Demystifier said:That statement, taken literally, was wrong. But it's clear (at least to me) that atyy wanted to say that the theory cannot make some of its predictions without a cut.
I would have said: the theory cannot make verifiable prediction without a cut.Demystifier said:That statement, taken literally, was wrong. But it's clear (at least to me) that atyy wanted to say that the theory cannot make some of its predictions without a cut.
Even after measurement you still don't have a value - only a (hopefully) more precise probability !atyy said:Because in classical mechanics the particle is there whether you look at it or not. In quantum mechanics, the formalism does not assign the particle a position until you look at it.
But how is it you don't buy your own preferred interpretation ?vanhees71 said:Again for me this is the very statement, I don't buy. There is no difference between interaction and measurement. This is vaguely formulated, so maybe I understand you and other proponents of this claim in this thread in a wrong way. For me this says that you and others claim that there's a difference in the interaction of the measured object with the measurement apparatus and all other interactions.
Maybe in the lab... but you seem to be doubting that... I don't. And again, it is not the "problem". The problem is to accurately analyse the theory itself.vanhees71 said:This doesn't make sense to me since the same physical laws apply to interactions no matter whether it's the interaction with a measurement apparatus or not.
Ok, then my mistake. When do you use the Born rule inside the Schrodinger equation ?vanhees71 said:Neither in classical nor in quantum theory is any dichotomy in the applicability of the rules to measurement apparati and other objects.
That's an ontological claim (that I share btw).vanhees71 said:Measurement apparati are made of the same stuff as anything else, and also all physical laws apply to measurement devices as to any other object. That's all I'm claiming.
But there is no need to. The minimalist interpretation is fine. You believe in ensemble, and the Born rule applied. Period.vanhees71 said:Maybe we have to reformulate our claims, but I don't know, in which way I can reformulate mine.
No, the units don't match in QM, they do in CMvanhees71 said:Both phase space in classical mechanics and the operators in Hilbert space are representing properties of observable facts about objects, described in an abstract mathematical way.
As far as I known, probabilities are not complex numbers... even (0,0)vanhees71 said:In QT the description is explicitly probabilistic
What about my examples?atyy said:I meant the theory cannot make any predictions without a cut
RUTA said:Wow, it always amazes me how many human-IQ-hours have been invested trying to find a way to reinvent QM so as to rid it of the measurement problem (see Schlosshauer quote in #135). Accepting QM as supplying spatiotemporal constraints on the distribution of quantum events, rather than dynamical laws for the behavior of quantum systems, automatically rids us of the MP. Then, QM is seen as complete by simply accepting quantum-classical contextuality. There is nothing in Nature that demands we recover classical reality from a quantum reality in toto. Certainly not with any empirical consequences. That's just a reductive bias. If Weinberg tried and failed, it's certainly above my pay grade! But, it looks to be entertaining lots of brilliant mathematical minds, so by all means, enjoy :-)
In quantum mechanics a particle is there too, provided there's a conservation law ensuring this. If there is no conservation law there's a certain probability that the particle vanishes by interaction with other particles. The only difference is that the position of a particle is never determined, and thus in any state the probability distribution has a finite width around a point (if you consider a state where the particle is pretty well localized) or it might even be a very broad distribution or the distribution might peak around different locations (if the particle is not so well localized).atyy said:Because in classical mechanics the particle is there whether you look at it or not. In quantum mechanics, the formalism does not assign the particle a position until you look at it.
In quantum mechanics, there is a fundamental difficulty with applying the quantum state to the whole universe including the observer. In classical mechanics, there is no equivalent difficulty (there is a difficulty to include the whole universe from the singularities of GR, but that is different from needing to exclude the observer).
Bhobbas perspective (especially on symmetry) has been quite different than mine in past discussions on here, but I fully agree here that the above is indeed at the heart of the discussions! So we probably agree roughly where the core of the issues are but not on the resolution.bhobba said:Of course when speaking about probabilities you have different views on that - Vanhees and myself take the Frequentest view - as many people in areas that apply probability do - but it is far from the only one. The frequentest view naturally leads to the Ensemble interpretation. As John Baez says much of the argument about QM interpretations is the same as arguments about what probability means:
http://math.ucr.edu/home/baez/bayes.html
Me and Vanhees do not ascribe to the Bayesian view - but really its just philosophy and in applying it makes no difference in practice - well most of the time anyway.
Thanks
Bill
Then please precisely explain to me what you mean when you say "measurements are special" (within quantum mechanics). I have no clue what that should mean if you admit that measurement devices are usual "stuff" and thus behaves according to the generally valid physical laws. Indeed, measuring a force with a balance invokes the very laws the concept of force is based on within the theory (necessarily Newtonian mechanics, because the force concept only makes sense within Newtonian mechanics). I'm not doubting that, but you do, if I understand the statement "measurements are special". I'm arguing against this claim of the Copenhagen-like interpretation all the time.Boing3000 said:But how is it you don't buy your own preferred interpretation ?
But first things first, I don't (nor anybody else) think (let's say on a philosophical/ontological level) that the "stuff" of the laboratory (or the universe or whatnot) is made of two different "categories" of stuff, obeying different rule. For example I am quite confident that classical mechanics assume you can measure things of the theory (like force and mass and ...) with the same thing in the laboratory (force and mass) (in the same unit)
Also the discussion here is only about phenomenology, and differences between them (and their completeness)
Maybe in the lab... but you seem to be doubting that... I don't. And again, it is not the "problem". The problem is to accurately analyse the theory itself.
That's exactly what I meant above: The wave function, which is a way to describe the quantum state for a special case, i.e., for systems of a fixed set of stable particles that can be described non-relativisticall, is not directly observable, but with the Hamiltonian of the it provides position or momentum probablity distributions (depending on whether you work in the position or momentum representation, but you can always convert from one to the other) given an initial condition. This time evolution is, for a closed system, described by a unitary time-evolution operator, and of coarse QT is causal (and even in a narrower sense causal, because it's also local in time, i.e., you need to know the initial condition just at one initial time, not the entire history of the wave function in the past). QT is, however, not deterministic (within the minimal interpretation and most other interpretations too). One has to distinguish between causality (knowing the state in the past tells you precisely the state in the future) and determinism (all observables of a system always have determined values, no matter in which state this system is in). Again: QT is causal but not deterministic.What is uncontroversial, in that in the model/theory the physical law describe imaginary(hmmm complex) vector in arbitrary dimension. From what I understand the Schrodinger equation is deterministic and continuous.
Where I think you make a unconscious philosophical leap, is to believe that measurement apparatus (used to test QM) are "displaying" those imaginary pointer from other dimensions... they don't. Not because they are macroscopic, but because the unit don't even match those of the theory...
...because the complete minimal interpretation must add something fundamentally different to classical mechanic, in order to make it scientific (testable).
This process (the Born rule) is discrete, and only happens "on measurement" (not on interaction), and is probabilistic. But at least probabilities of "stuff" in the same unit as the laboratory (all classical).
What do you mean by that? I don't use Born's rule inside the Schrödinger equation. For me Born's rule is an independent postulate, necessary to give an interpretation to the wave function (in this very special case of systems, where a wave function is a sufficient description of the (pure) quantum states of the system) usable in the lab. The wave function and the Schrödinger equation is just a means to calculate these probabilities. There's no (direct) ontic meaning of the states (in the general case represented statistical operators) and obserables (represented by essentially self-adjoint operators). These are only tools to calculate the probabilities, which can be observed (on ensembles of equally prepared systems).Ok, then my mistake. When do you use the Born rule inside the Schrodinger equation ?That's an ontological claim (that I share btw).
But you don't claim that. You are claiming (as far as I understand) that the epistemology is not based on such a dichotomy.
Exactly. So far there's nothing else.But there is no need to. The minimalist interpretation is fine. You believe in ensemble, and the Born rule applied. Period.
Well, it might well be that one day we'll find another more comprehensive theory, where QT turns out to be an effective theory with the Born rule derived from the more comprehensive theory. It's, maybe, even likely, when we understand quantum gravity better than we do now. So far the Born rule seems to be an independent postulate, necessary to give a minimal interpretation needed to apply the QT formalism to real-world observations.You seem to believe that one day another interpretation will derive the Born Rule. Why not ? As far I can tel RUTA's one is a good start. It is even based on a classical axiom...
But as thing are currently, the current minimal interpretation does make such a distinction.
I have no clue, what you want to tell by this statements. The same units are used in QT as in classical physics. Already now many units are based on QT, because that's much more precise than using the historical original definitions based on classical physics. It is almost certain that the entire SI will be based on QT already next year, 2019.No, the units don't match in QM, they do in CMAs far as I known, probabilities are not complex numbers... even (0,0)
The statement of QT is indeed not "When position of the particle is measured, then position of the particle is such and such" but "When the position of the particle is measured the probability distribution for the outcome of this measurement is given by Born's rule". Within QT there's nothing else known about the position than these probabilities. It seems as if we agree in fact about this. The difference only is that in classical mechanics it's postulated that all observables always have a determined value and of course that means that if you measure these observables you observe these determined values, while QT tells us that not all observables can take determined values, no matter in which state the system may be prepared, and thus the only sensible meaning of the quantum state are the probabilities given by Born's Rule.Demystifier said:Newton's equation is a statement of the form "position of the particle is such and such". It is not a statement of the form "When position of the particle is measured, then position of the particle is such and such".
But quantum mechanics is different. QM does not state that "probability of the position of the particle is such and such". It states that "When position of the particle is measured, then probability of the position of the particle is such and such".
Well, I think there is no measurement problem for the simple reason that QT works extraordinary well to describe what's observed in Nature and measured with high precision in the lab.atyy said:I guess your interpretation is not an "interpretation" in traditional quantum terminology since it retains the cut and doesn't attempt to solve the measurement problem.
Especially since you frame it with Wheeler's question, which was not about solving the measurement problem, I guess your programme is more like trying to provide alternative axioms for quantum theory, like the odl quantum logic thinking of von Neumann, Birkhoff, Mackey, etc, and the more recent ones of Lucien Hardy https://arxiv.org/abs/quant-ph/0101012 or of Chiribella and colleagues https://arxiv.org/abs/1011.6451 ?
I couldn't agree more!RUTA said:Wow, it always amazes me how many human-IQ-hours have been invested trying to find a way to reinvent QM so as to rid it of the measurement problem (see Schlosshauer quote in #135). Accepting QM as supplying spatiotemporal constraints on the distribution of quantum events, rather than dynamical laws for the behavior of quantum systems, automatically rids us of the MP. Then, QM is seen as complete by simply accepting quantum-classical contextuality. There is nothing in Nature that demands we recover classical reality from a quantum reality in toto. Certainly not with any empirical consequences. That's just a reductive bias. If Weinberg tried and failed, it's certainly above my pay grade! But, it looks to be entertaining lots of brilliant mathematical minds, so by all means, enjoy :-)
bhobba said:There is no physical content of any theory without measurements
if not you can't compare it to experiment so its not testable ie its not science.
The issue with QM is defining, using nothing but QM itself, what a measurement its.
It has long been my 'feeling' that some issues in QM people worry about are also present in other theories like probability and classical mechanics, however they are generally not worried about in those areas - except maybe by philosophers.
martinbn said:I thought that QT can make predictions without any cut. Say, if you smash these particles, then the probability to get those is so and so. No cut and a very spesific prediction. Or something along the lines a black hole will radiate and loose energy, no cut. Or is the cut somewhere implicit.
How exactly in these examples? A photon will not decay to a proton. What detection is needed to make such a prediction? Just for the prediction, not to actually test it. Or black holes radiate, where is the detection here? I am not saying that it isn't there, it is just not obvious to me.stevendaryl said:Quantum mechanics gives the amplitudes for particle interactions. To actually get probabilities out of them, you have to assume that somewhere down the road, someone is going to be detecting those particles.
martinbn said:How exactly in these examples? A photon will not decay to a proton. What detection is needed to make such a prediction? Just for the prediction, not to actually test it. Or black holes radiate, where is the detection here? I am not saying that it isn't there, it is just not obvious to me.
atyy said:I guess your interpretation is not an "interpretation" in traditional quantum terminology since it retains the cut and doesn't attempt to solve the measurement problem.
Especially since you frame it with Wheeler's question, which was not about solving the measurement problem, I guess your programme is more like trying to provide alternative axioms for quantum theory, like the odl quantum logic thinking of von Neumann, Birkhoff, Mackey, etc, and the more recent ones of Lucien Hardy https://arxiv.org/abs/quant-ph/0101012 or of Chiribella and colleagues https://arxiv.org/abs/1011.6451 ?
stevendaryl said:Okay. My remark is about the non-exceptional probabilities, that are neither 0 nor 1, but somewhere in between. I guess I would agree that if QM predicts that the probability amplitude for something is 0 or 1, then you don't need to know anything more than that.
RUTA said:No, no, our interpretation totally solves the MP and keeps QM intact. The MP obtains because physicists want a model of physical reality that is dynamical and reductive, but Nature is under no obligation to be the way we want it to be.
RUTA said:No, no, our interpretation totally solves the MP and keeps QM intact. The MP obtains because physicists want a model of physical reality that is dynamical and reductive, but Nature is under no obligation to be the way we want it to be.
atyy said:But I thought you retain the classical-quantum cut?
stevendaryl said:I don't think that's true. Newton's laws have the same physical content even in the absence of human beings and measuring devices.
atyy said:I meant the theory cannot make any predictions without a cut. If the observer is included in the wave function and all we have is the unitarily evolving quantum state, the theory makes no predictions.
So is the cut necessary to predict that electric charge will be conserved?atyy said:I meant the theory cannot make any predictions without a cut. If the observer is included in the wave function and all we have is the unitarily evolving quantum state, the theory makes no predictions.
Consider a classical stochastic process, e.g. a random walk. The observables are not deterministic, but given by a probabilistic law. Yet, observables have definite values at each time, irrespective of whether you measure them or not. I think the key to understand QM is to explain what exactly is the difference between QM and classical stochastic processes.vanhees71 said:The difference only is that in classical mechanics it's postulated that all observables always have a determined value and of course that means that if you measure these observables you observe these determined values, while QT tells us that not all observables can take determined values, no matter in which state the system may be prepared, and thus the only sensible meaning of the quantum state are the probabilities given by Born's Rule.
Demystifier said:So is the cut necessary to predict that electric charge will be conserved?
Classical stochastic processes (as described, e.g., by Langevin equations) only occur, because we are not able to describe the detailed equations of motion of the classical system (e.g., the Brownian particle in a fluid consisting of very many classical particles, with which this Brownian particle interacts) and instead describe the interaction of a subsystem (e.g., the Brownian particles) in terms of a friction force and a randomly fluctuating force in the sense of classical statistical physics. The system as a whole is still deterministic, i.e., here we use probabilistic arguments to mimic the interactions which we cannot fully describe due to the complexity of the situation.Demystifier said:Consider a classical stochastic process, e.g. a random walk. The observables are not deterministic, but given by a probabilistic law. Yet, observables have definite values at each time, irrespective of whether you measure them or not. I think the key to understand QM is to explain what exactly is the difference between QM and classical stochastic processes.
Where would you put the cut in these examples?atyy said:Yes, because there is no physical interpretation to the wave function alone.
I mean precisely what is said in the minimal interpretation of QM. See post #127 or #142, and for that matter nearly ever other post in this thread.vanhees71 said:Then please precisely explain to me what you mean when you say "measurements are special" (within quantum mechanics)
This is the salient point of your misunderstanding. My belief, or your belief, are inconsequential here. We are not discussing what you call philosophy (some taste based word salad). We are asserting the coherence of some statement, only on the merit of what is written, nothing more.I have no clue what that should mean if you admit that measurement devices are usual "stuff" and thus behaves according to the generally valid physical laws.
OK, but then you argumentation must be based on a version off QM that does not contains the Born rule. Yours does.I'm arguing against this claim of the Copenhagen-like interpretation all the time.
That is insufficient, the theory must also predict new/unknown phenomena, and this is very important. I suppose you'll agree that the future of physics is not to find zillion of equivalent abstract phenomenology (like string theory, ...)All of physics is about phenomenology. Theory aims at ever more comprehensive and ever more precise description of phenomena that are objectively observable in Nature.
OK, given the time you have taken to explain, I'll use that word like you do. Although that I don't think it's the correct word to encompass the uncertainty relations, because I have always read that the Schrodinger equation is all there is, and even if every knowledge cannot be known "at once", all is continuous and unitary (and thus determined)Again: QT is causal but not deterministic.
Really, all I wanted you is to admit the following and ...What do you mean by that? I don't use Born's rule inside the Schrödinger equation.
...that this independent postulate is only for the lab, which need a special interpretation. There is no such thing in classical mechanics, which treat all the stuff in the universe equally.For me Born's rule is an independent postulate, necessary to give an interpretation to the wave function (in this very special case of systems, where a wave function is a sufficient description of the (pure) quantum states of the system) usable in the lab.
{...}
So far the Born rule seems to be an independent postulate, necessary to give a minimal interpretation needed to apply the QT formalism to real-world observations.
The same you've made above. We are on the same page now.Which "distinction"?
No. That's not even the same field. And going to real by using a modulo is one thing, but the squaring implies that the unit of the Hilbert space is "square root" of probabilities...I have no clue, what you want to tell by this statements. The same units are used in QT as in classical physics.
I don't, and that's exactly what I write ==> "As far as I known, probabilities are not complex numbers... even (0,0)"Probabilities are of course numbers between 0 and 1. I've no clue, why you think probabilities might be complex numbers.
vanhees71 said:Then please precisely explain to me what you mean when you say "measurements are special" (within quantum mechanics). I have no clue what that should mean if you admit that measurement devices are usual "stuff" and thus behaves according to the generally valid physical laws. Indeed, measuring a force with a balance invokes the very laws the concept of force is based on within the theory (necessarily Newtonian mechanics, because the force concept only makes sense within Newtonian mechanics). I'm not doubting that, but you do, if I understand the statement "measurements are special". I'm arguing against this claim of the Copenhagen-like interpretation all the time.
Again you just claim this, but that's not what standard QT claims. According to standard QT the functioning of measurement apparati are completely consistent with the laws of physics valid for all matter observed yet (usually one assumes also that that's how all matter in the universe behaves, but that's of course an extrapolation which never can be tested empircially). My point is that there is no measurement problem at all. What's called a measurement problem is usually a metaphysical quest for an ontological interpretation of the notion of quantum states, which is however not subject of science but only of philosophy.Boing3000 said:This is the salient point of your misunderstanding. My belief, or your belief, are inconsequential here. We are not discussing what you call philosophy (some taste based word salad). We are asserting the coherence of some statement, only on the merit of what is written, nothing more.
QM that you claim to appreciate for its coherence and simplicity (which is fine) does make the distinction between interaction and measurement. Why does it have to do that distinction, while the universe is obviously only make of the same "stuff" ? That's the measurement problem.
vanhees71 said:Again you just claim this, but that's not what standard QT claims. According to standard QT the functioning of measurement apparati are completely consistent with the laws of physics valid for all matter observed yet (usually one assumes also that that's how all matter in the universe behaves, but that's of course an extrapolation which never can be tested empircially). My point is that there is no measurement problem at all. What's called a measurement problem is usually a metaphysical quest for an ontological interpretation of the notion of quantum states, which is however not subject of science but only of philosophy.
vanhees71 said:Where in Landau Lifshitz is the claim you are not willing to state explicitly in this thread? It's strange that you always make these claims about measurement devices being outside of the standard laws of QT but never explaining in which sense you mean it and then point to textbooks and not giving the clear statement nor where to find it in these books. I've never heard such a statement nor read it in any serious textbook about QT, and LL for sure is one very serious textbook.
vanhees71 said:This must be the very first chapter, where exactly the contrary is stated to the claim you make. They say that classical behavior of macroscopic devices is understood as an approximative limit of QT. They also bring the very example of the cloud-chamber traces for an electron that I also stated in this thread. In other words, what I read in LL is completely consistent with what I stated. They are very careful and only use a very weak version of the collapse postulate, more careful than most other books following the Copenhagen doctrine. I guess that's because Landau is following more Bohr's than Heisenberg's opinion.
stevendaryl said:As was said in a previous comment, a measurement device plays two different roles in the minimal interpretation:
In role #1, there is no distinction between measurement devices and any other physical system. In role #2, there is a big distinction. Probabilities only appear in quantum mechanics if you have measurements, not for any other interactions.
- It is a physical system, and so it is described by the Schrodinger equation.
- It determines a "preferred basis" for computing probabilities.
I don't understand why, when the issue is #2, people keep bringing up that #1 doesn't distinguish measurements from other interactions.
But also #2 doesn't distinguish measurements from other interactions. The "preferred basis" is just the observer's choice which observable s/he likes to measure. That's the only meaning in which a basis has to be chosen to evaluate probabilities: To get the probabilities for the outcome of measurements you need the eigenbasis of the self-adjoint operator representing this observable. It's not more special then the observer's choice in classical physics too. If I measure the position of a particle I need another device than when I measure its momentum.stevendaryl said:As was said in a previous comment, a measurement device plays two different roles in the minimal interpretation:
In role #1, there is no distinction between measurement devices and any other physical system. In role #2, there is a big distinction. Probabilities only appear in quantum mechanics if you have measurements, not for any other interactions.
- It is a physical system, and so it is described by the Schrodinger equation.
- It determines a "preferred basis" for computing probabilities.
I don't understand why, when the issue is #2, people keep bringing up that #1 doesn't distinguish measurements from other interactions. That's true, but it's only half the story.
QT is about what's observable in nature, and to observe we need macroscopic objects, which are describable to sufficient accuracy with classical physics. That's all what LL state in their marvelous textbook on QM, and since the validity of the classical limit can be understood from QM there's no contradiction in that, i.e., there are no special laws for macroscopic objects (i.e., no quantum-classical cut) and no specialty of measurement devices in terms of the physical description in theory from any other kind of matter, which is self-evident, because obviously measurement devices must be made of the matter around us. They are only special in the sense that physicists construct them to measure the one or the other observable, but they are still consisting of the matter around us. Of what else shoud they be made?atyy said:Of course classical mechanics is a limit of quantum mechanics. One can see this in the saddle point approximation to the path integral.
However, what you are not understanding and which Landau and Lifshitz state clearly, is that quantum mechanics cannot be formulated without "classical concepts" also in its assumptions. It is not possible to derive classical physics from "purely quantum" assumptions.
One can use different language to state this assumption, but they are all essentially equivalent - measurement has a different status than the interactions described in the Hamiltonian.
This is not true. Given the measurement device as a quantum object, the observer has no choice which observables to measure - it can only measure the observables that can be read off from (or calculated from reading of) the measurement device.Thus there must be a way to determine the preferred basis directly from the quantum device, without choices by a further observer.vanhees71 said:The "preferred basis" is just the observer's choice which observable s/he likes to measure.
vanhees71 said:So indeed I agree with the statement that to understand measurements one needs classical concepts, but that doesn't mean that a measurement is anything different from any other interaction of the measured system with a macroscopic object that's not used as a mesurement device.
And yet, you have admitted that you don't use the Born rule inside the Schrodinger equation. That clearly means that there is no "preferred base" picking in QM interaction. None.vanhees71 said:But also #2 doesn't distinguish measurements from other interactions.
Really ? Just ? So it should be easy for you to provide a derivation (without any cut) of the Born rule. This must be an very interesting proof, because it will DEFINE what a measure is. It would be the first theory to actually create its own version of what an observation is, not related to an event in a lab, but to some VAGUELY defined ensemble of events.The "preferred basis" is just the observer's choice which observable s/he likes to measure.
You've just said you cannot measure the position of a particle (only a probability in an ensemble). In fact "speed" it does not exist in the interaction picture (its a complex mixture of imaginary speed)That's the only meaning in which a basis has to be chosen to evaluate probabilities: To get the probabilities for the outcome of measurements you need the eigenbasis of the self-adjoint operator representing this observable. It's not more special then the observer's choice in classical physics too. If I measure the position of a particle I need another device than when I measure its momentum.
Well, this is semantics. The observer constructs the measurement device to measure the observable he likes to measure. If you now start to discuss the ability of this free choice of the observer to measure the observable he likes you get into funny discussions about "consciousness" and "free will" and all kinds of esotrical philosophy around it. I was shocked to see that this is even publishable in serious scientific publishing companies like Springer. Well, there's no law forbidding to publish nonsense in serious science publishing companies, which like to make money with anything they can find. A funny anecdote is that when I went into a big bookshop in Munich to look for quantum theory textbooks I couldn't find it in the very small science corner of this bookshop. Asking a nice employee of the bookshop, whether they don't have also quantum theory textbooks, she answered "Oh, you are complete wrong here. That's in the shelf with book on esoterics, which in fact was much larger than the little shelf they sold science textbooks." Well, they had no quantum theory textbooks but all kinds of "quantum nonsense" (as Bricmont calls it in his book "Quantum sense and quantum nonsense", of which I currently read the German translation; it's pretty entertaining to read although sometimes rather imprecise in popularizing QT; I also don't buy the "solution" of the interpretational problems in terms of de Brogli-Bohm theory since so far nobody could make sense of it in context relativistic QFT).A. Neumaier said:This is not true. Given the measurement device as a quantum object, the observer has no choice which observables to measure - it can only measure the observables that can be read off from (or calculated from reading of) the measurement device.Thus there must be a way to determine the preferred basis directly the quantum device, without choices by a further observer.
Not again this wrong statement. You cannot admit at the same time that the classical behavior is derivable from QT and then claim that there is a cut. That's a contradictio in adjecto!atyy said:There you have made the subjective classical-quantum cut.
Quantum objects have all the observables which can be defined on them. For massive particles these are particularly their energy, momentum, angular momentum, and their position. The point in QT is that not all the observables can take determined values at once (some cannot take determined values at all, which is the case for all observables having a continuous spectrum only like energy, momentum, and position).Boing3000 said:Whatever your version of QM is, individual particles have no speed or momentum or whatnot. And yet, nature only "hidden ontology", can only be approached and probed, (and this is even more true in QM), with unique individual event in the lab (and that is a that individual level, that all conservation law work).
Your view that only "ensemble of identically prepared thing" exist, and this is a complete physical phenomenology of nature, is highly incoherent with the fact that quanta do exist, and only them, and their individual interaction, are ever observed in a laboratory, or elsewhere.
That's not what I claim. Of course single electrons exist, and we can prepare them in many quantum states quite accurately. All I say is that within the ensemble interpretation quantum theory only describes the probabilities, and these probabilities can be empirically measured only on ensembles of equally prepared systems.Your view that only "ensemble of identically prepared thing" exist, and this is a complete physical phenomenology of nature, is highly incoherent with the fact that quanta do exist, and only them, and their individual interaction, are ever observed in a laboratory, or elsewhere.
I don't object to the choice. But after the observer has chosen the device (by whatever rule), there remains the pure quantum problem to show that the device actually produces on each reading the numbers that qualify as a measurement, in the sense that they satisfy Born's rule.vanhees71 said:The observer constructs the measurement device to measure the observable he likes to measure. If you now start to discuss the ability of this free choice of the observer
But each individual system produces definite result (or appears to produce definite result). And either you have something to say about that, and then you participate in discussions about "collapse" and alternatives, or you keep agnostic position and do not say anything like "collapse is superfluous"/"collapse is required".vanhees71 said:Of course single electrons exist, and we can prepare them in many quantum states quite accurately. All I say is that within the ensemble interpretation quantum theory only describes the probabilities, and these probabilities can be empirically measured only on ensembles of equally prepared systems.
So far so good...vanhees71 said:That's not what I claim. Of course single electrons exist,
No you cannot. There is no phenomenon as "state preparation" in nature. You (the observer) only do it in a lab, because you need that to match the ensemble with the esoteric Hilbert space, by using an ad-hoc Born rule. This ensemble exist only in your head. CM does not need any ad-hoc projection for observation, nor does nature (as per QM Schrodinger equation).and we can prepare them in many quantum states quite accurately.
You say much more then that. You made make hidden assumptions (often circular) and quite astonishing claim (like QM completeness). You say noticeably that there is no epistemological difference with CM.All I say is that within the ensemble interpretation quantum theory only describes the probabilities, and these probabilities can be empirically measured only on ensembles of equally prepared systems.
