I added to my answer an authoritative quote from Landau and Lifschitz.vanhees71 said:The point is that we got totally off topic although it's fully clear, how I meant the term "ensemble" here. Thanks for giving the simple answer. I try to call it "statisical sample" in this forum from now on, and we can get back to the really interesting discussions.
It's not just me; there is a whole community of physicists who think that the "standard answer", while it is, as a I said, fine and workable in a practical sense, does not actually resolve the measurement problem at a foundational level.vanhees71 said:why you don't accept the standard answer to the question, how "classical behavior" of macroscopic systems are understood by the pracitioners of the field
The community of physicists I just referred to above are not using hand-waving arguments of 80 years ago. They are looking at the most up to date developments in, for example, decoherence theory. And, as I said, they do not think that all those developments have solved the measurement problem.vanhees71 said:Why do you think, we must still refer to the hand-waving arguments of 80 years ago like a "quantum-classical cut" or "collapse of the state", etc.?
So because you don't personally know anyone who thinks it's a problem, you don't see a problem.vanhees71 said:I don't say their viewpoint doesn't exist although I don't know that any of my colleagues would think that there's a measurement problem.
Yes, we know that. But other people think there is one, even if they can't explain why to your satisfaction. And you have given no argument at all about why there isn't one; you have simply asserted without argument that the practical methods you describe are, in your opinion, good enough. Yes, we know that's your opinion. But there's no way to have a productive discussion on that basis. So when other people want to discuss what they see as a measurement problem, it does not help at all for you to jump in for the umpteenth time and assert that you don't think there is one. That adds no value.vanhees71 said:I don't understand, where there is a problem
Speak for yourself. If you seriously can't see any productive use for such discussions, why do you keep posting in them and hijacking them?vanhees71 said:The discussions about this topic is so unproductive
That's because, as I posted in the other thread just now on Gleason's Theorem where we are having a similar exchange, I have concluded that doing so with you is a waste of my time.vanhees71 said:You also don't tell us, what precisely it is what you think QT is lacking!
From the perspective of theory evolution, the problem I have with this pragmatic perspective ö is that you always end up with an effective theory, that is experimentally fine tuned. That gives you a description, but very little explanation meaning its hard to see the pointers forward.vanhees71 said:you can't expect more from the natural sciences than precisely describing what's observed.
Sure, we don't have a theory of everything, and all theories we have so far are as you describe: On a fundamental basis we have the Standard Model of elementary particle physics with 20+x free parameters, which have to be determined by experiment. This, to the dismay of most physicists looking for "physics beyond the Standard Model", describes all known matter in terms of quarks, leptons, gauge bosons, and the Higgs boson.Fra said:From the perspective of theory evolution, the problem I have with this pragmatic perspective ö is that you always end up with an effective theory, that is experimentally fine tuned. That gives you a description, but very little explanation meaning its hard to see the pointers forward.
That's indeed a very common opinion. The hope is that with new theories we find new relations of the kind you imply.Fra said:For me the better explanation there is, the less finetuning you need. Explanation to me means how all things that seem tuned, really are related.
Indeed, that's the really big fundamental question, and not fruitless philsophical quibbles about the result of 20th century physics that Nature is inherently random and to be described by QT rather than classical deterministic models.Fra said:The things that are fine tuned in QM/QFT are for example the 4D spacetime continuum background. Here I am sure we disagree, but I personally associate this background structure to the "macroscopic classical environment" that to Bohr is the "observer". This is a connection between dynamics of spacetime background and the QM foundations (dynamics of observers). Here also the fact that there are no "infinite ensembles" in nature and that the ensemble is fiction, compares to that a fixed spacetime background is also a fiction.
I never denied these obvious facts. How do you come to that conclusion? What I deny is the assumption that one makes progress by philosophical speculations about how Nature should behave rather than finding solid empirical hints to find a new ansatz for a new, more comprehensive theory, e.g., discovering new particles to get an idea, how dark matter might be described or a hint, how to find a satisfactory QT description of the gravitational interaction, maybe implying that the classical space-time description is also an emergent phenomenon as the classical behavior of macroscopic objects is from the point of view of quantum many-body physics.Fra said:But you denied this connection, as does many others. And maybe on reasonable grounds: that the experimental signs of this is out of reach. But could fine tuning problems be a symptom of this? One can of course think that naturalness is not a must.
Fra said:/Fredrik
I don't understand this association. A quantum theory of gravity/spacetime would be as equally subject to various interpretations and discussions about observers, closed systems etc as quantum mechanics, as you would still presumably have a noncommutative algebra of observables.Fra said:The things that are fine tuned in QM/QFT are for example the 4D spacetime continuum background. Here I am sure we disagree, but I personally associate this background structure to the "macroscopic classical environment" that to Bohr is the "observer". This is a connection between dynamics of spacetime background and the QM foundations (dynamics of observers). Here also the fact that there are no "infinite ensembles" in nature and that the ensemble is fiction, compares to that a fixed spacetime background is also a fiction.
vanhees71 said:I never denied these obvious facts. How do you come to that conclusion?
vanhees71 said:(everything except gravitation and spacetime).
vanhees71 said:What I deny is the assumption that one makes progress by philosophical speculations about how Nature should behave rather than finding solid empirical hints
I rather see it this way. The rate at which we do find new empiritcal hints, will increase if we know precisely where to look. And questions is then: What clues to be have from where we are? This is what this is all about for me. Is keep spending money to be increase accelerator energies the only way forward? I am not convinced, are you?vanhees71 said:Philosophy is "incomprehensibly ineffective", as Weinberg once put it.
Exactly, which is to me another way of saying, as long as we ignore the different between finite and infinite "observers" or "ensembles". Your arguments are clear to me, so you are consistent so I think I understand your perspective. I prefer to keep looking for clues, where you seem to "wait for more data". Isn't the fine tuning and lack of even a coherent GUT, enough food for thought? Do we need more data to realize that we have no clear understanding on how one effective theory merges into another one, over the energy ranges, this seems be a conclusion you can draw from looking at the theory? The problem isn't nature, the problem is our theories. We can see it already now I think.vanhees71 said:Particularly, I don't believe that we find a solution of these problems by thinking about a "measurement problem". For that QT is simply too successful in describing all empirical facts within the above described realm of applicability
But very briefly:Morbert said:I don't understand this association. A quantum theory of gravity/spacetime would be as equally subject to various interpretations and discussions about observers, closed systems etc as quantum mechanics, as you would still presumably have a noncommutative algebra of observables.
You don't expect more, but many others (including myself) expect more, namely to have a mathematically coherent explanation of the measurement process in terms of the fundamental dynamics realized in the universe.vanhees71 said:you can't expect more from the natural sciences than precisely describing what's observed.
But rough means refinable. Interpretation questions become relevant when one investigates the possibilities for refinement.vanhees71 said:I don't think that there'll be much more possible to be learnt concerning at least the rough picture we have today,
Finding the right framework in which to solve tough mathematical problems that have been unsolved for years in spite of many attempts usually involves much philosophical pondering about the "interpretation" of the problem!vanhees71 said:I think it's rather tough mathematical problem than any philosophical pondering about"interpretation".
In your quantum tomography paper you say "A suggestive notion for what constitutes a quantum detector and for the behavior of its responses leads to a logically impeccable definition of measurement.". Is it your position that the thermal interpretation is a solution to the mathematical problems of measurement? Or more specifically, that it offers "a mathematically coherent explanation of the measurement process in terms of the fundamental dynamics realized in the universe"?A. Neumaier said:Finding the right framework in which to solve tough mathematical problems that have been unsolved for years in spite of many attempts usually involves much philosophical pondering about the "interpretation" of the problem!
The philosophical part goes away only after the problems have been solved.
Almost. The definition of measurement is already impeccable, and within the formal framework of quantum mechanics. Thus - unlike in Born's rule, where measurement is an undefined notion - one can prove mathematical facts about measurement processes. The theory in the quantum tomography paper together with the thermal interpretation already goes a long way towards a solution. There are some unsettled issues (discussed towards the end of my paper), but the remaining issues are of a purely mathematical nature, and hence seem tractable (or can be refuted if incorrect).Morbert said:In your quantum tomography paper you say "A suggestive notion for what constitutes a quantum detector and for the behavior of its responses leads to a logically impeccable definition of measurement.". Is it your position that the thermal interpretation is a solution to the mathematical problems of measurement? Or more specifically, that it offers "a mathematically coherent explanation of the measurement process in terms of the fundamental dynamics realized in the universe"?
Do you mean this as beeing of pure matematical nature?A. Neumaier said:Almost. The definition of measurement is already impeccable, and within the formal framework of quantum mechanics. Thus - unlike in Born's rule, where measurement is an undefined notion - one can prove mathematical facts about measurement processes. The theory in the quantum tomography paper together with the thermal interpretation already goes a long way towards a solution. There are some unsettled issues (discussed towards the end of my paper), but the remaining issues are of a purely mathematical nature, and hence seem tractable (or can be refuted if incorrect).
yes. Purely mathematical concepts (in the shut up and calculate style) informed by the philosophy of the thermal interpretation.Fra said:Do you mean this as being of pure mathematical nature?
... on the mathematical characterization of such quantum systems.Fra said:"It was pointed out that to fully solve the quantum measurement problem, more research is needed on the characterization of quantum systems that are nonstationary on experimentally directly accessible time scales."
- page 91 in your paper https://arxiv.org/pdf/2110.05294.pdf
Objectivity is properly discussed in Section 10.4 (p.84f) of my paper. Of course, observation of unique events of fleeting duration are only as objective as the observer taking notes of the event is. But this is in the nature of objectivity, and not a conceptual weakness.Fra said:If so, don't you see potential conceptual complications with this, regarding to establish objectivity?
Do we presume your interpretation(which everyone may not), and then its purely mathematical given your framework. If so I may understand better.A. Neumaier said:yes. Purely mathematical concepts (in the shut up and calculate style) informed by the philosophy of the thermal interpretation.
Note sure I follow. In 10.4 you refer repeatedly in the arguments to stationarity.A. Neumaier said:Objectivity is properly discussed in Section 10.4 (p.84f) of my paper. Of course, observation of unique events of fleeting duration are only as objective as the observer taking notes of the event is. But this is in the nature of objectivity, and not a conceptual weakness.
Assumed are the definitions given in the paper, which are formal and mathematical, together with their interpretation, which are informal and philosophical, also given in the paper.Fra said:Do we presume your interpretation(which everyone may not), and then its purely mathematical given your framework. If so I may understand better.
Yes, verifiable objectivity is tied (even in classical physics) to approximate repeatability. This either requires a sufficiently stationary source, or a nonstationary source that can be taken to be a stationary source of identically distributed short time nonstationary processes. Such a nonstationary source must exhibit some form of ergodicity (discussed on p.77f), to be proved or taken as empirically given.Fra said:Note sure I follow. In 10.4 you refer repeatedly in the arguments to stationarity.
"Through quantum tomography, the quantum state of a sufficiently stationary source, the quantum measure of a measurement device, and the transmission operator of a sufficiently linear and stationary filter can in principle be determined with observer-independent protocols. Thus they are objective properties of the source, the measurement device, or the filter, both before and after measurement."
But there are many solutions (for particularly simple cases though), deriving (semi-)classical transport equations from quantum many-body theory or the entire field of "open quantum systems", using Markovian approximations in terms of quantum master equations (Lindblad). I think this vast work gives enough glimpses on more comprehensive descriptions to exorcize any philosophical speculations ;-)).A. Neumaier said:Finding the right framework in which to solve tough mathematical problems that have been unsolved for years in spite of many attempts usually involves much philosophical pondering about the "interpretation" of the problem!
The philosophical part goes away only after the problems have been solved.
I know all this. But unless one adopts the thermal interpretation, it doesn't answer questions about observations on single systems. For example, Lindblad equations and all decoherence arguments always average over a whole ensemble of identically prepared systems.vanhees71 said:But there are many solutions (for particularly simple cases though), deriving (semi-)classical transport equations from quantum many-body theory or the entire field of "open quantum systems", using Markovian approximations in terms of quantum master equations (Lindblad). I think this vast work gives enough glimpses on more comprehensive descriptions to exorcize any philosophical speculations ;-)).
A. Neumaier said:Finding the right framework in which to solve tough mathematical problems that have been unsolved for years in spite of many attempts usually involves much philosophical pondering about the "interpretation" of the problem!
The philosophical part goes away only after the problems have been solved.
I think that the "philosophical pondering" and the "philosophical part" here should not be confused with "philosophical speculations". More likely, the "philosophical pondering about the interpretation of the problem" will turn out to be mostly metamathematics, with a small amount of linguistics and semantics. We know that you are not a huge fan of semantics either, but words do have meaning, and mathematical formalisms can have meaning too.vanhees71 said:I think this vast work gives enough glimpses on more comprehensive descriptions to exorcize any philosophical speculations ;-)).
gentzen said:My impression is that linguistic and metamathematics are a huge part of analytical philosophy, and perhaps most of the stuff called "philosophy" in this forum should also better be just called metamathematics.
gentzen said:And if analytic philosophy had never happened, this would be totally unproblematic. They tried to "save" philosophy from metaphysics and postmodern nonsense. But because of them, substantial parts of most structural sciences and linguistic are now part of philosophy.
Of course, they do that formally, but as discussed many times, you can also interpret it as averaging over parts of a system over microscopically large, macroscopically small, space-time volumes. Of course, this assumes a separation of scales in this sense, i.e., that "quantum fluctuations" are on small space-time scales, while the "relevant" macroscopic observables, referring to local but microscopically large numbers of "microscopic degrees of freedom" are varying on large macroscopic space-time scales. This is behind the idea of the gradient expansion to go from the full microscopic Kadanoff-Baym equations (or many-body Dyson-Schwinger equations) to a semiclassical Boltzmann-like transprot equation in the Wigner representation.A. Neumaier said:I know all this. But unless one adopts the thermal interpretation, it doesn't answer questions about observations on single systems. For example, Lindblad equations and all decoherence arguments always average over a whole ensemble of identically prepared systems.
But you cannot do this to analyze a single measurement of a single particle, say. At least the analysis is highly nontrivial, and nobody succeeded in giving for this a precise analysis without smuggling in Born's rule, which assumes many measurements to be meaningful. This is precisely the step that is missing in the solution of the measurement problem through the thermal interpretation.vanhees71 said:Of course, they do that formally, but as discussed many times, you can also interpret it as averaging over parts of a system over microscopically large, macroscopically small, space-time volumes. Of course, this assumes a separation of scales
Did you ever heard of Pasch's axiom? It was THE axiom missing from Euclid's axioms. You may think, why is it missing, isn't it SO OBVIOUS that we don't even need to write down that axiom? Well, if you just look at the theory defined by Euclid's axioms, then that theory would also allow other models for which many constructions from Euclid would not work, and many theorems from Euclid would not be true. Of course, we all know that those models were not intended by Euclid, and that is precisely why we can say that Pasch's axiom was missing.vanhees71 said:What do you think is still missing in the understanding of classical behavior from the underlying microscopic (quantum) dynamics? I thought this is indeed much in the spirit of your "thermal interpretation", although you deny the standard use of probabilities as defined by the general Born rule, for a reason I still do not understand.
You may wonder, what is the alternative to there being only a single world. Well, there could be two worlds, or three worlds, or 42 worlds, or infinitely many worlds. And if you have for example three worlds, then there are some ways how those three worlds could related to our experiences.gentzen said:However, the state might not be the only reason, why there is a measurement problem. For example, A. Neumaier's thermal interpretation uses q-expectations and q-corrections instead of the state. But even here, you don't "automatically" solve the problem of unique results. The thermal interpretation needs an additional assumption for that (the assumption is stated as: there is only a single world).