Is Relational Quantum Mechanics the Key to Understanding Quantum Interactions?

[physika]

"really only exist as they relate to another system." "the interaction between systems" "network of interactions" “Everything measures everything else”.

...just an interactive dependence; "A" makes "B" existent or "D" makes "K" existent or "Z" makes "J" (whatever) an vicious infinite regress , an endless iteration.

A circular argument.

.

 

[*now*]

I am actually curious about the link between Grete Hermann's 1930's relative interpretation of QM, and Rovelli's. It seems she is the originator of relational QM? I find her articulation very elegant and clear..l

It is an easy read.

Hermann, Grete, and Dirk Lumma. "The foundations of quantum mechanics in the philosophy of nature." The Harvard Review of Philosophy 7.1 (1999): 35-44.

https://www.hcs.harvard.edu/~hrp/issues/1999/Hermann.pdf

Nice introduction to Hermann, Jarvis, a fascinating person whose accomplishments include studying mathematics under Emmy Noether, exchanges with Heisenberg and this-
...” in 1935, Hermann published a critique of John von Neumann's 1932 proof which was widely claimed to show that a hidden variable theory of quantum mechanics was impossible. Hermann's work on this subject went unnoticed by the physics community until it was independently discovered and published by John Stewart Bell in 1966, and her earlier discovery was pointed out by Max Jammer in 1974. Some have posited that had her critique not remained nearly unknown for decades, her ideas would have put in question the unequivocal acceptance of the Copenhagen interpretation of quantum mechanics, by providing a credible basis for the further development of nonlocal hidden variable theories, which would have changed the historical development of quantum mechanics.[1]”
https://en.m.wikipedia.org/wiki/Grete_Hermann

This seems despite her not favouring such views, and while I think Heisenberg reportedly also saw clarity in the view she penned.

 

[CarlB]

I wouldn't call relational a circular argument. It's that to have any information about a quantum state, say a particle, you need something to measure it with and that will be another quantum state or at least a system.

An example is the "candle dance" where the professor holds a candle (or more likely a cup of coffee, the basic idea is to have it be something a bit hazardous so the students will find it more interesting as they suspect that their instructor is a klutz) and walks around it with the candle not rotating. The result is that his arm ends up twisted. Then he walks around again and surprise-surprise his arm untwists. This "explains" why the wave states of electrons take a -1 when rotated by 2 pi (perpendicular to their spin direction) rather than the expectation - i.e. unchanged. And this shows that swapping two identical particles (fermions) can give a -1 to their wave function.

However, the demonstration depends on two objects, the candle and the professor, and this is the relational principle; information about quantum states is actually about their relationship to some other thing.

If someone could show how information about a quantum state could exist in the absence of any interactions with other states, I might find it a good argument against the relational principle. In the absence of such, one must consider all quantum information as relational only. The example Rovelli gives is positional information. He denies the existence of a preferred reference frame so that all positional information is relational only. The assumed position of a single particle system is information that physically does not exist and so, like the absolute reference frame, should not be assumed in the physics.

 

[Fra]

I think the relational idea is good, but the question then, is how you view the relations themselves.

I think the solution to the apparent circularity or chicken/egg situation is to see that it's not just circular reasoning, there is a feedback loop and an evolution. You need some premises or starting point, in order to be able to formulate a question, or a measurement for that matter. But the result from the measurement may modify the starting point, so the future measurment is tuned.

I think Rovellis relational start out wel but, the problem is that even the relations themselves, needs to be relationally inferred, and this would imply IMO at least, an evolutionary view on physical law as well, and a view where symmetries are typically emergent only, rather than constraints. Ie. it takes a third observer to describe the relation between two other observers. But Rovelli never analyses this to completion IMO. Instead he assumes this third observer describes the relation between the other two as per "described by quantum mechanics". Unfortunately that all avoids the foundational problems of QM. The ultimate relational interpretation IMO suggests that QM itself needs reconstruction, as QM as it stands is not relational - it implies a background observer. Rovelli does not solve this in any way.

/Fredrik

 

[CarlB]

<<Ie. it takes a third observer to describe the relation between two other observers. But Rovelli never analyses this to completion IMO. Instead he assumes this third observer describes the relation between the other two as per "described by quantum mechanics".>>

I'm at least sympathetic to this; my feeling is that Rovelli's work is too philosophical and not enough physical. But I agree at heart with his idea; that the only things we should look at are relational in nature. My paper attempting to correct the "not enough physical" problem, "A Relational Analysis of Quantum Symmetry" is still under review at Foundations of Physics now since May 2021. I've never had a paper sit that long without any editorial decision or feedback and I'm wondering why. I'm guessing the problem is that I'm using two math ideas that physicists are not familiar with, Harmonic Analysis and Module theory and my present project is writing some papers explaining those ideas for physicists. Quantum mechanics was developed just after mathematicians invented matrices and used them extensively. Now math has moved on to modules but physics hasn't moved much past matrices. Modules are a nice generalization. And harmonic analysis gives a nice understanding of the relationship between Fourier transforms, symmetry and wave equations.

 

[CarlB]

Schwinger's "Measurement Algebra" is a formulation of QM that is more compatible with Rovelli's relational principle in that it talks about interactions instead of properties of quantum states. He's not avoiding an observer but is taking into account the interaction between the measuring apparatus and the quantum object:

"The classical theory of measurement is implicitly based upon the concept of an interaction between the system of interest and the measurement apparatus that can be made arbitrarily small, or at least precisely compensated, so that one can speak meaningfully of an idealized measurement that disturbs no property of the system. The classical representation of physical quantities by numbers is the identification of all properties with the results of such nondisturbing measurements. It is characteristic of atomic phenomena, however, that the interaction between system and instrument cannot be indefinitely weakened. Nor can the disturbance produced by the interaction be compensated since it is only statistically predictable. Accordingly, a measurement of one property can produce uncontrollable changes in the value previously assigned to another property, and is without meaning to ascribe numerical values to all the attributes of a microscopic system."
https://www.pnas.org/content/pnas/45/10/1542.full.pdf

Schwinger wrote the above in the early 1950s IIRC; my description of the same thing expands it to include thermodynamics, which I think is natural as quantum mechanics is a statistical theory, and also modernized some of the language:
https://file.scirp.org/pdf/JMP_2018032615223977.pdf

 

[Fra]

<<Ie. it takes a third observer to describe the relation between two other observers. But Rovelli never analyses this to completion IMO. Instead he assumes this third observer describes the relation between the other two as per "described by quantum mechanics".>>

I'm at least sympathetic to this; my feeling is that Rovelli's work is too philosophical and not enough physical. But I agree at heart with his idea; that the only things we should look at are relational in nature. My paper attempting to correct the "not enough physical" problem, "A Relational Analysis of Quantum Symmetry" is still under review at Foundations of Physics now since May 2021.

"It is possible to compare different views, but the process of comparison is always a physical interaction, and all physical interactions are quantum mechanical in nature. I think that this simple fact is forgotten in most discussions on quantum mechanics, yielding serious conceptual errors. Suppose a physical quantity q has value with respect to you, as well as with respect to me. Can we compare these values? Yes we can, by communicating among us. But communication is a physical interaction and therefore is quantum mechanical."
-- Rovelli, https://arxiv.org/abs/quant-ph/9609002

I think Rovellis is too fast in the last scentence where things go hazy for me. If we are trying to understand/interpret QM, and we explain it as the view relative to the observers, we can not use the term "quantum mechanical" again to explain "communication" how objectivity is restored, it adds no explanatory value, and seems a bit circular indeed. It's precisely the physical basis and corresponding constraints on this communication we need to reconstruct IMO, to understand the interactions.

My suggestion is to start in the other end. Let's try to describe how two general observers, can possibly establish a communication protocol and then communicate with reasonable reliability. If we instead can instead define possible communication protocols and transceiver microstructures, we can use that to construct from the first principles (ie. communication and information processing principles), QM. This would also be relational, but the strategy is different and more radical. This is the part that I am missing in Rovellis analysis, and where I lost interest. I am guessing your objections to Rovellis philosophy is different. I skimmed your paper and I find no handles on these questions in there.

/Fredrik

 

[Fra]

Unless it wasn

If we are trying to understand/interpret QM, and we explain it as the view relative to the observers, we can not use the term "quantum mechanical" again to explain "communication" how objectivity is restored, it adds no explanatory value, and seems a bit circular indeed. It's precisely the physical basis and corresponding constraints on this communication we need to reconstruct IMO, to understand the interactions.

Unless it was not clear, what I meant was that as Rovelli seems to think he has EXPLAINS communication between general observers by saying "its described by QM" - as if QM was made for that. But part of the discussion here is that some of us think that QM as it stands is not made for this. What Rovelli says would make more sense applied to the yet unknown reconstructed theory of which QM is a limiting case. This is why I feel there is no explanatory value here. Merely reinterpreting things does not solve any of these problems as I see.

Just to raise one simple question: Does it not seems reasonable to expect that the mass of the observer should constrain the possible communication protocols it can run with timley responses? I think Rovelli does not use the physical communication process in it's deepest sense, but more like an informal term. It seems to be QM can at best, describe how two "subatomic" parts interact, but this is then an extrinsic description of their inteaction, from a third observer which is implicitly VERY massive and classical - is it not?

/Fredrik