Against "interpretation" - Comments

[atyy]

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 measurement problem is most clearly stated in the minimal view, since it begins with a classical/quantum cut or gives the observer or measurement apparatus a special status. You can get out of it by just saying it's fine FAPP, and physics is just FAPP. But many also choose to say there is clearly a measurement problem. Either way, it is meta-physics, which is fine, at least as fine as meta-mathematics.

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.

I think the minimal view is what Peres has (maybe Peres has very minor errors, but I think his book is beautifully written), and that should be the same as shut-up-and-calculate. Any minimal view that is not like what Peres has is just not properly informed by tradition.

 

[Minnesota Joe]

Against "interpretation"
Continue reading the Original Blog Post.

To what extent do you think stressing "interpretation" instead of "theory" is a holdover from the logical positivism that gripped some of the founders of quantum mechanics (and their students, and their students, and...)?

Logical positivism is a very attractive view for people who do not want to worry about what they cannot observe. It is ultimately a theory about meaning, about the content of a theory. According to the positivists, a theory says no more than its observable consequences.

Logical positivism has been killed many times over by philosophers. But no matter how many stakes are driven through its heart, it arises unbidden in the minds of scientists. For if the content of a theory goes beyond what you can observe, then you can never, in principle, be sure that any theory is right. And that means there can be interminable arguments about which theory is right that cannot be settled by observation.

Tim Maudlin

 

[Lord Jestocost]

As remarked by Paul K. Feyerabend in “Physics and Philosophy: Volume 4: Philosophical Papers”:

"The issue concerning the foundations of the quantum theory can therefore be solved only by the construction of a new theory as well as by the demonstration that this new theory is experimentally at least as valuable as the theory that is being used at the present time; it cannot be solved by alternative interpretations of the present theory.⁴⁹"

And in footnote 49 he adds:

“If I am correct in this, then all those philosophers who try to solve the quantum riddle by trying to provide an alternative interpretation of the current theory which leaves all laws of this theory unchanged are wasting their time. Those who are not satisfied with the Copenhagen point of view must realize that only a new theory will be capable of satisfying their demands.”

[Italics in original, LJ]

 

[A. Neumaier]

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

It has no problems if one considers (as you do) Born's rule to be just an axiom without asking further what a measurement is on the level of theory. But the measurement problem appears once you want to give the notion of measurement a mathematical meaning (and only then Quantum mechanics including Born's rule is a mathematical theory).

As a physical theory QM is amazingly successful, and there are no foundational problems.

There are no foundational problems at the level where QM is actually applied - namely in the microscopic domain. There are foundational problems if one wants to extend QM to the macroscopic regime and still stay faithful to its textbook foundations.

I think the minimal view is what Peres has (maybe Peres has very minor errors, but I think his book is beautifully written), and that should be the same as shut-up-and-calculate. Any minimal view that is not like what Peres has is just not properly informed by tradition.

You gave this statement your Like - so you can probably explain why Peres wrote Chapter 12 of his book, titled ''The measurement problem'' if the latter does not exist. Peres deliberately and faithfully follows the minimal interpretation dogma that you also advocate until he reveals that he has to give it up in this chapter:

There are questions, such as “what is the numerical value of the pointer position,” which make sense in the classical language, but are meaningless in the quantum language.

This would cause no conceptual difficulty with quantum theory if the Moon, the planets, the interstellar atoms, etc., had a well defined state ρ. However, I have insisted throughout this book that ρ is not a property of an individual system, but represents the procedure for preparing an ensemble of such systems. How shall we describe situations that have no preparer?

You must have noted the difference between the present pragmatic approach and the dogmas held in the early chapters of this book. It was then asserted that any operator which can be written by a theorist can also be measured in the laboratory. This fiction was needed in order to establish a formal framework for quantum theory.

The dogmatic part is mathematical physics and has unsolved consistency problems in which people like me or DarMM are interested. The pragmatic way out is FAPP only but satisfies those like you who don't care about mathematical consistency of theoretical physics as long as the predictions are successful.

 

[vanhees71]

Though I like Peres's book, I don't have to agree with everything he writes. If he writes that there's a measurement problem I disagree with him, but as Peres seems to me also to be a "minimal interpreter" I don't think that he consideres the measurement problem a physics problem either.

I disagree with him in the sense that I don't think one has to explain that there are clearly defined pointer readings in an experiment, because that's one of the assumptions you make as a theoretical physicist because that's established by experience. If there were no clear pointer readings the entire probabilistic interpretation of the formalism wouldn't be sufficient too. Maybe QT would have been forgotten as some curiosity and some other theory would have been discovered, but now there are in fact clear pointer readings. You don't need to derive this from theory but you just take it as an empircal fact and use it as such to formulate the theory. Of course, as any empirical fact, it's subject to further empirical tests, and if it's found to be invalid under some circumstances, it may well be that QT would have to be updated by something more comprehensive.

 

[A. Neumaier]

I don't think one has to explain that there are clearly defined pointer readings in an experiment, because that's one of the assumptions you make as a theoretical physicist because that's established by experience.

Yes. But this is where the mathematics of quantum physics has a consistency problem when it tries to model the whole experiment in terms of a microscopic description. You say you don't care because its established by experience. Others like me care because its not established by the theory.

Thus whether there is a measurement problem depends on which standards one requires for the theory. A mathematical physicist has higher standards than a theoretical physicist.

I still don't understand your argument.

Clearly there is no way we can agree. But perhaps you can at least understand why others, including me, consider the measurement problem as something real.

 

[Demystifier]

To what extent do you think stressing "interpretation" instead of "theory" is a holdover from the logical positivism that gripped some of the founders of quantum mechanics (and their students, and their students, and...)?

To a great extent. Let me also add that logical positivism is self-contradictory. That's because the main claims of logical positivism (e.g. that "only the measurable has a meaning") are themselves philosophical claims not obtained from measurements. What logical positivists really say is: "All philosophy is meaningless, except our philosophy."

 

[Minnesota Joe]

To a great extent. Let me also add that logical positivism is self-contradictory. That's because the main claims of logical positivism (e.g. that "only the measurable has a meaning") are themselves philosophical claims not obtained from measurements. What logical positivists really say is: "All philosophy is meaningless, except our philosophy."

Yes it is infamously self-defeating and you would have to special plead to hold it. As Maudlin points out, you still encounter the attitude in the sciences however.

 

[Reductionist89]

Which interpretation makes the least amount of assumptions in your opinion - Copenhagen or Many Worlds? Both take the data at face value but in radically different ways.

 

[vanhees71]

The interpretation making the least amount of assumptions is the minimal statistical interpretation, which I'd consider one flavor of the Copenhagen interpretation. I think it comes pretty close to Bohr's version, though I think Bohr is in favor of a quantum-classical cut on a fundamental basis though there's not the slightest hint for it ever observed.

I can't comment on Many Worlds since I've never understood how it relates the formalism to the observable facts.

 

[ftr]

I wonder which is the more serious "problem"(in quotation to avoid ..) the fact that in QM the particles have undefined properties(before measurement) or that measurement is classical in the end.

 

[vanhees71]

There's no problem in either. The fact that in QM a particle has precisely the probabilistic properties due to its preparation, described by the corresponding quantum state $\hat{\rho}$ is, as far as all experiments show, precisely what's observed when measuring an observable of this particle.

That measurement devices, as macroscopic objects, behave classical is also no surprise but just due to sufficient course graining of the macroscopic observables. A "pointer position" of a measurement device is such a coarse-grained macroscopic observable.

 

[ftr]

The fact that in QM a particle has precisely the probabilistic properties due to its preparation, described by the corresponding quantum state ^ρρ^\hat{\rho} is

Is it "due" to or inherently, because that is how the electron in hydrogen atom is modeled?

 

[ftr]

That measurement devices, as macroscopic objects, behave classical is also no surprise but just due to sufficient course graining of the macroscopic observables. A "pointer position" of a measurement device is such a coarse-grained macroscopic observable.

In the age of gravity wave detection experiments isn't possible to do the same for quantum. I mean couldn't they use a thin sheet of single carbon or whatever atom and have some miniature source using femto cameras and such. Money should be no problem, right?