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1. Apr 3, 2018

### vanhees71

Indeed. Even the most appealing creative thought has to be confronted with observations and accurate measurements. If you cannot make contact to observables, it's a nice mathematical idea at best or just philosophical gibberish at worst. If your predictions are clearly countered by observation, it's a physical theory that's wrong and needs to be modified (at best) or abandoned (at worst)! As all natural sciences physics after all is an empirical science.

2. Apr 4, 2018

### Lord Jestocost

Sir Arthur Stanley Eddington in "The Nature of the Physical World“:

"Scientific instincts warn me that any attempt to answer the question “What is real?” in a broader sense than that adopted for domestic purposes in science, is likely to lead to a floundering among vain words and high-sounding epithets."

3. Apr 4, 2018

### Peter Morgan

vanhees71, I can't see which comment you're referring to here. I understand if you might not want to use QUOTE, but it would help a lot if you would cite a comment number. TBH, I'm saying this because I've been unsure what or who you've been referring to a number of times, not just because of this one comment. Sorry! I won't say this again until I forget that I said it.

4. Apr 4, 2018

5. Apr 4, 2018

### Peter Morgan

I look forward to reading a review from you, RUTA. Having been to the talk Adam gave last night in New York, I'm not very enthusiastic. The last time I remember someone landing hard on a conversation at a foundations of physics conference with "Copenhagen says X, so everything you're saying is nonsense", was in the early 90's, and my sense is that physicists now more often fall back on decoherence (notwithstanding that the last mile from a mixed state to actual events is glossed), an interpretation which Adam didn't mention in his talk (I suppose because many philosophers would be loath to call decoherence an interpretation at all). Furthermore, I just read that Feyerabend in 1962 said (cited in arXiv:1509.09278, page 43)
which seems a clear statement, 56 years ago, of what seemed to be a large part of Adam's argument for why Copenhagen is still given lip service today.
Adam at one point said that he hopes to give his talk to physics departments, but TBH with nothing at all said about QFT (is there anything about QFT in the book?), and decoherence unmentioned, I can't see physicists taking him seriously. One high point of going to Adam's talk was that I talked to several Masters and PhD students and postdocs, all of whom seemed quite knowledgeable about and willing to talk about the interpretation of QFT.

6. Apr 4, 2018

### RUTA

I'm in Adam's chapter 6 on Bohm and Everett. I haven't seen anything about QFT mentioned in the other reviews and he has made little mention of it so far in his book, so I doubt he talks about interpretations of QFT. We offer an interpretation of QFT in chapter 5 of our book and that chapter opens with the following:

As for progress in this area, Healey notes, “no consensus has yet emerged, even on how to interpret the theory of a free, quantized, real scalar field” [Healey,
2007, p. 203]. And, “There is no agreement as to what object or objects a quantum field theory purports to describe, let alone what their basic properties would
be” [Healey, 2007, p. 221].

Foundations of physics (FoP) doesn't spend much time on this subject. FoP's attitude is that the weird/fun stuff is in QM, the only mysteries about QFT are technical, e.g., Haag's theorem, so FoP deals almost exclusively with QM. In my 24 years of attending FoP conferences and talks, I don't remember even one presentation on QFT issues. I'm very interested in your interpretation of QFT, as you know, because it looks to fill in technical gaps with my interpretation of QFT. With your help, I'll figure it out :-)

In the first 5 chapters, Adam has focused on the history of the Copenhagen interpretation (in its many variations) and why we're stuck with it now. His coverage of interpretational issues of QM has been sparse to this point. Based on reviews I've read, I'm assuming he'll plug those holes in part 3 of the book.

7. Apr 4, 2018

### Peter Morgan

Different circles! I think you're right, although I haven't been to a Foundations of physics conference, $lo$, the last ten years. Perhaps it's more the philosophers who have taken up the philosophy of QFT, and there are several mathematicians who have tried to make sense of the mathematics of renormalization/interacting QFT with what seem almost philosophical motivations. I filter out a majority of non-QFT foundations these days, so it seems quite the opposite way round. QFT changes the game totally, IMO, makes everything much easier, partly because there are already fields, so it's fields/waves duality, which I think is easier to live with, but of course I have to convince anyone of that.

8. Apr 5, 2018

### RUTA

I just finished Adam's analysis of the Bell inequality via a roulette wheel. I've heard this before in a different context, but it's a very nice way to introduce the Bell inequality to laymen. His claim afterwards is that only one of three logical possibilities exists: nonlocality, superdeterminism, or QM is wrong. Most people accept the experimental results vindicating QM, so few if any argue for the third option anymore (it was more common when I started working on this in 1994). I'm assuming he believes retrocausality falls into the SD camp? It's semantics, but I'd disagree with that since the "common cause" resides in both the future and past. I wouldn't say that any of the three options applies to the ontology of Relational Blockworld (RBW) where explanation is adynamical and QM is certainly correct. Therein, the fundamental ontological element is 4-dim and QM provides a distribution function for these 4D "spacetimesource elements" in the context of a classical block universe. So, we do have "realism" and there are no superluminal signals required in the explanation of the distribution of these real 4D objects in spacetime. I'm not even sure that the concept of nonlocality is relevant when discussing 4D objects (careful, this nonlocality has to do with superluminal signaling, not the locality assumed in differentiable manifolds). Silberstein and I are giving a talk to the foundations group at the Univ of MD next Wed, so I'll solicit their opinions. But, he and I agree that the standard analyses of Bell inequalities tacitly assume dynamism and are meaningless for adynamical explanation. Continuing, there is certainly no SD in RBW because there is no dynamical causation in adynamical explanation. In other words, when Adam claims to have exhausted all logical possibilities for the implications of Bell's inequality, he has failed to consider adynamical explanation.

9. Apr 6, 2018

### vanhees71

I only quote if I refer to a posting not immediately before the posting I'm answering to.

10. Apr 6, 2018

### vanhees71

He forgot the third, which is the contemporary solution of this apparent problem, which is local microcausal relativistic QFT. It's local (i.e., fulfilling the linked-cluster principle) and allows for the long-range correlations described by entanglement of parts of quantum systems that are observed at far-distant points. Of course, you have to give up naive collapse interpretations, which introduce an artificial action at a distance, which is in clear contradiction to the very foundations the Standard Model rests upon, namely locality and microcausality. Of course QM is only a non-relativistic approximation of the relativstic QFT and thus becomes wrong when applied to situations where the approximation is invalid.

11. Apr 6, 2018

### RUTA

That's not true, the formalism maps beautifully onto the experimental set-ups and data. There are many analyses, but one for undergrads that I use in my QM course is attached. There's nothing in the formalism that resolves this issue.

#### Attached Files:

• ###### Dehlinger Entangled Photons AJP 2002.pdf
File size:
224.5 KB
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24
12. Apr 6, 2018

### Peter Morgan

Quantum theory, being probabilistic, only makes predictions about statistics associated with recorded measurements. As a probabilistic theory, it has nothing to say about individual recorded events, only about their statistics. As a statistical theory, it includes the notion of microcausality, that measurements associated with space-like separated regions commute, but this is consistent with us being able to prepare states in which there are correlations at space-like separation.
I see this as resolving the difference between vanhees71 and yourself, that quantum theory is microcausal as a probabilistic theory, whereas a theory that non-stochastically predicts the precise timings of individual recorded events would appear to have to be either nonlocal or superdeterministic (or some combination thereof: any such model might require infinite information to be predictive if there's any chaos, so I can't see how we could determine what a non-stochastic theory would be, I think we have no honest choice but to say "hypotheses non fingo").

I can see some merits to the paper you attach, but, of course, I'd like something better. In particular, IMO the role played by the incompatibility of the pairs of measurements at each end should be emphasized: if we were to perform only compatible measurements at each end separately, there would be no violation of any Bell inequalities. That there are incompatibilities means that there are time-like dependencies, but between the two measurements at A and between the two measurements at B, not between the ends (that is, if we have two measurements at A and two measurements at B, $[A_i,B_j]=0, [A_1,A_2]\not=0, [B_1,B_2]\not=0$.) And I'd prefer "particles" not to be mentioned at all (instead of the word appearing 34 times): to be trite, for the quantized EM field there's just a wave/field duality. But that's a different paper altogether.

13. Apr 6, 2018

### Lord Jestocost

As I haven't read the book yet, I don't know Adam Becker's attitude.

14. Apr 6, 2018

### Boing3000

That is a nice refresher for those who think that quantum theory is a description of reality, instead of just a description of what would happens to "equally prepared state", that is "in a laboratory"

As a layman, do you know of any resource that will explains how QFT micro-causality is supposed to solve the EPR macro stochastic causality behaviors ?

Also Ruta's point on block -universe "interpretation" seems quite interesting, I'll try to dig into that also...

Aouch .. Latin hurts more than math On this topic of timing, isn't Bohmian's mechanic supposed to have more predictive power over classical QM ? If some spin value is observed to be X by Alice, isn't the (entangled?) pilot wave time dependency suppose to make more accurate prediction over the entangled value over time (and space) at Bob's end ?

15. Apr 6, 2018

### Peter Morgan

What I said, that QM/QFT is a probabilistic theory —which can be understood to model, and hence in appropriate circumstances to predict, statistics of recorded experimental events—, seems to me not inconsistent with quantum theory being "a description of reality". I think of QM/QFT, admittedly loosely, as being as much as we can say about "reality" because to predict individual events in a chaotic world would require more information than I think we can plausibly have access to, perhaps even might require infinite information.

I have a terrible memory, I'm afraid. I retain concepts more-or-less, once I've grokked them, but I too often forget where I learned about them and where the good references are. That said, I don't think of microcausality as solving EPR. Microcausality —that measurements are compatible with and don't change the statistics of other measurements that are at space-like separation— is apparently consistent with experiment, whereas in fact we can set up states in which there are correlations and Bell inequality violations between space-like separated measurements.

I think of Bohmian mechanics more as retrodicting a trajectory, given an individual actual event, if we know (or think we know) the quantum dynamics. That is, if the event is caused by a particle, that particle must have come from somewhere, because that's what particles do. We can massage the quantum dynamics to give us an equation that determines a trajectory when it's given just a single point on that trajectory (it's sometimes cited as a conceptual difficulty for Bohmian mechanics that we don't need to know the velocity as well as the position to determine the trajectory —differently from the case for classical mechanics, that is). BUT, at least in those cases where we do not observe more than one point (not high energy physics, and not a football or anything else large, in other words, but for most low energy experiments, because then the particle is absorbed and doesn't carry on along the same trajectory), that's not a prediction. To claim that de Broglie-Bohm is empirically equivalent to QM, one has to say that de Broglie-Bohm is a probabilistic theory.
Personally, I'm OK with de Broglie-Bohm trajectories for the non-relativistic case, except that, crucially, the math is a mess compared to just using Hilbert spaces. When we use QFT, however, I've not seen de Broglie-Bohm work out well enough. Most physicists just cite the QFT case as a one-line dismissal.

16. Apr 6, 2018

### Staff: Mentor

QFT "micro-causality" means that spacelike separated measurements must commute (i.e., the results must not depend on the order in which they are performed). Bell-inequality violating experiments meet this condition. So I don't see what there is to "solve".

17. Apr 6, 2018

### RUTA

Thnx for intervening, hopefully this exchange will educate those who are likewise confused :-) The issue isn't with the formalism and it isn't with the data (I hope that isn't what you're implying). The formalism maps beautifully onto the data, as you can see in the paper. The issue is what you appear to brush aside. The statistical data is collected one event (coincidence) at a time (within the 25-ns coincidence window), just like the roulette balls in Adam's analogy. Therefore, any explanation for the correlation in the statistical data should be based on the nature of reality as it pertains to each trial (and it's not accidental coincidences as you can see from the last column of Table 1).

Bring your explanation supra to bear on Adam's roulette wheel analogy and you'll see where it's lacking. That is, you'd be attempting to resolve the mystery by saying, "I have a statistical mathematical formalism that maps onto the statistical data." That answer in no way tells me what is causing the two balls to land in the same color every time the two experimentalists choose the same wheel number, but land in the same color only 25% of the time that the two experimentalists choose a different wheel number. [This is exactly the Mermin analogy, see my QLE explanation, where we expect at least 33% agreement for different wheel numbers in order to account for 100% agreement for same wheel numbers.] Giving up on finding the underlying cause for the experimental correlations is your choice, but that in no way resolves the issue for those of us who haven't given up.

The experiment instantiates a QM violation of a Bell inequality. There is nothing more needed to experimentally confirm the mystery a la Adam's roulette wheels or Mermin's device, unless you believe there is something wrong with QM (Adam's third option). Is that what you're implying?

18. Apr 6, 2018

### Peter Morgan

It's the theoretical gloss in the paper that I find lacking. I'm confident the experiment as given, using off the shelf components, violates Bell inequalities, and I'm reading you to be saying that your students have done the experiment dozens of times over the years? I asked for Gregor Weihs' raw data at one time and analyzed it in a way that showed him a new feature, though it's not earth-shattering (arXiv:1207.5775, also on my very irregularly maintained blog, https://quantumclassical.blogspot.com/2010/03/modulation-of-random-signal.html — astonishing, for me, to see that that is 8 years ago).
So I don't doubt the weirdness.
I'm by no means saying that others can't tackle classical chaos in sophisticated ways in an attempt to model quantum level systems deterministically, it'd be great if someone could give us a toe-hold on that, but I'm certain I'm not a good enough mathematician to tackle that head on. My only hope would be to notice something serendipitously as a result of being so immersed in the relationship between quantum and random fields, although I think that's probably already given in to the urge to address chaos with probability.

19. Apr 7, 2018

### RUTA

Just finished Part II. Chapter 8 is what the Copenhagenists, instrumentalists, operationalists, and positivists among you should read.

He’s advocating for dBB and MWI, not because he necessarily believes those are “right,” but simply because they offer counterexamples to Copenhagen. I didn’t realize Copenhagen was so dogmatic, I thought it was merely instrumentalist, which I have always considered “agnostic.” Adam’s take on instrumentalism is a la positivism and operationalism, both of which strike me as more dogmatic. Physicists who are just not interested in analyzing various interpretations aren’t impeding progress, since their lack of interest means they wouldn’t likely contribute anything meaningful anyway. It’s those who naively believe they don’t even possess an interpretation themselves and actively dissuade younger physicists from asking those questions. Part II presents an interesting history explaining how the attitudes of Copenhagen, instrumentalism, positivism, and operationalism became so popular among physicists when philosophers have long since dismissed them on intellectual grounds.

20. Apr 7, 2018

### atyy

It depends on whose Copenhagen. I go to both churches without any sense of conflict.

21. Apr 7, 2018

### AlexCaledin

The thing is, everyone naturally has his own wishful thinking! To avoid offending someone's sacred hopes (like materialism or many worlds or Divine Choice), it's necessary to keep certain wise dogmas developed by Niels Bohr and company .

Last edited: Apr 7, 2018
22. Apr 7, 2018

### George Jones

Staff Emeritus
I cannot tell whether this post is tongue-in-cheek or serious.

I didn't know that Niels Bohr developed any wise dogmas. Dogmas, yes.

23. Apr 8, 2018

### AlexCaledin

- but don't forget, Bohr had Einstein to discuss things with; - and nowadays you only have guys whose Most Sacred Hope is just to attain unto perfect non-existence in the end; - so, to you, Bohr's ideas are of no use of course.

24. Apr 8, 2018