Superdeterminism and the Mermin Device
Superdeterminism as a way to resolve the mystery of quantum entanglement is generally not taken seriously in the foundations community, as explained in this video by Sabine Hossenfelder (posted in Dec 2021). In her video, she argues that superdeterminism should be taken seriously, indeed it is what quantum mechanics (QM) is screaming for us to understand about Nature. According to her video per the twin-slit experiment, superdeterminism simply means the particles must have known at the outset of their trip whether to go through the right slit, the left slit, or both slits, based on what measurement was going to be done on them. Thus, she defines superdeterminism this way:
Superdeterminism: What a quantum particle does depends on what measurement will take place.
In Superdeterminism: A Guide for the Perplexed she gives a bit more technical definition:
Theories that do not fulfill the assumption of Statistical Independence are called “superdeterministic” … .
where Statistical Independence in the context of Bell’s theory means:
There is no correlation between the hidden variables, which determine the measurement outcome, and the detector settings.
Sabine points out that Statistical Independence should not be equated with free will and I agree, so a discussion of free will in this context is a red herring and will be ignored.
Since the behavior of the particle depends on a future measurement of that particle, Sabine writes:
This behavior is sometimes referred to as “retrocausal” rather than superdeterministic, but I have refused and will continue to refuse using this term because the idea of a cause propagating back in time is meaningless.
Ruth Kastner argues similarly here and we agree. Simply put, if the information is coming from the future to inform particles at the source about the measurements that will be made upon them, then that future is co-real with the present. Thus, we have a block universe and since nothing “moves” in a block universe, we have an “all-at-once” explanation per Ken Wharton. Huw Price and Ken say more about their distinction between superdeterminism and retrocausality here. I will focus on the violation of Statistical Independence and not worry about these semantics.
So, let me show you an example of the violation of Statistical Independence using Mermin’s instruction sets. If you are unfamiliar with the mystery of quantum entanglement illustrated by the Mermin device, read about the Mermin device in this Insight, “Answering Mermin’s Challenge with the Relativity Principle” before continuing.
In using instruction sets to account for quantum-mechanical Fact 1 (same-color outcomes in all trials when Alice and Bob choose the same detector settings (case (a)), Mermin notes that quantum-mechanical Fact 2 (same-color outcomes in ##\frac{1}{4}## of all trials when Alice and Bob choose different detector settings (case (b)) must be violated. In making this claim, Mermin is assuming that each instruction set produced at the source is measured with equal frequency in all nine detector setting pairs (11, 12, 13, 21, 22, 23, 31, 32, 33). That assumption is called Statistical Independence. Table 1 shows how Statistical Independence can be violated so as to allow instruction sets to reproduce quantum-mechanical Facts 1 and 2 per the Mermin device.
Table 1
In row 2 column 2 of Table 1, you can see that Alice and Bob select (by whatever means) setting pairs 23 and 32 with twice the frequency of 21, 12, 31, and 13 in those case (b) trials where the source emits particles with the instruction set RRG or GGR (produced with equal frequency). Column 4 then shows that this disparity in the frequency of detector setting pairs would indeed allow our instruction sets to satisfy Fact 2. However, the detector setting pairs would not occur with equal frequency overall in the experiment and this would certainly raise red flags for Alice and Bob. Therefore, we introduce a similar disparity in the frequency of the detector setting pair measurements for RGR/GRG (12 and 21 frequencies doubled, row 3) and RGG/GRR (13 and 31 frequencies doubled, row 4), so that they also satisfy Fact 2 (column 4). Now, if these six instruction sets are produced with equal frequency, then the six case (b) detector setting pairs will occur with equal frequency overall. In order to have an equal frequency of occurrence for all nine detector setting pairs, let detector setting pair 11 occur with twice the frequency of 22 and 33 for RRG/GGR (row 2), detector setting pair 22 occur with twice the frequency of 11 and 33 for RGR/GRG (row 3), and detector setting pair 33 occur with twice the frequency of 22 and 11 for RGG/GRR (row 4). Then, we will have accounted for quantum-mechanical Facts 1 (column 3) and 2 (column 4) of the Mermin device using instruction sets with all nine detector setting pairs occurring with equal frequency overall.
Since the instruction set (hidden variable values of the particles) in each trial of the experiment cannot be known by Alice and Bob, they do not suspect any violation of Statistical Independence. That is, they faithfully reproduced the same QM state in each trial of the experiment and made their individual measurements randomly and independently, so that measurement outcomes for each detector setting pair represent roughly ##\frac{1}{9}## of all the data. Indeed, Alice and Bob would say their experiment obeyed Statistical Independence, i.e., there is no (visible) correlation between what the source produced in each trial and how Alice and Bob chose to make their measurement in each trial.
Here is a recent (2020) argument against such violations of Statistical Independence by Eddy Chen. And, here is a recent (2020) argument that superdeterminism is “fine-tuned” by Indrajit Sen and Antony Valentini. So, the idea is contested in the foundations community. In response, Vance, Sabine, and Palmer recently (2022) proposed a different version of superdeterminism here. Thinking dynamically (which they don’t — more on that later), one could say the previous version of superdeterminism has the instruction sets controlling Alice and Bob’s measurement choices (Table 1). The new version (called “supermeasured theory”) has Alice and Bob’s measurement choices controlling the instruction sets. That is, each instruction set is only measured in one of the nine measurement pairs (Table 2). Indeed, there are 72 instruction sets for the 72 trials of the experiment shown in Table 2. That removes the complaint about superdeterminism being “conspiratorial” or “fine-tuned” or “violating free will.”
Table 2
Again, that means you need information from the future controlling the instruction set sent from the source, if you’re thinking dynamically. However, Vance et al. do not think dynamically writing:
In the supermeasured models that we consider, the distribution of hidden variables is correlated with the detector settings at the time of measurement. The settings do not cause the distribution. We prefer to use find [sic] Adlam’s terms—that superdeterministic/supermeasured theories apply an “atemporal” or “all-at-once” constraint—more apt and more useful.
Indeed, they voice collectively the same sentiment about retrocausality that Sabine voiced alone in her quote above. They write:
In some parts of the literature, authors have tried to distinguish two types of theories which violate Bell-SI. Those which are superdetermined, and those which are retrocausal. The most naive form of this (e.g. [6]) seems to ignore the prior existence of the measurement settings, and confuses a correlation with a causation. More generally, we are not aware of an unambiguous definition of the term “retrocausal” and therefore do not want to use it.
In short, there does seem to be an emerging consensus between the camps calling themselves superdeterministic and retrocausal that the best way to view violations of Statistical Independence is in “all-at-once” fashion as in Geroch’s quote:
There is no dynamics within space-time itself: nothing ever moves therein; nothing happens; nothing changes. In particular, one does not think of particles as moving through space-time, or as following along their world-lines. Rather, particles are just in space-time, once and for all, and the world-line represents, all at once, the complete life history of the particle.
Regardless of the terminology, I would point out that Sabine is not merely offering an interpretation of QM, but she is proposing the existence of a more fundamental (deterministic) theory for which QM is a statistical approximation. In this paper, she even suggests “what type of experiment has the potential to reveal deviations from quantum mechanics.” Specifically:
This means concretely that one should make measurements on states prepared as identically as possible with devices as small and cool as possible in time-increments as small as possible.
According to this article in New Scientist (published in May 2021):
The good news is that Siddharth Ghosh at the University of Cambridge has just the sort of set-up that Hossenfelder needs. Ghosh operates nano-sensors that can detect the presence of electrically charged particles and capture information about how similar they are to each other, or whether their captured properties vary at random. He plans to start setting up the experiment in the coming months.
We’ll see what the experiments tell us.
PhD in general relativity (1987), researching foundations of physics since 1994. Coauthor of “Beyond the Dynamical Universe” (Oxford UP, 2018).
Do you consider the literature on decoherence, when it is applied in the context of a collapse interpretation, to be "bona fide Copenhagen"? Because the fact that macroscopic objects are continually decohering themselves is an obvious consequence of decoherence theory in general. And, as I have argued in prior posts, unless you are going to say that collapse only happens when a human is looking, any collapse event in a macroscopic object is going to be close to a decoherence event.
We can't prove when collapse happens. But that doesn't mean we can't say anything at all about when it happens.
No, the quantum Zeno effect does not say the system is "frozen in time". It only says that the probability of a quantum system making "quantum jumps" from one eigenstate of an observable to another can be driven to zero by measuring that observable at shorter and shorter time intervals. But there is nothing that says that the eigenstate it is being "held" in by continuous measurement has to be "frozen in time." If the system is a macroscopic object, then the "eigenstate" it starts out it is just a set of classical initial conditions, and being "held" in that eigenstate by continuous collapse just means it executes the classical motion that starts from those initial conditions.
To put it another way, a macroscopic object behaving classically does not have to make quantum jumps. It just behaves classically. If it is collapsing continuously, that just means it's following the classical trajectory that was picked out by its initial classical state.
But within a pretty narrow window of time in any actual case. Unless, as I said, you're going to take a position that, for example, the Moon only has a single trajectory when humans are looking at it. If we limit ourselves to reasonable places to put the collapse for macroscopic objects, so that they behave classically regardless of whether they are being looked at, any place you put the collapse is going to be pretty close to a decoherence event, because macroscopic objects are always decohering themselves.
You're quibbling. Collapse is needed for time evolution on any collapse interpretation. You agree with that in your very next sentence:
And this being the case is already sufficient to disprove your claim, which originally started this subthread, that the no communication theorem is anthropomorphic. The theorem applies to any collapse, not just one triggered by a human looking.
The Born rule can't be anthropocentric if collapse isn't. Except in the (irrelevant for this discussion) sense that humans are the ones who invented the term "Born rule" and so that term can only be applied to human discussions of QM, not QM itself. And if you are going to take that position, then your claim that the no communication theorem has to do with the Born rule is false: the theorem has to do with QM itself, not human discussions of QM. And, as I said above, the theorem applies to any collapse events, not just ones that humans are looking at.
See above.
Basically, you seem to be expounding a "consciousness causes collapse" interpretation. In such an interpretation, yes, you could call the no communication theorem anthropomorphic, because anything to do with measurement at all is anthropomorphic. But once again, you are then saying that no measurements at all took place anywhere in the universe until the first conscious human looked at something.
If that is your position, once again, we are talking past each other and can just drop this subthread.
If it is not your position, then pretty much everything you are saying looks irrelevant to me as far as the discussion in this thread is concerned. Yes, I get that decoherence doesn't cause collapse, and collapse can't be proven to occur in a collapse interpretation whenever decoherence occurs, but once you've adopted a collapse interpretation, and once you've adopted an interpretation that says collapse doesn't require consciousness to occur, so a macroscopic object like the Moon can be continually collapsing itself, you are going to end up having measurements and decoherence events be pretty much the same thing. And neither decoherence nor measurements nor anything associated with them will be anthropomorphic.
This is basically assuming the MWI. Again, see my post #79 above.
On any interpretation where measurements have single outcomes, no, just the wave function and the Hamiltonian are not enough.
Any time Nature has to decide what single outcome a measurement has when there are two or more quantum possibilities, it is making use of the Born rule.
(For why I am assuming that measurements have single outcomes, see my post #79 just now.)
I know that. That's why I said that what we are discussing is ultimately a matter of interpretation. You are free to adopt an interpretation like the MWI, in which there is no collapse at all, and in such an interpretation it would not be true that the Moon has a single position.
However, in such an interpretation your claim that the no communication theorem is anthropocentric is still not true, because in an interpretation like the MWI it makes no sense to even talk about whether Bob can do something to affect Alice's measurement results and thus send Alice a signal, since measurements don't even have single outcomes to begin with. This is just an aspect of the issue that it's not clear how the Born rule even makes sense in the MWI.
In any case, as I said before, if you are using an interpretation like the MWI, then you should say so explicitly. Then we can simply drop this whole subthread since we have been talking past each other: I was assuming we were using an interpretation in which measurements have single outcomes, so the Born rule makes sense and it makes sense to talk about whether or not Bob can send Alice a signal using measurement results on entangled particles.
(Note also that this thread is about superdeterminism, which also makes no sense in an interpretation like the MWI, since the whole point of superdeterminism is to try to reconcile violations of the Bell inequalities with an underlying local hidden variable theory in which measurements have single outcomes determined by the hidden variables, by violating the statistical independence assumption of Bell's theorem instead of the locality assumption. So the MWI as an interpretation is really off topic for this thread.)
If you are not using the MWI, and you are using an interpretation in which measurements do have single outcomes, then your statement quoted above, while true, is pointless. Yes, decoherence by itself does not make measurements have single outcomes, but in any interpretation where we are assuming that measurements do have single outcomes anyway, decoherence is an excellent way of defining what counts as a "measurement". That is the only use I am making of decoherence in my arguments, and you have not responded to that at all.
Alice and Bob are anthropocentric notions, I'll give you that!
Objects with a huge number of quantum degrees of freedom, like the Moon, can have center of mass positions and momenta that, while not delta functions, will both have widths that are much, much narrower than the corresponding widths for a single quantum particle (narrower by roughly the same order of magnitude as the number of particles in the object). That is what I mean by "well-defined" in this connection.
But the Moon doesn't have "one or more" trajectories. It has one. And that was true 4 billion years ago. The Moon didn't have to wait for humans to start observing it to have one trajectory. Or at least, if you are taking the position that it did–that the Moon literally had multiple trajectories (each decohered, but still multiple ones) until the first human looked at it and collapsed them into one, then please make that argument explicitly.
"It doesn't matter whether someone was there" in the sense that the Moon had one single trajectory back then?
You do in order for the Moon to have just one trajectory instead of multiple ones. More precisely, you need the Born rule to tell you what the probabilities were for various possible trajectories 4 billion years ago. And then you need to realize that, because the Moon is constantly measuring itself, it will have picked just one of those trajectories 4 billion years ago. And then you need the Born rule to tell you what the probabilities were for various possible trajectories 4 billion years minus one second (let's say–I think the decoherence time for the Moon is actually much shorter than that, but let's say one second for this discussion) ago–and then the Moon picks one of those. And then you're at 4 billion years minus two seconds ago…etc., etc.
SR is a principle theory, per Einstein. Did you read the Mainwood article with Einstein quotes?
And, yes, the information-theoretic reconstructions of QM, whence the relativity principle applied to the invariant measurement of h, give you the Hilbert space formalism with its non-commutative algebra. So, it's figured out in principle fashion. Did you read our paper?
Again, this is a matter of interpretation. According to decoherence theory, the Moon had a perfectly well-defined orbit 4 billion years ago, when there were no humans around. In terms of the Born rule, the probabilities for the Moon to be at various positions were perfectly well-defined 4 billion years ago, and the no communication theorem would apply to them.
Whereas on the viewpoint you are taking here, the Born rule was meaningless until humans started doing QM experiments.
I think that is a matter of interpretation. In decoherence theory, for example, "measurement" can be defined as any situation in which decoherence occurs. For example, the Moon is constantly measuring itself by this definition, whether or not a human being looks at it. And the no communication theorem would therefore apply to the Moon (and would say, for example, that the Moon's orbit cannot be affected by what is happening on Pluto at a spacelike separated event, even if particles in the Moon and particles in Pluto are quantum entangled).
Yes, and even Einstein tried "mechanisms" aka "constructive efforts" to explain time dilation and length contraction before he gave up and went with his principle explanation (relativity principle and light postulate). Today, most physicists are content with that principle explanation without a constructive counterpart (no "mechanisms", see this article), i.e., what you call "the modern interpretation." So, if you're happy with that principle account of SR, you should be happy with our principle account of QM (relativity principle and "Planck postulate"). All of that is explained in "No Preferred Reference Frame at the Foundation of Quantum Mechanics". Here is my APS March Meeting talk on that paper (only 4 min 13 sec long) if you don't want to read the paper.
For me, it is like a 19th century critique of atomic explanation of thermodynamics based on the idea that it requires fine tuning of the rules of atomic motion to fulfill the 2nd law (that entropy of the full system cannot decrease) and the 3rd law (that you cannot reach the state of zero entropy). And yet, as Boltzmann understood back than and many physics students understand today, those laws are FAPP laws that do not require fine tuning at all.
Indeed, in Bohmian mechanics it is well understood why nonlocality does not allow (in the FAPP sense) communication faster than light. It is a consequence of quantum equilibrium, for more details see e.g. https://arxiv.org/abs/quant-ph/0308039
Not in the sense in which it is used in the no communication theorem. That sense is basically the information theoretic sense, which in no way requires humans to process or even be aware of the information.
Right, as Sabine points out in her video:
Once you've committed to explaining entanglement with a mechanism (HV), you're stuck with violating at least one of Locality or Statistical Independence.
Maybe. But with this notion of semantics the question is: what topic regarding interpretations and foundations of established physics isn't semantics?
I find it difficult to discuss this because there are problems with the role of probabilities in the MWI which may or may not be solved. For now, I would say that I don't see the difference between my experience of the past right now belonging to a maverick branch vs. a single world view where by pure chance, I and everybody else got an enormous amount of untypical data which lead us to the inference of wrong laws of physics.
Isn't it obvious? We are talking about a lack of statistical independence between a photon source at A and light sources in two quasars, each a billion light-years from A in opposite directions. How else could that possibly be except by some kind of pre-existing correlation?
Sort of. Correlations between the "sources of randomness" and the patient would be similar, yes. (And if we wanted to be extra, extra sure to eliminate such correlations, we could use light from quasars a billion light-years away as the source of randomness for medical experiments, just as was done in the scenario I described.) But that has nothing to do with the placebo effect, and is not what I understood you to be talking about before.
I don't study SD, so I don't know what they're looking for exactly. Maybe they can't control sample preparation well enough for radioactive decay? Just guessing, because that seems like an obvious place to look.
Exactly. On p. 3 of Superdeterminism: A Guide for the Perplexed, Sabine writes:
I disagree. There could be a superdeterministic theory underlying QM which isn
I find this difficult to discuss because the MWI still has the problem of how to make sense of probabilities. This might be a problem in which case I'm inclined to agree with you. But
I don't see how the two have anything to do with each other.
Consider the following experimental setup:
I have a source that produces two entangled photons at point A. The two photons go off in opposite directions to points B and C, where their polarizations are measured. Points B and C are each one light-minute away from point A.
At each polarization measurement, B and C, the angle of the polarization measurement is chosen 1 second before the photon arrives, based on random bits of information acquired from incoming light from a quasar roughly a billion light-years away that lies in the opposite direction from the photon source at A.
A rough diagram of the setup is below:
Quasar B — (1B LY) — B — (1 LM) — A — (1 LM) — C — (1B LY) — Quasar C
In this setup, any violation of statistical independence between the angles of the polarizations and the results of the individual measurements (not the correlations between the measurements, those will be as predicted by QM, but the statistics of each measurement taken separately) would have to be due to some kind of pre-existing correlation between the photon source at A and the distant quasars at both B and C. This is the sort of thing that superdeterminism has to claim must exist.
Whether this is true or not (that question really belongs in the medical forum for discussion, not here), this is not the placebo effect. The placebo effect is where patients who get the placebo (but don't know it–and in double-blind trials the doctors don't know either) still experience a therapeutic effect.
I don't see how this has an analogue in physics.
I think that all three somewhat break with simple ideas about how science is done and what it tells us but to a different degree.
Copenhagen says that there are limits to what we can know because we need to split the world into the observer and the observed. The MWI does away with unique outcomes. Superdeterminism does away with the idea that we can limit the influence of external degrees of freedom on the outcome of our experiment. These might turn out to be different sides of the same coin but taken at face value, the third seems like the most radical departure from the scientific method to me.
There's also the point that unlike Copenhagen and the MWI, superdeterminism is not an interpretation of an existing theory. It is a property of a more fundamental theory which doesn't make any predictions to test it (NB: Sabine Hossenfelder disagrees) because it doesn't even exist yet.
In principle, yes.
No, because in theories such as Bohmian mechanics, the no communication theorem is a FAPP (for all practical purposes) theorem.
Roughly, this is like the law of large numbers. Is it valid for ##N=1000##? In principle, no. In practice, yes.
If I understand you correctly you are saying that it is (or might be) possible but it has not been found yet. Doesn't this contradict the no communication theorem? It would require that QM needs to be modified completely or may be superdeterminism is the explanation.
How does non-locality require fine tuning?
How is non-locality anthropocentric?
There is no any conspiracy. See https://www.physicsforums.com/threa…unterfactual-definiteness.847628/post-5319182
It is probably the phrasing that you use that confuses me, but I still don't understand. For example the past light cone of the event = production of the second pair of photons, contains the whole life of the first photon, that no longer exists. All the possible light cones that you can pick intersect.
You'd think so! But these photons never existed in a common light cone because their lifespan is short. In fact, in this particular experiment, one photon was detected (and ceased to exist) BEFORE its entangled partner was created.
In this next experiment, the entangled photon pairs are spatially separated (and did coexist for a period of time). However, they were created sufficiently far apart that they never occupied a common light cone.
High-fidelity entanglement swapping with fully independent sources (2009)
https://arxiv.org/abs/0809.3991
"Entanglement swapping allows to establish entanglement between independent particles that never interacted nor share any common past. This feature makes it an integral constituent of quantum repeaters. Here, we demonstrate entanglement swapping with time-synchronized independent sources with a fidelity high enough to violate a Clauser-Horne-Shimony-Holt inequality by more than four standard deviations. The fact that both entangled pairs are created by fully independent, only electronically connected sources ensures that this technique is suitable for future long-distance quantum communication experiments as well as for novel tests on the foundations of quantum physics."
And from a 2009 paper that addresses the theoretical nature of entanglement swapping with particles with no common past, here is a quote that indicates that in fact this entanglement IS problematic for any theory claiming the usual locality (local causality):
"It is natural to expect that correlations between distant particles are the result of causal influences originating in their common past — this is the idea behind Bell’s concept of local causality [1]. Yet, quantum theory predicts that measurements on entangled particles will produce outcome correlations that cannot be reproduced by any theory where each separate outcome is locally determined by variables correlated at the source. This nonlocal nature of entangled states can be revealed by the violation of Bell inequalities.
"However remarkable it is that quantum interactions can establish such nonlocal correlations, it is even more remarkable that particles that never directly interacted can also become nonlocally correlated. This is possible through a process called entanglement swapping [2]. Starting from two independent pairs of entangled particles, one can measure jointly one particle from each pair, so that the two other particles become entangled, even though they have no common past history. The resulting pair is a genuine entangled pair in every aspect, and can in particular violate Bell inequalities.
"Intuitively, it seems that such entanglement swapping experiments exhibit nonlocal effects even stronger than those of usual Bell tests. To make this intuition concrete and to fully grasp the extent of nonlocality in entanglement swapping experiments, it seems appropriate to contrast them with the predictions of local models where systems that are initially uncorrelated are described by uncorrelated local variables. This is the idea that we pursue here."
Despite the comments from Nullstein to the contrary, such swapped pairs are entangled without any qualification – as indicated in the quote above.
As Sabine points out, if you want a constructive explanation of Bell inequality violation, it's nonlocality and/or SD. That's why we pivoted to a principle account (from information-theoretic reconstructions of QM). We cheated a la Einstein for time dilation and length contraction.
As I have already said, he didn't. He never said anything in the Deutsch paper you referenced was wrong. He just said it wasn't relevant to the entanglement swapping experiments he has referenced. He also gave a specific argument for why (in post #11, repeated in post #24).
Your only response to that, so far, has been to assert that the Deutsch paper is relevant to the entanglement swapping experiments @DrChinese referenced, without any supporting argument and without addressing the specific reason @DrChinese gave for saying it was not.
I don't see any quotes from that paper in any of your posts. You referenced it, but as far as I can tell you gave no specifics about how you think that paper addresses the issues @DrChinese is raising.
It's perhaps not a fair question but what odds would you give on SD being that mechanism? Would you bet even money on this experiment proving QM wrong? Or, 10-1 against or 100-1 against?
I wonder what Hossenfelder would be prepared to bet on it?
This is not a valid argument. There are many papers that never get rebuttals but are still incorrect.
This is not a valid argument either; many papers have had mistakes that are not easily pointed out. Nor is it relevant to what @DrChinese is saying. @DrChinese is not claiming there is a mistake in Deutsch's paper. He is saying he doesn't see how Deutsch's paper addresses the kind of experiment he is talking about (entanglement swapping) at all. If you think Deutsch's paper does address that, the burden is on you to explain how.
I read the 1999 Deutsch article, and unfortunately it did not map to my 2012 reference. There is actually no reason it should (or would), as the experiment had not been conceived at that time.
As I mentioned in another post, Deutsch's reputation does not need defending. However, I would not agree that his well-known positions on MWI should be considered as representing generally accepted science. Some are, and some are not, and I certainly think it is fair to identify positions as "personal" vs "generally accepted" when it is relevant. There is nothing wrong with having personal opinions that are contrary to orthodox science, but I believe those should be identified.
Show me where Zeilinger (or any of the authors of similar papers) says there are local explanations for the kind of swapping I describe, and we'll be on to something. From the paper: "The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime." I just don't see how SD can get around this: it is supposed to restore realism and locality to QM.
Can you clarify. How can there be no common overlap? Any two past lightcones overlap.
1. Relevant here if he is stating something that is not generally accepted (and the part in quotes was actually from another physicist). Local explanations of swapping are not, and clearly that is the tenor of the paper. Deutsch is of course a respected physicist (and respected by me), that's not the issue.
2. I specifically indicated how your citation differed from swapping using independent sources outside of a common light cone (which does not occur in Deutsch's earlier paper). There are no "local" explanations for how 2 photons that have never existed within a common light cone manage to be perfectly correlated (entangled) a la Bell. That you might need information from a classical channel to postselect pairs is irrelevant. No one is saying there is FTL signaling or the like.
3. Of course swapping adds to the mystery. And it certainly rules out some types of candidate theories. How can there be a common local cause when there is no common light cone overlap?
Well, my understanding is that the experiments will check for violations of randomness where QM predicts randomness. That means we should look for a theory X underwriting QM so that QM is just a statistical approximation to theory X. Then you can infer the existence of hidden variables (hidden in QM, but would be needed in theory X) whence either or both of nonlocality or/and the violation of Statistical Independence. Just my guess, I don't study SD.
I should be more precise, sorry. In the quantum-classical contextuality of RBW, "local" means "nothing moving superluminally" and that includes "no superluminal information exchange." That's because in our ontology, quanta of momentum exchanged between classical objects don't have worldlines.
Notice also that when I said RBW does not entail violations of Statistical Independence because the same state is always faithfully produced and measured using fair sampling, I could have said that about QM in general. Again, what I said follows from the fact that there are no "quantum entities" moving through space, there is just the spatiotemporal (4D) distribution of discrete momentum exchanges between classical objects. And that quantum-classical contextuality conforms to the boundary of a boundary principle and the relativity principle.
So, how do we explain violations of Bell's inequality without nonlocal interactions, violations of Statistical Indendence, or "shut up and calculate" (meaning "the formalism of QM works, so it's already 'explained'")? Our principle explanation of Bell state entanglement doesn't entail an ontology at all, so there is no basis for nonlocality or violations of Statistical Independence. And, it is the same (relativity) principle that explains time dilation and length contraction without an ontological counterpart and without saying, "the Lorentz transformations work, so it's already 'explained'". So, we do have an explanation of Bell state entanglement (and therefore of the Tsirelson bound).
So is your response (although since your statements about Deutsch are positive, it might be better termed a "pro homine" argument):
None of these are any more relevant to whether Deutsch's arguments are valid than the things you quoted from @DrChinese. What is relevant is what Deutsch actually says on the topic and whether it is logically coherent and consistent with what we know from experiments.
1. Certainly, RBW is local in the sense that Bohmian Mechanics is not. Bohmian Mechanics does not feature superluminal signaling either, and we know we don't want to label BM as "local".
So I personally wouldn't label RBW as you do ("local"); as I label it "quantum nonlocal" when a quantum system (your block) has spatiotemporal extent (your 4D contextuality) – as in the Bell scenario. But I see why you describe it as you do: it's because c is respected when you draw context vertices on a block (not sure that is the correct language to describe that).
2. Thanks for the references.
Correct, I'm definitely not arguing for SD. If Statistical Independence is violated and QM needs to be underwritten as Sabine suggests, physics is not going to be fun for me anymore
Right, we have no idea exactly how Statistical Independence is violated because it's all "hidden." My Table 1 is just an example to show what people refer to as the "conspiratorial nature" of SD. Sabine addresses that charge in her papers, too.
Sabine points out that to evade the conclusion of Bell, you need to violate either or both of Statistical Independence or/and locality. She also points out that SD could violate both, giving you the worst of both worlds. I'll let the experimental evidence decide, but I'm definitely hoping for no SD
We uphold locality and Statistical Independence in our principle account of QM as follows. Locality is not violated because there is no superluminal signaling. Statistical Independence is not violated because Alice and Bob faithfully reproduce the most accurate possible QM state and make their measurements in accord with fair sampling (independently and randomly). In this principle account of QM (ultimately based on quantum information theorists' principle of Information Invariance & Continuity, see the linked paper immediately preceding), the state being created in every trial of the experiment is the best one can do, given that everyone must measure the same value for Planck's constant regardless of the orientation of their measurement device. RBW is nonetheless contextual in the 4D sense, see here and here for our most recent explanations of that.
What exactly do you mean by non-classicality?
I thought that the motivation for superdeterminism wasn't to avoid nonlicality but nonclassicality. The claim being that the world is really classical, but somehow (through the special initial conditions and evolution laws) it only seems like quantum theory is a correct description.
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."
I think this quote perfectly explains how super-determinism avoids quantum nonlocality. Not by replacing it with locality, but by replacing it with super-nonlocality!
In ordinary nonlocality, things get correlated over distance due to nonlocal forces. In super-nonlocality one does not need forces for that. They are correlated just because the fundamental laws of Nature (or God if you will) say so. You don't need to fine tune the initial conditions to achieve such correlations, it's a general law that does not depend on initial conditions. You don't need any complicated conspiracy for that, in principle it can be a very simple general law.
In your reference (1999), its Figure 3 is not a fair representation of the experiment I presented (2012). Deutsch is not what I would call a universally accepted writer on the subject, and "is a legendary advocate for the MWI". "Quantum nonlocality" is generally accepted in current science. And we've had this discussion here many a time. The nature of that quantum nonlocality has no generally accepted mechanism, however. That varies by interpretation.
The modern entanglement swapping examples have entangled particles which never exist in a common backward light cone – so they cannot have had an opportunity for a local interaction or synchronization. The A and B particles are fully correlated like any EPR pair, even though far apart and having never interacted*. That is quantum nonlocality, plain and simple. There are no "local" explanations for entanglement swapping of this type (that I have seen), of course excepting interpretations that claim to be fully local and forward in time causal (which I would probably dispute). Some MWI proponents makes this claim, although not all.
*Being from independent photon sources, and suitably distant to each other.
[And of course I know you are not arguing in favor of superdeterminism in your Insight.]
My mistake, yes, I see now that is a feature of the table. So basically, that would equivalent to saying that for the 23 case (to be specific) – which in the table is marked as follows (where rows 2/3/4, the 23 cases will add to 100% as follows:
-Row 2 occurs 50% of the time when 23 measurement occurs. Because this is doubled by design/assumption.
-Row 3 occurs 25% of the time when 23 measurement occurs.
-Row 4 occurs 25% of the time when 23 measurement occurs.
Total=100%
Could just as rationally be:
-Row 2 occurs 75% of the time when 23 measurement occurs.
-Row 3 occurs 0% of the time when 23 measurement occurs. This is so rows 2 and 3 add to 75%.
-Row 4 occurs 25% of the time when 23 measurement occurs.
Total=100%
…Since the stats add up the same. After all, that would cause the RRG & GGR cases to be wildly overrepresented, but since we are only observing the 23 measurements, we don't see that the other (unmeasured) hidden variable (1) occurrence rate is dependent on the choice of the 23 basis. Since we are supposed to believe that it exists (that is the purpose of a hidden variable model) but has a value that makes it inconsistent with the 23 pairing (of course this inconsistency is hidden too).
Obviously, in this table, we have statistical independence as essentially being the same thing as contextuality. Which more or less orthodox QM is anyway. Further, it has a quantum nonlocal element, as the Bell tests with entanglement swapping indicate*. That is because the "23" choice was signaled to the entangled source so that the Row 2 case can be properly overrepresented. But in an entanglement swapping setup, there are 2 sources! So now we need to modify our superdeterministic candidate to account for a mechanism whereby the sources know to synchronize in such a way as to yield the expected results. Which is more or less orthodox QM anyway.
My point is that the explicit purpose of a Superdeterministic candidate is to counter the usual Bell conclusion, that being: a local realistic theory (read: noncontextual causal theory) is not viable. Yet we now are stuck with a superdeterministic theory which features local hidden variables, except they are also contextual and quantum nonlocal. I just don't see the attraction.
*Note that RBW does not have any issue with this type of quantum nonlocal element. The RBW diagrams can be modified to account for entanglement swapping, as I see it (at least I think so). RBW being explicitly contextual, as I understand it: "…spatiotemporal relations provide the ontological basis for our geometric interpretation of quantum theory…" And on locality: "While non-separable, RBW upholds locality in the sense that there is no action at a distance, no instantaneous dynamical or causal connection between space-like separated events [and there are no space-like worldlines.]" [From one of your papers (2008).]
If the instruction sets are produced in concert with the settings as shown in the Table, the 23/32 setting would produce agreement in 1/4 of the trials, which matches QM.
In the New Scientist article, it did say Ghosh was planning an experiment proposed by Sabine.
Sorry, I accidentally inserted my link as an author to that Insight. Hopefully, it's fixed now :-)
So yes, you could simply say there are violations of Statistical Independence (SI). In your example, the 32/23 combinations produce a different outcome sets for certain hidden variable combinations. In an actual experiment with the 32 or 23 settings as static, you'd notice that immediately (since the results must still match prediction) – so there must be more to the SI violation so that this result does not occur. And just like that, the Superdeterminism candidate must morph yet again.
But one thing has mystified me in these discussions. Always, the superdeterminism candidate is presented as local (since the ultimate purpose of the candidate is to restore determinism and locality). In your reference to the Chen article, there is reference to the idea that "one can always conjecture that some factor in the overlap of the backwards light cones has controlled the presumably random choices".
There are at least 2 problems with this. First problem, that there needs to be *random choices* for the experiment to show SI. Unless the superdeterministic candidate has a mechanism to discern whether the measurement choice is being varied or not, it need not be random or subject to free will at all – it could be static (and therefore not demonstrate any deviation from the quantum mechanical expectation value – which is what we needed to demonstrate as a viable possibility). Second, and most importantly, the entangled particles subject to the Bell test need not have ever existed in a common light cone. And in fact, they need not have ever co-existed to be entangled. Or come from a common source at all. I'll supply more references as needed.
https://arxiv.org/abs/1209.4191
Entanglement Between Photons that have Never Coexisted
Yes, there seems to be a violation of SI. But that must simply be a result of quantum contextuality itself. And such contextuality must have a nonlocal element. But it is a special kind of nonlocal, not the kind that appears in Bohmian Mechanics (for example) where there are instantaneous effects regardless of distance. The overall context is traced out by components that are individually limited to c.