetry of deterministic models we use.

[Heinera]

So superdeterminism sounds like that the initial conditions were maliciously chosen having in mind all these human physicists testing Bell inequality?

Yes, exactly.

[Jarek]

So what happens when there is no human physicist around?
E.g. in this natural Stern-Gerlach: ions in strong magnetic field of pulsar having to choose parallel or anti-parallel alignment - does they use the problematic square from Born rule in this choice?
Or photons in quite analogous Malus law?

[minkwe]

So what happens when there is no human physicist around?
E.g. in this natural Stern-Gerlach: ions in strong magnetic field of pulsar having to choose parallel or anti-parallel alignment - does they use the problematic square from Born rule in this choice?
Or photons in quite analogous Malus law?

Obviously, neither of you actually read Sabine's article.

[minkwe]

If we are going to make any progress in understanding this Bell mess, we have to be more precise and less hand-wavy in our discussions. Most often, words are selected to describe concepts that don't really fit the word, then people object to specific words based on their own limited understanding of what the word might mean without a careful understanding of what really is being talked about. "Superdeterminism" is one of the culprits/scapegoats but it really is not more/less scientific than any of the other words associated with Bell such as "non-locality", "non-realism", etc.

For the EPRB experiment we have three "correlation" quantities.





From which Bell derives an inequality



Relying on the assumption that .

Experimentally, for the purposes of comparing with the inequality, we can measure



for which we implicitly assume that



for a large enough number of measurements. Since measurements are always countable, we have





Where, , and therefore, not only do we carry forward Bell's assumption that , we now have a distinct an even stronger assumption that , since it is possible and likely for to be true and to be false. Experimentally, are disjoint but even if the sets are not exactly the same, probability distributions may be so similar that you should still have and thus obtain almost the same expectation values as if they were equal.

Realism is the idea that three ensembles originate from the same sample space implying that . Experimentally, the only way an experimenter can enforce this, is to measure the three averages simultaneously on the same set of particle pairs -- a practical impossibility. Note that this understanding of realism, does not translate to mystical notions of the moon not being there when nobody is looking, or fanciful notions of whether particles have properties before measurement. Also, note that, it is abject stupidity to claim to have ruled out realism on the basis of Bell's theorem, if you did not perform all your measurements on the same set of particle pairs at the same time.

Locality is the idea that Bell's outcome functions A(., .), and B(.,.) generate the the outcomes based only on inputs from within the light-cone of each experimental station. Imagine a process producing the ensembles

.

These ensembles are now dependent on the settings, thus effectively converting Bell's outcome functions from to . This is the form most commonly associated with non-locality. By placing the stations far apart and carefully timing the measurements, the only way for Alice's setting to influence Bob's outcome is by non-local transmission of the setting to the other side. It begs the question then, why can't we transmit information this way? Anyway, the main result is that the ensembles are different, contrary to Bell's key assumption. "Backward-causation", "instantaneous" communication, and "non-locality" are slight variations of the same thing.

Contextuality is not very different from the locality case either. Except we now have the ensembles:

.

Which is saying, in order to measure those outcomes, we need three distinct and incompatible experimental preparations (contexts), and therefore we end up with ensembles that are necessarily different. Isn't this in fact what is done in EPRB experiments? Note that preparation involves not just the things you do before the experiment, but must include everything, including setup and post-selection of the data used directly in calculating the averages. Therefore, the mere act of selecting subsets of data based on what settings were used on both sides, makes the resulting post-selected data statistically dependent on the settings on both sides. Hess, De Raedt, Accardi and others argue that when measuring on different sets of particles at different times, it is natural to expect differences in context that are angle dependent.

Superdeterminism is the idea that Alice and Bob, when performing an EPRB experiment do not have the freedom to make . In other words, it is impossible to eliminate the statistical dependence between and , etc that result in different ensembles. Note that superdeterminism says nothing about the experimenter's free-will to pick specific settings at specific times. It simply says, no matter what they can do freely, don't have the freedom to make the ensembles statistically independent of the context.

To conclude, note that everything centers whether the ensembles are the same or not. Even loopholes are mechanisms for introducing context-dependent (settings dependent) differences between the ensembles. For example detection loophole: some particle pairs are less likely to be detected at certain angles than others; coincidence loophole: the likelihood of matching a pair varies with angle difference.

This is why I think some key aspects of this article (https://doi.org/10.1103/PhysRevA.57.3304) have been overlooked even by the authors themselves.

[Heinera]

I'm happy to see that your understanding of Bell's theorem has improved considerably over the years I have been a member of this forum.

From "it's wrong" to "there are a lot of loopholes".

My own take on the loopholes is that they have either been disproved experimentally, and the rest (like superdeterminism) are beyond experimental falsification. And that it is anyway not a satisfying approach trying to save local realism at any price by introducing something that is even more far-fetched than QM, while at the same time making no new predictions.

[gill1109]

I'm happy to see that your understanding of Bell's theorem has improved considerably over the years I have been a member of this forum.

From "it's wrong" to "there are a lot of loopholes".

My own take on the loopholes is that they have either been disproved experimentally, and the rest (like superdeterminism) are beyond experimental falsification. And that it is anyway not a satisfying approach trying to save local realism at any price by introducing something that is even more far-fetched than QM, while at the same time making no new predictions.

Indeed. The "experimental" loopholes have all been made irrelevant by rigorous experimental design, including fast randomisation of choices of measurement settings. What remains are "metaphysical" loopholes. You can always argue that the mere fact that the experiment was going to be done, and the setting choices that the experimenter thought they were "freely" making, were all predetermined at the time of the big bang, hence any correlations whatever are possible. Now you have a hard job in explaining why we Alice can't see, from her measurement outcomes, what measurement choices Bob is making, and vice versa. If everything is so delicately pre-determined why is it so delicately-determined to make it *appear to us* that outcomes at Alice's place are random and not dependent on settings at Bob's place? When that is actually not the case, because actually, Bob's setting choices were predetermined and therefore in principle "known in advance" at Alice's place.

Well, people who take this point of view (such as Gerard 't Hooft) so far did not succeed in reconstructing very much of modern physics, let alone unifying quantum theory and general relativity. I think the reason that there is no success in this venture is because the people who work in quantum gravity are incapable of understanding that there are pretty fundamental barriers to unifying the two theories. If the geometry of space-time is determined by the distribution of mass yet that distribution does not exist till small bits of mass have interactions with other bits far away, and waves collapse and become particles, you have a big, big problem. You want to unify two theories which do not share any common ground at all.

PS, there is only one author of https://journals.aps.org/pra/abstract/10.1103/PhysRevA.57.3304, I don't know why Michel referred to "authors". Maybe just a typo?

[minkwe]

I'm happy to see that your understanding of Bell's theorem has improved considerably over the years I have been a member of this forum.

My understanding of Bell's theorem hasn't changed. And neither has your smugness. You just haven't been listening all this while. You are welcome to go back and try to find any of my posts that diverge from anything I'm saying now. Given that you lack any understanding of Bell's theorem, your opinion on this matter is worthless. I discuss every day with people I disagree with but never never have disliked engaging anyone in a conversation as much as I do you.

[minkwe]

PS, there is only one author of https://journals.aps.org/pra/abstract/10.1103/PhysRevA.57.3304, I don't know why Michel referred to "authors". Maybe just a typo?

I cited the wrong article. I meant this one: https://iopscience.iop.org/article/10.1 ... 04-10124-7

[minkwe]

From "it's wrong" to "there are a lot of loopholes".

Hopefully you are not ascribing that erroneous description to me because I was starting to have hope. Can we please for once have a nuanced discussion these issues?! Just because I understand in detail what Bell's theorem is all about and can boil it down to its essential features does not mean I agree with it. Come on guys are you really that shallow?

My own take on the loopholes is that they have either been disproved experimentally, and the rest (like superdeterminism) are beyond experimental falsification.

Like I mentioned, the ultimate issue is that we make sure the ensembles are the same in order to draw the conclusions Bell draws. This is the ultimate lacuna. All the loopholes are symptoms of the deeper problem of disjoint ensembles. Detection loophole, coincidence loophole, memory loophole, "new undiscovered loophole", etc., are all symptoms of this one issue. Once you start asking the question -- How did the experimenters in those experiments ensure that the ensembles would be the same? you start to realize they didn't, and all they accomplished was add duct-tape to "fix" superficial issues, without addressing the main issue.

And that it is anyway not a satisfying approach trying to save local realism at any price by introducing something that is even more far-fetched than QM, while at the same time making no new predictions.

Realism does not need saving, nor does locality. What needs saving is Bell's theorem. The "realism" that is relied on in Bell's theorem -- ie, the assumption that the outcomes A, B, C are random variables from the same sample space, is false in the EPRB experiment by default, since the experiment is actually three separate sample spaces ( or 4 in the case of CHSH). You don't need Bell's theorem to determine this, this is already a fact of the experiment. To save Bell's theorem, you have to demonstrate that the separate sample spaces are really a single one.

But if by "realism" you are thinking about whether particles have properties before measurement, or whether the moon exists when nobody is looking, then sorry, Bell's theorem says absolutely nothing about that.

The "experimental" loopholes have all been made irrelevant by rigorous experimental design

,
I disagree, experimenters have become more skilled at generating different ensembles in ways that are not obvious. See my discussion above about loopholes. Did you know that more than 100 years ago, Boole worked directly on this problem? His main goal was to find a way to tell if outcomes originated from the same experiment (cf sample space) or not. That's how he derived Boole's conditions of possible experience, which to him meant the random variables or experimental outcomes must obey those rules, if they originate from the same sample space/experiment. Boole's inequalities are exactly the inequalities rediscovered by Bell many years later. So-called violations of Bell's inequality are simply confirming to us what we should already know, that the ensembles are different, that the random variables do not originate from the same sample space, which we should already know from the experimental design. The reason https://iopscience.iop.org/article/10.1 ... 04-10124-7 is important is because the authors demonstrate how the inequalities change as the ensembles deviate from being equal. I'm sure you know this . Unfortunately, you've been asking the wrong questions. The issue is not which loophole was closed in what experiment, but what mechanisms are present in the experiment to ensure that the ensembles would be the same. Simply generating settings randomly is not sufficient, as the settings do not generate the outcomes all by themselves. (see this thread viewtopic.php?f=6&t=181 for a discussion of why randomness does not work) In fact, most experimenters in the field are not even knowledgeable about these issues, and rely on sometimes questionable advice from those who should know better.

You can always argue that the mere fact that the experiment was going to be done, and the setting choices that the experimenter thought they were "freely" making, were all predetermined at the time of the big bang

You misunderstand superdeterminism, so it is difficult to engage here.

Now you have a hard job in explaining why we Alice can't see, from her measurement outcomes, what measurement choices Bob is making, and vice versa.

Perhaps you should explain why Bob can't send superluminal or backward in time messages to Alice and vice versa, based on your understanding of Bell's theorem. What is your understanding of how the differences in the ensembles originate? Please be precise and not hand-wavy about your answer.

If everything is so delicately pre-determined why is it so delicately-determined to make it *appear to us* that outcomes at Alice's place are random and not dependent on settings at Bob's place? When that is actually not the case, because actually, Bob's setting choices were predetermined and therefore in principle "known in advance" at Alice's place.

[Heinera]

The first three passages you cited were mine, not Richard's. See if you can still edit your post to correct it. (But it's not a big deal since we agree on these things)

[Jarek]

Fresh post, now with arxiv:
https://backreaction.blogspot.com/2019/ ... -take.html
https://arxiv.org/pdf/1912.06462

I agree with superdetermism, but how the initial state of the Universe could be already prepared for all future measurnments????

Sounds radical ... unless we remind that nearly all physics we successfully use have time/CPT symmetry: unitary evolution, or using Lagrangian formalism (from QCD to GR).

For example Lagrangian formalism has equivalent formulation through the least action principle - e.g. that the history of the universe is action optimization result of fixing state e.g. in Big Bang in the past, and Big Crunch in the future.

Assuming history of the Universe was chosen in such time/CPT symmetric way, switching to mathematically equivalent Euler-Lagrange forward in time evolution, its state was chosen also accordingly to all future measurements - superdeterminism.

[Joy Christian]

***
I am not sympathetic to superdeterminism. Not only is it unnecessary for understanding the strong or quantum correlations, but it is also a fundamentally misguided idea.

For the enterprise of physics to have meaning, it is essential that the experimenters have complete, unadulterated freedom of choice in choosing whatever experimental parameters they wish to choose for performing their experiments. If that freedom of choice is compromised in some way, or predetermined by the initial conditions of the Universe, thereby depriving the experimenters of their "free will" in making last-minute changes in their choices, then there is no point in doing physics. Because then the results of our experiments are predetermined before we even conceive an idea of performing the experiment. That would attribute the Universe a "divine" power to know beforehand that we are going to make a last-minute change in the choices of our experimental parameters even before we come to know our wish to make such a change.

***

[Jarek]

So QM is only relevant in presence of (human?) experimenter having "free will"?
Such condition restricts its applicability to practically negligible part of space and time of the history of the universe - how do e.g. atoms work outside applicability of this condition?

And where exactly is the source of our "free will"? Pineal gland?
We can decompose brain function into exchanges of neurotransmitters etc. - do some of them have "free will"?

[Joy Christian]

So QM is only relevant in presence of (human?) experimenter having "free will"?

No, that is not what I have written. QM, or any physical theory, has nothing to do with this. The issue is about the experimenters' ability to freely choose whatever parameters they wish to choose for their experiments and be able to change their minds about them at the very last minute without any "divine" intervention.

And where exactly is the source of our "free will"?

That too is an irrelevant question for the issue at hand. The issue is about the freedom of choice experimenters must have to make their measurements, not its source.

***

[Jarek]

The experimenter is made of the same atoms, governed by the same physics - I just don't understand what is so special about him or his "free will"?

We have two separate perspectives here, which are not exclusive:
- from perspective of physics, it just evolves its state of the universe using e.g. Euler-Lagrange equations (from QFT to GR) - no "objective free will",
- but from perspective of experimenter, he doesn't have this complete information, hence can make decisions which from his incomplete information perspective used his (subjective) "free will" ... but decomposing functions of his brain into single neural impulses, unless pointing some way of going around physics for "objective free will", these decisions are just results of current situation and structure of neural network (being a result of personal history).

For superdeteminism we just have to accept time/CPT symmetry (which is at heart of all physics we use) - that history of the universe was chosen e.g. by the least action principle, then going to equivalent Euler-Lagrange equations, its state was chosen also accordingly to all future measurements ... and all decisions of made of atoms human experimenters: who from their perspectives used (subjective) "free will".