Interestingly Bohr Did Not Believe in Wavefunction Collapse

[Fra]

My question is, if you think states collapse - do you think probabilities do as well?

Yes I do. (Ie given that the state collapse, so does the normative probability).

However, I think the concept of the state collapse (as an information update) in the first place as beeing instant makes no sense if you look at the detailed information processing.

- In the decoherenc pictures, it takes TIME for the information to propagate into the environment (which together makes up the "observer"). So its not really instant.

- In the observer/agent picture, it similarly takes time for the internal processing, the new informaiton should hardly be assigned infinite confidence, it has to be rationally procressd and joined with hte prior information the agent has. I envision concepts of intertai and time here as well. So it's not instant. Ie. the agents "behaviour" will change only after a certain processing delay of the new information. The "probability distributions" are I think approximations (in a continuum view) of the agents state.

So even if you take the collapse seriously, it doesn't necesarily mean it's instant. That makes not sense to me at all as I see it involving information processing (which an outside observer, might in principle interpret as internal physical processes of the agent, but for small quantim systems these tende to be "hidden" and subject to no-cloning, so the outside observer cant really see it. etc)

So the instant information update to me is a simplification you can use, when the timescale of the actual "processing" is irrelevant. But to think it's actually instant makes no sense to me.

/Fredrik

 

[Lord Jestocost]

And that is why I am dubious of the existence of wave-function collapse as anything but something that occurs in a theorist's calculations.

To my mind, the term “wave-function collapse” is really misleading as it can give rise to the strangest flapdoodle. As Freeman Dyson remarks in “Thought Experiments in Honor of John Archibald Wheeler“ (in “Science and Ultimate Reality”, Cambridge University Press, New York, 2004):

“What really happens is that the quantum-mechanical description of an event ceases to be meaningful as the observer changes the point of reference from before the event to after it. We do not need a human observer to make quantum mechanics work. All we need is a point of reference, to separate past from future, to separate what has happened from what may happen, to separate facts from probabilities.”

 

[vanhees71]

Exactly. And that is why I am dubious of the existence of wave-function collapse as anything but something that occurs in a theorist's calculations. This is bolstered by Gleason's Theorem, where the state is seen as merely a mathematical convenience to calculate probabilities (of course, an important one). My question is, if you think states collapse - do you think probabilities do as well? Note - you can take that position if you like, but those into probability usually don't.

I don't think that "collapse" is more than the standard update of the knowledge after the result of a random experiment has been obtained. It's not a physical process. This would contradict the mathematical description within relativistic microcausal (=local) QFT.

Exactly how our classical world arises from such a view is an interesting question, still under investigation. The latest I have heard about it is the following I have posted before:

https://www.sciencenews.org/blog/context/gell-mann-hartle-spin-quantum-narrative-about-reality

And, of course, Peter is correct. Many, including me, think everything is quantum, but experimental justification is lacking.

The best experimental justification is that there's not a single exeption of QT behavior observed, although QT is the best tested theory ever.

 

[PeterDonis]

don't coarse graining and decoherence predict the absence of interference effects for macroscopic collective coordinates?

Not quite. They predict that interference effects should get very small (or get harder to keep track of because they would require tracking more and more degrees of freedom from the environment), but not that they should vanish altogether.

 

[vanhees71]

Well, one simple model of decoherence is to assume that the phases of the waves describing the scattering a single (quasi-)particle in a macroscopic many-body model are random, and in the superposition thus interference effects get averaged out.

 

[LittleSchwinger]

Not quite. They predict that interference effects should get very small (or get harder to keep track of because they would require tracking more and more degrees of freedom from the environment), but not that they should vanish altogether.

Sorry I meant "experimentally absent" in that paragraph, I was clearer in the following paragraph:

interference should be absent experimentally

So quantum theory predicts we shouldn't detect interference effects for most macroscopic objects, correctly models those that do such as SQUIDS and correctly derives the material constants of macroscopic bodies. Hence I would agree with vanhees71 that there isn't a hint QM becomes invalid for macroscopic objects.

Although I should mention there are forms of decoherence in nonperturbative QED where interference effects literally vanish.

 

[Fra]

Exactly how our classical world arises from such a view is an interesting question, still under investigation. The latest I have heard about it is the following I have posted before:

https://www.sciencenews.org/blog/context/gell-mann-hartle-spin-quantum-narrative-about-reality

I think the reflections in that article are very good!

Trying to acknowledge that the "map" itself is a participator is even in analogy to GR. But I see many pitfalls along the path. One is to get confused with human consciousness and the other is to be tempted to root explanatory power not from algorithmic learning but from a fixed fictional "in principle" perspective that disrespects any information capacity if a real agent/ real map - which tend to result in fine tuning a and renormalization problems impossible to overcome.

/Fredrik

 

[vanhees71]

That's kind of a "many-words interpretation" ;-(. SCNR.

 

[Fra]

That's kind of a "many-words interpretation" ;-(. SCNR.

If we can talke about a kind of "many-worlds" that INTERACT, then then it's the same as "interacting agents", each agent holds a map of the world. But the maps are subject to evolution and selection.

My view is more of a many-map interpretations, but where the maps are physically encoded and interact and evolve. By their evolution can't be captured by dynamical law; it's more a matter of actual learning or evolution like in biology. (But as some equiblirium, perhaps one can envision this in a holographic sense, the world is generated as a hologram from the map, so the physical map does not even need the same dimensionality as the illusion from hologram)

That article was fuzzy, it was a good elaboration but no clear conclusion. But reflection is a good start anyways. Some refuse to reflect even.

/Fredrik

 

[vanhees71]

I wrote "many WORDS" (no L!). What do you expect from an article without formulae? There's no way to write something understandable about QT without using math! That's what I meant with "many WORDS" (not "worlds").

My opinion on the "many-worlds interpretation" is that it's simply empty. I don't see, what problem it should solve to begin with, and nobody has ever been able to find the slightest hint of all these overcountably many worlds, only because I choose to look at a light source, and my retina absorbs some photons.

Also the idea of a "state of the entire universe" is an empty phrase since it cannot be prepared nor can its pobabilistic predictions be tested. We can simply not observe the "entire universe", but only local observations in the "neighborhood" of our detectors.

 

[Lord Jestocost]

My opinion on the "many-worlds interpretation" is that it's simply empty.

Is “many worlds” no more than a strange expression for “many possibilities”?

 

[vanhees71]

But the "many possibilities" are there also in the minimal interpretation, as it is present in any probabilistic description. E.g., if I prepare an Ag atom in the Stern-Gerlach experiment to have a determined spin-$z$-component of $+\hbar/2$ and then ask what value the spin-$x$ component has, i.e., if I do a Stern-Gerlach experiment with the magnetic field oriented in $x$ direction on a beam of particles prepared in the state $|\sigma_z=+\hbar/2$, for each such Atom there are always 2 possibilities, i.e., $\sigma_x \in \{\hbar/2,-\hbar/2 \}$, and these values occur with 50% probability each, i.e., there are 2 possibilities for the outcome of the $\sigma_x$-measurement. What the "many-worlds people" claim is that the universe splits in two universes where the one or the other value has been measured, but that nobody has ever been able to observe in the lab. In our "real-world" labs there's a unique outcome for each Ag atom, and all QT tells me before the measurement is done are the probabilities. That's what the quantum state seems to mean and not that the universe splits with each observation (i.e., with each interaction between a quantum system with some measurement apparatus).

 

[Fra]

My opinion on the "many-worlds interpretation" is that it's simply empty. I don't see, what problem it should solve to begin with, and nobody has ever been able to find the slightest hint of all these overcountably many worlds, only because I choose to look at a light source, and my retina absorbs some photons.

Also the idea of a "state of the entire universe" is an empty phrase since it cannot be prepared nor can its pobabilistic predictions be tested. We can simply not observe the "entire universe", but only local observations in the "neighborhood" of our detectors.

Agreed completely!

But we do seem to have multiple "maps" of the single world, but agents sometimes navigate the real one world, with their eyes on the map ;)

Which makes me thinking of the classic joke, with two theoretical physicists lost at the top of a mountain.

But the joke aside, it's not as stupid as one may think, because in a game of expectations, each player chooses his actions not based on the unknown reality, but on it's own expectations. This how expectations can be created, and supported in a local community to the point where it's hard to tell from reality. I think the stock market is a good source of intuitive examples of such games, where it at some point doesn't matter what the fundamental values are, if the whole environment have a given expectation (right or wrong) that defines the optimal strategy for you.

/Fredrik

 

[Fra]

Is “many worlds” no more than a strange expression for “many possibilities”?

That would also be my positive interpretation, on par with the strangeness of labelling "spacelike correlations" by "FTL correlations"?

But many writings on mwi seem to perhaps suggest they think it's more than that? I don't recall which on here that are mwi proponents that could explain? Explaining one interpretation from the perspective of another one may tend to be unfair i guess.

/Fredrik

 

[Couchyam]

I don't think that "collapse" is more than the standard update of the knowledge after the result of a random experiment has been obtained. It's not a physical process. This would contradict the mathematical description within relativistic microcausal (=local) QFT.

The best experimental justification is that there's not a single exeption of QT behavior observed, although QT is the best tested theory ever.

I think I can see where you're coming from: for example, it's hard to recognize interference effects in single-count measurements (such as the lived experience of a typical person), and the observed phenomenon of wave function collapse could be an illusion of sorts (maybe related to the illusion of 'active' as opposed to 'passive' measurement) determined by some unknown initial data. That being said, it's hard to convince any but the most agreeable skeptics that Quantum Mechanics can account for all observable physical phenomena however without addressing a few apparent (though possibly illusory) shortcomings of unitary QM, such as the origins of consciousness, or why it might be that the quantum world distills and presents a few choice morsels of interpretable data and not others of a completely different kind (if not wave function "collapse" per se, then why it is that we perceive what we perceive.) I think to a certain person (possibly Bohr), the existence of a conscious self that is capable of experiencing and observing a moment-by-moment definite universe in real time would prove that quantum mechanics is incomplete, that speckled or point-cloud interference patterns on various screens or thermal noise in quantum opto-mechanical setups and so on evidence a significant departure from the quantum model; from that perspective, it would also seem to be the conservative choice to say that quantum mechanics must necessarily be incomplete (rather than the arguably even more conservative stance to allow also that it might not be.) Such a person might also have difficulty reconciling the 'super-unitary' view of nature with widespread acceptance of the anthropic principle, or of the many-worlds hypothesis. It's possible that quantum mechanics is sufficient to explain everything, and that observed reality can be modeled as a giant S-matrix (or "S-event") of sorts, but it could also be that observable quantum phenomena are just the tip of a much much larger iceberg which might exhibit ordinary quantum-ness in some cases and in others behave weirdly in a completely different way.
First you need to convince such a person that definitive, time-stable measurements of the sort taken in existing laboratories can actually happen in a unitary quantum mechanical model (a model that doesn't rely tacitly on some external deciding process for when a measurement actually happens or is registered), and then you can explain that it is scientifically sound to act (with all due caution) on the hypothesis that quantum mechanics is fundamental until we find experimental evidence to the contrary.

 

[physika]

Quantum Mechanics can account for all observable physical phenomena

Decoherence not enough to describe the emergence of macroscopical realm.

 

[Couchyam]

Decoherence not enough to describe the emergence of macroscopical realm.

We might be misinterpreting each other. How broad/encompassing is your understanding/definition of decoherence?

 

[Quantum Waver]

My opinion on the "many-worlds interpretation" is that it's simply empty. I don't see, what problem it should solve to begin with, and nobody has ever been able to find the slightest hint of all these overcountably many worlds, only because I choose to look at a light source, and my retina absorbs some photons.

The measurement problem because it gets rid of collapse/non-unitary evolution. The "worlds" are just entangled environments where there's no arbitrary dividing line between what we call macroscopic and the microscopic. It's all quantum all the time. Your choice doesn't matter, the environment will decohere whether you look at the cat or whatever interaction is causing an entanglement.

There might be problems for MWI such as probability or deriving structure, but branching isn't one of them.

 

[Demystifier]

Today appeared a paper claiming that Bohr was a realist.
https://arxiv.org/abs/2308.00814

 

[PeterDonis]

Today appeared a paper claiming that Bohr was a realist.
https://arxiv.org/abs/2308.00814

I think Bohr might have said that realism and instrumentalism are complementary in much the same way that position and momentum are. Or perhaps that "realism" is what he called a Great Truth (a truth whose opposite is also a Great Truth).

 

[Lord Jestocost]

Today appeared a paper claiming that Bohr was a realist.
https://arxiv.org/abs/2308.00814

Such a claim needs some specifications. For example, Jan Faye in his article “Complementarity and Human Nature” (in “Niels Bohr and the Philosophy of Physics: Twenty-First-Century Perspectives” (edited by Jan Faye and Henry J. Folse, published 2017)).

in section "Realismus an Representation"

“Was Bohr really an instrumentalist? I once characterized Bohr as an objective anti-realist. (Faye 1991). By this expression I wanted to say that Bohr believed in the reality of atomic objects but abstained from holding a representational view of scientific theories. So, in my opinion, Bohr was a realist with respect to the existence of atomic objects, but an anti-realist with respect to the representational structure of quantum mechanics. But if the quantum mechanical formalism does not represent the world as it is, what then had Bohr in mind about its function? Well, it is not only an instrument for prediction; it is also an unambiguous means of communication about our experience concerning the quantum objects. The formalism provides us with the syntactical rules that determine the logical order and structures by which inferences and predictions become possible, whereas the physical interpretation of the formalism gives us the semantics of the mathematical symbols. However, such an interpretation is not due to free stipulations but is based on an already well-established linguistic practice which is formed by our common-sense experience........”

in section "Conclusion"

"I think some of these reflections were the philosophical assumptions behind Bohr's interpretation of quantum mechanics. His view was based on a naturalistic and a pragmatic approach to science. In the light of Darwin's discovery of human evolution, I think that Bohr's interpretation emerges as one of the most plausible interpretations today. It represents an interpretation that is most consistent with what we know about human origins and the evolution of our cognitive capabilities. By nature we are born realists. There is a world outside of ourselves, and it is more or less as we experience it. This kind of common-sense realism is included as a part of our innate cognitive understanding of the world. But it is the same instinct that drives many physicists to interpret their theories realistically. The disease which infects those physicists is not realism as such but representationalism, the view that "knowing" something means being able to "picture" what something looks like when nobody is looking at it, a canvas of reality painted by a ghost spectator. The realist instinct explains quite naturally their realistic tendencies. Yet, there are good reasons to believe that their realistic interpretation causes them to postulate a reality that we are completely unable to have knowledge about..........."

 

[vanhees71]

Cargo cult science delivers only more cargo cult science. That's a pretty common phenomenon ;-).

 

[Fra]

I think Bohr might have said that realism and instrumentalism are complementary in much the same way that position and momentum are. Or perhaps that "realism" is what he called a Great Truth (a truth whose opposite is also a Great Truth).

This makes sense to me, reactions to this was as if it was a joke, but I am not sure Peter meant it as a joke?

Rather than those that tries to suggest that "everything is quantum" (thus denying the observer), I find the copenhagen interpretation and Bohrs reasoning to be very honest and also "minimal". Namely that the formulation of quantum mechanics, requires the cut between quantum and macroscopic/"classical". And the latter is to most a very realist part. The "instrument" that makes QM possible is real; otherwise we would have trouble to define the quantum weirdness as well. So the duality here makes sense to me at least, os not sure if was a joke.

/Fredrik

 

[PeterDonis]

I am not sure Peter meant it as a joke?

Consider it as being in a superposition of "joke" and "not joke". Which Bohr would probably have been just fine with.

 

[bhobba]

'Was Bohr really an instrumentalist?'

As the Wikipedia article on Bohr says, 'Bohr has been seen as an anti-realist, an instrumentalist, a phenomenological realist or some other kind of realist.'

Bohr was always difficult to understand.

Thanks
Bill

 

[vanhees71]

This makes sense to me, reactions to this was as if it was a joke, but I am not sure Peter meant it as a joke?

Rather than those that tries to suggest that "everything is quantum" (thus denying the observer), I find the copenhagen interpretation and Bohrs reasoning to be very honest and also "minimal". Namely that the formulation of quantum mechanics, requires the cut between quantum and macroscopic/"classical". And the latter is to most a very realist part. The "instrument" that makes QM possible is real; otherwise we would have trouble to define the quantum weirdness as well. So the duality here makes sense to me at least, os not sure if was a joke.

/Fredrik

The cut is not physical. There's no such thing. At least nobody could empirically prove that quantum phenomena cease to exist for sufficiently large systems. To the contrary with ever refined technique experimentalists find quantum phenomena in larger and larger systems, e.g., in the motion of the LIGO mirrors with masses in the few 10kg range!

 

[Lord Jestocost]

As the Wikipedia article on Bohr says, 'Bohr has been seen as an anti-realist, an instrumentalist, a phenomenological realist or some other kind of realist.'

Bohr was always difficult to understand.

Thanks
Bill

Catherine Chevalley has identified three reasons why Bohr’s writings seem obscure to certain people (C. Chevalley, “Why do we find Bohr obscure?,” in Epistemological and Experimental Perspectives on Quantum Physics, ed. D. Greenberger, W.L. Reiter, and A. Zeilinger (Kluwer, 1999), pp. 59–73):

“My argument will be in three parts. (a) I shall first argue that what makes Bohr difficult to read is the fact that his views were identified with the so-called 'Copenhagen Interpretation of Quantum Mechanics', while such a thing emerged as a frame for philosophical discussion only in the mid-1950's. (b) In the second place, I would like to emphasize that Bohr's ideas were not located in their proper background, either scientific or philosophical, until quite recently. (c) And finally, I shall suggest that Bohr's conception of what philosophical thinking ought to be was so different from the conception that prevailed in the literature after the war that it is no wonder if the connection turned up to be difficult to make.”

 

[vanhees71]

Indeed, Bohr and Heisenberg are the main culprits in obscuring QT, because they produced a lot of philosophical clouds around it. Fortunately, nearly 100 years later, there is a simple no-nonsense interpretation followed more of less conciously by most physicists not involved in high-brow "foundational debates", i.e., the minimal statistical interpretation. If you want to understand the physics without being distracted from philosophical pseudo-problems like "wave-particle duality", "complementarity", "collapse of the quantum state", "measurement problem", then just read physics books rather than philosophy books. For me Bohr is the most overrated physicist of the 20th century. In some way he has been treated more like a priest than a fellow scientist by many of his colleagues.

 

[Fra]

The cut is not physical.

It depends what you mean. I agree it's about as "non-physical" as an effective theory that depends on the observation perspective. Different cuts - different effective theories yes. Which is why I wish to understand the physics of this theory space better than the renormalization group idea.

There's no such thing. At least nobody could empirically prove that quantum phenomena cease to exist for sufficiently large systems.

Agreed, but it does not mean the cut plays no role, it just means its relative. But at some point we indees get beyond Bohrs meaning.

Bohrs "cut" as I understand has no scale limit per see. It is the cut between the DOMINANT classical/macroscopic context, and a smaller subsystem. But yes the subsystem can be "large", but never larger than the observing context as then the theory breaks

/Fredrik

 

[Lord Jestocost]

Indeed, Bohr and Heisenberg are the main culprits in obscuring QT, because they produced a lot of philosophical clouds around it. Fortunately, nearly 100 years later, there is a simple no-nonsense interpretation followed more of less conciously by most physicists not involved in high-brow "foundational debates", i.e., the minimal statistical interpretation. If you want to understand the physics without being distracted from philosophical pseudo-problems like "wave-particle duality", "complementarity", "collapse of the quantum state", "measurement problem", then just read physics books rather than philosophy books. For me Bohr is the most overrated physicist of the 20th century. In some way he has been treated more like a priest than a fellow scientist by many of his colleagues.

With all due respect, I have the feeling that you are distracted from – as you call it – “philosophical pseudo-problems” like ‘wave-particle duality’, ‘collapse of the quantum state’, ‘measurement problem’.
As Carl Friedrich von Weizsäcker remarks in the preface of his book “The Structure of Physics” (the book is a newly arranged and revised English version of "Aufbau der Physik" by Carl Friedrich von Weizsäcker):

“The book reports on an attempt to understand the unity of physics. This unity began to manifest itself in rather unexpected form in this century. The most important step in that direction was the development of quantum theory; the emphasis of this book is therefore on the endeavor to understand quantum theory. Here, understand refers not merely to practical application of the theory – in that sense it has been understood for a long time. It means being able to say what one does when applying the theory.”

[Bold/Bold-Red by LJ]

 

[vanhees71]

Well, I don't comment on CFvW. I think that's really completely off-topic, particularly the mentioned book.

 

[AndreasC]

with vague gibberish like "complementarity" and a "divide in a classical and a quantum dynamics" ("Heisenberg cut").

It feels very rushed to say it was "vague gibberish". I haven't studied the original but the impression I'm getting from secondary sources (including scientists and philosophers who were previously of your point if view before engaging with it) is that that's a very unfair characterization that shouldn't have prevailed. Have you read his writings on the issue?

 

[Fra]

Indeed, Bohr and Heisenberg are the main culprits in obscuring QT, because they produced a lot of philosophical clouds around it.

Did they really? Perhaps Heisenberg a bit more but I have the impression that the cloud comes from confusion between humans and observers. If I remeber right Heisenberg was a bit more into the "observer" but Bohr was more into the "classicak side".. but they unified into the classical part beeing what the set of observers agree upon.

My view of Bohr is that he advocated honesty and simple clarity in how quantum theory does build upon a context. I always thought that this insight came naturally from someone that lived through the creation of QM from the perspective of classical physics. Unlike followers that has been brought up with beeing told about quantum wierdness in school, that grow up confused

/Fredrik

 

[AndreasC]

Well, I don't comment on CFvW. I think that's really completely off-topic, particularly the mentioned book.

Interestinly, it was Weizsacker who changed Feyerabend's opinion on Bohr, which was catalytic to his later development:

Von Weizsäcker showed how quantum mechanics arose from concrete research while I complained, on general methodological grounds, that important alternatives had been omitted. The arguments supporting my complaint were quite good… but it was suddenly clear to me that imposed without regard to circumstances they were a hindrance rather than a help: a person trying to solve a problem whether in science or elsewhere must be given complete freedom and cannot be restricted by any demands, norms, however plausible they may seem to the logician or the philosopher who has thought them out in the privacy of his study. Norms and demands must be checked by research, not by appeal to theories of rationality. In a lengthy article I explained how Bohr had used this philosophy and how it differs from more abstract procedures. Thus Professor von Weizsäcker has prime responsibility for my change to “anarchism”—though he was not at all pleased when I told him so in 1977. (SFS, p. 117).

So maybe @Lord Jestocost thought he was the right person to also change your mind!

 

[AndreasC]

Today appeared a paper claiming that Bohr was a realist.
https://arxiv.org/abs/2308.00814

That was I believe a big part of Fock's defense of Bohr and QM in the Soviet Union (where it was attacked for allegedly being idealist): https://www.sps.ch/en/artikel/gesch...defense-of-modern-theories-in-soviet-union-13

I am convinced that despite his slightly positivist language, Bohr believes as much as we do in the reality of phenomena of which he speaks, and then the difference between the views of Bohr and mine is more a difference of language than a difference of content