Living Opponents of the Copenhagen Interpretation

[jbmolineux]

I was wondering if anyone could tell me who are considered the leading opponents of the Copenhagen Interpretation who are alive today?--and even what would be the best way to get myself some formal physics education under such individuals?

I would love to learn more about physics, although I do not have any formal education in it. I do have a masters degree in education and bachelors in business. Is it possible for someone in my position to go straight to a masters? PhD? I have considerable informal learning in philosophy and philosophy of science, and a bit in physics (I've spent about 10 years in relative isolation in Nepal and spent much of my waking hours reading during that time).

Even though I don't have formal training in physics (and thus in one sense have no right to have a strong opinion), I still can't help but strongly feel based on what I understand that the Copenhagen Interpretation is not only based on a purely philosophical assumption--but an error. And I believe that predictive accuracy does not necessarily vindicate philosophical assumptions (to say nothing for errors).

But--granted--I have not been able to understand Bell's theorem and how the Aspect (and following) experiments are supposed to have vindicated the CI in light of it--which, as I understand, is the real heart of the argument.

Thus, I am eager to learn. On the one hand, I am willing to change my mind if the Bell-Aspect argument really is as strong as I have heard it is. But on the other hand, I almost can't even imagine it can vindicate what appears to me to be the grossest of philosophical errors (the empircal criterion of meaning, which is now all-but universally recognized in philosophy to be self-refuting) which underlay the origins of the Copenhagen Interpretation.

Sorry if anything here gives offense, and I crave instruction and guidance, so thanks for any help anyone can give!

 

[atyy]

Opponents of Copenhagen are either crackpots or Ballentine (and Ballentine is wrong).

The Copenhagen interpretation has not been falsified. All interpretations of quantum mechanics must have the Copenhagen interpretation as emergent. Thus for example, Bohmian scenarios do not oppose Copenhagen, rather the Copenhagen interpretation is emergent from Bohmian mechanics.

Some versions of Copenhagen have had errors, namely the versions that claimed that hidden variables were impossible, following von Neumann's erroneous proof. No modern versions make such a claim.

The Copenhagen type interpretation is also called "operational" or "instrumental", and apart from the orthodox shut-up-and-calculate interpretations in textbooks, other examples of operational/instrumental approaches are found in these alternate axiomatizations of finite dimensional quantum mechanics:

http://arxiv.org/abs/quant-ph/0101012
Quantum Theory From Five Reasonable Axioms
Lucien Hardy

http://arxiv.org/abs/1011.6451
Informational derivation of Quantum Theory
G. Chiribella, G. M. D'Ariano, P. Perinotti

 

[e.bar.goum]

There are many physicists who don't like the copenhagen interpretation! According to this poll, only 42% of the physicists they poll say their favourite interpretation is copenhagen (see page 8). I think it's only that high because it is what is taught first in undergrad classes.

Now, as to studying that? Arguing about interpretations of QM is mostly in the realm of philosophy of science. I think it's fair to say that most practising physicists actually subscribe to the "shut up and calculate" interpretation. I can think of a few physicists who study this as their "academic hobby". Sean Carroll has been publishing some stuff on MWI lately, and there are some people publishing about pilot wave stuff.

I don't know of anyone personally who has done a physics grad degree without an undergrad education in either physics, chemistry or mathematics. I don't know if it can be done! But look at the entrance requirements of your favourite university to be sure.

 

[Haborix]

I can't address your first question, but I have a few comments regarding some things you bring up in the remainder of your post. The spirit in which physicists attempt to confirm/reject interpretations is by looking for a contradiction with known results (thus rejecting the interpretation) or by making new predictions which can be verified experimentally. You seem to want to reject an interpretation on philosophical grounds. Given your background, you might consider looking for philosophy departments where people are researching the topics you're interested in.

I don't know how much physics you actually know, but it would be difficult to get into, and do well in, a physics graduate program given just your formal background. But given the right amount of interest and determination you can overcome those barriers. It's up to you. Good luck!

 

[atyy]

There are many physicists who don't like the copenhagen interpretation! According to this poll, only 42% of the physicists they poll say their favourite interpretation is copenhagen (see page 8). I think it's only that high because it is what is taught first in undergrad classes.

Now, as to studying that? Arguing about interpretations of QM is mostly in the realm of philosophy of science. I think it's fair to say that most practising physicists actually subscribe to the "shut up and calculate" interpretation. I can think of a few physicists who study this as their "academic hobby". Sean Carroll has been publishing some stuff on MWI lately, and there are some people publishing about pilot wave stuff.

The poll has 24% on "informational" which the authors comment is Copenhagen-like, which would make 66%. Also, it does not say that those who chose other interpretations are opposed to Copenhagen. Bohmian mechanics is consistent with Copenhagen, and Many-Worlds, if it works must recover Copenhagen and the Born rule for the individual observer in anyone world.

Incidentally, Carroll remains unsure whether MWI works. http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/

 

[bhobba]

I was wondering if anyone could tell me who are considered the leading opponents of the Copenhagen Interpretation who are alive today?--and even what would be the best way to get myself some formal physics education under such individuals?

There are a few around.

The three I am most aware of are Ballentine:
https://www.amazon.com/dp/9814578584/?tag=pfamazon01-20

It must be said however that his objection to it is based on a misunderstanding. We can chat about it when you reach that chapter in his book.

And David Wallice:
http://users.ox.ac.uk/~mert0130/books-emergent.shtml

Also Griffiths:
http://quantum.phys.cmu.edu/CQT/index.html

Griffiths isn't really a major departure from Copenhagen - as explained by Lubos a bit later it just fixes a relatively minor problem - but it is a problem.

The link provides a good introduction to the issues though and is well worth a read.

Trouble is you are into heavy math territory

Here is a reading list to build up to it:
https://www.amazon.com/dp/0471827223/?tag=pfamazon01-20
https://www.amazon.com/dp/0465075681/?tag=pfamazon01-20
https://www.amazon.com/dp/0465036678/?tag=pfamazon01-20

But, as alluded to before, I have to tell you there is no major issue with Copenhagen (only a few minor things) - its basically just the formalism with the idea the quantum state is a state of knowledge:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

The issue is in Copenhagen QM is a theory about observations that appear in a common-sense classical world. But QM is supposed to explain that world.

For what its worth I hold to the ignorance ensemble interpretation:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Thanks
Bill

 

[jbmolineux]

e.bar, thanks for the reply! Here is my feeling: that (as you said) most physicists don't even talk about interpretation (on the one hand), but yet there is a sense in which the message that comes from physics is contains the philosophical prejudices (in my view, errors) which underlie the conclusions of the CI, and (and this is the key) implicitly defend those philosophical conclusions on the basis of the authority of their scientific expertise. Thus you can't really be a part of the conversation if you're not a physicist--despite the fact that most physicists are of the "shut up and calculate" type, and usually are not experts in philosophy of science and many don't even care.

In the poll you referenced, 58% said that the choice of interpretation is a matter of personal philosophical prejudice (question 14). And yet about the randomness of individual quantum events 0% said that there was a "hidden determinism!"

If this latter result is merely a matter of philosophical prejudice (as the former question suggests), then it certainly could be a philosophical error (as I suggest). But the error leads to a disbelief in determinism--the idea that events have causes--which is not only at the heart of scientific inquiry, but at the heart of the entire Western Intellectual tradition! And since physics is the hardest of the hard sciences, this is (in my view) driving society and the western intellectual tradition in a not-so-great direction.

Thus my interest in the question. I fear that coming at it from a philosophy-of-science angle may not be the most effective way to join the conversation, because it is really physicists (and not philosophers of science) who are seen as having the authority to pronounce on the proper interpretation of their field.

Do you know what I mean? Or am I wrong?--are philosophers of science considered authorities on the interpretation of physics?

 

[e.bar.goum]

The poll has 24% on "informational" which the authors comment is Copenhagen-like, which would make 66%. Also, it does not say that those who chose other interpretations are opposed to Copenhagen. Bohmian mechanics is consistent with Copenhagen, and Many-Worlds, if it works must recover Copenhagen and the Born rule for the individual observer in anyone world.

Incidentally, Carroll remains unsure whether MWI works. http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/

I read Carroll's blog post as being very pro-MWI. I think when talking about interpretations, it's foolish to be declarative on the matter. It's philosophy, not physics.

Saying that MWI must recover the born rule is true, but that doesn't mean that MWI is not opposed to Copenhagen. They have rather different philosophical groundings - unlike copenhagen, MWI is deterministic, has a real wave-function, doesn't have unique histories or collapsing wavefunctions, or a role for the observer. It is also local, and claims that a universal wave-function exists.

About the only things they agree on is counter-factual definiteness and hidden variables!

 

[bhobba]

Bohmian mechanics is consistent with Copenhagen, and Many-Worlds, if it works must recover Copenhagen and the Born rule for the individual observer in anyone world.

That's correct. Copenhagen is basically a minimalist interpretation with its own view of the quantum state as simply something that resides in a theorists head (a state of knowledge) similar to Baysian view of probability:
http://en.wikipedia.org/wiki/Bayesian_probability

If you are interested in BM our own Demystifer is really into it.
https://www.physicsforums.com/members/demystifier.61953/

Thanks
Bill

 

[e.bar.goum]

In the poll you referenced, 58% said that the choice of interpretation is a matter of personal philosophical prejudice (question 14). And yet about the randomness of individual quantum events 0% said that there was a "hidden determinism!"

AFAIK de broglie-bohm is the only popular-ish interpretation that has hidden variables, and you'll note that no-one in the poll voted for it. So that's actually completely consistent.

The Bell Inequalities tell us that there may be no local hidden variables, and most physicists accept this.

 

[Nugatory]

But--granted--I have not been able to understand Bell's theorem and how the Aspect (and following) experiments are supposed to have vindicated the CI in light of it--which, as I understand, is the real heart of the argument.

Bell's theorem and the Aspect experiments neither confirm nor deny the Copenhagen interpretation, or any other interpretation for that matter.

Bell's theorem says that the predictions of quantum mechanics are incompatible with any possible local hidden variable theory. All interpretations make the same predictions, so Bell's theorem favors none of them.

 

[bhobba]

Do you know what I mean? Or am I wrong?--are philosophers of science considered authorities on the interpretation of physics?

Some like David Wallice, who are also formally trained in physics, are. But from posts here I can say for sure some don't really understand it properly - of course some is not all - however its somewhat hit and miss.

I personally would be a bit wary.

Thanks
Bill

 

[jbmolineux]

So, if I felt strongly that the CI is (a) based on an error, and (b) a purely philosophical bias--what would be the best way to take part in (and perhaps even contribute to) the discussion--studying philosophy of science, or physics?

 

[bhobba]

So, if I felt strongly that the CI is (a) based on an error, and (b) a purely philosophical bias--what would be the best way to take part in (and perhaps even contribute to) the discussion--studying philosophy of science, or physics?

You should nut out the issues yourself.

That means understanding the physics.

I STRONGLY recommend the three books I gave before, the consistent history link, then Ballentine.

For example philosophers I have discussed this stuff with don't know about the very important Gleason's theorem or that Schroedinger's equation etc really follows from symmetry.

You must understand the exact axioms its based on and precisely what needs to be explained - unfortunately you need a book like Ballentine to do that.

Don't get too worried about the advanced math. When going through difficult derivations like you sometimes find in Ballentine it's not important from an understanding viewpoint to follow all the detail - you can come back to it later as your math matures.

Thanks
Bill

 

[rkastner]

I critique Bohr's orthodoxy in my CUP book (http://www.cambridge.org/us/knowledge/discountpromotion/?site_locale=en_US&code=L2TIQM)
. I also have a new book forthcoming in which I critique and offer an alternative to Bohr's 'Copenhagen' approach, which is heavily dependent on particular epistemological and metaphysical assumptions that can be questioned.

 

[jbmolineux]

Bhobba, I see six books that you recommend. What order would you suggest reading them?

If it matters, I was a math teacher although I haven't take calculus since freshman year in college. I've read most of Popper's work, and 5-6 other books on QM.

 

[atyy]

So, if I felt strongly that the CI is (a) based on an error, and (b) a purely philosophical bias--what would be the best way to take part in (and perhaps even contribute to) the discussion--studying philosophy of science, or physics?

The best way is to stop making your error. Physics is not about your philosophical prejudices, but it's about getting predictions that match observations, which Copenhagen-type/instrumental/operational interpretations do. The problem with Copenhagen-type/instrumental/operational interpretations is not philosophical bias. The problem is called the 'measurement problem'. One description of the measurement problem is found in John Bell's http://www.tau.ac.il/~quantum/Vaidman/IQM/BellAM.pdf.

For non-relativistic quantum mechanics, Bohmian mechanics and its variants provide one class of solutions. The main problem with Bohmian mechanics is that it is unclear whether it can also describe the relativistic quantum mechanics of the standard model, in particular whether it can describe the interactions of chiral fermions with non-Abelian gauge fields. Bohmian mechanics in general does predict deviations from quantum mechanics, and is in principle falsifiable.

Another approach to the measurement problem are the Many-Worlds proposals. However, there is at present no consensus on whether these proposals address all technical details. The book by Wallace recommended by bhobba is very good, and really tries to fill in the technical details and discuss the remaining problems. A shorter assessment of the problems of Many-Worlds is given by Sean Carroll at http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/.

 

[DrChinese]

So, if I felt strongly that the CI is (a) based on an error, and (b) a purely philosophical bias--what would be the best way to take part in (and perhaps even contribute to) the discussion--studying philosophy of science, or physics?

You won't find an "error" in CI in the normal sense of the word, as it has already proven itself useful in many many respects. After all, there is the experimental canon which is extremely deep. More study in science with convince you of that relatively easily.

You may find philosophical issues you feel are best addressed by other interpretations, however. Study of philosophy might help in that regard.

 

[carllooper]

Philosophy proper is an area of study in it's own right, quite distinct from physics or any other discipline. And it's not as if one depends on the other, or is a function of the other. Physics can function quite happily on it's own, without philosophy. And vice versa.

That said a concept in philosophy or physics might very well share some connection or affinity with the other. There can be overlap. And there will be crosstalk, and this might very well provide for further inspiration/elaboration in one, or the other, or both disciplines. Or not as the case may be.

Between art and physics, for example, there can be quite interesting crosstalk. A science fiction movie, for example, can find inspiration in some aspects of physics. And physics, for it's part, can find inspiration in movies, eg. in what sort of technology might be constructed for the creation of a movie: tools such as a camera, or photographic film, or a CCD chip, or digital projector.

An artist in residence at a particle collider, might draw inspiration from the marvellous visuals produced in particle collisions, and the mathematics used to transform such visuals (eg. a DFT) and might construct and display a giant collage out of all of this information. But it's not as if a particle accelerator is a tool for producing such artwork. But an artist that understands a collider in just such a way, might very well produce far more interesting work that way.

The Copenhagen Interpretation. I've always liked this interpretation. It's minimalism. And particularly it's observation-centric approach. It also provides a solution to the communication challenges the early architects of QM faced when introducing the physics for the first time. So it's quite an apt interpretation to use in an introductory course on QM.

But yes, interpretations will have tendency to end up more as a contribution to philosophy than to physics. But you never really know, following some particular line of interpretation, in which world you might end up.

C

 

[bhobba]

Bhobba, I see six books that you recommend. What order would you suggest reading them? If it matters, I was a math teacher although I haven't take calculus since freshman year in college. I've read most of Popper's work, and 5-6 other books on QM.

It does because math IS required. But fortunately for you, you simply need a bit of a refresher.

My order is:
https://www.amazon.com/dp/0471827223/?tag=pfamazon01-20
This is to bring your calculus back up to speed

https://www.amazon.com/dp/0465075681/?tag=pfamazon01-20
This is to get a reasonable understanding of the more advanced aspects of mechanics such as Poisson Brackets etc relevant to QM

https://www.amazon.com/dp/0465036678/?tag=pfamazon01-20
This starts you on QM proper

The author, Lenny Susskind, also has some associated video lectures:
http://theoreticalminimum.com/

Then Griffths, which gives a good introduction to the issues from the Consistent Histories viewpoint:
http://quantum.phys.cmu.edu/CQT/index.html

Then, what many such as myself, consider THE book on QM - Ballentine (very strong on the so called ensemble or statistical interpretation - but some small blemishes with misunderstandings of Copenhagen and not going into the important area of decoherence which for some reason he is negative toward):
https://www.amazon.com/dp/9814578584/?tag=pfamazon01-20

Then David Wallice:
http://users.ox.ac.uk/~mert0130/books-emergent.shtml

After that you will have a VERY good grounding in QM and its interpretive issues.

Its no easy task you have set yourself. It will take time, perseverance, and patience. But its not a race, take your time and enjoy the journey in full knowledge when you come out the end of it your understanding will be way beyond the, unfortunately, often 'junk' that is peddled in the populist press - not always mind you - but unfortunately often enough to cause those that know the real deal to wince.

Thanks
Bill

 

[bhobba]

You won't find an "error" in CI in the normal sense of the word, as it has already proven itself useful in many many respects. After all, there is the experimental canon which is extremely deep. More study in science with convince you of that relatively easily. You may find philosophical issues you feel are best addressed by other interpretations, however. Study of philosophy might help in that regard.

Indeed.

There is no error in Copenhagen - as Lubos explains in the link I gave previously there are a couple of blemishes - but no error.

I could start chatting about my view on such things. But I would rather not, because I STRONGLY believe, providing you have the willingness to learn QM, and the OP specifically stated that's what he wants to do, then its best you nut it out for yourself. That is by far the best way to true understanding.

Thanks
Bill

 

[bhobba]

The best way is to stop making your error. Physics is not about your philosophical prejudices, but it's about getting predictions that match observations, which Copenhagen-type/instrumental/operational interpretations do.

I think by studying QM proper, with his background in Popper etc, he can nut it out for himself.

From my experience, once you know the real deal, many of the philosophical issues fall away. Some remain, such as the very important problem of outcomes, but others such as collapse etc popularisations go on about are seen as non issues.

To the OP - the problem of outcomes is what these days replaces the collapse idea which when you read Ballentine you will find is really a non-issue - but again I don't want to discuss it now - best you discover it for yourself.

Thanks
Bill

 

[strangerep]

[crackpots or Ballentine]

Just because someone disagrees with your view does not necessarily make them a crackpot.

(and Ballentine is wrong).

You have not established that (and, with respect, I think that Ballentine is right).

But I won't debate that further here, since it's a bit tangential to this thread. If you are confident of your position, then please publish a paper on it in a reputable peer-reviewed journal. Without such a paper, you risk straying outside the PF guidelines.

 

[bhobba]

You have not established that (and, with respect, I think that Ballentine is right).

Ballentine is right. Just to be 100% clear on the issue - Ballentines analysis of Copenhagen is correct - with the caveat explained below.

What Atty is referring to is a misunderstanding he has in his analysis where he considers the version where the wave-function is thought of as real. That's fine as far as it goes - except virtually all versions of Copenhagen have it purely as a state of knowledge that resides in a theorists head. It matters not in the least such instantaneously collapses to a different state in filtering type observations.

To the OP. I didn't want to mention it specifically because its something you can spot for yourself.

Thanks
Bill

 

[atyy]

Just because someone disagrees with your view does not necessarily make them a crackpot.

You have not established that (and, with respect, I think that Ballentine is right).

But I won't debate that further here, since it's a bit tangential to this thread. If you are confident of your position, then please publish a paper on it in a reputable peer-reviewed journal. Without such a paper, you risk straying outside the PF guidelines.

Here is a peer-reviewed paper showing that Ballentine is wrong: Zurek, W. H. 1981. Pointer Basis of Quantum Apparatus: Into What Mixture Does the Wave Packet Collapse? Phys. Rev. D 24: 1516.

Also one can just take a look at standard texts like Landau & Lifshitz, Cohen Tannoudji, Diu & Laloe, Nielsen and Chuang, or Weinberg.

One can also find a discussion of an error made by Ballentine in http://arxiv.org/abs/quant-ph/0312059 (Rev.Mod.Phys.76:1267-1305,2004) and in http://books.google.com/books/about/Exploring_the_Quantum.html?id=QY6YuU-Qi-AC.

This is not a matter of taste like having a favourite interpretation. Ballentine is wrong.

 

[bhobba]

Here is a peer-reviewed paper showing that Ballentine is wrong: Zurek, W. H. 1981. Pointer Basis of Quantum Apparatus: Into What Mixture Does the Wave Packet Collapse? Phys. Rev. D 24: 1516.

If you consider the wavefunction as real, like Ballentine does in his analysis, you are making a very unnatural assumption in assuming it INSTANTANEOUSLY changes to another wavefunction. That's the sense Ballentine is correct.

Thanks
Bill

 

[atyy]

If you consider the wavefunction as real, like Ballentine does in his analysis, you are making a very unnatural assumption in assuming it INSTANTANEOUSLY changes to another wavefunction. That's the sense Ballentine is correct.

Thanks
Bill

Well, the basic problem with Ballentine is he insinuates that Copenhagen is wrong. One may say that Copenhagen has a measurement problem, and that may be incomplete - but not wrong. Ballentine tries to provide an example in which Copenhagen fails, but his analysis of the Stern Gerlach experiment is wrong, and the Zurek paper gets it right. So Ballentine tries to say that data falsifies Copenhagen, but in fact Copenhagen has not been falsified to date.

 

[jbmolineux]

Bill, thanks for the book order! I'll work on getting those! (I live in Nepal, so it will take time to figure out how to get them here…) But even if I LEARN it, am I wrong to assume that it would be very hard to get anyone to take anything I say seriously without a degree? Or would there be a way to learn it on my own first and then someone get a degree?

Atyy, the CI has not been falsified, because it is (in my view) unfalsifiable, as Carl Popper has argued extensively and convincingly. You say that "physics is not about philosophical prejudices, but about getting predictions that match observations"--but the philosophical prejudices constitute a significant portion of what is written about physics! What I feel is that sometimes physicists make bold philosophical statements and then retreat to the physics-is-not-about-philosophy position as soon as the philosophy behind those statements are questioned. And this may be considered "naïve realism," but for me if physics is not trying to describe "what the world is really like," then I can't possibly imagine what it is doing! But "what the world is really like" is significantly different than "making predictions that match observations." I feel it goes without saying (or should) that you want to find predictions that match observations because the statements in the theory about the world are true.

e.bar, you suggest that "it's foolish to be declarative about philosophy"--but I do think that there are some things in philosophy that can be known with certainty (and ultimately I believe that if nothing can be known in philosophy, then nothing can be known at all). For example, I think we can know the basic contents of logic, and this entails that a self-referentially incoherent statement is false. This is relevant because the positivism out of the which the CI sprang upheld the self-referentially incoherent statement "the only meaningful statements are those which can be verified by sense experience." If it is true, it is for that very reason meaningless and thus false (since it is itself a statement that cannot be verfied by sense experience).

Dr. Chinese, isn't it possible for a philosophy-laden theory to experimentally vindicated, but yet philosophically wrong? For example, I could have a theory that there is an invisible string connecting the moon and the Earth and thus the orbit. To refute that, you may bring in other observations (like that they are also spinning relative to one another), but at one point in the discussion (before the new observations were brought to bear) the philosophically-wrong theory matched at least some of the observations. That situation could be compared to the current situation with the failure to find a unifying theory.

Carllooper, I don't believe that physics CAN really function without philosophy. I know this will be a controversial and perhaps even offense statement, and I'm sorry for that!--but I don't mean by "philosophy" the stuff that is taught in the academy, but something like "first order principles that govern thought-towards truth" (sometimes called metaphysics, although widely rejected these days). I think when scientists appeal to the basic tools of thought they are simply appealing to these things. But if you get those principles wrong, the science will start to go astray, which is what seems to me to be happening. For example, if Einstein did not have a strong belief in the principle that nothing happens without a reason, would he have made the discoveries that he did? And if not, and given the widespread rejection of that very principle today….well, that's why I think these things are important.

I'm surprised that no one in the poll voted for a non-local determinism (which would itself be a type of hidden determinism). Doesn't that remain a viable option?

Thanks everyone!

 

[atyy]

Atyy, the CI has not been falsified, because it is (in my view) unfalsifiable, as Carl Popper has argued extensively and convincingly. You say that "physics is not about philosophical prejudices, but about getting predictions that match observations"--but the philosophical prejudices constitute a significant portion of what is written about physics! What I feel is that sometimes physicists make bold philosophical statements and then retreat to the physics-is-not-about-philosophy position as soon as the philosophy behind those statements are questioned. And this may be considered "naïve realism," but for me if physics is not trying to describe "what the world is really like," then I can't possibly imagine what it is doing! But "what the world is really like" is significantly different than "making predictions that match observations." I feel it goes without saying (or should) that you want to find predictions that match observations because the statements in the theory about the world are true.

That's wrong - at least if we take CI to be an interpretation of quantum mechanics. In that sense, a falsification of quantum mechanics, will also mean a failure of CI. Bohmian Mechanics for example, provides (with quite a big caveat) one possibility in which quantum-mechanics may fail.

The caveat about Bohmian Mechanics is that it is unclear at the moment whether it can also describe all present data on chiral fermions interacting with non-Abelian gauge fields. However, it can describe anything describable by non-relativistic quantum mechanics, which includes QED and QCD if we treat them as lattice theories.

Another type of theory (I'm not sure how consistent this is with the standard model either, but it does overlap QM quite a bit) that predicts a failure of QM are the spontaneous collapse theories. There are proposals to test spontaneous collapse and falsify QM: http://arxiv.org/abs/1410.0270.

BTW, you seem to be working with a version of CI that says "naive reality" does not exist, and QM shows that to be necessarily true. That flavour of CI did exist in the past, and you can even find traces of it in the Feynman lectures. That is not philosophical bias - that is mathematical error. That flavour of CI was based on an erroneous proof by von Neumann that hidden variables cannot exist. The error was known to a minority that probably included Einstein. However, it only became widely known after Bell's 1966 paper "On the Problem of Hidden Variables in Quantum Mechanics". So yes, if you oppose that version of CI, it has been discredited. Non-relativistic QM is consistent with naive realism. Of course, one can adopt other ontologies, but (non-relativistic) QM does not force one to do so anymore than classical mechanics does. You can find this discussed in Haag's book "Local Quantum Physics".

 

[carllooper]

I'm surprised that no one in the poll voted for a non-local determinism (which would itself be a type of hidden determinism). Doesn't that remain a viable option?

Non-locality isn't hidden. It's just not visible in a single location - for obvious reasons. An interference pattern is, for all intents and purposes, the visibility of non-localised information. It's visibility is embodied in the distribution of otherwise localised information (ie. distribution of particle detections). And there is a clear visible signal there. In terms of QM, to follow Bohr's lead, this signal is to be regarded as a composite signal, the individual components of which will be an individual signal (a particle) associated with a particle detection.

If the experimental setup is a solid state one (doesn't vary over time) then each component signal will be the same shaped signal, so the composite signal becomes just a clearer or amplified image of anyone signal considered on it's own. Each component signal is effectively the wave function associated with each particle detection, (well, the square of such, so not a quite a QM particle as such).

C

 

[bhobba]

Bill, thanks for the book order! I'll work on getting those! (I live in Nepal, so it will take time to figure out how to get them here…) But even if I LEARN it, am I wrong to assume that it would be very hard to get anyone to take anything I say seriously without a degree? Or would there be a way to learn it on my own first and then someone get a degree?!

You do have a degree - just not in physics.

Well surprise surprise neither do I - mine is in applied math. I taught myself QM - although I did study analysis and Hilbert Spaces as part of my degree which was a help.

Mate physicists generally listen to what people say - not what they put after their name.

Thanks
Bill

 

[bhobba]

An interference pattern is, for all intents and purposes, the visibility of non-localised information. It's visibility is embodied in the distribution of otherwise localised information (ie. distribution of particle detections).

Cant follow that.

Here is its explanation in terms of QM:
http://cds.cern.ch/record/1024152/files/0703126.pdf

Cant find anything about non locality there. Indeed on the issue of locality QM is pretty much agnostic - although it does depend on your definition of it in the first place. Mine is the cluster decomposition property - but it only applies to uncorrelated systems:
http://en.wikipedia.org/wiki/Cluster_decomposition_theorem

Anyway can't see how any of it applies to the double slit experiment.

Thanks
Bill

 

[harrylin]

[..] All interpretations of quantum mechanics must have the Copenhagen interpretation as emergent. [..]

I had the impression that the Copenhagen interpretation includes philosophy and claims about the unseen; but in view of your answer, that must be wrong, and also http://en.wikipedia.org/wiki/Copenhagen_interpretation must be wrong according to you. As it no doubt matters for the discussion, please give your definition of the Copenhagen interpretation (or a link to it) - thanks!

 

[carllooper]

Cant follow that.
Here is its explanation in terms of QM:
http://cds.cern.ch/record/1024152/files/0703126.pdf

I'm not suggesting anything controversial here - just probably (or obviously) not expressing it very well.

So we're talking about what is visible in a pattern of detections. Proposed was that non-locality is visible in such, ie. that it's not hidden. So the pattern is an image, or a signal. Given enough detections one can perform an FFT on this image and reconstruct a reasonable image of the two slits. The more detections the better. The pattern of detections makes visible the two slits. The pattern of detections therefore provides, or encodes, information about the slits, eg. if one or both are open. An FFT isn't necessary if one knows how to read the pattern of course. The FFT can be regarded as just a means to decode a more familiar image of the slits.

But this information is not localised in anyone detection, so it's "non-localised" in the sense that the information is distributed across the pattern of detections.

Arguably one might say that if only one slit is open the information is localised, but that only works if you already know only one slit is open. From the detections alone, until you accumulate enough detections to rule it in or out, you don't know if one slit is open or not. In other words the information is still not localised in anyone detection. The pattern for a single slit is still an interference pattern - just one which expresses that interference (in the usual sense) isn't happening.

C

 

[Fredrik]

I was wondering if anyone could tell me who are considered the leading opponents of the Copenhagen Interpretation who are alive today?--and even what would be the best way to get myself some formal physics education under such individuals?

What do you think the Copenhagen interpretation is? (If you can't define it, how can you have strong opinions about it?)

I avoid the term "Copenhagen interpretation" as much as I can, because it's very hard to find two people who mean the same thing by it. People who try to define it often include claims that look like extreme misunderstandings of Bohr's ideas.

it is really physicists (and not philosophers of science) who are seen as having the authority to pronounce on the proper interpretation of their field.
[...]
are philosophers of science considered authorities on the interpretation of physics?

Certainly not by physicists.

No one has the authority to label one interpretation as "proper". In fact, it would be very unscientific to do so.

 

[Fredrik]

Opponents of Copenhagen are either crackpots or Ballentine (and Ballentine is wrong).

Ballentine seems to think that his argument against a particular way of thinking about states proves that the way he's thinking about them is the right way. I would agree that he should have toned it down a bit, but you keep saying that "Ballentine" is wrong, as if his entire book can be dismissed. I strongly disagree with that view.

Here is a peer-reviewed paper showing that Ballentine is wrong: Zurek, W. H. 1981. Pointer Basis of Quantum Apparatus: Into What Mixture Does the Wave Packet Collapse? Phys. Rev. D 24: 1516.
Also one can just take a look at standard texts like Landau & Lifshitz, Cohen Tannoudji, Diu & Laloe, Nielsen and Chuang, or Weinberg.
One can also find a discussion of an error made by Ballentine in http://arxiv.org/abs/quant-ph/0312059 (Rev.Mod.Phys.76:1267-1305,2004) and in http://books.google.com/books/about/Exploring_the_Quantum.html?id=QY6YuU-Qi-AC.
This is not a matter of taste like having a favourite interpretation. Ballentine is wrong.

I read that first article years ago. I don't see how it could possibly be relevant. If Schlosshauer's article is anything like his book, that's also my comment about his article. You certainly can't just "take a look at standard texts" to see that Ballentine is wrong.

 

[Fredrik]

There are a few around.
The three I am most aware of are Ballentine:

Apparently you and atyy both consider Ballentine an opponent of Copenhagen. The view that Ballentine argues against is the view that the system can be literally identified with its state, i.e. that the state represents all the properties of the system. That view is the starting point of the MWI, so I find it odd to label it "Copenhagen".

I realize that people often include this view as a part of something they call "Copenhagen", and then they assume that there's a mysterious physical process called "collapse" that's supposed to eliminate the many worlds. To me that's just the MWI plus an absurd idea that probably makes the whole thing inconsistent. There's no evidence that Niels Bohr held beliefs like that, so I wouldn't call this "Copenhagen", even though I know that many people do.

 

[atyy]

Ballentine seems to think that his argument against a particular way of thinking about states proves that the way he's thinking about them is the right way. I would agree that he should have toned it down a bit, but you keep saying that "Ballentine" is wrong, as if his entire book can be dismissed. I strongly disagree with that view.

In this context, it is Ballentine's opposition to Copenhagen that is wrong, not the whole book. If you don't wish to label the view that Ballentine opposes as "Copenhagen", I can agree to that, which is why I talked about "Copenhagen-style/instrumental/operational" interpretations, by which I would include "orthodox" or "shut-up-and-calculate". Bohr in fact never wrote down his interpretation in a paper, so strictly speaking, Copenhagen does not exist (just like the quantum world :) To give a concrete example of what I am calling Copenhagen, I would give the interpretation given in Landau and Lifshitz. It is also true that the view Ballentine opposes is a misrepresentation of Copenhagen, so in that sense, one could also say that he does not oppose any correct view, merely a caricature of it, so in that sense Ballentine is right. However, Ballentine does make the view he opposes seem to be "mainstream", so he is at least misleading. My claim is not that the entire book by Ballentine can be dismissed, but applies to Chapter 9.

I read that first article years ago. I don't see how it could possibly be relevant. If Schlosshauer's article is anything like his book, that's also my comment about his article. You certainly can't just "take a look at standard texts" to see that Ballentine is wrong.

The quotation of standard texts shows that what I am saying is "mainstream physics", in response to strangerep's suggestion that I am violating PF's rules. It is clear that Ballentine is not mainstream physics, and is in opposition to virtually every other textbook.

Zurek's article is cited because the Stern-Gerlach experiment there is analyzed correctly, whereas Ballentine gets it wrong. Here is another correct version of the Stern-Gerlach experiment http://arxiv.org/abs/quant-ph/0306072.

The Schlosshauer article and the book by Haroche and Raimond are cited to show that Ballentine is wrong in criticizing the collapse postulate, yet effectively using it or an equivalent postulate when taking improper mixtures to be proper mixtures.

 

[DrChinese]

Dr. Chinese, isn't it possible for a philosophy-laden theory to experimentally vindicated, but yet philosophically wrong? For example, I could have a theory that there is an invisible string connecting the moon and the Earth and thus the orbit. To refute that, you may bring in other observations (like that they are also spinning relative to one another), but at one point in the discussion (before the new observations were brought to bear) the philosophically-wrong theory matched at least some of the observations. That situation could be compared to the current situation with the failure to find a unifying theory.

You can't really say the "invisible string" theory is incorrect unless it makes incorrect predictions that another theory does not. Quantum interpretations can be judged by their utility, which for now is equal among competing versions. Besides, I don't know that I would call CI a "a philosophy-laden theory". :-)

 

[DrChinese]

Arguably one might say that if only one slit is open the information is localised, but that only works if you already know only one slit is open. From the detections alone, until you accumulate enough detections to rule it in or out, you don't know if one slit is open or not. In other words the information is still not localised in anyone detection.

To use your line of thinking: you can place polarizers over BOTH slits. The relative orientation (parallel or orthogonal) will then determine whether there is interference or not. So in that manner, the variable [relative orientation of polarizers] is always "non-local".

 

[atyy]

I had the impression that the Copenhagen interpretation includes philosophy and claims about the unseen; but in view of your answer, that must be wrong, and also http://en.wikipedia.org/wiki/Copenhagen_interpretation must be wrong according to you. As it no doubt matters for the discussion, please give your definition of the Copenhagen interpretation (or a link to it) - thanks!

There is no single well-defined Copenhagen interpretation, which is why I have referred to Copenhagen-style/instrumental/operational interpretations. One example of what I mean is the interpretation in Landau and Lifshitz, which is associated with Bohr by Bell in his article "Against 'measurement'". Another example is the Copenhagen-style interpretation mentioned by Weinberg in his quantum mechanics textbook.

It is true that historically there is a flavour of Copenhagen which has asserted that quantum mechanics requires a rejection of "naive realism". As I have mentioned twice in this thread (posts #2 and #29), this is not philosophical bias, but mathematical error, and this view has been discredited. In non-relativistic quantum mechanics, we in fact know that there is no such theorem, because of counter-examples, the first of which was discovered by Bohm. Modern Copenhagen-style interpretations do not claim that quantum mechanics requires a rejection of "naive realism".

The key elements of what I consider a Copenhagen-style interpretation are a classical/quantum cut, and agnosticism as to whether the wave function is real. The classical/quantum cut is basically assumed in the quantum information literature, where you will see channels with classical and/or quantum output. The classical/quantum cut taken with relativity provides one way to argue that the wave function is not necessarily real, because only the classical outcomes and their probabilities are Lorentz-invariant, but not wave function evolution if state reduction is taken into account. For example, state reduction is not an "event" in the same sense that simultaneity is not absolute in special relativity (we can say of course say that simultaneity is absolute relative to a family of observers).

One example of a Copenhagen-style interpretation whose authors also support "naive reality" is Leifer and Spekkens's http://arxiv.org/abs/1107.5849. Leifer and Spekkens do have classical/quantum cuts, and they also say "the picture we have in mind is of the quantum state for a region representing beliefs about the physical state of the region, even though we do not yet have a model to propose for the underlying physical states."

 

[Fredrik]

The key elements of what I consider a Copenhagen-style interpretation are a classical/quantum cut, and agnosticism as to whether the wave function is real.

Some people consider "a classical/quantum cut" to be the idea that QM simply doesn't apply to some systems, in particular measuring devices. I find that notion absurd, and I think you do too. If two systems have Hilbert spaces $H_1$ and $H_2$, the composite system has Hilbert space $H_1\otimes H_2$. This is an essential part of the QM framework, and it implies that any object that consists of quantum systems, is a quantum system.

In my opinion, the proper way to talk about these things is this: Science defines a "theory" (roughly) as a set of statements about the real world that makes testable predictions. A testable prediction is a claim about what the result of a measurement will be, or what the average result of a sequence of measurements performed on identical systems will be. A measurement* is an interaction between a measuring device and the system that the theory is about, which leaves the measuring device in one of its possible final states. The possible final states must be easily distinguishable by a human observer. If they're not, we wouldn't consider the object a measuring device.

In the context of QM, these ideas are sometimes very inaccurately described as "a classical/quantum cut". They shouldn't be described this way, because they are just basic requirements of science. That makes them part of every theory of physics, including QM. So they do not need to be added as part of an interpretation, and in fact, it would be wrong to do so.

The kind of "classical/quantum cut" mentioned in my opening sentence could be part of an interpretation, but in my opinion, this is a crackpot idea that started as an extreme misunderstanding of things that Niels Bohr said. I could be wrong about what I'm about to say, but I think Bohr's view was essentially what I just said, and that he was misunderstood in part because this is a difficult subject, and in part because he never found a good way to explain these things.

Because of this, I wouldn't include either of these types of "classical/quantum cuts" in a definition of "Copenhagen".
*) Some of the simplest measurements aren't accurately described by this. For example, if you measure the length of your phone with a ruler, interactions between the phone and the ruler are irrelevant, and the number that we consider "the result" isn't associated with the final state of the ruler; it's associated with a final state of your brain. I suppose I could try to modify my definition of "measurement" to include every conceivable type of process that we might want to call a measurement, but for my current purposes, I think it's better to just keep the definition simple. I think that my definition is good enough for all possible theories, because in situations where a different type of "measurement" is possible, we always have the option to do a measurement that satisfies my definition and is for all practical purposes equivalent to the other measurement.

 

[atyy]

Some people consider "a classical/quantum cut" to be the idea that QM simply doesn't apply to some systems, in particular measuring devices. I find that notion absurd, and I think you do too. If two systems have Hilbert spaces $H_1$ and $H_2$, the composite system has Hilbert space $H_1\otimes H_2$. This is an essential part of the QM framework, and it implies that any object that consists of quantum systems, is a quantum system.

In my opinion, the proper way to talk about these things is this: Science defines a "theory" (roughly) as a set of statements about the real world that makes testable predictions. A testable prediction is a claim about what the result of a measurement will be, or what the average result of a sequence of measurements performed on identical systems will be. A measurement* is an interaction between a measuring device and the system that the theory is about, which leaves the measuring device in one of its possible final states. The possible final states must be easily distinguishable by a human observer. If they're not, we wouldn't consider the object a measuring device.

Because of this, I wouldn't include either of these types of "classical/quantum cuts" in a definition of "Copenhagen".

I think this is a subtle issue - is there a real difference between "naive realism" and "instrumentalism"? One can argue that "reality" is just a tool to help us predict the results of experiments, so in that sense "reality" is not necessarily "real".

But at a less refined level, the classical/quantum cut in Copenhagen is distinctive, because it means that Copenhagen does not assign any meaning to the "wave function of the universe". Copenhagen does not assert that the whole universe is a quantum system. One can contrast the classical/quantum cut with Many-Worlds (or a very literal form of Bohmian Mechanics), which tries to make sense of the "wave function of the universe". One can also contrast the classical/quantum cut with general relativity, in which there is in principle no problem to including the measuring apparatus in the state of the system, and we do believe that general relativity can be a theory of the whole universe.

 

[carllooper]

To use your line of thinking: you can place polarizers over BOTH slits. The relative orientation (parallel or orthogonal) will then determine whether there is interference or not. So in that manner, the variable [relative orientation of polarizers] is always "non-local".

Yes that's right.

 

[aleazk]

I think this is a subtle issue - is there a real difference between "naive realism" and "instrumentalism"? One can argue that "reality" is just a tool to help us predict the results of experiments, so in that sense "reality" is not necessarily "real".

But at a less refined level, the classical/quantum cut in Copenhagen is distinctive, because it means that Copenhagen does not assign any meaning to the "wave function of the universe". Copenhagen does not assert that the whole universe is a quantum system. One can contrast the classical/quantum cut with Many-Worlds (or a very literal form of Bohmian Mechanics), which tries to make sense of the "wave function of the universe". One can also contrast the classical/quantum cut with general relativity, in which there is in principle no problem to including the measuring apparatus in the state of the system, and we do believe that general relativity can be a theory of the whole universe.

That's certainly a subtle issue. According to Isham, we need a more realist (i.e., non-instrumentalist) interpretation of QM if we want to build a QG theory, and QC (quantum cosmology):

http://arxiv.org/pdf/1004.3564.pdf

Apparently, his solution to all these problems (in particular, the clash between the continuum in many of our theories and the supposed non-continuum spacetime of QG) is to rewrite all physics in terms of topos theory rather than set theory.

 

[kith]

It is also true that the view Ballentine opposes is a misrepresentation of Copenhagen, so in that sense, one could also say that he does not oppose any correct view, merely a caricature of it, so in that sense Ballentine is right. However, Ballentine does make the view he opposes seem to be "mainstream", so he is at least misleading.

I think that's one of very few passages in your posts about Ballentine where a person who is not familiar with the book doesn't get a heavily distorted view of it. As Frederik remarked, many of your posts make it seem like Ballentine is a really bad book.

I agree that Ballentine makes it seem like he is criticizing a mainstream view while he is actually arguing against collapse as a physical process. But disregarding this, most of his arguments are valuable and not present in many other standard texts.

Cohen-Tannoudji -which was my first book on QM-, for example states that there's a problem with measurements but instead of discussing it, he only writes half a page of vague things like that the interaction between system and measurement apparatus is important. My second book was Sakurai whose only comment on the matter is a quote from Dirac's book reading "A measurement always causes the system to jump into an eigenstate". After having read these two standard textbooks and having attended 2-3 graduate level courses on QM, my impression of collapse was exactly one of the wrong notions which Ballentine disproofs.

So I don't think that Ballentine does a bad job here. Sure, he should have chosen a more modest wording and he should acknowledge that QM can be interpreted in different ways. But I don't think you have more misconceptions about interpretations after reading Ballentine than after reading the average standard textbook on QM. (And Ballentine's presentation of the physics is far above average.)

 

[carllooper]

Carllooper, I don't believe that physics CAN really function without philosophy. I know this will be a controversial and perhaps even offense statement, and I'm sorry for that!--but I don't mean by "philosophy" the stuff that is taught in the academy, but something like "first order principles that govern thought-towards truth" (sometimes called metaphysics, although widely rejected these days). I think when scientists appeal to the basic tools of thought they are simply appealing to these things. But if you get those principles wrong, the science will start to go astray, which is what seems to me to be happening. For example, if Einstein did not have a strong belief in the principle that nothing happens without a reason, would he have made the discoveries that he did? And if not, and given the widespread rejection of that very principle today….well, that's why I think these things are important.

Any philosophical principles that Einstein may have used may very well have played an important, if not key role in his contribution to physics. Indeed, personally, I'm sure of it. But how can we conclude that if we "get those principles wrong" science will go astray? Bohr was equally inspired by philosophical principles, but a somewhat different set of principles, yet was perfectly able to make a contribution to physics.

The way in which physics generally works is that ideas are put to a physical test. If there's agreement between the physical test and the ideas that conceive it, then the idea is considered provisionally correct. Or useful. In other words, the idea could be philosophically right or wrong, but in terms of the physics it points out, (to the extent that it does) it wouldn't actually matter. What matters is whether it's physically so, (ie. physically wrong or provisionally correct). Not whether it's philosophically so.

Of course, in practice, it can get a lot more complicated than this.

C

 

[atyy]

Apparently you and atyy both consider Ballentine an opponent of Copenhagen.

I agree that Ballentine makes it seem like he is criticizing a mainstream view while he is actually arguing against collapse as a physical process. But disregarding this, most of his arguments are valuable and not present in many other standard texts.

Ballentine's book does not mention Copenhagen. However, Ballentine's earlier review is explicitly anti-Copenhagen, and the view opposed in his book is the strawman version of Copenhagen in his review.

 

[bhobba]

I agree that Ballentine makes it seem like he is criticizing a mainstream view while he is actually arguing against collapse as a physical process. But disregarding this, most of his arguments are valuable and not present in many other standard texts.

That's exactly what's going on.

I don't know why there has been this big discussion about it.

Thanks
Bill

 

[atyy]

That's exactly what's going on.

I don't know why there has been this big discussion about it.

To be honest, I have never imagined that Ballentine was arguing against collapse as a physical process till now - possibly because the view opposed in his book and review are the same, and the review labels it "Copenhagen". So if one is working in Copenhagen, and has already taken the classical quantum cut, and the wave function is taken as a tool to calculate the probabilities of experimental outcomes, then one can interpret the plain English statement that a pure state provides a "complete and exhaustive description of an individual system" as correct within Copenhagen. A pure state is "complete and exhaustive" in the sense that it is an extremal state - even very modern versions of Copenhagen such as Hardy's "Five Reasonable Axioms" identify pure states with extremal states - the difference being that the classical space is a simplex, but the quantum space is not. There is also no problem in Copenhagen if one takes a pure state to label an individual system, as long as one adds that the theory only predicts probabilities. It is completely a matter of taste whether the pure state labels an individual system or an ensemble - either way, there are no differences in predictions, and no deviations from current experiments.

Furthermore, the view Ballentine ends up with, if it is correct, is essentially some flavour of Copenhagen renamed. However, it is not a very coherent presentation of any flavour of Copenhagen. If Ballentine is proposing that the wave function is not necessarily real, then he has to take a classical/quantum cut to get observable results. If he does not take the classical/quantum cut, then he will get a wave function of the universe and all the problems associated with it. So let's say he takes a classical quantum cut, and the wave function is not necessarily real - in that case there is no problem with state reduction - yet he argues against state reduction, and claims to be able to derive it from unitary evolution alone. Ballentine's derivation of "effective" state reduction is flawed, because he has implicitly assumed that proper and improper mixtures are equivalent, which is implicitly assuming the very postulate he has rejected. If he had derived effective collapse from unitary evolution alone, he would have made decoherence (without additional assumptions) a plausible solution to the measurement problem! So in the end, it is completely unclear what interpretation Ballentine wants. In his review, he secretly wanted hidden variables (nothing wrong with that, but one should say so explicitly if that is the case). In his book that seems to be corrected, and it seems he wants some flavour of Copenhagen, since the wave function is not necessarily real. But he also secretly wants Many-Worlds, since he objects to state reduction and wants unitary evolution only.