What makes the interpretations of Quantum Mechanics so important?

[atyy]

What would be the implications if it went the other way? As in over Tsirelson's bound.

I don’t know of any theory predicting that

Not a theory, but semi-theories (like LQG): https://arxiv.org/abs/1403.4621

 

[vanhees71]

What you are describing is superdeterminism and most scientists do not believe that. The majority belief is that the scientist is free to make settings independently of the laws being tested. That’s why the experiment described by Hardy is important

No that's for sure not what the majority of physicists believes. Rather the physicists believe that the natural laws are universally applying to everything everywhere and at every time. It is quite sure that we don't know the exact natural laws, and that's why we still do experiments on the fundamental level to refine (and may be one day even radically change) or theories, but for sure the majority of physicists does not think that the physical laws are invalid for humans. The physical processes in our bodies are, as far as we know, not contradicting any of the known laws of physics, including quantum mechanics.

 

[Jimster41]

Not a theory, but semi-theories (like LQG): https://arxiv.org/abs/1403.4621

Interesting looking paper. Seems relevant to this discussion to me anyway. Problem is the axioms it begins with... interesting also, require grok.

(a) Free beer to anyone who would summarize!

 

[1977ub]

The physical processes in our bodies are, as far as we know, not contradicting any of the known laws of physics, including quantum mechanics.

Not only "not contradicting" but also presumably 100% constrained by.

 

[Sophrosyne]

Wouldn't this imply a proof that e.g. Many Worlds really exist or that the wave function really collapses?

I don't think that's necessarily the case. The answer could be something we haven't even imagined yet.

Who would have imagined in Newton's time that we would be talking about quantum mechanics and relativity?

The universe seems to be a far weirder place than we ever imagined.

 

[Jimster41]

From https://arxiv.org/abs/1403.4621 the paper linked to in post #141.

"10 Conclusion
In this paper we have studied the set Q˜ of almost quantum correlations. This set appears naturally in a variety of seemingly unrelated fields, such as quantum information science, graph theory and quantum gravity. The ubiquity of the almost quantum set, together with the fact that Q˜ is closed under classical operations, seems to suggest that Q˜ emerges from a reasonable (yet unknown) physical theory. To support this conjecture, we have proven that almost quantum correlations satisfy a number of physical principles, originally conceived to single out the set of quantum correlations. The relations between these principles, quantum mechanics and Q˜ are summarized in Figure 1. Note, however, that, despite our numerical evidence, we were not able to prove that Q˜ satisfies Information Causality [9]. The original proof for the quantum case relies on the existence of a well-behaved entropic quantity, and so it does not carry through easily to the almost quantum case. Since the definition of sophisticated notions such as the von Neumann entropy requires the structure of a generalized probabilistic theory, finding a ‘natural’ physical model whose non-locality is captured by Q˜ becomes imperative. Linking a physical theory with reasonable entropic inequalities to the almost quantum set would prove that Q˜ not only respects Information Causality, but also any future information-theoretic principle derived from, say, strong subaddititity, or the data processing inequality. In addition, an explicit ‘almost quantum theory’ would also suggest where to look for genuinely non-quantum behavior and thus could be the first step towards an experimental refutation of quantum theory.
"

Not that I followed the proofs etc. But I can sort of tell what they are talking about. (Wild projection of personal curiosity warning) It's interesting to me that they don't include in their conclusion the possibility that information causality might be violated in favor of some kind of a-causality or true simultaneity and that linking a physical theory (alternative to existing QM or not) to that violation might suggest that poorly behaved entropic quantities flag non-classical behavior - an alternative if un-palatable resolution to the classical/quantum... dilemma.

But then I don't understand at all most of what they say. Which is Especially frustrating w/respect to their proof of no-advantage to non-local computation.

what the heck is the difference between "reasonable" and "well-behaved" entropic quantities? Like is a "reasonable" entropic quantity one that you can... push around somewhat. Does the fact it doesn't actually go away, ever, it just does it's accounting somewhere else mean it's well behaved or more like annoying?

 

[RUTA]

The problem with humans deciding to put the lens in or not (humans replace beam splitters for Kim et al) is that most scientists want to believe human decisions could have been otherwise but that’s not true if the outcome is to obey QM in this case. Certainly for any given trial it is impossible to say but the end aggregate result will show that the person really could not have chosen otherwise on the whole. And that violates what most consider an important component of experimental science—the free will of the experimentalist. That was the first thing Hardy said to me at the Vaxjo conference in June “What about the free will of the experimentalist?” Ironically you’re saying what we predict in the paper I referenced (that there will be no difference between people and beam splitters) so we’re in agreement (although we assume adynamical constraints rather than superdeterminism). What I’m telling you is that this is where we get the biggest pushback on our adynamical block universe view — no free will as generally construed. Bub said “It’s worse than superdeterminism!” So I’m simply reporting my experience with many scientists when I tell you there are implications for either outcome. If QM is obeyed in this case it means the free will of the experimentalist is not at all what most people think — our decisions really could not have been otherwise. Again that’s entailed by block universe so it’s fine with me but that’s why most people hate block universe. Superdeterminism fairs no better in the scientific community.

 

[PeterDonis]

I’m simply reporting my experience with many scientists when I tell you there are implications for either outcome.

Scientists or philosophers of science? Bub is the latter, if I'm not mistaken.

The practicing scientists here don't seem to have any problem with compatibilism--the view that free will and determinism are compatible. There is an extensive philosophical literature on this, so it's a bit surprising that philosophers of science appear to have such a problem with it. But if that's your experience, it's certainly an interesting datum.

If QM is obeyed in this case it means the free will of the experimentalist is not at all what most people think — our decisions really could not have been otherwise.

This is a general consequence of any deterministic theory. However, I don't think it's actually a consequence of QM in this particular experiment. A detection of the signal photon at a particular location on the D0 detector is compatible with both choices the human could make for how to direct the idler photon. The idler photon has to "know" what happened to the signal photon in order to "decide" what to do after it is sent whichever way the human's choice sends it, but I don't see any reason why what happened to the signal photon would have to constrain the human's choice of which way to direct the idler photon. (This is basically the same point @charters made in post #140.)

 

[RUTA]

Scientists or philosophers of science? Bub is the latter, if I'm not mistaken.

The practicing scientists here don't seem to have any problem with compatibilism--the view that free will and determinism are compatible. There is an extensive philosophical literature on this, so it's a bit surprising that philosophers of science appear to have such a problem with it. But if that's your experience, it's certainly an interesting datum.

How I wish there more like you in the foundations community ... . Many philosophers have laid out the case against the notion of Libertarian free will I described, but still we encounter resistance to block universe on this point more than any other. It's mostly the physicists, I might add.

This is a general consequence of any deterministic theory. However, I don't think it's actually a consequence of QM in this particular experiment. A detection of the signal photon at a particular location on the D0 detector is compatible with both choices the human could make for how to direct the idler photon. The idler photon has to "know" what happened to the signal photon in order to "decide" what to do after it is sent whichever way the human's choice sends it, but I don't see any reason why what happened to the signal photon would have to constrain the human's choice of which way to direct the idler photon. (This is basically the same point @charters made in post #140.)

Let's look at the Sci. Am. version with electrons and scattered photons (same idea as Kim et al), so as to avoid confusion with "signal" and "idler." Suppose we first use a beam splitter to "decide" whether or not to destroy (erase) the which-path information of the electrons. We have a computer keep track and bin the electron detection events accordingly. We see two distinct patterns -- particle and wave -- exactly as QM predicts. It doesn't matter that the photons were detected after the electrons were detected. Now, suppose you are asked to create a list of "yes" and "no's" numbering in the ... hundreds. I take that list and use it instead of the beam splitter photon outcomes to bin the electron detection events. Do I still get those two distinct patterns? Not likely. I can certainly cherry pick the electron data and bin them into two equivalent (non-distinct) "patterns" if I want. No, we need the specific photon outcomes to bin the electron outcomes to create the two distinct patterns. So, the photon route through the beam splitter is not random, contrary to how we note the beam splitter works outside the context of this experiment. Hmmm, is there some causal mechanism at work? Something making the photon interact differently with the beam splitter in this context? How do the photon and beam splitter "know" which way the photon needs to be go at the beam splitter to be in accord with the electron detection location? Do they somehow "know" about the global experimental arrangement? What kind of causal mechanism is that?

Now replace the beam splitter with a human controlled mirror switch and suppose the person controlling the switch is using your list of "yes" and "no's." What happens? Well, you and I both agree we will now see the two distinct patterns (another version of this was done with the usual Bell inequality violation experiment and QM proved correct). So, how did that causal mechanism work in this situation? On you, in the past, while you were making your list? Or did the mere existence of the list contribute to the causal mechanism now acting on the electrons? What if the person decides to stop using the list right in the middle of the experiment? Does the causal mechanism now revert to controlling his decisions based on the electron events? Even if the electron detection event and person's decision are spacelike separated? [This is why Hardy is careful to keep decisions made at the pre-conscious level spacelike separated from opposing detection events, so that brain waves moving at the speed of light can't influence outcomes.]

As you admit, there certainly looks to be new physics here. If so, we came by it via foundations of physics because it wasn't the failure of QM that led us here, it was QM's success.

 

[charters]

We see two distinct patterns -- particle and wave -- exactly as QM predicts. It doesn't matter that the photons were detected after the electrons were detected

But this isn't correct. We don't see two distinct patterns. The key is that the *two* wave/interference patterns exactly blur each other out. The pattern at D0 is completely insensitive to whether or not the erasure happens on the partner. The D0 results are always just the basic reduced density matrix for the local subsystem of the entangled state.

For example, if you erase none of the photons, D0 can be thought of as the sum of the Left (D3 in Kim) and Right (D4) pattern. If you erase all the photons, D0 can be thought of as the sum of the Fringe (D1) and Anti-fringe (D2). But - and this is the crucial point - Left + Right = Fringe + Anti-Fringe, exactly. So, they are identical patterns at D0, as are any mixtures of erase/non-erase. Because the results are independent in this way, results at D0 don't have to conform to or compel what happens on the other wing of the experiment.

There is simply nothing in the experimental results that demands the sort of mechanism you are worried about.

 

[PeterDonis]

As you admit, there certainly looks to be new physics here

I said there would obviously have to be new physics if the Bell inequalities were not violated and the predictions of QM were not confirmed with a human in the experiment. But nothing you have described requires that to be the case. As you have described things, we have three different runs, each one consisting of some large number of trials, which are conducted as follows:

(1) The beam splitter "decides" whether which-way information is preserved or erased. No human plays any role in any part of the experiment.

(2) A human uses a pre-determined list of yes's and no's to determine where to put the switch that determines whether which-way information is preserved or erased.

(3) A human (for at least part of the experiment) "freely chooses" on every trial where to put the switch that determines whether which-way information is preserved or erased, without consulting any pre-determined list or any record of past results.

In all three of these cases, QM predicts that, if the results are binned based on the actual factual outcome of each trial--i.e., where the beam splitter or the switch actually sent the signal that determines whether which-way information got preserved or erased--the distinct patterns will appear and the Bell inequalities will be violated in the correlations. And I would fully expect that QM's predictions would be confirmed in all three cases.

 

[PeterDonis]

We don't see two distinct patterns.

They're "distinct" in the sense that if you look at each bin of results separately, you see them, and they're not identical. But they are, as you note, inverses of each other (where one is bright, the other is dark), so when added together, as in the actual results as a whole, they cancel each other out.

 

[charters]

They're "distinct" in the sense that if you look at each bin of results separately, you see them, and they're not identical. But they are, as you note, inverses of each other (where one is bright, the other is dark), so when added together, as in the actual results as a whole, they cancel each other out.

Right but, this is distinct *after* filtering. What matters here is the pre-filtering results, ie how the choice on the D1-D4 wing in no way changes or constrains the unfiltered pattern on D0. So the consistency constraint being suggested does not exist. A little thought would also show that if it did exist, you could violate causality/no-communication theorem.

 

[RUTA]

Look at Figures 3, 4, and 5 in Kim et al. Again, the Sci. Am. version is easier, but the Kim et al works, too. Figure 3 shows "electron" detections at D0 corresponding to photons with erased which-way info per detection at D1 (which means the "electrons" produce an interference pattern). This corresponds to the person choosing to insert the mirror in Sci. Am. Same with Figure 4 and photon detection at D2. Yes, these two interference patterns are pi out of phase with those in Figure 3, but that does not in any way eliminate the mystery of the R01 or R02 correlations, they are distinct correlation pairs. Figure 5 shows "electron" detections at D0 corresponding to photons without erased which-way info per detection at D3 (which means the "electrons" produce no interference pattern). Again, these are all three distinct correlated pairings. It's not the pre-binning outcomes that are mysterious, it's the post-binning results that are mysterious exactly as I described above.

 

[charters]

it's the post-binning results that are mysterious exactly as I described above.

This is just the basic EPR/entanglement question.

But you aren't arguing the outcome-outcome correlations are mysterious. You are saying there is an act-outcome correlation, ie that the human has to be forced to *choose* to erase or not, given a certain D0 outcome has already been registered. But this isn't true. For every single spot on D0, the conditional probability of "partner will be erased" is exactly the same as "partner won't be erased".

 

[RUTA]

And, no, you cannot use this to send superluminal signals anymore so than in standard EPR-Bell experiments (as you point out with the probability of any given outcome). And as with the standard EPR-Bell experiments, it's not the individual events themselves which prove mysterious, it's the correlations. The fact that QM predicts these correlations without providing a causal mechanism is precisely why Einstein thought QM was "incomplete" and this is precisely what Smolin meant when he said "[QM] doesn't make any sense because it's wrong [incomplete]."

 

[RUTA]

The correlation patterns obtain in Kim et al. exactly as described quantitatively in Sci. Am. That is what you need to explain, because QM does not provide an explanation, only a mathematical formalism mapping to the results.

 

[RUTA]

I must bow out of this conversation now, I've said everything I know to explain the mystery to you. Hopefully, some of the readers of the thread get it and see the relevance to the OP.

 

[charters]

The correlation patterns obtain in Kim et al. exactly as described quantitatively in Sci. Am. That is what you need to explain, because QM does not provide an explanation, only a mathematical formalism mapping to the results.

Does the causal mechanism now revert to controlling his decisions based on the electron events?

These are two different questions. The former is reasonable, and just EPR. The latter misunderstands the DCQE. There is no correlation between any given result at D0 and the choice on the other wing, so there is no need for a mechanism to control the human's *decision*.

 

[PeterDonis]

I've said everything I know to explain the mystery to you.

You've conflated two different "mysteries".

One is the general question of how correlations that violate the Bell inequalities can be produced. Everyone agrees that no local hidden variable model can do so (since that's what Bell's theorem proved). Beyond that there is no generally accepted answer in terms of a "mechanism". There are just various viewpoints and we're not going to resolve the question of which, if any, of them is the "right" one here. But I don't think anyone here needs to have that mystery "explained" to them. We all understand the question.

The other is your claim that a human placed into the experiment would somehow be "forced" to choose to put the switch a particular way in order to obey the laws of QM. That claim is false; @charters has repeatedly explained why.

 

[RUTA]

Here is a nice explanation of why the DCQE experiment is mysterious with great animations (if you just want to see the experiment, start at 4:45). "C" stands for "choice" precisely because Wheeler imagined a human making the decisions instead of a beam splitter. Everything else I said then follows -- including the human being "forced" to make the appropriate decisions if you believe we need a causal mechanism to account for the QM prediction, i.e., if you believe QM is incomplete as does Smolin (and many others in foundations). [This is precisely what we reject in our paper, i.e., we believe QM is complete and telling us we need to understand "the real external world" fundamentally via adynamical constraints, e.g., conservation per no preferred reference frame, rather than causal mechanisms, but I'm trying to convey the mystery per convention here.]

 

[charters]

including the human being "forced" to make the appropriate decisions

The human is not forced.

In order for the human (Alice) on the D1-4 wing to be forced, it would have to be possible for the human (Bob) at D0 to say something like "aha, I see a quite clear *wave* pattern has built up on my D0 screen! That means Alice, elsewhere and in the future, will be required to insert the beamsplitter for the vast majority of runs!"

But Bob simply can NOT ever see the wave pattern being built up, due to the phase shift! Therefore, Bob's results indicate nothing about Alice's choices, so nothing Bob sees constrains/compels/forces Alice to do anything.

 

[PeterDonis]

the human being "forced" to make the appropriate decisions

As has already been explained, there is no such "forcing" required, because the observed measurement result on one photon does not constrain which direction the other photon has to be sent (either by a beam splitter or by a human operating a switch--in the experiment as shown in the video, "which direction" is whether the photon is directed towards the A/B pair of detectors or the C/D pair of detectors; the beam splitters "decide" this in the video, but a human could similarly direct the photon by operating a switch). There is no correlation between the result on one photon and the direction the other photon has to go (A/B vs. C/D). There is only correlation between the observed result for one photon and the observed result for the other photon. @charters has repeatedly explained this.

This is precisely what we reject in our paper

Yes, which means you are trying to expound a point of view with which you disagree. It would be better to let the people who actually hold that point of view expound it, by giving some valid references (textbooks or peer-reviewed papers) that illustrate the claims you say Smolin and others are making about this. A pop science video doesn't help.

 

[vanhees71]

It would be nice to quote the article your are discussing about. I'm not sure, whether Sci. Am. as a popular-science journal (though the best one I know of this kind of popular-science writing) is accurate or not. To judge this, I'd need to look at the article of course.

Nevertheless, as far as I know, QT has passed all Bell tests so far, including also "quantum eraser" and "delayed-choice" setups. Thus there's not any new physics on the horizon in this realm.

 

[RUTA]

The Zeilinger experiment in this Insight is also a nice example of delayed choice. Again, every outcome in the pattern happens before the "choice" part happens, so if you want a forward-time causal mechanism (what I'm calling a "force") to explain the two distinct patterns, then the causal mechanism is at work on the "choice" not the pattern. It's that simple (and apparently differs from what you want the word "force" to mean). Here is the citation for the Sci. Am. article: R. Hillmer and P. Kwiat, “A do-it-yourself quantum eraser,” Scientific American 296, 90–95 (2007). As a physics professor, I have my students fit data using several methods, e.g., weak measurements for the DFBV experiment "Asking photons where they've been" and the Denkmayr et al. Quantum Cheshire Cat experiment, ΛCDM for the Union 2.1 data, modified Newtonian dynamics (MOND), Burkett halo DM, and Navarro-Frenk-White (NFW) halo DM dark matter fits of THINGS galactic rotation curve data, metric skew-tensor gravity (MSTG) and core-modified NFW DM fits of ROSAT/ASCA X-ray cluster mass profile data, and scalar-tensor-vector gravity (STVG) and ΛCDM fits of the Planck 2015 CMB angular power spectrum data, whether I agree with them or not (I only show my students fitting methods that have been refereed and published). I've been a physics professor for 31 years and working in foundations specifically for 25 years, so I'm simply using my expertise to answer the OP here, just as I do for my students in the classroom. Everything I've said represents conventional thinking in foundations of physics, as the references I posted show. If you want to disagree, get in the game and publish rebuttals (as I have done), then I can teach those as well.

 

[PeterDonis]

Everything I've said represents conventional thinking in foundations of physics, as the references I posted show.

References you've posted here, or in the Insights articles you just linked to?

As far as I can see, in this thread, you've posted repeated references that describe the experimental setups, which those posting in this thread are familiar enough with anyway. But none of those references make the claims you have described about a forward-time causal mechanism that would have to somehow constrain a human's choice of where to put the switch that determines whether which-way information is preserved or erased. And those latter claims appear to me to be obviously false (i.e., such a forward-time causal mechanism would not have to constrain the human's choice of where to put the switch), for the reasons that @charters has repeatedly explained. So I'm really curious who in the literature is explicitly making this obviously false claim, as opposed to the much weaker claim that how correlations that violate the Bell inequalities are produced is an open issue (which no one in this thread has disputed).

 

[PeterDonis]

The Zeilinger experiment in this Insight is also a nice example of delayed choice.

Has this experiment actually been done? I don't have the Zeilinger book that you reference in the Insight. Is there a published paper on the experiment itself?

 

[vanhees71]

The quoted experiment has been done and does in no way contradict standard QED. No need for blockworld formulations and other non-standard (personal) "theories".

There's a PhD thesis by B. Dopfer (in German):

https://www.univie.ac.at/qfp/publications/thesis/bddiss.pdf

 

[Michael Price]

Nevertheless, as far as I know, QT has passed all Bell tests so far, including also "quantum eraser" and "delayed-choice" setups. Thus there's not any new physics on the horizon in this realm.

Yes, the Bell tests are predictions of standard QT. And quantum erasers and delayed choice setups are just standard setups. Unless someone does an experiment and get unexpected results (they haven't) there is no new physics here.