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alexepascual
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Which interpretation of QM do you like?
That's called "spontaneous symmetry breaking" and I do not see why this should be impossible. It is used in the standard model of particle physics for instance.Count Iblis said:But that's impossible if the laws of physics are exactly symmetrical and the initial state respects this symmetry, no matter how you modify the unitary time evolution law.
humanino said:That's called "spontaneous symmetry breaking" and I do not see why this should be impossible. It is used in the standard model of particle physics for instance.
Count Iblis said:The MWI, because it is a minimal interpretation.
Fredrik said:QM is just an algorithm that tells us how to compute probabilities of possible results of experiments. It doesn't need an interpretation, and I doubt that it's even possible to find one that's both well-defined and logically consistent. I think the attempts to find a correct interpretation are fundamentally misguided. They are all trying to tell us what QM really describes, but a theory doesn't have to describe anything. All it has to do in order to be falsifiable is to make predictions about probailities of possible results of experiments.
Count Iblis said:But that's impossible if the laws of physics are exactly symmetrical and the initial state respects this symmetry, no matter how you modify the unitary time evolution law.
I have seen these kinds of arguments before, but for me this is a really strange attitude towards physics:Fredrik said:... but a theory doesn't have to describe anything. All it has to do in order to be falsifiable is to make predictions about probailities of possible results of experiments.
Fredrik said:QM is just an algorithm that tells us how to compute probabilities of possible results of experiments. It doesn't need an interpretation, and I doubt that it's even possible to find one that's both well-defined and logically consistent. I think the attempts to find a correct interpretation are fundamentally misguided. They are all trying to tell us what QM really describes, but a theory doesn't have to describe anything. All it has to do in order to be falsifiable is to make predictions about probailities of possible results of experiments.
Those "fitting simultion models" would be pretty bad theories because of their limited predictive power. We would always be trying to find better theories, e.g. by unifying several different theories into a new one, like we did with electricity and magnetism.ajw1 said:I have seen these kinds of arguments before, but for me this is a really strange attitude towards physics:
- you can make a fitting simulation model for any problem without knowing any law of physics.
- it would mean that physicist only needs to start thinking when an experiment contradicts their current models.
This is because before QM we could always claim that our theories at the very least are descriptions of "fictional" universes that are similar to our own. It's not clear that such a claim about QM even makes sense. I still haven't seen a well-defined and logically consistent many-worlds formulation of QM. (A "Copenhagenish" formulation of QM looks very much like it can't be interpreted as a description of the universe, since you can't include yourself in the physical system that you're trying to describe).ajw1 said:Furthermore it seems this view on physics is mostly used in relation to QM and its interpretaions.
I can't prove it conclusively, but arguments such as the one from section 9.3 in Ballentine's book look pretty strong to me. (I think that's the right section number, but it's from memory). Ballentine's view on these matters appears to be the same as mine, but he says it in a different way. His way is to say that a wavefunction isn't a representation of the properties of a physical system, but a representation of the properties of en ensemble of identically prepared systems.sokrates said:Don't youthink this is a little too humble? How do you reach the conclusion that it's "just an algorithm"?
Uhm, no. What would it even mean to do that?sokrates said:You are confusing the scientific method with intrinsic facts about nature.
Sounds like you think that's a fact. If you're sure about that, then you should be able to justify it.sokrates said:These are two independent things. Quantum Physics is at a level low enough to answer those very fundamental questions. It is definitely not "just an algorithm".
Yes. I think the right approach to these matters is to re-interpret questions like "do electrons exist?" to something like "does the theory that defines what an electron is make accurate predictions?".Count Iblis said:Yes, I think it is fair to say that if you think QM is "just an algorithm" you must also be similarly open minded about the very existence of particles like electrons, quarks etc. We can't directly detect them. All that we can directly observe are the states of macroscopic measurement devices.
I wouldn't have any problem with that, so I guess I'm theCount Iblis said:So, if I play the Devil's advocate, I could claim that Nature is described by a fundamental theory that one can turn into an effective theory yielding statistical predictions using a path integral formalism involving integrating over fictitious field configuarations.
The formalism is then the same as the Standard Model, except for the fact that only the sources and sinks of particles are real, not the particles themselves. So, when you compute amplitudes for process using Feynman diagrams, the external lines always start end end at detectors/sources. The amplitude is associated to the state of the detectors, not to particle states.
You do not know how it works maybe, however since (1932) Von Neumann wrote a book where he clearly explained why it is unnecessary to let go mathematical rigor (as Dirac did), as a matter of fact we have a pretty robust definition of every single step in the quantum algorithm. The book is elementary and pretty much requires no prior knowledge. There is nothing left unproven, to such an extent that the couple of flawed demonstration have been corrected by other authors.sokrates said:We don't even know how it works yet...
I do not know what "playing the devil advocate" has anything to do with the above statement. Any interpretation in disagreement with the above statement could not be falsified !Count Iblis said:when you compute amplitudes for process using Feynman diagrams, the external lines always start end end at detectors/sources. The amplitude is associated to the state of the detectors, not to particle states.
Count Iblis said:Yes, I think it is fair to say that if you think QM is "just an algorithm" you must also be similarly open minded about the very existence of particles like electrons, quarks etc. We can't directly detect them. All that we can directly observe are the states of macroscopic measurement devices.
So, if I play the Devil's advocate, I could claim that Nature is described by a fundamental theory that one can turn into an effective theory yielding statistical predictions using a path integral formalism involving integrating over fictitious field configuarations.
The formalism is then the same as the Standard Model, except for the fact that only the sources and sinks of particles are real, not the particles themselves. So, when you compute amplitudes for process using Feynman diagrams, the external lines always start end end at detectors/sources. The amplitude is associated to the state of the detectors, not to particle states.
Fredrik said:I can't prove it conclusively, but arguments such as the one from section 9.3 in Ballentine's book look pretty strong to me. (I think that's the right section number, but it's from memory). Ballentine's view on these matters appears to be the same as mine, but he says it in a different way. His way is to say that a wavefunction isn't a representation of the properties of a physical system, but a representation of the properties of en ensemble of identically prepared systems.
Fredrik said:Uhm, no. What would it even mean to do that?
I don't doubt that there are "intrinsic facts about nature", but the only knowable facts in science are statements about how accurate a theory's predictions are.
Fredrik said:Sounds like you think that's a fact. If you're sure about that, then you should be able to justify it.
humanino said:You do not know how it works maybe, however since (1932) Von Neumann wrote a book where he clearly explained why it is unnecessary to let go mathematical rigor (as Dirac did), as a matter of fact we have a pretty robust definition of every single step in the quantum algorithm. There is nothing left unproven, to such an extent that the couple of flawed demonstration have been corrected by other authors.
[...] So for the (N+1)th time, where N is an arbitrarily large number, when we say "shut up and calculate" we do not mean there is nothing to understand or interpret. We mean that there is nothing convincing enough to unite the community available on the market.
I'm sorry I can not read your mind when you are trying to repeat what you read Feynman said 50 years ago.sokrates said:When I said, "we don't even know how it works", I was referring to the existing problems of QM, i.e, non-locality, measurement problem, how different ways of thinking about it could possibly lead to different conclusions and so forth. As Feynman put it: We don't know the machinery was what I was implying.
Actually yes. It doesn't make much sense to say that a theory "describes" something unless it contains a mathematical representation of the properties of the system it's supposed to be describing (or at least an approximate version of it). I would say that that's the minimum requirement that must be satisfied. What else can we mean by a "description" or a "model"?sokrates said:Ballentine is emphasizing the statistical nature of the wavefunction, he's not making general epistemological arguments about what a theory could tell us, and what it means. I don't think anyone would object to the argument that
" a wavefunction isn't a representation of the properties of a physical system, but a representation of the properties of en ensemble of identically prepared systems."
Honestly, I find this irrelevant to your previous remark on Quantum Mechanics being "just an algorithm". Ballentine isn't implying that. Or is he?
The scientific method is unimaginative and boring?! That's a pretty controversial claim in a science forum.sokrates said:But overrating it, and blindly sticking to its "formulated" restrictions, I think, is unimaginative and rather boring.
Huh. I said these things myself. Why are you repeating them to me?sokrates said:The facts are out there, and we know that in some examples (as Count Iblis aptly pointed out) different "formulations" could explain the same facts - and WE get to decide which "algorithm" is better than the other and so forth. So this is like choosing a basis to explain an experiment. It is irrelevant.
This is a joke, right? The only thing that everyone agrees about is that QM is an algorithm that tells us the probabilities of possible results of experiments. The disagreement is about whether it's more than that. You're claiming it is. I'm claiming it isn't. How on Earth did you come to the conclusion that the burden of proof is on me?sokrates said:But in science, you know, the burden of proof is on the person asserting the positive claim, not on the skeptics to refute it.
On the contrary. My view (which I described above) is a version of the Copenhagen interpretation. I have really just removed the (in my opinion absurd) claim that "wavefunction collapse" is exact, and clarified a few points.Dmitry67 said:Interesting that nobody voted for Copenhagen :) Looks like it is finally declared dead :)
I must say it feels good to hear reasonable voices. So I wanted to thank you.Fredrik said:Actually, I strongly doubt that Bohr and Heisenberg really meant that the collapse is exact, or that measuring devices are exactly classical. They were too smart for that. It seems much more likely to me that they meant that for practical purposes, it's OK to use the approximation that wavefunction collapse is exact, and that measuring devices are exactly classical. So I would say that the CI is alive and well, and that the only problem with it is that people today are defining it in a way that the originators would have hated.
Fredrik said:Actually yes. It doesn't make much sense to say that a theory "describes" something unless it contains a mathematical representation of the properties of the system it's supposed to be describing (or at least an approximate version of it). I would say that that's the minimum requirement that must be satisfied. What else can we mean by a "description" or a "model"?
Fredrik said:The scientific method is unimaginative and boring?! That's a pretty controversial claim in a science forum.
Fredrik said:Huh. I said these things myself. Why are you repeating them to me?
Fredrik said:This is a joke, right? The only thing that everyone agrees about is that QM is an algorithm that tells us the probabilities of possible results of experiments. The disagreement is about whether it's more than that. You're claiming it is. I'm claiming it isn't. How on Earth did you come to the conclusion that the burden of proof is on me?
Yes it would. This is just crazy talk.sokrates said:If it was just an algorithm, it would have NO POTENTIAL for a future theory that will replace it.
Yes he does. But you seem to have misunderstood what I'm saying. I hope you have. I can't think of any other explanation for the bizarre claim of yours that I quoted first in this post.sokrates said:I am sorry but Ballentine isn't even remotely implying what you are saying here.
Yes I did, but thank you for proving that it's pointless to continue this discussion. I won't waste any more time on you.sokrates said:No; you didn't. And what's the point of such a question?
You're welcome.humanino said:I must say it feels good to hear reasonable voices. So I wanted to thank you.
Fredrik said:Yes I did, but thank you for proving that it's pointless to continue this discussion.
All physical laws are algorithms to cook predictions.sokrates said:Does an algorithm make predictions?
Fredrik said:By the way (this is unrelated to the content of this post), I don't see why people like the "relational interpretation" so much. I know that the basic idea, that systems don't have properties in an objective sense, but rather with respect to some other system, is pretty appealing. But to me this sounds a lot more like an ingredient of a many-worlds interpretation than like a standalone interpretation. Maybe it's possible to take Everett's MWI, which really only defines the "bird's view" properly, and complete it by adding something like the "relational interpretation" to define the "frog's view".
Fredrik said:By the way (this is unrelated to the content of this post), I don't see why people like the "relational interpretation" so much. I know that the basic idea, that systems don't have properties in an objective sense, but rather with respect to some other system, is pretty appealing. But to me this sounds a lot more like an ingredient of a many-worlds interpretation than like a standalone interpretation. Maybe it's possible to take Everett's MWI, which really only defines the "bird's view" properly, and complete it by adding something like the "relational interpretation" to define the "frog's view".
humanio said:All physical laws are algorithms to cook predictions.