Against "interpretation" - Comments

[A. Neumaier]

Yes, exactly. That's why I insist that it is impossible to sharply distinguish "interpretational" research from "non-interpretational" one.

In papers, on can easily distinguish this by looking at what is calculated and what is reasoned informally. Research is of course an umbrella for both.

 

[Demystifier]

In papers, on can easily distinguish this by looking at what is calculated and what is reasoned informally. Research is of course an umbrella for both.

I am talking about a paper as a whole, one cannot say this paper is interpretational and that paper isn't. Each paper contains elements of both.

 

[Dr. Courtney]

They are two equivalent mathematical frameworks which can be derived from one another through mathematical operations. Why should we use a definition of “interpretation” where a straight mathematical operation generates a new interpretation? Every line of every theorem or homework problem would then be using a unique interpretation. Is that what you want the word to mean?

I don't think the interpretation is in the mathematical operations, but rather in assertions regarding which quantities are more fundamental, especially which quantities that are not directly measured.

It is not so innocent as it may look. Some physicists interpret the 2nd Newton law not as a law but as a definition of force, defined as $F\equiv ma$.

The challenge with F = ma is that it can be viewed either as the definition of force or the definition of inertial mass. Of course, it cannot be the definition of both at the same time. Thus there is interpretation. Viewing F = ma as the definition of force requires some other definition of inertial mass - or a tacit understanding of some other fact such as inertial mass being the same as gravitational mass.

But good theories aren't. They are heavily constrained discoveries of the human mind, and cannot be falsified in their domain of validity.

I see this as somewhat circular, as history shows that that there is often not a clear distinction between falsification and narrowing of the domain of a theory's validity.

It's fine, but my objection is that there is no sharp borderline between "interpretational" and "non-interpretational" aspects of a theory. For instance, if we accept the wiki definition that interpretations are about reality, then even a shut-up-and-calculate approach to measurable quantities can be considered an "interpretation", because it is about measurable quantities which are real.

And which measurable quantities are fundamental. The thought often seems to be that quantities that are more directly measured (position, time) are somehow calculated from more direct measurements (energy, velocity). Of course, other viewpoints see energy as more fundamental than force.

 

[Elias1960]

This does not affect the validity of my statement.It simply takes some time before a theory can be known to be good.

But once we cannot know initially what is good, it fails to be an objection against the "free invention of the human mind". (Of course, the scientist himself will compare his invention with known empirical data, before he writes an article proposing it. But even this is a process, and even here the invention comes first, the check and rejection of the many false "good ideas" comes later.)

 

[Elias1960]

You need the, admittedly vague, notions of observations and experiments first to create physically successful theories. A really aesthetic argument for a theoretical physicist is not if there's a free invention (e.g., Bohr's model of the atom) but if there's almost no freedom given the empirical foundations (e.g., Einstein's GR, which is almost inevitable given the strong equivalence principle and relativistic spacetime structure).

Except that the equivalence principle itself was a free invention of Einstein's mind, one he was very happy that he has had it. And the relativistic spacetime structure is a metaphysical idea that has no relation to experiment at all, given that viable interpretations with absolute time and without any spacetime as a structure exist.

Which free inventions are valuable and which deserve to be forgotten is another question, and the great scientists are those who successfully throw away their bad inventions and develop their good inventions.

 

[Dale]

It's fine, but my objection is that there is no sharp borderline between "interpretational" and "non-interpretational" aspects of a theory. For instance, if we accept the wiki definition that interpretations are about reality, then even a shut-up-and-calculate approach to measurable quantities can be considered an "interpretation", because it is about measurable quantities which are real.

I am not sure what you think is un-sharp here. Shut-up-and-calculate is also (more correctly but less amusingly) known as the minimal interpretation, which as the name suggests is an interpretation.

A theory consists of one or more equivalent mathematical frameworks together with a minimal interpretation. That is what is necessary for using the scientific method, the mathematical framework is used to relate the various quantities within the theory and the minimal interpretation is used to link those quantities to experimental outcomes and predictions. Any interpretation going beyond the minimal interpretation can be removed or exchanged without changing the theory because any additional interpretation is not subject to investigation by the scientific method, but changing the minimal interpretation would change the theory since it would change the link between experiment and the mathematical quantities.

I suppose that there may be some people who argue that the minimal interpretation should not be considered an interpretation. Perhaps that is the concern you have and the reason you feel the distinction is not sharp. It seems pretty sharp to me.

 

[zonde]

(e.g., Einstein's GR, which is almost inevitable given the strong equivalence principle and relativistic spacetime structure)

I found this link interesting: A Peek into Einstein's Zurich Notebook
It does not seem from this that Einstein's path to GR was quite straightforward, but as most of mathematical details are lost on me I might be missing some possible insights.

 

[A. Neumaier]

There is, of course, the obvious restriction that the resulting predictions have to fit reality. But this does not tell you much about that theory.

It tells you whether it is a good theory. A good theory is one that has a known domain in which it is valid.
For example, we have lots of theories about quantum gravity but no good one.

Theories in general may be free inventions of the human mind, but good theories are not inventions; they are discoveries.

 

[bhobba]

If you will create it in the classical physics forum, please make a note/link here!

Good idea. About to do it now. It will be a little different to my other posts in that I will try a bit of a socratic approach. I will start with the questions posed in a quite old book on mechanics, I read long long ago, it never answered, then see what people say and hopefully be led to what John Baez explained to me.

Here is the link:
https://www.physicsforums.com/threads/what-do-Newtons-laws-say-when-carefully-analysed.979739/
Thanks
Bill

 

[Demystifier]

I am not sure what you think is un-sharp here. Shut-up-and-calculate is also (more correctly but less amusingly) known as the minimal interpretation, which as the name suggests is an interpretation.

So if even the minimal shut-up-calculate approach is an interpretation, it shows that it is impossible to do quantum physics without dealing with some interpretation. In other words, any work on quantum physics is an interpretation to a certain extent. So it doesn't make sense to accuse someone for dealing with interpretations instead of dealing with pure (quantum) physics.

 

[Dale]

So if even the minimal shut-up-calculate approach is an interpretation, it shows that it is impossible to do quantum physics without dealing with some interpretation. In other words, any work on quantum physics is an interpretation to a certain extent. So it doesn't make sense to accuse someone for dealing with interpretations instead of dealing with pure (quantum) physics.

Any work on any science requires using a minimal interpretation. That doesn't mean that work on science is an interpretation.

Since the minimal interpretation is non-controversial, there is nothing wrong with people complaining/accusing about all of the useless controversy and wasted time prompted by discussions about the various non-minimal interpretations in QM. The key distinction between the minimal interpretation and other interpretations is that the minimal interpretation can be scientifically investigated whereas none of the other interpretations can. They are philosophical rather than scientific, and hence the "accusations" you mention are both are both fair and self-consistent coming from a scientifically-minded person.

 

[DarMM]

Since the minimal interpretation is non-controversial, there is nothing wrong with people complaining/accusing about all of the useless controversy and wasted time prompted by discussions about the various non-minimal interpretations in QM

There are scenarios that can be constructed within quantum theory where it's not exactly clear what the minimal interpretation would predict or if it would forbid them. Although the interpretations are purely metaphysical for normal experimental situations, they do differ in these situations, e.g. the Frauchiger-Renner set up and Brukner's scenario.

 

[Elias1960]

Since the minimal interpretation is non-controversial, there is nothing wrong with people complaining/accusing about all of the useless controversy and wasted time prompted by discussions about the various non-minimal interpretations in QM. The key distinction between the minimal interpretation and other interpretations is that the minimal interpretation can be scientifically investigated whereas none of the other interpretations can. They are philosophical rather than scientific, and hence the "accusations" you mention are both fair and self-consistent coming from a scientifically-minded person.

I disagree. I have argued elsewhere that interpretations are the reasonable starting points for theory development. Development of new, more fundamental theories is certainly an important part of science, we value those who have succeeded in this as the greatest scientists at all. They can be, clearly, scientifically investigated. In particular, different interpretations usually have different sets of postulates and scientific principles that are fulfilled in that interpretation. Then, interpretations have weak points, which may be criticized. One may attempt to remove them, which would be reasonable for the defenders of the interpretation, and which often leads to a modification of the interpretation, and the result may be an empirically different theory. Defenders of an interpretation have also other possibilities - like to show that every reasonable interpretation will have the same problem. This was Bell's theorem.

Those who think such discussions are a waste of time are not obliged to participate. But any measures against such discussions beyond personal non-participation (like forbidding such discussions in a popular science forum) have an inherently anti-scientific character.

The importance of the discussion of interpretations is not restricted to advanced research with the aim to develop new theories. Interpretations have a strong influence on teaching and popularization. An incomprehensible interpretation will harm the teaching of the theory, the result will be incompetent scientists with inferior intuitions about what the theory predicts. Recommended reading here is Bell, how to teach special relativity.

In the worst case, the failure to teach the theory based on a comprehensible interpretation will create anti-scientific freaks - they think the theory (and not only the incomprehensible interpretation) is simply nonsense, and invent anti-scientific conspiracy theories.

 

[DarMM]

There are scenarios that can be constructed within quantum theory where it's not exactly clear what the minimal interpretation would predict or if it would forbid them. Although the interpretations are purely metaphysical for normal experimental situations, they do differ in these situations, e.g. the Frauchiger-Renner set up and Brukner's scenario.

To expand on this, I was trying to think of an analogue in GR. One might be if the blockworld interpretation and other interpretations differed on a spacetime that was very odd and artificial, but where proving that it is forbidden by the Energy conditions was a very difficult technical problem.

So there would be arguments as to whether such a spacetime could even occur, should we ignore the gap in the interpretations it exposes just because it is forbidden (if it is forbidden) etc.

 

[Dale]

I have argued elsewhere that interpretations are the reasonable starting points for theory development.

That is a common argument from the pro-interpretations crowd, but frankly the evidence supporting it is rather thin. No scientific study has demonstrated that and the historical evidence is (by its nature) highly anecdotal and not strongly supportive of the claim with respect to QM interpretations specifically. I am unconvinced.

I am also unconvinced that the mess of QM interpretations is helpful in either science education or popularization as you claim. Anecdotally, in my case I know it has been actively harmful in my personal education, and again I know of no systematic study supporting your claim.

 

[DarMM]

I also don't think it is definitely the case that interpretations will lead to future theories. Maybe they will, but just as easily it could come from out of left field.

I think the more important thing about interpretations is how they have driven advances in quantum information, e.g. Brukner's scenario gives a correlation class tighter than Bell's inequality that is useful in quantum cryptography. Analysis of quantum discord and other results.

 

[Dr. Courtney]

That is a common argument from the pro-interpretations crowd, but frankly the evidence supporting it is rather thin. No scientific study has demonstrated that and the historical evidence is (by its nature) highly anecdotal and not strongly supportive of the claim with respect to QM interpretations specifically. I am unconvinced.

I am also unconvinced that the mess of QM interpretations is helpful in either science education or popularization as you claim. Anecdotally, in my case I know it has been actively harmful in my personal education, and again I know of no systematic study supporting your claim.

I concur. QM didn't make much sense to me except for the "shut up and calculate" perspective. And I'm an atomic physicist. Computing quantum spectra and verifying quantum predictions with measurements were a big part of my career for many years. Too many folks debating interpretations without even a real understanding of how the "shut up and calculate" part of the deal works. I can't take discussions of interpretations seriously from folks who haven't proven their ability to "shut up and calculate." And then, my first question is always going to be:

Why testable predictions does your interpretation make differently from the "shut up and calculate" approach"?

If there are no different testable predictions, then you have metaphysics rather than physics.

 

[DarMM]

I concur. QM didn't make much sense to me except for the "shut up and calculate" perspective. And I'm an atomic physicist. Computing quantum spectra and verifying quantum predictions with measurements were a big part of my career for many years. Too many folks debating interpretations without even a real understanding of how the "shut up and calculate" part of the deal works. I can't take discussions of interpretations seriously from folks who haven't proven their ability to "shut up and calculate." And then, my first question is always going to be:

Why testable predictions does your interpretation make differently from the "shut up and calculate" approach"?

If there are no different testable predictions, then you have metaphysics rather than physics.

I'm not sure I'd totally agree with this. It sounds pragmatic and sensible, but there is some disconnect with why people actually like science and get interested in it. I think it's natural to wonder what the wavefunction actually is (knowledge/information or a real wave) and what QM actually implies about the world. Few kids get books about astronomy due to an interest in telescope cell excitations, with stars as simple "metaphysics". Students will wonder these things as they are learning.

There is plenty of time wasting and discussion of the meaning of QM here on the forum by people not well versed in QM. However Steven Weinberg doesn't have a section on it in his textbook and Asher Peres and Roland Omnès and many others don't have a whole books on it because the whole discussion is pointless. Despite how silly the discussions can get here from those uninformed about the formalism, it is an area of academic enquiry.

 

[atyy]

If there are no different testable predictions, then you have metaphysics rather than physics.

But if that is true then old fashioned renormalization would be perfectly fine too.

 

[Elias1960]

That is a common argument from the pro-interpretations crowd, but frankly the evidence supporting it is rather thin. No scientific study has demonstrated that and the historical evidence is (by its nature) highly anecdotal and not strongly supportive of the claim with respect to QM interpretations specifically. I am unconvinced.

There have not been that many cases where one can distinguish different interpretations. So, the amount of data is rather small. And, of course, it is hard to identify in history of science, given that only the theory developments which have been successful will be remembered. This gives at most one interpretation per theory where we can expect to find, in the retrospective, a theory development based on it.

For this small database, we have already clear examples.

Nelsonian stochastics was developed as an interpretation. After the Wallstrom objection, it appeared itself to be a different theory, namely, quantum theory where in the configuration space representation wave functions cannot have zeros.

We have the Lorentz ether (ok, SR with preferred frame). In classical physics, it is an interpretation. In quantum physics, without rejection of EPR realism and Reichenbach's common cause principle, they become different theories, given that only in the spacetime variant the Bell inequalities can be proven. The extension of the Lorentz ether interpretation to gravity leads to a theory different from GR, without wormholes and causal loops.

Historically, we have the success of the atomic theory, which was a long time only an interpretation. But a lot of theoretical development has been done during that period where the atomic theory was yet rejected by scientists like Mach.

There is the objective Bayesian interpretation of probability theory. In Jaynes's book, he argues a lot about the statistical methods based on the Bayesian interpretation being in some aspects different and better than what has been developed before. They reinterpreted the whole of statistical mechanics in a Bayesian way and also claim to have reached better results for non-equilibrium thermodynamics.

One can consider Ptolemaeus vs. Kopernicus as interpretations. Kepler's approach was based on some heliocentric mysticism, so, some interpretation.

I am also unconvinced that the mess of QM interpretations is helpful in either science education or popularization as you claim. Anecdotally, in my case I know it has been actively harmful in my personal education, and again I know of no systematic study supporting your claim.

The situation in relativity Bell has supported with anecdotical evidence. And I can say that he is right from own experience of popular discussions. There is no twin paradox for those who know the Lorentzian interpretation, and Bell's own rocket problem also works as described, showing a lot of confusion among those who know only the spacetime interpretation.

The teaching of quantum theory is certainly a mess. There is nothing comparable to Bell's paper about which interpretations are easier to understand and give better intuitions. Moreover, if one assumes that the easier to understand interpretations are the realistic and causal ones, there is no experience of teaching those interpretations first.

 

[atyy]

I think the more important thing about interpretations is how they have driven advances in quantum information, e.g. Brukner's scenario gives a correlation class tighter than Bell's inequality that is useful in quantum cryptography. Analysis of quantum discord and other results.

I imagine Bell might not have agreed. I think it's neat that his inequality has an operational significance for certifying randomness, but he was really interested in the measurement problem, which is traditionally the main motivation for interpretations.

 

[DarMM]

I imagine Bell might not have agreed. I think it's neat that his inequality has an operational significance for certifying randomness, but he was really interested in the measurement problem, which is traditionally the main motivation for interpretations.

You're right of course, what I should say is even if you are being pragmatic work on interpretations has given solid results in quantum information and given us a better understanding of the structure of the theory.

 

[ftr]

I imagine Bell might not have agreed. I think it's neat that his inequality has an operational significance for certifying randomness, but he was really interested in the measurement problem, which is traditionally the main motivation for interpretations.

It seems to me that the issue of randomness (which leads to measurement problem) is the main motivation for interpretations since it destroys the familiar particle concept.

 

[Demystifier]

Since the minimal interpretation is non-controversial

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.

 

[Lord Jestocost]

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.

As a physicist, I have learned over a long period of time that such questions are meaningless in physical sciences as they go beyond empirical science (an instrumentalist's point of view in physics). As a human being, however, I am interested in questions regarding what's behind the "empirical reality". As Richard Conn Henry puts it: “If you are not simply to be like a squirrel or a rabbit, you must choose some quantum mechanics interpretation (as it is called⎯ it is not really “an interpretation,” of course; it is your theory of yourself and of your experience of observations).”

 

[DarMM]

One thing though is why don't we do this for let's say classical electromagnetism. Classical EM describes fields $\textbf{E}$ and $\textbf{B}$. Now of course it describes these fields down to length scales we can't probe, so prior to QED somebody could have asked "Is the field really oscillating on such small length scales?". Nobody did however because it was clear what the theory was talking about. There are fields, they move as such, etc. One would still have philosophical questions like "Are these fields real or just a description...", but this wasn't a major issue.

However that's not what is going on in QM and I think some people's views here see the interpretations as revolving around theory external issues like asking "are the fields real?" in classical EM.

Rather the problem in QM is the measurement problem. If you take textbook QM the theory is actually incoherent about what is going or how to understand and relate the dual descriptions of the device. That's why you can exploit the dual description in textbook QM to set up contradictions like Brukner's experiment or Frauchiger-Renner.

If the interpretations of QM were just purely metaphysical questions and nothing more, I don't think there would be much discussion about interpretations. Just like there isn't for Classical Mechanics and General Relativity. The problem is an internal logical inconsistency in the theory as formulated in the 1930s and presented in the texts of Dirac and Von Neumann.

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?

 

[Lord Jestocost]

Cord Friebe, Holger Lyre, Manfred Stöckler, Meinard Kuhlmann, Oliver Passon and Paul M. Näger in “The Philosophy of Quantum Physics”:

“If one tries to proceed systematically, then it is expedient to begin with an interpretation upon which everyone can agree, that is with an instrumentalist minimal interpretation. In such an interpretation, Hermitian operators represent macroscopic measurement apparatus, and their eigenvalues indicate the measurement outcomes which can be observed, while inner products give the probabilities of obtaining particular measured values. With such a formulation, quantum mechanics remains stuck in the macroscopic world and avoids any sort of ontological statement about the (microscopic) quantum-physical system itself.”

 

[DarMM]

Cord Friebe, Holger Lyre, Manfred Stöckler, Meinard Kuhlmann, Oliver Passon and Paul M. Näger in “The Philosophy of Quantum Physics”:

“If one tries to proceed systematically, then it is expedient to begin with an interpretation upon which everyone can agree, that is with an instrumentalist minimal interpretation. In such an interpretation, Hermitian operators represent macroscopic measurement apparatus, and their eigenvalues indicate the measurement outcomes which can be observed, while inner products give the probabilities of obtaining particular measured values. With such a formulation, quantum mechanics remains stuck in the macroscopic world and avoids any sort of ontological statement about the (microscopic) quantum-physical system itself.”

That doesn't resolve the issue with the measurement problem.

For the formalism permits a self-adjoint operator $\hat{A}$ that corresponds to measurements on the device itself, representing a second device. Then unitary evolution predicts a state $\Psi$ for the entire device which via the same inner products predicts results that contradict the account where the first device is represented by an operator $B$ and we have a state $\psi$ for the system.

To remove the contradiction one has to say something more. It a purely logical problem internal to the theory.

 

[Demystifier]

I have never seen a clear presentation of the measurement problem in the so called "minimal" view.

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. This usually works for practical engineering purposes, but it contradicts the principle of reductionism according to which macroscopic phenomena (such as a measurement) can be reduced to more fundamental microscopic phenomena. A practical minimalist essentially says: "I don't care how exactly the measurement works at the microscopic level, as long as it works for my practical purposes in the laboratory". As long as the minimalist doesn't care about it, the problem of measurement doesn't exist for him.

But it can be said for any problem in science (and not only in science). The problem doesn't exist for you if you don't care about it. You may or may not have rational reasons for not caring about something, but that's not a problem. The problem is when someone insists that others should also not care about it, just because he doesn't care.

 

[Lord Jestocost]

That doesn't resolve the issue with the measurement problem.

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