High School Some questions about "superdeterminism" and Bell's Theorem

[stevendaryl]

So by local you mean not FTL (again) ?

I mean something stronger--that the result of a measurement is completely determined by facts in the region near where the measurement takes place. What sense of "non-local" do you mean?

 

[forcefield]

I mean something stronger--that the result of a measurement is completely determined by facts in the region near where the measurement takes place.

But your hidden variable was in terms of measurement results from distant regions...

What sense of "non-local" do you mean?

I mean not "local realism" as in Nick Herbert's proof. Why is that not a counter-example ?

 

[stevendaryl]

But your hidden variable was in terms of measurement results from distant regions...

No, they were in terms of Alice's and Bob's measurement choices, not their measurement results. Surely, there is nothing nonlocal about Alice deciding to always measure spin along the z-axis?

I mean not "local realism" as in Nick Herbert's proof. Why is that not a counter-example ?

I don't know Herbert's proof, but what I described is certainly locally-realistic theory in Bell's sense.

 

[ftr]

do not resemble a triangle

I just meant a triangle as an example of a mathematical structure and not literally a triangle.

 

[forcefield]

Surely, there is nothing nonlocal about Alice deciding to always measure spin along the z-axis?

Yes but when you combine that with what Bob decides you have a non-local source for your hidden variable. Also, consider the possibility that someone tells Alice and Bob what to do.

I'm not getting what you are trying to say. Do you have a valid reference ?

 

[stevendaryl]

Yes but when you combine that with what Bob decides you have a non-local source for your hidden variable. Also, consider the possibility that someone tells Alice and Bob what to do.

I'm saying that if both Bob's and Alice's choices are predictable, then there is no problem reproducing the predictions of QM for EPR. If you are computing the digits of pi, I don't need FTL signals to know what you're going to do, no matter how far away you are.

 

[DrChinese]

Also, consider the possibility that someone tells Alice and Bob what to do.

It is normal in any scientific experiment for the setup to be controlled (i.e. to tell Alice and Bob what to measure). There is nothing about a Bell test that makes "freedom of choice" a more significant issue than for any other experiment.

 

[ftr]

There is nothing about a Bell test that makes "freedom of choice" a more significant issue than for any other experiment

It seems to me stevendaryl is exactly saying the opposite.

 

[stevendaryl]

It seems to me stevendaryl is exactly saying the opposite.

I'm not arguing that there is any more reason to consider superdeterminism in EPR than in any other experiment. I'm just trying to explain why it is technically a loophole in Bell's argument. I'm not saying that it's a loophole that should be taken seriously.

 

[Jilang]

A Question if I may : Do Alice and Bob alter their settings for each measurement?

 

[Zafa Pi]

I think you misunderstood Andrei's point. As I pointed out, it's easy to come up with a local hidden-variables explanation for EPR if Alice's and Bob's measurement choices are predictable. He's saying that they actually may be predictable, in principle. That is a loophole in Bell's argument, but contrary to what Andrei says, there is no way to exploit this loophole to give a local explanation of EPR correlations without fine-tuning, conspiracies, etc.

I'm not convinced that @Demystifier misunderstood Andrei's point. Andrei is saying that they actually may be predictable by a particular mechanism and Demystifier is saying that mechanism is faulty. Andrei didn't say "in principle".

 

[Zafa Pi]

A Question if I may : Do Alice and Bob alter their settings for each measurement?

Possibly. Each has two possible settings, then each flips a coin to decide which option. Thus neither knows what option the other selected on a given trial. So with probability 1/4 two successive trials can have the same measurements for each party.

 

[penguin_surprise]

If we assume that
the universe is infinite (or at least is so large that light from the most distant regions have not yet reached us), and
the pattern of stars in the distant regions are unpredictable
then you can't have a superdeterministic theory of the type that would be needed to reproduce the predictions of QM for EPR without weird conspiracies.

On second thought I'm not so sure this argument goes through. My counterargument is probably wrong, but it seems like this assumes that it would actually be possible to freely choose that choice of experimental setup -- "They can decide which measurement to perform based on the number of new stars they discover in the time between the creation of the twin pair and their detection." This isn't necessarily the case, because we have superdeterminism and no CFD. The same thing by which the process used to generate measurement setting choices is correlated to the variable being measured (and predetermined) also means that the choice of measurement method is predetermined and correlated with the variable. The same thing responsible for the correlation between observed distant stars and the value being measured, and by which they must obey a certain pattern, means that Alice is not necessarily free to choose the method of using observations of distant stars to determine measurement settings in the first place. So it is not necessarily the case that this applies to any superdeterministic theory. And if we have a superdeterministic theory, if there's some type of measurement method that would have an undesirable, unintuitive, or maybe physically impossible effect, superdeterminism itself could be used to rule that out -- but that would qualify as a conspiracy itself. right?

Regardless your argument answers my question because the example of conspiracy you used makes it clear that before I was using a totally different (and incorrect) notion of what "conspiracy" meant, so thanks for the answer.

 

[penguin_surprise]

Finally rephrased what I was trying to ask; this question is for stevendaryl and/or anyone else who might be able to help: My misunderstanding of "conspiracy" was that the term referred to the fact that "superdeterminism" is formulated essentially to say the universe looks as if it conspires to deceive humans. What I wanted to ask about wasn't the existence of unnatural correlations caused by fine-tuning the initial conditions, but that this is only done when the result is that this would bias the result of Bell test experiments performed by conscious beings. This is what I was asking about.

Let's say we have a standard experimental setup, with entangled particles at a source, and Alice and Bob at distant locations measuring the spin with detectors with variable angles. Here was my question: is it accurate to say (as I've seen in arguments) that, under superdeterminism, for the universe in general, for a given pair of angle choices, the correlation between spins actually is some value, say 25%, that differs from the value which is observed in all Bell test experiments, say 40%. (This seems to be implied by saying, e.g. that the universe more or less "deceives us" to make us think QM is true.)

My question was that the impression I've gotten from arguments seems to be that there "could be" (in some sense... sort of... even though CFD doesn't hold?) choices of measurement which would not reproduce the predictions of QM, but that Alice and Bob choose in a way so that this doesn't happen, i.e. that more or less superdeterminism says QM appears to be true due to a systematic "sampling bias" (or at least that this is the way the loophole is typically argued for) so that we observe increasingly unlikely (as we perform more experiments) deviations from the norm. "Superdeterminism" seems to allow a loophole to experiments individually. Physics in general will not be the same as QM, it's just that our choices of experiments are such that this looks like the case. Is this impression of mine correct, or based on a misunderstanding or incorrect information?

Based on that impression, what I was asking was whether this has to be the case for "superdeterminism" or if it be made wider so it has less of a flavor of "the universe deceives us," or if for some statistical or physical reason or postulate, that can't be the case. My assumption is that it can't be.

Perhaps this question is still ill-formed because my understanding is still too lacking to ask such questions, and if that's the case I apologize. If anyone has suggestions for a good source for me to learn the physics and math involved, I'd be willing to do so and greatly appreciate it.

 

[penguin_surprise]

It is a possibility, but there is no point in believing in this possibility, because as you say:

So this possibility should be discarded on philosophical grounds as inconsistent with scientific approach.

Indeed. It's unscientific in several ways, actually:
1. Essentially says Nature is fine-tuned specifically so we get an incorrect picture of the world
2. Against the spirit of scientific enterprise due to being (imo) an ad-hoc hypothesis motivated by wanting to avoid hearing what Nature is very much trying to tell us
3. Superdeterminism in general (as opposed to some specific theory) probably cannot be falsified
4. The main part of it (i.e. except that it negates the derivation of Bell's inequality) is not unique to Bell test experiments at all and is a fully general counterargument to all scientific results, and there's no reason it'd more likely in this case. The logic applied generally would undermine all science.
5. There are no viable superdeterministic theories, no real progress towards creating one (unlike non-local hidden variable theories/interpretations of QM, indeterministic ones, etc. of which many good models have been fleshed out). In fact, it’s likely that one can’t be created at all.

Other things making it undesirable include:
1. Violation of the copernican principle
2. Creates a massive source of fine-tuning and a fine-tuning problem

And it has no benefit because:
1. Superdeterminism is ultimately vastly more pathological than indeterminism or non-locality
2. The part of QM that is intrinsically non-local-realist is the best part. Why throw it away?
3. AFAIK wouldn't even "save" local realism because there are other experiments superdeterminism wouldn't apply to

Those are all the objections I can think of. So there are a LOT of grounds to reject it that I can think of, and no doubt there are more.

 

[atyy]

I prefer to accept superdeterminism (as a theoretical possibility). There is no contradiction with accepting Copenhagen, Bohmian Mechanics and superdeterminism.

We can take Bohmian Mechanics as an effective theory of superdeterminism, and Copenhagen as an effective theory of Bohmian Mechanics.

 

[penguin_surprise]

I prefer to accept superdeterminism. There is no contradiction with accepting Copenhagen, Bohmian Mechanics and superdeterminism.

We can take Bohmian Mechanics as an effective theory of superdeterminism, and Copenhagen as an effectiv etheory of Bohmian Mechanics.

Thank you for responding. I've heard of the idea that the Bohm interpretation counts as "superdeterminist" under a certain technical definition, but that it avoids having to explain things using conspiracies and fine-tuning because it's non-local. That's what you mean you accept by saying superdeterminism, right?

I don't have any objections with that, personally; I was talking specifically about superdeterminism in local hidden variable theories and most of what I said was meant to apply only to those.

 

[atyy]

Thank you for responding. I've heard of the idea that the Bohm interpretation counts as "superdeterminist" under a certain technical definition, but that it avoids having to explain things using conspiracies and fine-tuning because it's non-local. That's what you mean you accept by saying superdeterminism, right?

I don't have any objections with that, personally; I was talking specifically about superdeterminism in local hidden variable theories and most of what I said was meant to apply only to those.

Well, let me take that back - I think what I said above is wrong. If Bohmian Mechanics were shown to be true under conditions of quantum nonequilibrium, then superdeterminism would be falsified.

 

[penguin_surprise]

I want to just try to phrase my question one more time (wish I could delete the old one). Here's an instance of the kind of argument I'm thinking of (just an example; I've seen many, many like this).

My question is, in what sense is it the case that there is a "true" value for correlations that observations are deviating from? What I mean is whether the experimental results caused by fine-tuning have to deviate from what typically happens in that universe (say, defining what typically happens by extrapolating to situations or interactions which are close to the conditions of, but don't totally match the experimental setup (since we're fine-tuning for specific results for all Bell test experiments, and don't have CFD) and aren't part of an experiment)? Is it that the universe definitely has behavior that doesn't fit QM and things are only being fine-tuned so that it is observed to look like QM when Bell test experiments are performed, in a biased sample of what's going on in the universe? (which could still have effects observable indirectly...) Or, instead, do the results of Bell test experiments deviate from the norm just in the sense that the observed behavior (matching QM predictions) is a result of the laws of physics only under very special initial conditions which are not representative of the "true," generic case for the local hidden variable theory with arbitrary initial conditions?

To put it succinctly, is superdeterminism an ad hoc contrivance saying "fine-tuning causes all the experiments we perform to get results making it look like QM is true," or is it / can it be one saying "under very special fine-tuned initial conditions the universe actually behaves like QM is true in a sense?"

If the former was the answer, I was also asking whether limiting the scope of the conspiratorial fine-tuning (i.e. just to fix results of Bell test experiments) is an essential part of the idea -- say, if for some reason trying to put in too much fine-tuning might cause a problem, and/or if, say, the universe overall can't behave too differently from the generic case. But the above is my main question.

I really hope this question is sufficiently concrete and clear about what I mean, and I would really appreciate it if someone could answer even briefly. ANY feedback would be greatly appreciated (even if it's just to say that my question makes no sense without explanation, that would be helpful. I hope what I'm saying isn't too crazy.)

 

[DrChinese]

My question is, in what sense is it the case that there is a "true" value for correlations that observations are deviating from? What I mean is whether the experimental results caused by fine-tuning have to deviate from what typically happens in that universe (say, defining what typically happens by extrapolating to situations or interactions which are close to the conditions of, but don't totally match the experimental setup (since we're fine-tuning for specific results for all Bell test experiments, and don't have CFD) and aren't part of an experiment)? ..
To put it succinctly, is superdeterminism an ad hoc contrivance saying "fine-tuning causes all the experiments we perform to get results making it look like QM is true," or is it ..."

That's a great question!

Let's call SD(theta) the "true" coincidence rate and QM(theta) the apparent (experimentally measured) coincidence rate for some group of entangled pairs. Let's assume QM(theta)=cos^2(theta) for angle difference of theta. Then QM(theta)-SD(theta) at various angles can be represented as Delta(theta).

Presumably, when theta=0, Delta(theta) is also 0. We also know that at 120 degrees, Delta(theta) must be at least .0833. After all, SD(theta) cannot be less than 1/3 and QM(theta) is 25%. So then the question becomes: how/why does nature conspire to yield a very specific difference at some angles, but no difference at other angles?

Personally, I find the concept of Delta(theta) very troubling. If it was off by a constant factor, that could make sense. But having this vary by angle seems implausible. In other words, we not only have a conspiracy to obscure the "true" coincidence rate; we also have one where the difference just happens to take us to the Bell (local realistic) limit.

 

[Nugatory]

This is too much fun, the monitors must be on the way. Being a solipsist perhaps I'll report myself.

At least one of them is having too much fun following this thread to interfere.
Although I'm wondering if I'm not observing a conspiracy among the participants to avoid drawing the mentors' attention to the thread ...

 

[Zafa Pi]

Well, let me take that back - I think what I said above is wrong. If Bohmian Mechanics were shown to be true under conditions of quantum nonequilibrium, then superdeterminism would be falsified.

I knew you would say that because I've seen a copy of the initial conditions at the big bang.

 

[Zafa Pi]

To put it succinctly, is superdeterminism an ad hoc contrivance saying "fine-tuning causes all the experiments we perform to get results making it look like QM is true,"

Are there really unicorns but SD constrains us to be always looking in the wrong direction making seem like they don't exist?

 

[DrChinese]

Are there really unicorns but SD constrains us to be always looking in the wrong direction making seem like they don't exist?

I see unicorns all the time, what are you talking about?

 

[Zafa Pi]

I see unicorns all the time, what are you talking about?

Ok, so I gave a bad example.
Perhaps I should have said: Does SD constrain us to respond to DrChinese in spite of his his actual non-existence.
I find this thread amazing, but I fear that someone will show it to Trump and he'll use as a excuse to defund all federal research in physics.

 

[DrChinese]

Does SD constrain us to respond to DrChinese in spite of his his actual non-existence.

Yes, I see unicorns. But because I don't exist, I can't point them out to others. That's why you don't see them.

 

[Zafa Pi]

Yes, I see unicorns. But because I don't exist, I can't point them out to others. That's why you don't see them.

I believe you have just adequately captured my position on superdeterminism. Thank you.

 

[OCR]

I knew you would say that because I've seen a copy of the initial conditions at the big bang.

I knew you would say that, because I put it there for you to see, and remember, it's a copy... I keep possession of the original.

I also understand why you are losing bits of information you should have retained... I distinctly recall ending this...

Does SD constrain us to respond to DrChinese in spite of his his actual non-existence.

With a question mark, not a period.

I find this thread amazing...

Of course ... it was meant to be.

...but I fear...

The fear, results from becoming a sloppy solipsist... rather than to continue firmly on a course of action in spite of difficulty... as a pure solipsist.

About the unicorns... You and DrChinese are both right, of course... that's just the way things are....

 

[Zafa Pi]

The fear, results from becoming a sloppy solipsist.

I've been called worse. If I were a pure solipsist I wouldn't bother responding.
Thanks for the question mark?

 

[OCR]

... I wouldn't bother responding.

To whom ?? ..