Against "interpretation" - Comments

[DarMM]

In case you avoid any ontological assumption regarding the pre-measurement situation, the measurement problem doesn't exist.

There's no ontological assumption about the pre-measurement situation here though. Simply two contradictory accounts of the same measurement. What's the ontological assumption here? The formalism itself allows these operators of the kind I described, that's not an "ontological assumption".

The minimal view asserts that there is no measurement problem. More precisely, the minimal view considers "measurement" as a primitive fundamental concept that does need to be explained in terms of something more fundamental

Is that what's going on here though? What I'm saying just follows from the existence of observables like $A$ and $B$ above which the formalism permits. Unless by "view measurement as a primitive" you mean "exclude observables like $A$". However this requires a modification of the bare formalism, i.e. forbidding some observables. Asher Peres does this, but I still think it means we need to make some clear statements about the formalism, a fairly strong one in fact.

 

[vanhees71]

I have never seen a clear presentation of the measurement problem in the so called "minimal" view. The measurement problem is a logical incoherence in the theory, not just metaphysics. I don't think you can get out of it just by being positivist/empiricist. Or could somebody give me a clear explanation of the measurement problem in the minimal view?

I think the minimal view is usual that what's presented in standard textbooks, and there measurements are just taken as "primitives" within the theory which are not necessary to be defined any further than by the specific setups the experimentalist uses to measure. Quantum theory provides a framework to predict probabilities of such defined measurements.

In classical physics it's not that different. Nobody in a theoretical-physics textbook talks about measurement processes simply because it's taken as described above. Of course as in QT you have to think about, how to construct a measurement device to measure some given quantity.

You had the example of the classical electromagnetic field, and already here it's not so clear a priori how to measure it. We start with some qualitative notion of light (given the hypothesis by Maxwell that light is nothing else than an electromagnetic wave field in free space). What we "see" (in the literal sense) are qualities as color and intensity. Of course nowadays we know that color is in fact not a physical but a physiological quantity, but roughly speaking we can consider it as a quality related to the frequency (and thus equivalently to wavelength) of the electromagnetic wave and the intensity as a quality related to the amplitude of the electromagnetic field.

Now the question occurs how to quantify it. From a theorist's point of view one looks at what is natural to define, and the only idea one can come up with is to take energy density (a positive definite gauge-invariant quantity) and/or energy-flow density as measures. Now you construct some device supposed to measure energy or energy-flow densities like a photoplate and compare with the predictions from theory. If you get agreement within the limits of uncertainty/accuracy you say the theory is successful in describing quantitatively the phenomena.

 

[DarMM]

I think the minimal view is usual that what's presented in standard textbooks, and there measurements are just taken as "primitives" within the theory which are not necessary to be defined any further than by the specific setups the experimentalist uses to measure. Quantum theory provides a framework to predict probabilities of such defined measurements.

In classical physics it's not that different

The problem isn't that measurement isn't dealt with in textbooks or that doing so is complex. It's that by trying to do so I can derive a contradiction very quickly. Which is why Asher Peres says the "Minimal Interpretation" is really textbook QM + there are no superobservers.

If by the minimal view we mean what Peres has in his book that's fine. If we mean textbook QM/what most people mean by "shut up and calculate" then no that does have a contradiction.

 

[Dale]

You may be right about this, but what I don't believe is that someone may fully accept the minimal interpretation in his heart. Don't you ever wonder, in your heart, what the atom looks like when nobody observes it? I fully understand that a physicist may be afraid of asking such questions because they cannot be answered by the scientific method, but I cannot understand that a physicist never asks himself such a question anyway.

Sure. I completely agree with you here. I ask myself many non-scientific questions. I just (a) recognize that they are non-scientific (b) don’t ask them here (c) don’t bother to argue about them at all (d) keep an open mind and (e) switch positions as often as I find convenient.

For me, the biggest problem here on PF is (c). You all argue incessantly and interminably about this stuff. It is all opinion! It may be the opinion that you hold in your heart, but it is just an opinion. Why do you all argue so much about opinions?

Interpretations (beyond the minimal interpretation) have little scientific value, and only this “in your heart” emotional attachment. So please (all of you) tone down the arguments substantially.

 

[DarMM]

For me, the biggest problem here on PF is (c). You all argue incessantly and interminably about this stuff. It is all opinion! It may be the opinion that you hold in your heart, but it is just an opinion. Why do you all argue so much about opinions?

Because it's an actual debate in the scientific community and by discussing it you learn more about the formalism and because it's the motivation behind several scientific discoveries and because the minimal/textbook interpretation is internally incoherent.

I get the sentiment, but it's not as clear cut as you're making it, otherwise it wouldn't be in textbooks for QM.

 

[Demystifier]

Why do you all argue so much about opinions?

Interpretations (beyond the minimal interpretation) have little scientific value, and only this “in your heart” emotional attachment.

Opinions are not only emotional attachments. We all have more-or-less rational arguments for those opinions. Sure, the arguments are not strictly scientific, but they are still rational. Or you may call those arguments philosophic, I'm fine with that, but philosophy is based on reason, not on emotions. I think that's the reason we like to argue about it so much.

I perfectly understand that most physicists don't like to talk so much about it, and that's perfectly fine too. But I don't understand why those who do not like to talk about see a problem in the fact that some of us do like it. The community of physicists is not uniform, we like to talk about different things, and I see no problem in it.

 

[Dale]

by discussing it you learn more about the formalism

I disagree about the pedagogical value of interpretations arguments. In my personal (anectdotal) case it is definitely an obstacle to learning, not a benefit. And I challenge you to find any professional scientific study that actually demonstrates a statistically significant learning benefit to arguments about interpretations. Frankly, I think this claim is completely unsubstantiated and not very credible on its face. I suspect that the only reason that you believe it is because you and the other interpretations fans tell it to each other to justify your arguments.

Because it's an actual debate in the scientific community

I think that you are vastly overstating the level of debate in the scientific community. Certainly, it is not as incessant professionally as it plays out here. In any case, how about you all just tone it down a notch or three? Would the scientific community's debate be compromised if on PF you were all a little less strident and continuous in your repetitive squabbles?

 

[Demystifier]

I get the sentiment, but it's not as clear cut as you're making it, otherwise it wouldn't be in textbooks for QM.

As a support for this claim, I remind everybody of the list of general QM textbooks that contain a substantive discussion of interpretations: https://www.physicsforums.com/threads/qm-textbooks-with-interpretations.912703/

 

[Demystifier]

I think that you are vastly overstating the level of debate in the scientific community. Certainly, it is not as incessant professionally as it plays out here. In any case, how about you all just tone it down a notch or three? Would the scientific community's debate be compromised if on PF you were all a little less strident and continuous in your repetitive squabbles?

One of benefits of Physics Forums is that here we can discuss physics related questions that cannot so easily be discussed in physics journals. Technical non-interpretational aspects are perhaps sufficiently covered in journals, so we don't have so much need to discuss it here.

 

[DarMM]

I disagree about the pedagogical value of interpretations arguments. In my personal (anectdotal) case it is definitely an obstacle to learning, not a benefit. And I challenge you to find any professional scientific study that actually demonstrates a statistically significant learning benefit to arguments about interpretations

There's very little research on the pedagogy of QM particularly for higher areas like QFT and interpretations. I'd also have opinions on the best way to teach QFT. There's no studies about it, but I do think it for reasons that come from lecturing and talking to other lecturers. I've had a bit about interpretations at the end of my QM lectures. No there is no study, but there aren't really many such studies for any higher area of physics. I have one anecdotal experience as a lecturer, you have another as a moderator here. Yes we can't say more than that since there are no studies, but I don't think that makes my view ridiculous.

I suspect that the only reason that you believe it is because you and the other interpretations fans tell it to each other to justify your arguments

Or, instead of reading weird motivations into my behavior, it comes from experience as a lecturer and somebody who tried to understand QM and is my genuine experience and opinion. Not held to justify arguments.

interpretations fans

In any case, how about you all just tone it down a notch or three? Would the scientific community's debate be compromised if on PF you were all a little less strident and continuous in your repetitive squabbles?

Sorry but "interpretation fans", telling me to be "less strident", "repetitive squabbles"? I just like talking about QM, I don't even really hold to an interpretation. I've had long discussions with say @Demystifier above. Fourteen pages where we disagreed such as on the Frauchiger-Renner thread, then in the end he was right, I thanked him and we concluded. Friendly disagreement. I don't particularly like this characterisation. What opinion do I hold that I am being strident with? I'm actually trying to take a middle ground here, why do I need to "tone it down"?

 

[Dale]

Or you may call those arguments philosophic, I'm fine with that, but philosophy is based on reason, not on emotions.

Fair enough. I accept that. The attachment includes emotion, reason, and aesthetics, as do most philosophical preferences.

Here is the difference I see. In my personal life I have strong philosophical positions to which I am quite firmly attached, e.g. I am a devoutly religious person. I don't argue about those positions at all. I will explain to someone why I hold that position and the value to me in holding that position, but I simply do not argue about it. If my reasons for holding my opinion are not convincing or interesting to them then I do not pursue it further and simply leave the opportunity open if they ever do become interested in the future. When I was younger I argued about such things, but I grew out of it. Furthermore, I don't bring that stuff here, the P in PF is physics, not philosophy. There is a time and place for such things, and you all seem to have no sense of that here.

 

[Dale]

Fourteen pages where we disagreed such as on the Frauchiger-Renner thread, then in the end he was right, I thanked him and we concluded. Friendly disagreement. I don't particularly like this characterisation. What opinion do I hold that I am being strident with?

Umm, how about right there? Fourteen pages!

 

[DarMM]

Umm, how about right there? Fourteen pages!

How is discussing a subtle issue in a new paper for a long time strident? Even the community didn't know exactly how to analyse the FR argument. At no point were we aggressive with each other and it just took a long time to sort out the details. What's wrong with it being 14 pages? It's a new and difficult paper.

I find this a bit unfair. It's characterising enjoying a long discussion on the topic as being a strident opinionated loon. What opinion am I being strident about?

EDIT: It was actually 8 pages

 

[vanhees71]

The problem isn't that measurement isn't dealt with in textbooks or that doing so is complex. It's that by trying to do so I can derive a contradiction very quickly. Which is why Asher Peres says the "Minimal Interpretation" is really textbook QM + there are no superobservers.

If by the minimal view we mean what Peres has in his book that's fine. If we mean textbook QM/what most people mean by "shut up and calculate" then no that does have a contradiction.

How can there be a contradiction, since that's how our theories are applied by experimentelists and also the other way around, how models and maybe finally theories are developed from analysis of experiments.

I think Peres's textbook is the most (if not the only) sensible textbook on interpretational issues I know.

 

[vanhees71]

Because it's an actual debate in the scientific community and by discussing it you learn more about the formalism and because it's the motivation behind several scientific discoveries and because the minimal/textbook interpretation is internally incoherent.

I get the sentiment, but it's not as clear cut as you're making it, otherwise it wouldn't be in textbooks for QM.

Yeah, it's a great topic to discuss at lunch, if the weather is too boring to talk about ;-).

 

[DarMM]

How can there be a contradiction, since that's how our theories are applied by experimentelists and also the other way around, how models and maybe finally theories are developed from analysis of experiments.

I think Peres's textbook is the most (if not the only) sensible textbook on interpretational issues I know.

See Chapter 9 of Peres's book, particularly the section called "The consistency problem", p. 376 if I remember right. I suspect you already have what Peres says built into your view so there's no issue with what you call the "Minimal view", but technically it's an issue with textbook QM.

If you like his style I'd look at some of his papers from the 1980s like "The classical paradoxes of quantum theory".

 

[vanhees71]

There's very little research on the pedagogy of QM particularly for higher areas like QFT and interpretations. I'd also have opinions on the best way to teach QFT. There's no studies about it, but I do think it for reasons that come from lecturing and talking to other lecturers. I've had a bit about interpretations at the end of my QM lectures. No there is no study, but there aren't really many such studies for any higher area of physics. I have one anecdotal experience as a lecturer, you have another as a moderator here. Yes we can't say more than that since there are no studies, but I don't think that makes my view ridiculous.

I think, pedagogical studies can have there merits but I'm highly suspicious, though I like one type of empirical studies: You teach some topic in different ways to different groups and then look at the outcome of problem-solving sets/exams, including also asking conceptual questions. It's amazing what sometimes comes out from such studies. E.g., there's a recent textbook on school students' (of various grades) as well as university students' understanding of standard physics concepts. In quantum theory even at the university level there are amazing outcomes of such studies: E.g., in one study they found out that after a QM lecture students (5-11 semester at the university) just had the "particle idea of light/photons" but have not associated any wave aspects of light anymore. This is amazing given the fact that in teaching QM usually one starts with empasizing the wave-particle-duality aspect pretty much, but it seems that the "photons as miniature bullets" idea sticks, and for me this confirms that one should from the very beginning emphasize that this old picture a la Einstein is simply wrong and that for a full understanding of photons they have to wait for the QFT lecture.

I think there are some merits in discussing foundational aspects for the reason that some students are interested in them and one can use them to teach the applications of the formalism. E.g., I find an experiment like the quantum eraser with entangled photons or the entanglement-swapping experiment with two entangled photon pairs atmost fascinating from purely physics scientific point of view, and you can discuss them with quite uncomplicated basic parts of the formalism used in QED (in its quantum-optics flavor of course). I think this can be easily implemented for 1-2 90minute lectures within the QFT 1 lecture.

 

[Demystifier]

In my personal life I have strong philosophical positions to which I am quite firmly attached, e.g. I am a devoutly religious person. I don't argue about those positions at all.

I also have strong opinions about some religious questions (for instance I think I can prove that omnipotent God is a logical contradiction) and like you, I also don't argue those positions here. But ...

... the P in PF is physics, not philosophy.

... unlike you, I don't think that something is not philosophy just because it is physics. I think many topics, including quantum foundations, are both. In fact, the very first post in this thread is precisely an argument that it doesn't make sense to make a clear cut between interpretations (that is, philosophy) and theories (that is, physics).

 

[Demystifier]

I disagree about the pedagogical value of interpretations arguments. In my personal (anectdotal) case it is definitely an obstacle to learning, not a benefit.

My personal anecdotal experience is precisely the opposite. With some intuitive interpretation in my mind, I find it easier to deal with some practical questions too. For me, interpretations are not definite but mutually exclusive truths, but practical mutually complementary tools. I find it hard to think about practical details if I don't have a big intuitive picture of all this in my mind. My understanding of Bohmian mechanics or many worlds helps me to be a better "Copenhagenian" when it's appropriate. But I guess that's very individual.

 

[atyy]

I disagree about the pedagogical value of interpretations arguments.

I hope you at least agree that quantum mechanics in the minimal interpretation requires - different people say this differently - a "classical-quantum" cut or grant the observer or measurement apparatus a special status. After all, this is right at the start of Landau & Lifshitz, one of the most famous textbooks.

 

[dextercioby]

Sure. I completely agree with you here. I ask myself many non-scientific questions. I just (a) recognize that they are non-scientific (b) don’t ask them here (c) don’t bother to argue about them at all (d) keep an open mind and (e) switch positions as often as I find convenient.

For me, the biggest problem here on PF is (c). You all argue incessantly and interminably about this stuff. It is all opinion! It may be the opinion that you hold in your heart, but it is just an opinion. Why do you all argue so much about opinions?

Interpretations (beyond the minimal interpretation) have little scientific value, and only this “in your heart” emotional attachment. So please (all of you) tone down the arguments substantially.

Hi Dale, I understand your position, but not only the community here thinks the topic "interpretations of Quantum Physics" is actual real physics research, simply because there is no agreement in the literature on a common way to interpret/translate what the theory is saying.
For me, these discussions are worth reading for the sake of (educated) argumentation and I press the "like" button -like on other social media- each time I agree with what is written (content and even more so flow of ideas).

You have the option to not moderate these borderline physics/philosophy discussions which you acknowledge bring little value to you. We have Peter Donis who has lately migrated from moderating the relativity section into the QP one.

What you just did, metaphorically speaking, is just tell people "I hate the music you listen to", when you have the option to not simply listen to it...

From my point of view, I consider the whole "string/LQG theory" simply a useful exercise in mathematics (perhaps I am not aware of their true predictive power wrt experiments), but I do not go them to tell them "Hey, your work on string theory is partly/mostly/totally useless. By what argument do you expect me to believe its Quantum Gravity explanation?"

So you think some Netflix series is junk, wasted money. Then simply turn to HBO or Amazon Prime...

 

[Dale]

I find it easier to deal with some practical questions too. For me, interpretations are not definite but mutually exclusive truths, but practical mutually complementary tools. I find it hard to think about practical details if I don't have a big intuitive picture of all this in my mind.

This approach I like. If an interpretations discussion took this approach then I could believe it would be pedagogically beneficial. Something along the lines of introducing a particular type of problem, introducing a specific interpretation that is well suited to that type of problem, and allowing that interpretation to guide the solution of the problem.

Do such threads exist here?

 

[Dale]

What you just did, metaphorically speaking, is just tell people "I hate the music you listen to", when you have the option to not simply listen to it...

Here is the personal frustration: I would like to know more QM than I do, but I find the interpretations discussions here to be a severe obstacle to doing so. I hate the music you listen to partly because you are playing it so loud and so continuously that it drowns out the music that I want to listen to.

I am hoping that the new Interpretations forum will alleviate this issue in the future. But in the past this has been a problem for me personally.

So you think some Netflix series is junk, wasted money. Then simply turn to HBO or Amazon Prime.

I would but the junk Netflix series was being continuously broadcast on top of Amazon Prime. Unless they fixed it recently.

You have the option to not moderate these borderline physics/philosophy discussions

I don’t moderate them, I am not qualified. I am not here as a moderator, just a participant, and only as a participant because the title was “Against Interpretation” so I thought it would be a thread specifically for voicing my kind of opinion.

 

[Demystifier]

This approach I like. If an interpretations discussion took this approach then I could believe it would be pedagogically beneficial. Something along the lines of introducing a particular type of problem, introducing a specific interpretation that is well suited to that type of problem, and allowing that interpretation to guide the solution of the problem.

Do such threads exist here?

I'm not sure about whole threads, but posts of that form exist. See e.g. my
https://www.physicsforums.com/threads/wigners-friend-and-incompatibility.976587/page-3#post-6226655https://www.physicsforums.com/threads/wigners-friend-and-incompatibility.976587/page-2#post-6225640

 

[ftr]

I am hoping that the new Interpretations forum will alleviate this issue in the future. But in the past this has been a problem for me personally.

Physics has several main problems that many physicists (almost all bloggers) debate. How else would people solve these problems. People here with a spectrum of knowledge strength give their "opinion" , that is part of the process (whether PF or any other place).

 

[Minnesota Joe]

My personal anecdotal experience is precisely the opposite. With some intuitive interpretation in my mind, I find it easier to deal with some practical questions too. For me, interpretations are not definite but mutually exclusive truths, but practical mutually complementary tools. I find it hard to think about practical details if I don't have a big intuitive picture of all this in my mind. My understanding of Bohmian mechanics or many worlds helps me to be a better "Copenhagenian" when it's appropriate. But I guess that's very individual.

Anecdotal, yes, but it describes very well the problems I had with my first quantum mechanics class and I've heard similar things from peers. A balanced discussion of the various ideas about what it could mean would have been a very useful guide to thinking. A close second would have been "This is the recipe and we don't know why" as opposed to strong metaphysical positions on indeterminacy, non-realism, etc. I hope that has changed at least.

Anyway, what you wrote really resonates with me at least.

 

[vanhees71]

I hope you at least agree that quantum mechanics in the minimal interpretation requires - different people say this differently - a "classical-quantum" cut or grant the observer or measurement apparatus a special status. After all, this is right at the start of Landau & Lifshitz, one of the most famous textbooks.

Well, I disagree, even though LL is among the best textbooks I know. The classical description of macroscopic situations, including measurement devices, is an effective description which can be understood from quantum theory by basic statistical arguments (law of large numbers etc.), and then I can use the effective description of the macroscopic measurement device to understand why I measure the observable of the "quantum object" I want to measure. There is no cut but just the applicability of a "classical" description for many-body systems and some appropriate coarse grained macroscopic observables. FAPP of course you can argue with a cut. The observable outcome is the same.

Whether or not there is really a cut on the fundamental level, i.e., if there is some limit of the validity of QT at which the classical behavior cannot be understood from QT, or (in another twist of this issue) if at one point a macroscopic system cannot show specific "quantum behavior" anymore (e.g., intereference effects of objects consisting of many particles). Just recently the boarder of this "classical-only behavior" has been pushed to huge molecules with de Broglie wavelengths in the fm range. So far there's no single hint for such a "fundamental quantum-classical cut". Of course, there might be one somewhere, but at least today there's no hint for such a thing.

 

[A. Neumaier]

I have never seen a clear presentation of the measurement problem in the so called "minimal" view. The measurement problem is a logical incoherence in the theory, not just metaphysics. I don't think you can get out of it just by being positivist/empiricist. Or could somebody give me a clear explanation of the measurement problem in the minimal view?

Englert's article and the books by Ballentine's and by Peres have something. Englert and Ballentine sweep the problem under the carpet of very soft arguments. Peres admits towards the end of his books (see your post #303) that there is a problem when one applies quantum mechanics to a full model of the measurement problem. I concur with Peres, who (unlike Ballentine, Englert, and @vanhees71) is very precise in his arguments.

 

[A. Neumaier]

How can there be a contradiction, since that's how our theories are applied by experimentalists and also the other way around, how models and maybe finally theories are developed from analysis of experiments.

Successful use does not exclude logical deficiencies. It is similar to the foundations of set theory. It had been used very successfully for over 20 years before Russell discovered a contradiction in naive set theory, and it took another 20 years to fix it through axiomatic set theory. Today most people still don't care since they can use naive set theory without problems.

In quantum physics, the contradiction is not in the relation to experiment but in the theory, once Born's rule assumed together with the claim that experimental arrangements and hence measurements can be fully accounted for by quantum physics. Those like you who never model the latter will not run into the contradiction, so everything seems fine to them.

 

[vanhees71]

I still don't understand your argument. Of course, the issues with set theory were mathematical issues and had to be resolved to have a solid foundation of set theory and given its importance as a basic tool in all branches of mathematics also of mathematics as a whole.

Quantum mechanics, at least the non-relativistic flavor, has no mathematical problems as far as I can see. This of course includes Born's rule, and given this set of postulates/axioms you have a special kind of probability theory, if you just consider QM as a mathematical construct.

Now when it comes to physics all you need in addition is a relation between what's observed in nature and the formalism, and with the minimal statistical interpretation there are no problems either. If there were problems, QM wouldn't be as successful as it is in describing the observations. If there is a discrepancy, we'd learn something fundamentally new. That's how (theoretical) physics works.

Of course it's desirable to have mathematical sound and solid formulations of physical theories, but it's a different issue to consider a mathematical theory, which does not necessarily need to describe nature but just has to be mathematically sound and solid. E.g., Newtonian mechanics is a mathematically well-defined theory providing rules to derive differential equations and some general and beautiful tools for their solution. Particularly the entire field of Lie-group and -algebra theory has been triggered by it. Nevertheless it's not sufficient to describe all observations and thus had to be modified (including the necessity of new descriptions of space and time in relativity theory and QM).

Another type of trouble is classical electrodynamics. As long as you deal with continuum mechanical models of charged matter the issue from the point of view of mathematics is quite the same as with Newtonian mechanics. Here we have a well-defined classical relativistic field theory providing PDEs and some nice tools to solve them. Nevertheless we know it's incomplete as soon as it comes to models for matter in terms of point particles. There's no satisfactory closed dynamics for fields and point particles. The best one could come up with for more than 100 years is the Landau-Lifshitz approximation. Of course it's known that classical point particles are a lousy model of matter on a microscopic level and one has to use QT, and in this case the best one could come up with is relativistic QFT, which has the known problems as a mathematical theory, which however can be overcome in the typical pragmatic manner physicists ignore mathematical problems by dealing with hand-waving arguments. For a mathematician there's of course still a lot to be desired, and maybe one day there's a more comprehensive mathematically sound and solid microscopic theory that describes all observations as well as relativistic QFT does as an "effective theory" today.

All these examples show that there's a strong overlap between math and theoretical physics, but the goals are partially different. As a physical theory QM is amazingly successful, and there are no foundational problems. You just have to accept probabilistic arguments as a fundamental feature of nature. Quibbles with this view are metaphysical and have nothing to do with either math or the natural sciences.