- #71
Fra
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I guess we simply think differently on this point. Which is not necessarily a problem.vanhees71 said:Yes, and this has nothing to do with a quantum-classical cut either.
/Fredrik
I guess we simply think differently on this point. Which is not necessarily a problem.vanhees71 said:Yes, and this has nothing to do with a quantum-classical cut either.
As you phrase it like this, it to me, seems that you are missing my point?vanhees71 said:The "appearance of a classical world" out of QT
vanhees71 said:This is an unfounded claim. Nothing in contemporary experiments hints at a quantum-classical cut
Fra said:But our mesaurement apparatouses, and all the data we get from observations are stored in reliable records, that - modulo special relativity - all observers agree upon. Ie. there is no non-commutativity or no-cloning issues with information sharing of measurement results. This is the classical cut. Without this cut, how can you imagine reliably preparing and repeating experiments, that all observers agree upon?
You are the one who interprets the cut as something that should show-up in experiments.vanhees71 said:Yes, and this has nothing to do with a quantum-classical cut either. The "appearance of a classical world" out of QT is much better understood today than at Bohr's times!
I think you "interpret this" (yes, here we go again with interpretations) differently that I do. What I mean with Bohrs clarity, you take as evidence for that he claims that "classical world is needed"!vanhees71 said:or whether there's at some point the necessity of generic classical physics, as claimed by Bohr, among others of the Copenhagen camp
Fra said:I agree with Martinbn, I find Bohr to express things in honest and clear ways, in particular how QM is defined relative to the classical/macroscopic side of the cut. This to me, both clearly explains that QM can not be defined without a "classical/macroscopic observer". Yet, Bohr to my knowledge never claimed that there is a classical reality that is more fundamental, nor that there is a quantum reality.
Taken together, this both states clearly what QM is AND it's limitations. While others may pretend there is only a quantum reality, but without realizing that without the "macro background" we can not DEFINE QM. I think Bohr never made any exaggerated claims here, he expressed what we know, not more, not less, this is why he has my respect.
/Fredrik
Yes, that is the right hypothetical question.GarberMoisha said:If quantum mechanics is fundamental and classical physics "emergent" from it, how come it's impossible to define QT without using these purpotedly emergent macro properties?
There isn't even 1 tangible thing anywhere in existence that cannot be described mathematically. Not 1. To claim it's somehow a 'coincidence' is to detract from the real substance that is of real value for the purpose of understanding the world.Fra said:Yes, that is the right hypothetical question.
IMO the fallacious thinking of, that I percieve is happening, is that you first describe a spatially and temporally small subsystem, from the perspective of the macroscopic environment. And then you extract the mathematical pattern, which suddently is timeless and appearing godlike. Then you for forget about where it came from, and think that the same mathematics is universally valid for any system, even those where the subsystem assymmetry obviously is not fulfilled. (https://arxiv.org/abs/1201.2632)
/Fredrik
I guess those experiments try to test theories like GRW, CSL, or gravitational collapse models like those of Penrose or Diósi. See for example:vanhees71 said:I thought the aim of all these experiments aiming at demonstrating "quantum phenomena" on ever larger systems are about answering the question, whether QT is really complete or whether there's at some point the necessity of generic classical physics,
I guess you are simply wrong here. That QT is complete is one of the claims of the Copenhagen camp. And Bohr would have been the last one to claim otherwise.vanhees71 said:as claimed by Bohr, among others of the Copenhagen camp.
And Bohr would have been the last one to expect otherwise.vanhees71 said:I only stress that so far no such thing has been found but that even really macroscopic objects like the LIGO mirrors show quantum behavior if sufficiently accurately observed.
Pauli ment something else with his "not even wrong". And you basically repeat in slightly weakened form your claim that Bohr and Heisenberg created confusion regarding QM, but don't explain why you are so determined to do so:vanhees71 said:I think Bohr and Heisenberg are not even wrong, they are just confusing.
gentzen said:Why are you so determined to claim that Bohr and Heisenberg have been wrong, and are responsible for all the confusion caused by QM?
Mathematical law is not conincidence, on the contrary - it would be almost unavoidably, when you study a spatially and temporally limited system, that you will find timeless patterns. Just think about, fourier analysis for example. That is the whole point. This is both the power and a limitation. It's not all bad! BUT, how the pattern scales as you increase complexity is not given. I think sometimes we are seduced by the power, and generalized it a bit too far because it's tempting.GarberMoisha said:To claim it's somehow a 'coincidence' is to detract from the real substance
gentzen said:The grammar feels wrong: "... questions ... is settled ...". It is stated as some fact: "foundational questions ... EPR ... settled ... by all the Bell tests ...
Yes, i.e., these are models beyond standard QM, trying to solve the socalled "measurement problem". So far no hint of any such thing has been found though!gentzen said:I guess those experiments try to test theories like GRW, CSL, or gravitational collapse models like those of Penrose or Diósi. See for example:
https://plato.stanford.edu/entries/qm-collapse/#CSLExpe
Well, as I said, for me Bohr is ununderstandable. On the one hand he says, QT were complete, but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?gentzen said:I guess you are simply wrong here. That QT is complete is one of the claims of the Copenhagen camp. And Bohr would have been the last one to claim otherwise.
I am not determined to do this, it's just an observation.gentzen said:And Bohr would have been the last one to expect otherwise.Pauli ment something else with his "not even wrong". And you basically repeat in slightly weakened form your claim that Bohr and Heisenberg created confusion regarding QM, but don't explain why you are so determined to do so:
For me i read that Bohr means; given a classical background, QM is defined and is complete, relative to the same. Ie QM is a theory that is relative to the classical background. No background - no QM (or QFT for that matter)!vanhees71 said:QT were complete, but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?
Why is that a problem? Why should QM be formulated without measurement devices?vanhees71 said:Well, as I said, for me Bohr is ununderstandable. On the one hand he says, QT were complete, but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?
To my mind, quantum theory can be understood as a nonclassical probability theory – to put it in this way. One can use classical physics as a FAPP approximation when the inclusion of more variables – so to speak the “degrees of freedom” – into the quantum-theoretical description is no longer necessary to approximately predict observable outcomes.GarberMoisha said:If quantum mechanics is fundamental and classical physics "emergent" from it, how come it's impossible to define QT without using these purpotedly emergent macro properties?
Einstein attacked QM, and Bohr somehow got the task to try to defend it, at least at the Solvay conference in 1927. Maybe not every one of his defence was perfect, but remember that he had only one night for each of those defenses.vanhees71 said:Well, as I said, for me Bohr is ununderstandable. On the one hand he says, QT were complete,
This is a misunderstanding, but probably unrelated to Bohr's vagueness. I guess it is more related to Bohr being cited by many different people, who all try to explain his thoughts, and often do this by highlighting certain features relevant for their current discussion. In your case, this was probably Bell, but Fra/Frederik gives a more current example how this happens in practice. Bohr's thoughts were simpler and more practical than Fra/Frederik's goals.vanhees71 said:but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?
The EPR paper is anyway somewhat unfortunate. Einstein himself didn't like it, saying it's burying the real argument under "erudition". The way more concise paper is in Dialectica 1 of 1948 (in German), where it becomes clear that the real point for Einstein was indeed inseparability. The answer by Bohr is a complete enigma to me. The real scientific breakthrough was, of course, finally Bell's work translating the vague philosophical "erudition" of the EPR paper into an experimentally decidable scientific question. The results are well known: full consistency of the QM predictions with all empirical findings. If you accept that what EPR had in mind is "local realism" (with all the vagueness of the meaning of these words), then they are clearly disproven.gentzen said:Einstein attacked QM, and Bohr somehow got the task to try to defend it, at least at the Solvay conference in 1927. Maybe not every one of his defence was perfect, but remember that he had only one night for each of those defenses.
Then in 1935, the EPR paper was yet another attack on QM, a more tricky one, and Einstein's role was tricky too. And Einstein's bomb also made its appearance as Schrödinger's cat in 1935. This time, Bohr worked a longer time on his defence, and only responded to Einstein's paper, but not to Schrödinger's paper or Einstein's bomb.
I don't think that Schrödinger added much to the interpretational confusion, and also Einsteins standpoint is quite clear.gentzen said:My impression is that Bohr felt that he was able and expected to communicate with Einstein (and disprove him), but felt uneasy to respond to Schrödinger. Heisenberg did respond to some later papers by Schrödinger, and his response was quite respectful. This further encouraged people to engage with Schrödinger's thoughts, which are probably more responsible for the many different quantum interpretations than Einstein's "suggested thought experiments" or Bohr's answers to them.
Complementarity is another useless confusion, indeed.gentzen said:This is a misunderstanding, but probably unrelated to Bohr's vagueness. I guess it is more related to Bohr being cited by many different people, who all try to explain his thoughts, and often do this by highlighting certain features relevant for their current discussion. In your case, this was probably Bell, but Fra/Frederik gives a more current example how this happens in practice. Bohr's thoughts were simpler and more practical than Fra/Frederik's goals.
The confusion for which Bohr himself is mainly responsible is only the role of complimentarity, I guess.
The following short section in Werner Heisenberg's memoir "Der Teil und das Ganze" puts Einstein’s stubbornness regarding QM in a nutshell:gentzen said:Einstein attacked QM, and Bohr somehow got the task to try to defend it ....
gentzen said:experiments to test theories on collapse.
I agree that the issues of unification of all forces, was not a major thing at that time.gentzen said:This is a misunderstanding, but probably unrelated to Bohr's vagueness. I guess it is more related to Bohr being cited by many different people, who all try to explain his thoughts, and often do this by highlighting certain features relevant for their current discussion. In your case, this was probably Bell, but Fra/Frederik gives a more current example how this happens in practice. Bohr's thoughts were simpler and more practical than Fra/Frederik's goals.
I read in Moore's biography of Schrödinger that he received a letter from Einstein where he described a similar experimental setup using an explosive instead of a cat, before Schrödinger had finished his famous cat paper. See for example SEP ERP 1.3 Einstein’s versions of the argument:vanhees71 said:What do you mean by "Einstein's bomb"?
[...] The similarity between the gunpowder and the cat is hardly accidental since Schrödinger first produced the cat example in his reply of September 19, 1935 to Einstein’s August 8 gunpowder letter. There Schrödinger says that he has himself constructed “an example very similar to your exploding powder keg”, and proceeds to outline the cat (Fine 1996, pp. 82–83). Although the“cat paradox” is usually cited in connection with the problem of quantum measurement (see the relevant section of the entry on Philosophical Issues in Quantum Theory) and treated as a paradox separate from EPR, its origin is here as an argument for incompleteness that avoids the twin assumptions of separability and locality."The system is a substance in chemically unstable equilibrium, perhaps a charge of gunpowder that, by means of intrinsic forces, can spontaneously combust, and where the average life span of the whole setup is a year. In principle this can quite easily be represented quantum-mechanically. In the beginning the psi-function characterizes a reasonably well-defined macroscopic state. But, according to your equation [i.e., the Schrödinger equation], after the course of a year this is no longer the case. Rather, the psi-function then describes a sort of blend of not-yet and already-exploded systems. Through no art of interpretation can this psi-function be turned into an adequate description of a real state of affairs; in reality there is no intermediary between exploded and not-exploded. (Fine 1996, p.78)
Usually in physics by "paradox" is meant an unintuitive consequence of the theory, like the twin paradox. None of them are actual paradoxes.vanhees71 said:It's of course no paradox ...
And I think Einsteins original view is sound, that there has to be a "hidden variable", of some kind. My view is no different. Not to explain the outcomes, but their correlations.vanhees71 said:His real quibble was with the "inseparability" of far-distant parts of entangled quantum systems.
This idea is usually based on the philosophical belief that nature presents a harsh reality that is simply true regardless of your beliefs. I stress this point because I also believe that, but @vanhees71 keeps stating that before measurement there is no realism about the quantum state.vanhees71 said:Nature doesn't care about
But everything we've learned since then points to no hidden variables!Fra said:And I think Einsteins original view is sound, that there has to be a "hidden variable", of some kind. My view is no different. Not to explain the outcomes, but their correlations.
I usually avoid the word "reality", because its meaning is uncertain ;-)). The quantum state describes a preparation procedure for a quantum system. Having prepared the system in a given quantum state, you know the probabilities for the outcome of measurments of observables on the system, no more, no less, and that's what describes all observations with utmost precision.Structure seeker said:This idea is usually based on the philosophical belief that nature presents a harsh reality that is simply true regardless of your beliefs. I stress this point because I also believe that, but @vanhees71 keeps stating that before measurement there is no realism about the quantum state.
So I wonder, @vanhees71 , before interpreting measurement results we all start with our 'take' on things, our philosophical worldview. If you don't believe quantum wavefunctions are a reality, how do you justify that nature doesn't care about what people believe should be true about these wavefunctions? If you give no answer, your opinion that nature doesn't care is your belief about wavefunctions and we, as realists, can answer: nature (reality) doesn't care that you think our beliefs are superseded by measurement results.
No, you missed a fine detail of my point. I think Vanhees did too.martinbn said:But everything we've learned since then points to no hidden variables!
I am not saying that it is 100% certain that there are no HV, only that so far all we know points in that direction. What makes you think that there could be HV (non Bell type of course)?Fra said:No, you missed a fine detail of my point. I think Vanhees did too.
There is no bell style HV, yes. I am with all this.
Which is a very specific HV with additional assumptions on how the average action is formed, which i think is the problem.
/Fredrik