I Interestingly Bohr Did Not Believe in Wavefunction Collapse

[bhobba]

I was reading an article 'What Einstein Really Thought about Quantum Mechanics' in Scientific American. There they mentioned something I didn't know - Bohr did not believe in Wave Function Collapse as an issue (I don't either - but that's just my opinion, so means nothing). I found this surprising because just about everyone cites it as an issue eg Sabine Hossenfelder. So I dug a bit deeper and found a paper on Bohr's views:

https://arxiv.org/pdf/1603.00353

People might find it interesting.

BTW aside from Bohr's view on QM the Scientific American article didn't contain anything that has not been discussed here before. For those that may not have seen discussions on this, the usual remarks such as God does not play dice misses the mark on his real issue(s). If it is not behind a paywall here is the link:

https://www.scientificamerican.com/article/what-einstein-really-thought-about-quantum-mechanics/

Thanks
Bill

 

[Demystifier]

R. Tumulka, in the recent book "Foundations of Quantum Mechanics" (2022), explained Copenhagen interpretation in a very lucid way. I particularly like the following part:

"Narratives, But No Serious Ones

When calculating predictions that can be compared to experimental data, adherents of CI often tell a story about the physical meaning of the mathematical elements of the calculation. This story may involve particles or waves, may be imprecise, may conflict with other stories told on another occasion, or may contain several parts conflicting with each other. But this story is not intended to describe what actually happens. On the contrary, CI insists that such narratives should not be taken seriously. They are just metaphor, or allegory, or analogy; they just serve as a mnemonic for the calculation, as a help for remembering the correct formulas or for setting up the corresponding formulas in similar calculations. In contrast, theories such as Bohmian mechanics or GRW or many-worlds are hypothesizing about what actually happens in nature and correspondingly aim at providing a single, coherent story that fits all experiments and situations."

 

[Demystifier]

So when Bohr and other adherents of Copenhagen/standard/orthodox/minimal type of interpretations talk about interpretations, one should not take them very seriously. One should take seriously their calculations, and their measurable predictions, but not their narratives in which they try to explain what that means. After all, they don't take very seriously their own narratives themselves.

 

[vanhees71]

The collapse contradicts the formalism of relativistic microcausal QFT. So naive collapse interpretations are self-contradictory. I always thought the still big "fan club" of Bohr always claim Bohr never had introduced a collapse. Einstein's advice about theorists is wise: "Don't listen to their words, look at their deeds."

 

[LittleSchwinger]

Well in his essays Bohr never mentions collapse. The closest he gets is discussing filtering, that's about it.

This is no different from the history of physics in general though. Even in Classical Mechanics the "folk history" is completely different from the actual history of what Langrange, D'Alembert, Hamilton, etc did. In my general experience you have to read the original sources and proper academic histories, which are surprisingly uncommon in physics, instead of the storybook version most texts will recount.

 

[LittleSchwinger]

I always thought the still big "fan club" of Bohr always claim Bohr never had introduced a collapse. Einstein's advice about theorists is wise: "Don't listen to their words, look at their deeds."

Could you expand on what you mean here?

 

[vanhees71]

I think Einstein meant, you should look at what the theorists really have achieved than listening to their "philosophy", and for me it's completely ununderstandable, why Bohr was such a celebrity in connection with "modern quantum mechanics", where he wrote a lot of philosophical rather than solid physics papers with vague gibberish like "complementarity" and a "divide in a classical and a quantum dynamics" ("Heisenberg cut"). His influence was rather destructive to people who dared to question this "Copenhagen doctrine". This was broken only in the early 80ies, when Bell's work of the 60ies slowly became to be realized in the lab. Bell himself warned young colleagues to touch the issue, because he thought it could be destroying their careers, and he emphasized that he could dare to go into the foundational-QM issues only because he had a solid tenured job.

 

[LittleSchwinger]

for me it's completely ununderstandable, why Bohr was such a celebrity in connection with "modern quantum mechanics", where he wrote a lot of philosophical rather than solid physics papers

It's also interesting how there are many people who were a major influence on the emerging theory, but don't get included in the folk story. For example Jordan, Majorana, Kramers, etc.
I think it's a common tendency to concentrate history into a few "mythic" figures.

 

[vanhees71]

Jordan is the most underestimated, but it's due to his idiosyncratic political behavior during (and even before!) 1933-1945:

https://physicstoday.scitation.org/doi/10.1063/PT.3.5158
https://physicstoday.scitation.org/do/10.1063/PT.6.4.20230104a/full/

What were Majorana contributions? I must admit, I don't know. Of course I'm aware of his work in connection with relativistic theory ("Majorana fermions" and all that).

Kramers role was to have been involved with Bohr in a famous failure shortly before modern quantum theory was discovered by Born, Jordan, based on Heisenberg's Helgoland idea. In this paper the authors gave up the conservation laws, particularly energy conservation. This was famously refuted shortly thereafter by Bothe's coincidence method applied to Compton scattering.

 

[Lord Jestocost]

I was reading an article 'What Einstein Really Thought about Quantum Mechanics' in Scientific American. There they mentioned something I didn't know - Bohr did not believe in Wave Function Collapse as an issue (I don't either - but that's just my opinion, so means nothing). I found this surprising because just about everyone cites it as an issue eg Sabine Hossenfelder.

In order to avoid any 'nonsense' that might have been circulated about Bohr's thinking, I recommend to read “Niels Bohr and the Philosophy of Physics: Twenty-First-Century Perspectives” (edited by Jan Faye and Henry J. Folse, published 2017).

 

[LittleSchwinger]

What were Majorana contributions? I must admit, I don't know. Of course I'm aware of his work in connection with relativistic theory ("Majorana fermions" and all that).

Well first of all just that. Everybody knows the name, but himself as an actual person is rarely discussed in the history of physics, which is odd because I think it's one of the more interesting stories. Outside of that he was the first to make major progress in the treatment of the spectroscopy of heavier elements and the first to correctly identify and treat the neutron.

Kramers role was to have been involved with Bohr in a famous failure shortly before modern quantum theory was discovered by Born, Jordan, based on Heisenberg's Helgoland idea. In this paper the authors gave up the conservation laws, particularly energy conservation. This was famously refuted shortly thereafter by Bothe's coincidence method applied to Compton scattering.

Well for example Kramer's 1924 dispersion theory paper and his January 1925 paper with Heisenberg was the biggest influence on Heisenberg's 1925 Helgoland paper.

 

[vanhees71]

Well first of all just that. Everybody knows the name, but himself as an actual person is rarely discussed in the history of physics, which is odd because I think it's one of the more interesting stories. Outside of that he was the first to make major progress in the treatment of the spectroscopy of heavier elements and the first to correctly identify and treat the neutron.

He also considered field quantization already in the "Dreimännerarbeit". It had to be rediscovered by Dirac in 1927/28, because it was ignored at the time.

Well for example Kramer's 1924 dispersion theory paper and his January 1925 paper with Heisenberg was the biggest influence on Heisenberg's 1925 Helgoland paper.

That's true. Of course Kramers contributed a lot more later to "new QM" like the WKB approximation etc.

 

[LittleSchwinger]

He also considered field quantization already in the "Dreimännerarbeit". It had to be rediscovered by Dirac in 1927/28, because it was ignored at the time.

Sorry, in case I wasn't clear, in the above I referred to Majorana not Jordan.

 

[vanhees71]

I see. I must say, I don't know much about Majorana's contributions to early QT.

 

[LittleSchwinger]

I see. I must say, I don't know much about Majorana's contributions to early QT.

Yeah, unfortunately he was very private and quiet, mostly known to only people in Fermi's group and died young under mysterious circumstances.

 

[vanhees71]

Indeed, most writings on him are speculations about his mysterious disappearance rather than about his science :-(.

 

[PeroK]

It's also interesting how there are many people who were a major influence on the emerging theory, but don't get included in the folk story. For example Jordan, Majorana, Kramers, etc.
I think it's a common tendency to concentrate history into a few "mythic" figures.

You could argue both cases. E.g. if Bohr had never lived, then QM would have progressed along parallel lines in a similar time frame. Or, it could have held up progress for a decade or more.

The case is less clear, IMO, if Einstein had never emerged from the patent office. Somebody would have produced SR, surely? But, how long after 1905?

 

[vanhees71]

I think, Bohr had in fact pretty little influence on the development of modern quantum mechanics, except that he provided opportunities for the scientists to work in his famous institute. I think at least Schrödinger's wave mechanics would have been also developed without the presence of Bohr, since it was triggered by de Broglie's work with considerable support by Einstein. One can even speculate, whether we'd have been spared all these philosophical debates. On the other hand, it triggered also the scientific case in terms of Bell and the development of all the scientifically fruitful developments celebrated by the recent Nobel Prize in physics and the development of new technologies like quantum cryptography, quantum informatics, etc.

 

[Lord Jestocost]

........ why Bohr was such a celebrity in connection with "modern quantum mechanics", where he wrote a lot of philosophical rather than solid physics papers with vague gibberish like "complementarity" and a "divide in a classical and a quantum dynamics" ("Heisenberg cut"). His influence was rather destructive to people who dared to question this "Copenhagen doctrine".

With all due respect, are you really serious about your comment?

In “BOOJUMS ALL THE WAY THROUGH: Communicating Science in a Prosaic Age” (first published 1990), N. David Mermin remarks in chapter 14 “The philosophical writings of Niels Bohr”:

“But against the sometimes maddening frustration brought about by a study of these ponderous essays is the indisputable fact that nobody has succeeded in saying anything manifestly better in the sixty years since Bohr started talking about complementarity. How he could have known that they would fail, right from the start, is yet another puzzle. As a philosopher Bohr was either one of the great visionary figures of all time, or merely the only person courageous enough to confront head on, whether or not successfully, the most imponderable mystery we have yet unearthed.”

 

[LittleSchwinger]

Without Bohr the field of discussing Bohr would have been held back decades

 

[gentzen]

You could argue both cases. E.g. if Bohr had never lived, then QM would have progressed along parallel lines in a similar time frame. Or, it could have held up progress for a decade or more.

The case is less clear, IMO, if Einstein had never emerged from the patent office. Somebody would have produced SR, surely? But, how long after 1905?

This is ridiculous. Both made discoveries that were not foreshadowed in any way. Why are you so sure that they would have been discovered without them? But we should also be clear that both delivered their groundbreaking work in young years, and especially not past 1926. Bohr had the wisdom to support young researchers, and this is a second important part of his lasting contributions. Einstein occasionally also managed to support other researchers, like Bose or de Broglie. Don't underestimate that part.

 

[Demystifier]

E.g. if Bohr had never lived, then QM would have progressed along parallel lines in a similar time frame.

https://arxiv.org/abs/physics/0702069

 

[vanhees71]

SR was more or less already there, particularly by Poincare. I think it wouldn't have taken long without Einstein to realize that there's no need for an aether at all.

Bohr's great achievement was the old quantum theory of atoms, paving the way to the modern development, when the failure of this concept was obvious pretty soon in the vigorous research on spectroscopy. The idea of the new quantum theory came from Heisenberg in 1925 and, independently, from Schrödinger in 1926, not from Bohr.

I agree with the importance of Bohr's establishment of his famous institute and the mentoring of many young scientists.

 

[bhobba]

Indeed, most writings on him are speculations about his mysterious disappearance rather than about his science :-(.

That is true. I know him from a television special about strange disappearances.

Thanks
Bill

 

[bhobba]

SR was more or less already there, particularly by Poincare. I think it wouldn't have taken long without Einstein to realize that there's no need for an aether at all.

In another forum where the question of if anyone nearly had SR before Einstein was asked, I mentioned Poincare. But he was 'stuck' in old thinking and even asked Einstein what the dynamical principle behind SR was. Of course, Poincare had the mathematical ability to invent even the modern version, but the issue was his worldview. Einstein, of course, was the bridge between the old and modern worldviews. I laughed when someone responded that Minkowski came up with the geometrical interpretation - not Einstein. That was the point - Poincare has the mathematical ability to do that, and I am a bit surprised Minkowski did it before him purely on mathematical grounds. But perhaps his preconceptions may have held him back. Even there, Poincare came tantalisingly close:
https://shs.hal.science/halshs-01234449/document

Thanks
Bill

 

[Fra]

As far as I have concluded from recall reading somewhere sometimes there was a tension between Bohr and Heisenbergs view, where Heisenberg emphasised the cut between observer and system, where the "collapse may have been more emhpasises", while Bohr was more thinking of the "classical vs quantum" cut, but IMO the unification of these views is that, as long as all the "Heisenberg observers" share the same common classical reality, they can communicate and make a joint agreement about things. In this sense the set of all possible Heisenberg observers, seems to be the same as the classical observer of Bohr. This is how at least I always thought of it, and they are thus not really in contradiction. Both views make sense and complement each other. So together this nifcely defines the Copenhagen interpretation.

The only problem with this, is when you put in classical objects as "quantum systems", but then - it is not the puropose of QM, the purpose of QM is a theory of the subatomic world we only indirectly can access.

/Fredrik

 

[vanhees71]

But QT describes everything, including macroscopic systems. That's what zillions of condensed-matter physicists work about with great success! There is also no hint yet that there's an upper limit in size, where all of a sudden the fundamental laws of QT get invalid and classical physics takes over. As I repeatedly quoted, even ~10 kg objects like the LIGO mirrors show quantum behavior. It's only a matter of the technical ability to prepare macroscopic systems such that quantum phenomena become observable.

 

[Hornbein]

Einstein occasionally also managed to support other researchers, like Bose or de Broglie. Don't underestimate that part.

Einstein awarded his Einstein Prize to Schwinger and Feynman.

 

[LittleSchwinger]

But QT describes everything, including macroscopic systems. That's what zillions of condensed-matter physicists work about with great success! There is also no hint yet that there's an upper limit in size, where all of a sudden the fundamental laws of QT get invalid and classical physics takes over. As I repeatedly quoted, even ~10 kg objects like the LIGO mirrors show quantum behavior. It's only a matter of the technical ability to prepare macroscopic systems such that quantum phenomena become observable.

Zurek has some fun papers modelling Hyperion, a moon of Saturn, with QM:

• Zurek, W.H.: Pointer basis of quantum apparatus: Into what mixture does the wave packet collapse? Phys. Rev. D 24, 1516–1525 (1981)
• Zurek, W.H.: Environment-induced superselection rules. Phys. Rev. D 26, 1862–1880 (1982)
• Zurek, W.H.: Preferred states, predictabilty, classicality, and the environment-induced decoherence. Prog. Theor. Phys. 89, 281–312 (1993)
• Zurek, W.H.: Decoherence, chaos, quantum–classical correspondence, and the algorithmic arrow of time. Phys. Scr. T 76, 186–198 (1998)

 

[Fra]

But QT describes everything, including macroscopic systems.

Except gravity, which you leave for last (as you think it has nothing todo with this), but this is where we disagree. I also think there are other indirect implicitations; we still have no GUT. I also think this is relevant to this. But, yes it's just my hunch, we you can label philosophy if you wish.

It's only a matter of the technical ability to prepare macroscopic systems such that quantum phenomena become observable.

Yes! This is also my point, believe or not, but while you seem to think it's this is jus a practical limit or the scientific technolgoy at hand, I take it more seriously and suggest this: It is a matter of ability of the OBSERVER/AGENT to represent/control/process the part of it's environment in a way that makes it possible to implement the inference and measurements, produce statistics etc. The only reason why i insist that QM works best for SMALL systems, is that this is where we can keep this assymmetry.

For more general cases, I think QM/QFT needs to be relaxed and improved.

I kind of like your sticking to experimentally accessible things, but my "philosophy" is that this is more than just a practical matter of human technolgoy, I take this seriously which has led me to my own stance with interatting agent initerpretations.

From the practical perspective, I can't disagree with you.

/Fredrik

 

[Fra]

Except gravity, which you leave for last (as you think it has nothing todo with this), but this is where we disagree. I also think there are other indirect implicitations; we still have no GUT. I also think this is relevant to this. But, yes it's just my hunch, we you can label philosophy if you wish.

Unless it is clear what I meant, the problem of hte GUT is to unify interactions at different scales, it's hard to "connect them" from the perspective of inference.... so even if gravit is at the extremal scale, we have "scale issues" already in the quest for GUT. This is in short why I see a common issue here. It's early signs, that simply get unsurmountable if you include gravity. For the GUT, we may overcome it, but perhasp there is an easier way, that will also reduce the number of free parameters.

/Fredrik

 

[vanhees71]

Except gravity, which you leave for last (as you think it has nothing todo with this), but this is where we disagree. I also think there are other indirect implicitations; we still have no GUT. I also think this is relevant to this. But, yes it's just my hunch, we you can label philosophy if you wish.

Gravity is completely negligible for the description of macroscopic bodies. It's treated semiclassically whenever one investigates the quantum behavior in the gravitational field of the Earth (e.g., the famous experiment with cold neutrons, which is well explained by treating the gravitational field as $V(\hat{\vec{x}})=-m \vec{g} \cdot \hat{\vec{x}}$ in the Hamiltonian).

Yes! This is also my point, believe or not, but while you seem to think it's this is jus a practical limit or the scientific technolgoy at hand, I take it more seriously and suggest this: It is a matter of ability of the OBSERVER/AGENT to represent/control/process the part of it's environment in a way that makes it possible to implement the inference and measurements, produce statistics etc. The only reason why i insist that QM works best for SMALL systems, is that this is where we can keep this assymmetry.

It's simply technologically simpler to handle small systems such that quantum behavior becomes observable. There's not a single hint that QT becomes invalid for macroscopic systems.

For more general cases, I think QM/QFT needs to be relaxed and improved.

There's no empirical evidence for this claim.

I kind of like your sticking to experimentally accessible things, but my "philosophy" is that this is more than just a practical matter of human technolgoy, I take this seriously which has led me to my own stance with interatting agent initerpretations.

The problem is that there is not the slightest hint for the necessity to claim that sufficiently large bodies cannot be described by QT. It's just a philosophical feeling that there must something be wrong with QT, for whatever reason you have this feeling.

 

[PeterDonis]

There's not a single hint that QT becomes invalid for macroscopic systems.

Yes, there is: macroscopic systems do not show quantum interference effects. That was Schrodinger's original point in his cat thought experiment.

The usual QT response is that if we are someday able to do, say, double slit experiments with macroscopic objects like rocks, we will find that they do show quantum interference effects. But that's not a claim based on actual evidence: it's a claim about what kind of future evidence we will find. There is no actual evidence that macroscopic objects show quantum interference effects, and mountains of evidence that they do not. That is a hint that QT might not be valid for macroscopic systems, or at the very least that there might be corrections at the macroscopic level to the QT that works well for microscopic systems.

 

[bhobba]

But QT describes everything, including macroscopic systems.

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.

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.

Thanks
Bill

 

[LittleSchwinger]

Yes, there is: macroscopic systems do not show quantum interference effects. That was Schrodinger's original point in his cat thought experiment.

But don't coarse graining and decoherence predict the absence of interference effects for macroscopic collective coordinates? In addition quantum condensed matter correctly derives the macroscopic physical properties (e.g. friction, dielectric and many other coefficients).

So the predictions of QM for macroscopic bodies is that they should possess various effective constants that they have been shown to possess and also that interference should be absent experimentally. In fact the absence of interference is often directly related to the value of their frictional coefficients.

It would be one thing if quantum theory predicted the presence of interference effects and wrong values for the effective constants of materials, but as far as I can see it everything it is know to predict is observed in macroscopic bodies.

I mean even at a simple level quantum statistical mechanics correctly predicts how rapidly a macroscopic body heats up. Similarly simple you need QM to explain macroscopic stability, i.e. that macroscopic bodies don't energetically prefer dividing in smaller macroscopic bodies:

E. H. Lieb and R. Seiringer, The stability of matter in quantum mechanics, 1st ed. (Cambridge Univ. Press, Cambridge, UK, 2010).

 

[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.