# Against “interpretation”

I am against “interpretations” of Quantum Mechanics (QM) in a sense in which John Bell [1] was against measurement in QM and Travis Norsen [2] is against realism in QM. Bell was not against doing measurements, he was against using the concept of measurement as a central concept in quantum foundations. Norsen does not think that realism does not exist, he thinks that the existence of realism is so obvious and basic that one should not even talk about it. In a similar spirit, I do not think that physicists should not study interpretations, I think that it is misleading to talk about interpretations as something different from theories. The titles “Against measurement” [1] and “Against realism” [2] were chosen by Bell and Norsen with an intention to provoke, by imitating the provocative style of Paul Feyerabend – the famous philosopher of science who was “Against method” [3]. My intentions here are of a provocative nature too.

Physicists often say that in physics we need theories that make new measurable predictions and that we don’t need interpretations that make the same measurable predictions as old theories. I think it’s nonsense. It’s nonsense to say that theories are one thing and interpretations another. The interpretations **are** theories. Making a distinction between them only raises confusion. So we should ban the word “interpretation” and talk only about the theories.

Let me explain. Suppose that someone develops a theory called T1 that makes measurable predictions. And suppose that those predictions were not made by any previous theory. Then all physicists would agree that T1 is a legitimate theory. (Whether the predictions agree with experiments is not important here.)

Now suppose that someone else develops another theory T2 that makes the same measurable predictions as T1. So if T1 was a legitimate theory, then, by the same criteria, T2 is also a legitimate theory. Yet, for some reason, physicists like to say that T2 is not a theory, but only an interpretation. But how can it be that T1 is a theory and T2 is only an interpretation? It simply doesn’t make sense.

To resolve that issue, one might say that both T1 and T2 are interpretations. Fine, but then what is the theory? T1 was a legitimate theory before someone developed T2, but now T1 ceased to be a theory just because someone developed T2? It doesn’t make sense either.

Or perhaps the theory is just the set of final measurable predictions of T1 and T2, while all the other “auxiliary” elements of T1 and T2 are the “interpretation”? It doesn’t make sense either, because there is no theory in physics that deals **only** with measurable predictions. All physics theories have some “auxiliary” elements that are an integral part of the theory.

Or perhaps an interpretation is a theory that emphasizes philosophical aspects? I think this is what most physicists **really** mean by interpretation, even if they don’t want to say it explicitly. The problem with this definition is that it cannot be put into a precise form. All theories have some philosophical aspects, some theories more, some less. So exactly how much of philosophy a theory has to have to call it an interpretation? It’s simply impossible to tell. And where exactly is the borderline between philosophy and non-philosophy? There is no such borderline.

To conclude, we can talk about a theory, we can distinguish the measurable predictions of the theory from other elements of the theory that cannot be directly measured, but it doesn’t make sense to distinguish an interpretation from a theory. There are no interpretations of QM, there are only theories.

References:

[1] J. Bell, Against measurement, https://m.tau.ac.il/~quantum/Vaidman/IQM/BellAM.pdf

[2] T. Norsen, Against “realism”, http://de.arxiv.org/abs/quant-ph/0607057

[3] P. Feyerabend, Against method, https://en.wikipedia.org/wiki/Against_Method

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Theoretical physicist from Croatia

And disagreements about such preferences can never be resolved (which is why PF threads on such topics tend to go on and on until one of the Mentors gets fed up enough to close the thread).That raises the question of why we allow public debate of interpretations on PF. Or why respected textbooks include chapters on interpretations.

If it was just a case of competing equivalent models, as @fresh_42 pointed out, then there is nothing to debate. The wise analyst keeps all possible models in his toolkit ready to use when advantageous. The value of a model is its utility.

Personally I am with Dirac on this one. I do not think QM is complete – it will slowly and gradually be superseded and in that vein you can look on interpretations as attempts to understand what direction the next step may take us.That may be the answer to why allow it and why we support continued research. An interpretation might be described as a theory extension wannabe. Researchers hope to find a case where T[SUB]1[/SUB] and T[SUB]2[/SUB] predict different outcomes, so that experiment may prove one of them useful and the other not useful. But such hope should not be eternal. At some point, the rational thing to do is to declare the search futile, and deploy our resources elsewhere.

Should Wilson's interpretation of renormalization be considered theory or interpretation?If only more Bohmians understood the depth and importance of this question …

I thought that BM gives different predictions in some cases?Some versions of BM do, but the standard "minimal" version doesn't.

There are many examples, but my favored one is this: T1 = standard textbook QM, T2 = Bohmian mechanics.I thought that BM gives different predictions in some cases?

Traditionally, an interpretation is a solution of the measurement problem:

However, another meaning of interpretation is simply the meaning physical or operational meaning assigned to mathematical operations.

A third meaning of interpretation is the one that is disfavoured in the Insight of the OP.

Thus the Copenhagen Interpretation is the only valid interpretation (since BM is not an interpretation, but a different theory) of QM. However, the Copenhagen Interpretation is not a valid interpretation in the sense of being a possible solution of the measurement problem (it is basically the poster boy for having a measurement problem). Bohmian Mechanics is not an interpretation, but a different theory. However, since it is the only currently known possible solution of the measurement problem for a sufficiently broad domain of QM, BM is the only valid interpretation of QM even though it is a different theory.

What is an example of T1 and T2?There are many examples, but my favored one is this: T1 = standard textbook QM, T2 = Bohmian mechanics.

So my understanding is, that T1 (Heisenberg) and T2 (Schrödinger) are two different models of the same physics, and as such equivalent theories or models, whereas Kopenhagen and MWI are actually interpretations, namely metaphors to visualize the equations.Then what about Bohmian mechanics? Is it a T3, or is it just a metaphor?

What is an example of T1 and T2?

Should Wilson's interpretation of renormalization be considered theory or interpretation?I would call it an approach. My understanding is its equivalent to say dimensional regularization – but others that know more about it than me may correct me on that.

Thanks

Bill

Should Wilson's interpretation of renormalization be considered theory or interpretation?

Insofar as a given theory is some specific mathematical construction from some set of axioms and all its mathematical consequences, and all equivalent constructions from different axioms, different interpretations of that one theory (1) put different emphasis on one axiomatic construction or another, all isomorphic to each other, and/or (2) give a different relationship between elements of the theory and whatever experimental raw data there may be. I like Lakatos's term for (2),

bridge principles, which, being between things mathematical and things in the world are neither of mathematics nor of the world. I think it's the bridge principal concept that your polemic misses. Mathematics is unworldly and not everything is mathematics: we have to learn and teach and experience and come to an intuition of the connection between mathematics and the world.I suppose I'm saying that theory/interpretation/world is just a variant of the map/how to grok the map/territory problem, over which much ink has been spilt, so battle lines will have to be drawn.

Demystifier,

The admirable deed is that you walked all the way to the border!

When you manage to cross it, you will see wonderful things that reasoning cannot even imagine!

Keep it on!

T1 &T2 are approximations just like classical mechanics to special relativity

I think one the issues regarding interpretations is to consider them complete in some sense. Copenhagen fell into that trap eg the state is a complete description of the quantum system. I have posted it before, but I consider the following debate between Dirac and Heisenberg instructive:

http://philsci-archive.pitt.edu/1614/1/Open_or_Closed-preprint.pdf

Personally I am with Dirac on this one. I do not think QM is complete – it will slowly and gradually be superseded and in that vein you can look on interpretations as attempts to understand what direction the next step may take us.

Already we have no-go theorems putting constraints on acceptable interpretations that help us see in what direction research may lead us.

Thanks

Bill

Borrowing from military jargon, the professionals — scientists, engineers, mathematicians, and their students — work to understand and utilize theory and models. Civilians; depending on their training, ability, and access to correct reliable information; are often satisfied with various interpretations.

As an example consider the science writer James Gleick and his still popular

interpretationof chaos theory Chaos: Making a New Science. I first read his book back in the 1970's in order to discuss it with my father, a trained chemist and electrical engineer but also a fan of popular science. Gleick's writing led to productive conversations. We even drove to Half-Moon Bay to observe the "fractal coastline" (and a neat sunset). Despite using aspects of chaos theory in my work, I never referenced Gleick's books, instead using math and science textbooks for actual applications.Accurate factual interpretations perhaps with the math explained rather than read as-is, may be a fair method for civilians to understand science. Students and teachers should be held to the more rigorous standard of understanding theory, the underlying models, and the limits of corroborating data.

So you think that Copenhagen and MWI are two different theories that happen to share 99.9% of the theoretical part and disagree only about 0.1% of interpretation??? Then quantum mechanics would be a collection of 20 or so theories that differ only marginally???

I follow your argumentation and appreciate its clearness. But don't you just merge the two terms and therewith shift all problems the term

interpretationis charged with into the now new definition oftheory? My impression is, that you merely shifted the problem of inconsistency into the unregarded territory oftheoryandmodel. The termtheoryis to me a very unfortunate one, not the least as it is regularly in conflict with what commonly is meant by it, namely a hypothesis. I admit that the termmodelmay partly be in conflict with the specific meaning it has in logic, but that shouldn't be a problem here.Thus my suggestion to solve the discrepancies wouldn't be the merger of

theoryandinterpretation, but the merger oftheoryandmodel. I think this is what physicists usually mean: a theory – or model – is a mathematical framework to describe the experimental results, including possible predictions. On the other hand, aninterpretationis merely an informal description of named theory / model to describe the mathematical framework in common language and by the frequent use of aphorisms and metaphors. In this sense, T1 and T2 are different models, which either coincide, i.e. are different but equivalent sets of mathematical language, or they make distinguishable predictions. Interpretations of T1 and T2, however, may differ a lot, as they were only descriptions a lecturer uses to explain the models behind them.So my understanding is, that T1 (Heisenberg) and T2 (Schrödinger) are two different models of the same physics, and as such equivalent theories or models, whereas Kopenhagen and MWI are actually interpretations, namely metaphors to visualize the equations. This is in my opinion closer to the actual use of the terminology and doesn't need the merger

theorywithinterpretation, the more astheoryandmodelhas already been merged. Furthermore, it doesn't create the next problem to explain whyinterpretationandmodelwill be the same, nor does it leave a vacancy, namely: what are verbal descriptions of mathematical frameworks be called?Interesting viewpoint! I tend to dislike talk about "interpretations" as well, but I'm not sure if it's for the same reason, so let me briefly explain my reason.

In the article you give the example of two theories, T1 and T2, that both make the same experimental predictions. That means that it is not possible to decide by experiment which of the two theories is correct (or "more correct", or "better", or whatever comparative term you want to use). So any preference that someone has for one theory over the other can only be based on subjective judgments of one sort or another. And disagreements about such preferences can never be resolved (which is why PF threads on such topics tend to go on and on until one of the Mentors gets fed up enough to close the thread).

To me, the word "interpretation" (particularly when talking about QM) is a signal that the above situation exists, i.e., that whatever disagreement is being discussed can't be resolved, because the two theories (or "interpretations") being discussed both make the same experimental predictions. And since such a disagreement can't be resolved, I see very limited value, at best, in discussing it.

In the particular case of QM, at least, there is another aspect as well. Interpretations of QM not only all make the same experimental predictions, they do so via provably mathematically equivalent machinery. So the rationale for calling them different theories, as opposed to different interpretations of the same theory, is weaker than it would be if the different interpretations used mathematically distinct machinery, that just happened to result in the same predictions for experiments.

I think there is a negation too many in there:

Norsen does not think that realism does not exist

It might be something wrong with the voting inside the article; at least it didn't work for me.