The quantum state cannot be interpreted statistically?

[DrChinese]

And PS to my post above: I don't mean to debate the point here because it has nothing to do with PBR. We should start a separate thread if we want to discuss RBW or free photons.

 

[qsa]

This is really bothering me as I still can't believe how physicists can have such opposing interpretations of PBR theorem:

thank you, I see finally 200 posts later somebody is answering my #171 post

So what is the relation between the nature of psi, its interpretation and the wave-particle daulity. would a choice for one affect the others. or is that too much to ask.

now I hope it will not take another 200 posts to respond to this question.

a Circle would be concidered an ontic entity and so are the numbers 4 ,100, ...

but the circle must be described in some way and there are multiples of them and so are the numbers ( 1+3=4, 2+2=4 ... ). SO, are the descriptions themselves are ontic or epistemic?

 

[DevilsAvocado]

... They came up with the theory first and then started working on its application. This is a result, which is rare to see from QM interpretations as you must admit. I would call that first rate science regardless of where it leads.

Agree 100%.

 

[DevilsAvocado]

Harrigan & Spekkens contains at least one explicit example of a ψ-complete ontological model for QM. They call it the Beltrametti-Bugajski model. The ontic state space $\Lambda$ of the Beltrametti-Bugajski ontological model for the quantum theory with Hilbert space $\mathcal H$ is the set $\mathcal P\mathcal H$ of 1-dimensional subspaces of $\mathcal H$.

Okay, so the Beltrametti-Bugajski model must be non-local then (ontic state space)? But how could a non-local model be considered complete, I don’t get it...?

PBR says nothing about ψ-complete ontological models for quantum theories. Their argument is specifically against ψ-epistemic ontological models.

Okay, but if you adopt the realist ψ-complete view, isn’t that that 'compatible' to ψ-epistemic ontological models?? Or, am I missing something...

From the preface:

...contemporary analytic metaphysics, a professional activity engaged in by some extremely intelligent and morally serious people, fails to qualify as part of the enlightened pursuit of objective truth, and should be discontinued.
[...]
...a group of highly trained professionals have been wasting their talents—and, worse, sowing systematic confusion about the nature of the world, and how to find out about it...
[...]
We care a great deal about philosophy, and are therefore distressed when we see its reputation harmed by its engagement with projects and styles of reasoning we believe bring it into disrepute, especially among scientists.
​

This reminds me of Steven Weinberg's "Dreams of a final theory". It's been 15 years or so since I read it, but I think I remember a comment that said roughly that the only times when philosophers have made valuable contributions to science, have been when they've told us that we can ignore what some other philosophers have been saying.

Yes, the very first sentence "This is a polemical book."

I’m still reading, and I jumped directly to chapter 3 (curious), but chapter 1 is quite a rough duel whit some colleagues in the business... and "is partly destructive in aim"... interesting book indeed...

 

[DevilsAvocado]

Do the photons from the CMBR exist free independent of observation?

Yay! I’ve 'stressed' RUTA about this and he know it’s a "problem", i.e. every photon needs to be predestined with its target to make this work (the links), and apparently there are (too) many photons "on the run" (= no target) in current models... but this is something for a new thread.

 

[bohm2]

So what is the relation between the nature of psi, its interpretation and the wave-particle daulity. would a choice for one affect the others. or is that too much to ask.

I trust Leifer's summary more than anybody else's. His conclusion is that there are only 2 options left after PBR:

1.Wavefunctions are epistemic. This is the Bohrian-type interpretation and it's variants. All seem to be instrumental, in my opinion. Although I'm sure someone like Fuchs and KenG on this forum will disagree.

2.Wavefunctions are ontic. This includes Everett, deBroglie/Bohm, GRW, etc. This is the scientific realist perspective. The other scientific realist position got axed after PBR.

I hi-lite the "scientic realist" because that's how Leifer refers to it. The other scientific realist option got shot down by PBR. But even this term (scientific realism) seems a bit imprecise:

Scientific Realism
http://plato.stanford.edu/entries/scientific-realism/

 

[Fredrik]

Okay, so the Beltrametti-Bugajski model must be non-local then (ontic state space)? But how could a non-local model be considered complete, I don’t get it...?

You may need to look at the definition of an ontological model for a quantum theory again. It involves a set $\Lambda$ whose members are called ontic states. The members of $\Lambda$ are assumed to satisfy an equality like $$\sum_{\lambda\in\Lambda} P(\lambda|\psi)P(k|A,\lambda)=|\langle k|\psi\rangle|^2.$$ This exact notation is only appropriate when $\Lambda$ is finite, and the ontological model is non-contextual, but it's sufficient to illustrate the general idea. This requirement makes it convenient to think of

• $\lambda$ as a complete specification of all the properties of the system,
• $P(\lambda|\psi)$ as the probability that the system has properties λ, given that the preparation procedure is consistent with $|\psi\rangle$,
• $P(k|A,\lambda)$ as the probability that the result will be k, given that the properties of the system are λ, and that the measurement procedure is consistent with A.

The function $\lambda\mapsto P(\lambda|\psi)$ is called the epistemic state associated with the equivalence class of preparation procedures that the quantum theory associates with $|\psi\rangle$.

The Beltrametti-Bugajski model is just saying that each quantum theory defines an ontological model for itself in an almost trivial way, so it's not surprising that it's ψ-complete.

Okay, but if you adopt the realist ψ-complete view, isn’t that that 'compatible' to ψ-epistemic ontological models?? Or, am I missing something...

No ontological model for a quantum theory is both ψ-complete and ψ-epistemic. See fig. 3 at the top of page 6.

 

[DevilsAvocado]

No ontological model for a quantum theory is both ψ-complete and ψ-epistemic.

I must say of all these interpretations the frea**ng Danish Smørrebrød drives me crazy!

Of course you are right, if you have a complete description of some underlying reality, there must be an ontic state corresponding to that description, and even if we don’t not exactly what constitutes ("in reality"), it’s there (when entangled particle starts its journey) = Local Realism.

This means that the Beltrametti-Bugajski ψ-complete ontological model is also = Local Realism, it doesn’t matter if the "ontic states are parameterized by the Bloch vectors" etc...

One has to choose – either is Local Realism or it’s not.

And either way, Bell is going to kick some a**es, and to me, that would mean it will be very hard to claim any complete description of reality. This (strangely enough) is also what Spekkens is saying on the very first page in the very same paper:

http://arxiv.org/abs/0706.2661]Einstein[/PLAIN] had already shown a failure of locality for the ψ-complete view with a very simple argument at the Solvay conference in 1927. It is also well-known in such circles that a slightly more complicated argument given in 1935 — one appearing in his correspondence with Schrödinger, not the Einstein-Podolsky-Rosen paper — provided yet another way to see that locality was ruled out for the ψ-complete view. What is not typically recognized, and which we show explicitly here, is that the latter argument was actually strong enough to also rule out locality for ψ-ontic hidden variable theories. In other words, Einstein showed that not only is locality inconsistent with ψ being a complete description of reality, it is also inconsistent with ψ being ontic, that is, inconsistent with the notion that ψ represents reality even in an incomplete sense. Einstein thus provided an argument for the epistemic character of ψ based on locality.

This confusing... one could hardly claim that Einstein showed that locality is inconsistent with ψ being a complete description of reality on page one, and then one page 6 say that:

– Hey, look what we found! The ψ-complete ontological Beltrametti-Bugajski model, and it works!​

That’s just nuts... if the ψ-complete ontological Beltrametti-Bugajski model works, it must be non-local, and that could not be compatible with a complete description of reality. And if it’s local, it must be non-real = ψ-epistemic, and this is impossible, if it claims to ontological model... Mamma Mia...

I give up.

 

[kith]

/edit: Hmm, what I had written here is probably not true.

I'm just getting into the subject and will probably have lots of questions, by the time I've worked through Leifer's blog and the first two articles. ;-)

 

[Ken G]

And yet the answer could easily have cosmological implications. I can think of a few choice ones myself. So I am not so sure that a future QM interpretation might not have some things to say about cosmology.

I'll restrict any response to just saying what you might expect me to say-- I don't think that will happen. Interpretations of physics theories don't tell us about reality, reality tells us how to interpret our theories. You're right that this discussion is for another thread, albeit a very interesting one (I pretty much agree with Mentz114, though I would argue that the distinctions drawn there are not scientifically important, they are too ontological).

 

[Ken G]

This reminds me of Steven Weinberg's "Dreams of a final theory". It's been 15 years or so since I read it, but I think I remember a comment that said roughly that the only times when philosophers have made valuable contributions to science, have been when they've told us that we can ignore what some other philosophers have been saying.

Yes, Weinberg started out in philosophy, decided there were no answers for him there, shifted to physics, and won a Nobel prize. So it's easy to see where he is coming from, but it's pretty much a personal tale. In my opinion, Weinberg falls into the trap of imagining that everything he personally regards as true (like multiple universes and anthropic explanations of reality) is science, and anything different that is regarded by someone else as true is philosophy. It's a bit too convenient.

 

[Fra]

So I am not so sure that a future QM interpretation might not have some things to say about cosmology.

Provided we aren't just talked about pure interpretations of the fixed mathematics of QM, but with "future QM interpretations" include also the possibility that there is a generalized measurement theory, then my personal opinon is that I am close to convinvced that there is a strong link there between cosmological theories vs theories for small subsystems and generealized measurement theory vs QM. The issue is also closely related to open vs closed system, where the point would be that one can not always treat and open system like embedded in a bigger close system, because the information capacity needed to envode the description too too high.

My own personal stance is that QM formalism as it stands, simply fails to be a good framework for cosmological systems. It is designed, tested and good for small subsystems (ie atomic physics). I think it's a kind of fallacy on it's own to project this onto cosmological scenarios (where the point is that the observer is EMBEDDED and depending on the very system (=environment) it is observing. The assymmetry to an S-matrix description of a scattering experiment is so enormous that we shouldn't even need to fall into this trap.

What I do not think however, is that QM as it stands, will be able to produce any clever clues to cosmology. We need a new framework for that.

Edit: I think in a larger context, this is also exactly the CORE of the issue of what the "statistical interpretations means". I mean, it's clear what is means for repetable small-systems. But it's uttrely unclear for cosmological observables, for obvious reasons. (user=Fredrik will jump on me know for brining this up, so I apologize in advance:).

/Fredrik

 

[bohm2]

Interpretations of physics theories don't tell us about reality, reality tells us how to interpret our theories.

Now I'm confused. I pegged your position as a bit Kantian but that argument doesn't sound Kantian, I think. But I'm so lost that I may be mistaken. A Kantian would probably argue that we do not interpret the world but only representations of the world. Any interpretation, is always exercised on internal models of the environment, never on the environment itself. So that, perception of "external reality" is always mediated/filtered through our mental organs. The environment (in an objective sense) would not represent the final/ultimate object of any perception/model, for various reasons like underdetermination of theory by data, etc. It would just act as a "trigger". A modern neo-Kantian/innatist is Chomsky, I think?

I think we are forced to abandon many commonly accepted doctrines about language and knowledge. There is an innate structure that determines the framework within which thought and language develop down to quite precise and intricate details. Langauge and thought are awakened in the mind, and follow a large, predetermined course, much like other biological properties. They develop in a way that provides a rich structure of truths of meaning. Our knowledge in these areas, and I believe elsewhere-even in science and mathematics-is not derived by induction, by applying reliable procedure and so on; it is not grounded or based on "good reason" in any useful sense of the notion. Rather it grows in the mind, on the basis of our biological nature, triggered by appropriate experience, and in a limited way shaped by experience that settles options left open by the innate structure of mind. The result is an elaborate structure of cognitive systems of knowledge and belief, that reflects the very nature of the human mind, a biological organ like others with its scope and limits.
This conclusion, which seems to me well-supported by the study of language and I suspect holds true far more broadly, perhaps universally in domains of human thought, compels us to rethink fundamental assumptions of modern philosophy and our general intellectual culture, including assumptions about scientific knowledge, mathematics, ethics, aesthetics, social theory and practise and much else, questions too broad and far-reaching, for me to try to address here, but questions that should, I think, be subjected to serious scrutiny from a point of view rather different than those that have conventionally been assumed.

http://sammelpunkt.philo.at:8080/1284/1/Chomsky.pdf

What's surprising is he also considers himself sympathetic to "scientific realism" although he prefers the term "methodological naturalist". So many confusing terms.

 

[DevilsAvocado]

More philosophers rambling out of their butt – Steven Weinberg is now an "ex philosopher"?

Steven Weinberg Bio:

• Born May 3, 1933
• Graduated from Bronx High School of Science 1950
• Received his bachelor's degree (B.Sc.) from Cornell University 1954
• Graduate studies and research at the Niels Bohr Institute in Copenhagen 1955
• Received his Ph.D. degree in Physics at the Princeton University 1957
• Post-doctoral researcher at Columbia University 1957–1959
• Post-doctoral researcher at University of California, Berkeley 1959
• Promoted to faculty at Berkeley 1960–1966
  (Where he did research in a variety of topics of particle physics, such as the high energy behavior of quantum field theory, symmetry breaking, pion scattering, infrared photons and quantum gravity)
• Loeb Lecturer at Harvard 1966
• Visiting professor at M.I.T. 1967
• Professorship in the Physics Department at M.I.T. 1969
• Higgins Professor of Physics at Harvard 1973
• Nobel Prize in Physics 1979
  (For the theory of electroweak unification based on spontaneous symmetry breaking)

Steven Weinberg, a co-architect of the (very pragmatic) Standard Model, has never been a "philosopher" and probably never will be, what is true though, is that he in 1982 moved to the physics and astronomy departments at the University of Texas at Austin, to focus on astronomy.

 

[bohm2]

More philosophers rambling out of their butt.

The quote above is not from a philosopher and either am I (just for the record). But as you get older there's a natural tendency to reflect on what you were doing in your field, when you were younger, I think? Not that there's anything wrong with pure philosophy as long as they meet Friedman's quote below (in my opinion):

The philosophers of the modern tradition from Descartes are not best understood as attempting to stand outside the new science so as to show, from some mysterious point outside of sciences itself that our scientific knowledge somehow mirrors an independently existing reality. Rather, they start from the fact of modern scientific knowledge as a fixed point, as it were. Their problem is not so much to justify this knowledge from some 'higher' standpoint so as to articulate the new philosophical conceptions that are forced upon us by the new science. In Kant's words, mathematics and the science of nature stand in no need of philosophical inquiry for themselves, but for the sake of another science: metaphysics.

And that's what posters are doing on here, for the most part, I think.

 

[bohm2]

Here's another good blog by a physicist (Steve Hsu) that does a good job of discussing the implications of PBR:

Technically, the (lambda, q) formalization describes a model in which

(i) there is an underlying reality (some Mysterians apparently do not actually believe this) and
(ii) the state vector Psi does not describe the underlying reality but rather an observer's knowledge about it.

The fact that a given underlying reality lambda has probability q of being consistent with two different preparations of a state, which each yield different pure states phi_0 and phi_1 (their notation), is meant to capture (i) and (ii) above. Remember that to a Mysterian the pure state is a description of a state of knowledge, not of reality. So nonzero q means that two different states of knowledge (preparations) are consistent with the same underlying state of reality.

http://infoproc.blogspot.com/2011/11/is-wavefunction-real.html

I don't understand why he says in his comments:

I think it means wavefunctions don't collapse.

He must be joking?

 

[akhmeteli]

Here's another good blog by a physicist (Steve Hsu) that does a good job of discussing the implications of PBR:



http://infoproc.blogspot.com/2011/11/is-wavefunction-real.html

I don't understand why he says in his comments:

I think it means wavefunctions don't collapse.

He must be joking?

I have no idea if he is joking or not, but if he is not, he is not alone - see the quote from Schlosshauer's review (M. Schlosshauer, Annals of Physics, 321 (2006) 112-149) at https://www.physicsforums.com/showpost.php?p=2534950&postcount=41

 

[qsa]

Here's another good blog by a physicist (Steve Hsu) that does a good job of discussing the implications of PBR:

thanks for the link

here is one of his comments



They explicitly note in the paper (for the really clueless) that they aren't trying to show that qm is really deterministic. In fact they entertain much more general classes of theories than ordinary qm, including stochastic hidden variables.

and another from other posters

Guess it's time to take Weinberg's advice and rethink the entire QM


I say yes to both. You know why, lines!

 

[bohm2]

I have no idea if he is joking or not, but if he is not, he is not alone - see the quote from Schlosshauer's review (M. Schlosshauer, Annals of Physics, 321 (2006) 112-149) at https://www.physicsforums.com/showpost.php?p=2534950&postcount=41

I was hoping that there was some argument in PBR that can eliminate spontaneous collapse theories like GRW. Anything that narrows down interpretations is a good thing. I really don't care which other interpretation gets shut down. The more the merrier. Let's just hope we reach that ONE interpretation before we reach our graves

 

[DevilsAvocado]

The quote above is not from a philosopher and either am I (just for the record). But as you get older there's a natural tendency to reflect on what you were doing in your field, when you were younger, I think? Not that there's anything wrong with pure philosophy as long as they meet Friedman's quote below (in my opinion):

And that's what posters are doing on here, for the most part, I think.

I’m sorry for that sentence, it was over the line. And it should have been in singular, not plurals. (I you know what I mean...)

I have no problem with philosophy, it’s cool, especially when put under the "Friedman restriction" in your quote; "Their problem is not so much to justify this knowledge from some 'higher' standpoint so as to articulate the new philosophical conceptions that are forced upon us by the new science. In Kant's words, mathematics and the science of nature stand in no need of philosophical inquiry for themselves, but for the sake of another science: metaphysics".

This perfectly okay, and I think everybody agrees on that.

IMHO the problem starts when a "philosopher" (and it’s not you I’m talking about) wants to bring down the "firewall" between science and philosophy, and then (naturally) what 'sets the rules' in a situation like this is the "philosopher" and his "philosophy".

This can never be right (and I think many of the hundred of posts in this thread is an example of this failure and confusion).

Another thing that could cause severe trouble is the fact the metaphysics is a "blurry thing", if not specified exactly, and could mean Ontology, Natural Theology/Religion* or Universal science.

In this place we’re supposed to stick to the facts, and if I claim something 'extraordinary', like; "Bertrand Russell started out as a High energy physicist, but he failed and there were no answers for him there, and he therefore shifted to philosophy", I need a source to backup this preposterous claim!

This particular attack on Steven Weinberg is extremely dull-witted, since he’s known for being an down-to-earth atheist and a hardnosed scientific realist, sticking to the facts, and a strong opponent of postmodernists questioning scientific objectivity. There are probably very few "metaphysical molecules" in this body... if you know what I mean. And the claim that the Nobel laureate Steven Weinberg is just a "personal guesser" is a full-blown disgrace, and just on the edge to being reported!


*This is not place or the time to deal with the following, but jfyi: I have seen "the subject" advocating for a position where it’s not okay to refute a claim that the Earth is only 6000 years old, if the (creationist) opponent is referring to "a belief" and not scientific facts – "this is a religious statement about which science is of course completely moot"... I hope you agree that this 100% crap and has nothing to do with science or philosophy of science.

 

[qsa]

IMHO the problem starts when a "philosopher" (and it’s not you I’m talking about) wants to bring down the "firewall" between science and philosophy, and then (naturally) what 'sets the rules' in a situation like this is the "philosopher" and his "philosophy".

This can never be right (and I think many of the hundred of posts in this thread is an example of this failure and confusion).

Another thing that could cause severe trouble is the fact the metaphysics is a "blurry thing", if not specified exactly, and could mean Ontology, Natural Theology/Religion* or Universal science.

I agree, please check your PM.

 

[apeiron]

I’m sorry for that sentence, it was over the line.

But mysteriously you always seem to get away with it. Need we mention Netanyahu's eyes?

I enjoy your contributions but do you need to get into these personal feuds based on misunderstandings and misinterpretations? They are fun for a while, then sour badly.

...just on the edge to being reported!

If you are looking for reportable comments in this thread, no need to look much further than multiple instances of this kind of stuff...https://www.physicsforums.com/showpost.php?p=3657619&postcount=380

If you are looking for some amusement, ask the semi-intellectual Professor Gobbledygook

 

[ThomasT]

Let's just hope we reach that ONE interpretation before we reach our graves

My guess is that most working physicists operate with a minimalist interpretation of qm -- which essentially entails not taking the formalism, the formal mathematical maps ... literally (ie., as necessarily referring to the underlying territory) , but still appreciating that certain inferences about the underlying reality might reasonably be made, based on the notion that there's no particular reason to believe that the underlying reality is essentially different from the reality of our sensory experience.

Wrt the OP, I was taught not to think of quantum states as depictions of reality. The qm formalism as a whole involves classical conceptions as well as mathematical abstractions which obviously are not descriptions of reality but are calculational tools.

Can the quantum state be interpreted statistically? Well, the quantum theory is a statistical/probabilistic theory. The precise relationship between the mathematical formalism and the underlying reality is, and will remain, a matter of speculative conjecture.

It's been an interesting/entertaining thread, but I think that it's probably run its course. The unsatisfying answer, imo, to the question of the meaning of the quantum theory is that there can't be any definitive answer to that question.

 

[bohm2]

I’m sorry for that sentence, it was over the line. And it should have been in singular, not plurals. (I you know what I mean...)

No problem. It wasn't over the line. I just might be that I'm a bit of a whimp/sensitive. It's my anxiety/ASD? I feel like people are screaming at me even when they're not even talking/referring to me.

 

[apeiron]

No problem. It wasn't over the line. I just might be that I'm a bit of a whimp/sensitive. It's my anxiety/ASD? I feel like people are screaming at me even when they're not even talking/referring to me.

Avocado wasn't referring to you. The clue is in: "it should have been in singular, not plurals. (I you know what I mean...)"

 

[Ken G]

Indeed, he was referring to himself, or more correctly a caricature that he has created. He thinks he's referring to me, but he has no idea what I'm saying, so he is referring to something he sees in the mirror. As it has nothing to do with me, I take no offense, it's rather amusing.

For those who want to know what I'm actually saying, they should also ignore DevilsAvocdo's fantasy version, and consider this: my point can be summarized by noting the error in what was said by Steve Hsu quoted above:

Technically, the (lambda, q) formalization describes a model in which

(i) there is an underlying reality (some Mysterians apparently do not actually believe this) and
(ii) the state vector Psi does not describe the underlying reality but rather an observer's knowledge about it.

What is incorrect here? Well, it certainly isn't "technically" true, because it leaves out a very important step in the logic. Hsu, and many others it would seem, have tacitly, and without even realizing, assumed this huge leap of faith:

(ia) the existence of an "underlying reality" requires that what happens in that reality be determined by the parameters in some theory!

Why else would assumption (i) amount to a hill of beans, what possible scientific meaning does assumption (i) have without assumption (ia)? So no, it is not "gobbledygook" to point out a simple yet crucial logical oversight. And it is certainly not "mysterion" to question (ia), on the grounds that it has never been true yet. The problem is that people keep confusing what realism should mean, belief in an underlying reality (as I've argued above it should mean), with what it actually means in the standard lexicon. "Realism" is not the belief in an underlying reality, it is the belief that the properties of our theoies are the properties of the reality. In short, realism involves committing a category error, which can also be called the mind projection fallacy, because that's what it is. If reality "underlies" (or overlies, or sideways-lies) our theories, then we certainly should not, in the very next breath, mistake our theories for that reality.

Some have tried to rescue realism with what has been termed "structural realism", which asserts that although the properties of reality are not the properties of our theories, still they share some basic structural similarity. I have no issue with that, except that it is really too vague to be saying anything important. I cannot see any meaning behind it, other than merely saying the obvious truth that scientific theories work to some high degree of usefulness, which I called effective truth. If there can be any other meaning to sharing structure then I'd call it a darn vague one, and nothing that science needs to care about. What's more, I've pointed out that the entire term "realism", though applied in the traditional way, is actually a misnomer, because believing that the properties of our theories are the properties of reality, when it is demonstrably true that theories are generated in and exist in our minds, requires associating a product of our mind with the fundamental truth of reality-- which is called idealism and is usually considered the opposite of realism. Throw in how completely counter to the historical evidence is the belief that the properties of theories are the properties of nature, and I cannot think of any view less realistic (and more like a "mysterion") than what is passed off as realism in science, as demonstrated by the above logical omission.

 

[Ken G]

More philosophers rambling out of their butt – Steven Weinberg is now an "ex philosopher"??

As this involves more than just your factual errors about what I said (I never said he was an ex-philosopher, for example), I will correct your factual errors about Weinberg because it is relevant to his mindset. I'm certainly glad to see you can read a Wiki bio, but unfortunately bios only tell part of the story. Better to actually know something about Weinberg, such as what he says about himself. Consider this quote from his well-known essay "Against Philosophy":
"It is only fair to admit my limitations and biases in making this judgment. After a few years' infatuation with philosophy as an undergraduate I became disenchanted. The insights of the philosophers I studied seemed murky and inconsequential compared with the dazzling successes of physics and mathematics."

So I took "years of infatuation" and, not having the quote in front of me, paraphrased it as "started out in philosophy." That was a bit of an overstatement, but I did not imply he was a professional philosopher, so could ever be an "ex philosopher", but it is certainly true that we considers himself an "ex enthusiast" of philosophy, having started out with a serious interest in it ("years of infatuation"). This is all that is required to make the logical step I used it to make: that his views on philosophy are informed by his own personal experience of disenchantment with it. Then I pointed out that for someone who claims to be disenchanted with philosophy, he certainly does not hesitate to wax philosophical about science, religion, metaphysics, and the anthropic principle. This was the point I was making.

On the other hand, the ridiculous interpretation you gave to my remarks above, claiming that I said Weinberg was an ex philosopher and citing his bio to refute what was never said, is certainly symptomatic of all your problems understanding plain English. I think you should look to that problem before you offer any more insights into what others are saying.

 

[bohm2]

"Realism" is not the belief in an underlying reality, it is the belief that the properties of our theories are the properties of the reality.

I think the authors do note the possibility in the PBR paper where they write:

The first (assumption) is that if a quantum system is prepared in isolation from the rest of the universe, such that quantum theory assigns a pure state, then after preparation the system has a well defined set of physical properties.This assumption is necessary for the question we address to make sense: if such physical properties don't exist, it is meaningless to ask whether or not the quantum state is among them...We have shown that this is only possible if one or more of the assumptions above is dropped. More radical approaches (e.g. Fuchs, yourself?) are careful to avoid associating quantum systems with any physical properties at all.

So that "more radical approach" is to drop the belief that quantum systems have any physical properties? It is this option that you and Fuchs (I think) refer to that I don't understand. To me, it seems to degenerate into instrumentalism and goes against the spirit of "scientific realism" even though you didn't believe that this is necessarily true since you wrote:

scientific realism is already more or less a given

I'm just a bit lost. Do you think that Leifer is correct that taking your position (or Fuchs's) is taking a position against scientific realism leading to instrumentalism and making physics "the science of meter readings"? At the least, it seems that there can be no in between stance; that is, you are either an anti-realist/Bohrian or a scientific realist so that you can't be both a Bohrian and a scientific realist? I think that's why Bell kept asking the question: Whose information? Information about what?

Here are three possible answers to this question:
1.Wavefunctions are epistemic and there is some underlying ontic state. Quantum mechanics is the statistical theory of these ontic states in analogy with Liouville mechanics. (Scientific realism)

2.Wavefunctions are epistemic, but there is no deeper underlying reality. (Instrumentalism/anti-realist)

3.Wavefunctions are ontic (there may also be additional ontic degrees of freedom, which is an important distinction but not relevant to the present discussion. (Scientific realism)

Options 1 and 3 share a conviction of scientific realism, which is the idea that there must be some description of what is going on in reality that is independent of our knowledge of it. Option 2 is broadly anti-realist, although there can be some subtleties here.

So your position is one of those subtleties as is Fuch's. I don't understand it at all. Leifer questions this subtlety also:

The subtlety is basically a person called Chris Fuchs. He is clearly in the option 2 camp, but claims to be a scientific realist. Whether he is successful at maintaining realism is a matter of debate.

I have the same problem understanding Chomsky's position noted in my quote. He considers himself a scientific realist and yet takes a similar position to you and Fuchs, I think? And I see all 3 of you are far more intelligent than myself, so I'm just trying to understand how that is possible.

 

[Maui]

And the claim that the Nobel laureate Steven Weinberg is just a "personal guesser" is a full-blown disgrace, and just on the edge to being reported!

Can you provide the exact quote where someone said that? Or are you going to report yourself for spreading misinformation?

 

[Ken G]

So that "more radical approach" is to drop the belief that quantum systems have any physical properties?

Quite so, and indeed I reject the label "radical" in favor of the label "consistent with everything we know about science."

To me, it seems to degenerate into instrumentalism and goes against the spirit of "scientific realism" even though you didn't believe that this is necessarily true since you wrote:

I think I can clear up the consistent thread here. I would like to distinguish three flavors of realism, which don't all officially get called realism but the one that does seems the least realistic to me. Let's call them:
1) naive realism-- the properties that our theories attribute to natural systems in order to predict and understand their behavior are actual properties those systems possesses independently of how we reason, perceive, and do science.
2) structural realism-- the properties of our theories are just what we can demonstrate them to be: properties of our theories. However, they must work for some reason, to whatever extent they do work, so we'll say that they work because they share some vague "structural similarity" to the actual reality, whatever that means.
3) instrumentalism-- actual reality is a meaningless scientific concept, what we are applying science to is the outcomes of observations so everything that is real is titrated through some kind of instrument, and all we ever do is predict the behaviors of those instruments.

Here are my criticisms of each:
1) It's ridiculous, ignores how the human mind works, and is oblivious to the entire history of the endeavor of physics. It's just obviously wrong. Random example: Newton's action at a distance, which for generations was adopted as one of these "true properties" of the universe (not by Newton, by the way).
2) This one is at least logically self-consistent, but is pretty vague. I view it as basically correct, but only because it is not saying much. It's main purpose is to reassure ourselves that we have good reason to speak in ontological language, but in fact the real reason for doing that is simply because it is convenient. This convenience is what I meant by it being "a given" that scientists are going to invoke ontological language, and hence adopt a form of scientific realism, the issue is merely how literally will they take themselves.
3) This one is on the most rock solid foundation, but is overly restrictive. It loses sight of the fact that we don't just do science to predict stuff, we also do it to gain a sense of understanding. We seek unifying principles and powerful idealizations, so if all we were doing was predicting our instruments we wouldn't need those conceptual tools, and we'd lose a lot of the aesthetic wonder.

I'm just a bit lost. Do you think that Leifer is correct that taking your position (or Fuchs's) is taking a position against scientific realism leading to instrumentalism and making physics "the science of meter readings"?

No, that's the excluded middle: he thinks we are either just reading meters, or else physical systems have to have actual properties that determine their behavior. Where's the logic there? How about the far more likely case that applies to neither of those extremes?

 

[bohm2]

I would like to distinguish three flavors of realism, which don't all officially get called realism but the one that does seems the least realistic to me. Let's call them: 2) structural realism-- the properties of our theories are just what we can demonstrate them to be: properties of our theories. However, they must work for some reason, to whatever extent they do work, so we'll say that they work because they share some vague "structural similarity" to the actual reality, whatever that means.

Here are my criticisms of each:
2) This one is at least logically self-consistent, but is pretty vague. I view it as basically correct, but only because it is not saying much. It's main purpose is to reassure ourselves that we have good reason to speak in ontological language, but in fact the real reason for doing that is simply because it is convenient. This convenience is what I meant by it being "a given" that scientists are going to invoke ontological language, and hence adopt a form of scientific realism, the issue is merely how literally will they take themselves.

No, that's the excluded middle: he thinks we are either just reading meters, or else physical systems have to have actual properties that determine their behavior. Where's the logic there? How about the far more likely case that applies to neither of those extremes?

Maybe everybody is just misunderstanding each other? Isn't Leifer’s scientific realism and PBR fully compatible with your structural realism? I actually felt that Leifer is arguing that Fuch’s position is somewhere in between instrumentalism and your structural (scientific) realism. He seems skeptical that this can be done. I also got the impression that PBR and Leifer don’t believe that there is some direct one-to-one mapping between the properties of the theory and mind-independent reality. In fact, I take this to be the case where PBR write:

Nevertheless most physicists and chemists concerned with pragmatic applications successfully treat the quantum state as a real object encoding all properties of microscopic systems

.

I think this is the same point that Norsen makes regarding the misinterpretation of Bell’s stuff:

Note that everything in the above discussion refers to some particular candidate physical theory. For example, there is a tendency for misplaced skepticism to arise from Bell’s use of the concept of “beables” in the formulation of local causality. This term strikes the ears of those influenced by orthodox quantum philosophy as having a metaphysical character and/or possibly committing one (already, in the very definition of what it means for a theory to respect relativistic local causality) to something unorthodox like “realism” or “hidden variables.” Such concerns, however, are based on the failure to appreciate that the concept “beable” is theory-relative. “Beable” refers not to what is physically real, but to what some candidate theory posits as being physically real. Bell writes: “I use the term ‘beable’ rather than some more committed term like ‘being’ or ‘beer’ to recall the essentially tentative nature of any physical theory. Such a theory is at best a candidate for the description of nature. Terms like ‘being’, ‘beer’, ‘existent’, etc., would seem to me lacking in humility. In fact ‘beable’ is short for ‘maybe-able’.”

A complete specification of beables in some spacetime region simply means a specification of everything (relevant) that is posited by the candidate theory in question. There is no presumption that such a full specification actually correspond to what really exists in the relevant spacetime region, i.e., no presumption that the candidate theory in question is true.

Local Causality and Completeness: Bell vs. Jarrett
http://philsci-archive.pitt.edu/4163/1/BvJ.pdf

 

[my_wan]

Here are my criticisms of each:
1) It's ridiculous, ignores how the human mind works, and is oblivious to the entire history of the endeavor of physics. It's just obviously wrong. Random example: Newton's action at a distance, which for generations was adopted as one of these "true properties" of the universe (not by Newton, by the way).
2) This one is at least logically self-consistent, but is pretty vague. I view it as basically correct, but only because it is not saying much. It's main purpose is to reassure ourselves that we have good reason to speak in ontological language, but in fact the real reason for doing that is simply because it is convenient. This convenience is what I meant by it being "a given" that scientists are going to invoke ontological language, and hence adopt a form of scientific realism, the issue is merely how literally will they take themselves.
3) This one is on the most rock solid foundation, but is overly restrictive. It loses sight of the fact that we don't just do science to predict stuff, we also do it to gain a sense of understanding. We seek unifying principles and powerful idealizations, so if all we were doing was predicting our instruments we wouldn't need those conceptual tools, and we'd lose a lot of the aesthetic wonder.

I see one shortcoming in these criticisms. That is that 2) can potentially, and has in the past, provided the instrumentalism of 3). First time was with Newton's laws. Then later with the development of statistical mechanics as a model of classical thermodynamics culminating in empirical verification with Brownian motion.

The instrumentalist is of course fully justified in sticking with their position. The instrumentalist take is in fact all that structural realism ever actually provided. It certainly never proved structural realism as a fact. Is was simply an instrumentalist tool that lead us to QM.

Now we are in the domain of QM with a lot of open questions left. The fact that QM is pretty immaculate in the predictions it provides says nothing about what it leaves out, such as GR. Even if you take that as fundamentally separable issue there are things like the vacuum catastrophe. The question about structural realism is not whether it is factual or not, but whether or not it can play an instrumentalist role in synthesizing and or expanding the value of our instrumental formalism. Just like statistical mechanics could not be derived from classical thermodynamics, but classical thermodynamics is easily derived from statistical mechanics structural realism may turn out to be the only way to move physics beyond a certain point today.

Maybe not to, but to throw 2) out on the grounds of what we do not, or even cannot, know is instrumentally absurd. Hence, taking 2) and 3) as entirely separable is invalid from either the perspective of 2) or 3).

 

[Ken G]

Maybe everybody is just misunderstanding each other? Isn't Leifer’s scientific realism and PBR fully compatible with your structural realism?

I would say not. Here's the key difference. In what I would call structural realism, properties are always attributes of a theory, but reality is never beholden to the theory-- it is the theory that is beholden to the reality. So we can say "here are the properties of theory X" and ask if reality behaves in accordance with the predictions of those properties, but one can never assume there must be some theory Y whose properties determine what happens in the reality. That's just backward logic, it's not even naive realism. In naive realism, we say that the properties of the theories we already have are the properties of reality, but there's no requirement to postulate some other theory that we don't have and apply realism to it in absentia. So we need yet another brand of realism, call it 'reductionist realism", that holds not only that our theories refer to true properties, but that true properties determine what happens, so some theory is possible that will describe exactly what nature is doing. I do not believe the PBR theorem goes through without that assumption.

I actually felt that Leifer is arguing that Fuch’s position is somewhere in between instrumentalism and your structural (scientific) realism. He seems skeptical of this. I also got the impression that PBR and Leifer don’t believe that there is a one-to-one mapping between the properties of the theory and mind-independent reality. In fact, I take this to be the case where PBR write:[/quote]Yet what PBR write there, and the assumptions that go into their theorem, are quite different.

I think this is the same point that Norsen makes regarding the misinterpretation of Bell’s stuff:

Indeed, Bell's words are quite clearly what constititutes anti-realism, the way the term is normally used. That's what I've been saying-- the narrow application of the term "realism" is actually not very realistic at all, and Bell's view would not qualify, nor would that staunchest of realists Bohm (when he starts talking about the electron as an information processor, that is not a property of any current theory of electrons, so is not a realist perspective).

 

[bohm2]

Indeed, Bell's words are quite clearly what constititutes anti-realism, the way the term is normally used. That's what I've been saying-- the narrow application of the term "realism" is actually not very realistic at all, and Bell's view would not qualify, nor would that staunchest of realists Bohm (when he starts talking about the electron as an information processor, that is not a property of any current theory of electrons, so is not a realist perspective).

Okay, I think I like the structural realist version of scientific realism (despite the criticisms given in the link) and I think this is the view Bell, Weinberg and Chomsky were arguing for but I didn't fully comprehend. I think I finally got it. I hope But note the part discussing that we shouldn't be anti-realists:

According to Worrall, we should not accept standard scientific realism, which asserts that the nature of the unobservable objects that cause the phenomena we observe is correctly described by our best theories. However, neither should we be antirealists about science. Rather, we should adopt structural realism and epistemically commit ourselves only to the mathematical or structural content of our theories. Since there is (says Worrall) retention of structure across theory change, structural realism both

(a) avoids the force of the pessimistic meta-induction (by not committing us to belief in the theory's description of the furniture of the world) and
(b) does not make the success of science (especially the novel predictions of mature physical theories) seem miraculous (by committing us to the claim that the theory's structure, over and above its empirical content, describes the world).

http://plato.stanford.edu/entries/structural-realism/

And now the interesting questions:

1. Does PBR support the spirit of this view?
2. Which interpretation of QM is most consistent with this view?

I would say not. Here's the key difference. In what I would call structural realism, properties are always attributes of a theory, but reality is never beholden to the theory-- it is the theory that is beholden to the reality. So we can say "here are the properties of theory X" and ask if reality behaves in accordance with the predictions of those properties, but one can never assume there must be some theory Y whose properties determine what happens in the reality. That's just backward logic...

But aren't all of the symbols introduced in PBR, "theory-relative" to use Norsen's term, just as in Bell's theorem? Again I'm referring to his paper:

Local Causality and Completeness: Bell vs. Jarrett
http://lanl.arxiv.org/PS_cache/arxiv/pdf/0808/0808.2178v1.pdf

 

[Ken G]

Maybe not to, but to throw 2) out on the grounds of what we do not, or even cannot, know is instrumentally absurd. Hence, taking 2) and 3) as entirely separable is invalid from either the perspective of 2) or 3).

I don't actually think that (2) and (3) are separable in terms of what claims we can scientifically substantiate, they are only different in terms of how we frame what science is about. There's a tradeoff between what we can demonstrate science is about, versus what we'd like to think science is about, and the order of the three goes from overly stressing the latter to perhaps overly stressing the former.