- #106
PeterDonis
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zonde said:
So what is the definition of "spacelike separated" in Newtonian mechanics? There isn't one--the concept simply does not exist in Newtonian mechanics.
zonde said:we can say that there can be no photon or any massive particle that has trajectory trough both events if they are spacelike separated by definition.
This answerPeterDonis said:Is there one?
to the commentDemystifier said:That's because wave functions, described by relativistic wave equations (such as Dirac or Klein-Gordon equation), do not propagate faster than c.
seems to suggest that there is one. But no reference is given...DrChinese said:So I would ask any Bohmian why there is a limit - in a nonlocal theory - to entanglement which exactly matches the limits given by c.
ShayanJ said:Well, you said "I agree", so I thought that's what you got from what I said!
Anyway, that's exactly what I wanted to say. The physics community now is divided. The majority of physicists are happy with quantum mechanics and see no problem in it and just want to use it. There are some people who see some problems and want to solve them. These are not only Bohmians. Everyone who does some research on foundational issues is in this camp. So its not that there are problems that only Bohmians see, its just that Bohmians have their own way of looking at these problems. And I really don't see anything different here and that's what confusing me. Why everyone treats Bohmian mechanics so much different than other interpretations? Its not better than others but its not worse too!
A. Neumaier said:There is a lot of rigorous statistical mechanics done in mathematical physics. See, e.g., the nice book by Ruelle. The only approximation made there is the thermodynamic limit, replacing numbers like ##N=10^{23}## by infinity. One can then even estimate the relative error made by this replacement, and it is of the order ##N^{-1/2}##, hence very tiny. Thus there is no barrier of the kind you seem to suggest. At least rigorously proving the validity of QM to 11 decimal places is in principle feasible.
Demystifier said:Does this book explain why a priori probability density in the phase space is uniform? Or is it just an axiom?
No it doesn't. The weirdness of QM is encapsulated in its violation of Bell-type inequalities. Bell guaranteed that we can't think about the microscopic world using our intuition from the macroscopic world. Any theory that violates Bell-type inequalities still has some of that weirdness and BM is no exception. Its true that in BM particles have definite positions and momenta at all times, but you have the quantum potential with its weird behavior and probably other weird things.atyy said:it removes the weirdness from QM.
ShayanJ said:No it doesn't. The weirdness of QM is encapsulated in its violation of Bell-type inequalities. Bell guaranteed that we can't think about the microscopic world using our intuition from the macroscopic world. Any theory that violates Bell-type inequalities still has some of that weirdness and BM is no exception. Its true that in BM particles have definite positions and momenta at all times, but you have the quantum potential with its weird behavior and probably other weird things.
As I said, I myself don't like BM because I like a smart nature that can handle its business without giving that much attention to its details. I really don't like BM to be the actual mechanism behind the nature and I don't think it is. But this is not a physical argument and I won't let this undermine my ability to assess actual physical arguments for and against BM. What I don't like is when some people think that "I don't like it" is actually a physical argument!
I think Bell's assumptions are a good description of what we'd call non-weird. Its not something subjective, Newtonian mechanics is not weird. But relativity is, and any theory that violates Bell-type inequalities is. Weird means non-intuitive and strange to our common sense and our intuition and common sense come from years of living as macroscopic beings dealing with other macroscopic beings and always moving much slower than light w.r.t. each other.atyy said:The Bell inequalities say reality is nonlocal. Reality is not weird unless you think nonlocality is weird.
ShayanJ said:I think Bell's assumptions are a good description of what we'd call non-weird.
DrChinese said:So I would ask any Bohmian why there is a limit - in a nonlocal theory - to entanglement which exactly matches the limits given by c. You never see 2 entangled particles unless they were in contact (limited by c) with some other system that gave rise to the entanglement. I would think that non-local mechanism would give rise to entanglement of all kinds of other things where c is not a limiting factor, if it is also the "out" that explains quantum non-locality. (And yes I know BM is supposed to be equivalent to QM, but this question still seems open to me.)
Its an old book, thus it definitely doesn't tell the state of the art. But in math, old books don't become obsolete, truth is truth at all times.atyy said:what Ruelle's book exactly states, not the present state of the art.
Why did you then complain when I argued that physicists make choices based on with what they can feel happy? It is not a physics argument but an argument why one is prepared to consider certain assumptions or arguments as fruitful. Fruitful is also a subjective aspect, but very important in the development of science!ShayanJ said:What I don't like is when some people think that "I don't like it" is actually a physical argument!
A. Neumaier said:Its an old book, thus it definitely doesn't tell the state of the art. But in math, old books don't become obsolete, truth is truth at all times.
Most results, however, are not based on the ergodic theorem, so what you write is not so relevant.
So, if I understood you correctly, the first spin is EPR real (because it is measured by Alice), the second spin is also EPR real (because it is measued by Bob), but both spins together are not EPR real (because nobody observed both spins). Is that what you are saying?RockyMarciano said:If by real you mean EPR real, they are not.
I think this should be called non-determinism.DrChinese said:So my point is that non-realism has nothing to do with saying "nothing exists". It only has to do with saying: "no initial configuration determines the observed outcome."
This is non-realism. But I never understood why so many people think that non-determinism and non-realism is the same.DrChinese said:We live in a subjective universe, and how we choose to observe actively shapes the reality we see.
Any book or review paper on BM, or the original Bohm's two papers from 1951.A. Neumaier said:But no reference is given...
It is a statistical effect. See e.g.A. Neumaier said:I'd be interested to know what happens in a relativistic version of Bohmian mechanics. Do the microscopic particle positions respect Einstein causality, or is the latter considered to be a statistical effect?
He wrote several books, which you conflate. You seem to refer to his book Thermodynamic Formalism. The Mathematical Structures of Equilibrium Statistical Mechanics whereas I was referring to https://www.amazon.com/dp/9810238622/?tag=pfamazon01-20.atyy said:You are clearly not familiar with the work you cite! Ruelle's resulst are axiom A results!
Demystifier said:So, if I understood you correctly, the first spin is EPR real (because it is measured by Alice), the second spin is also EPR real (because it is measued by Bob), but both spins together are not EPR real (because nobody observed both spins). Is that what you are saying?
Because they are the same in the EPR definition of realism as deterministic. They are of course not the same in the philosophical definition of realism I gave that you normally use when referring to realism.Demystifier said:This is non-realism. But I never understood why so many people think that non-determinism and non-realism is the same.
Thanks. I didn't know this paper. When viewed in the large ##N## limit, does your many-particle relativistic quantum mechanics reproduce macroscopic continuum mechanics? Or is it just a proposal studied for its own sake?Demystifier said:It is a statistical effect. See e.g.
https://arxiv.org/abs/1205.1992
This is not a thread to discuss and correct notions of ''real'' but one on Bohmian mechanics. Please keep your remarks on topic.RockyMarciano said:You keep conflating the broadest philosophical meaning and the EPR meaning of "real".
Yes (but not in a way you naively expect).A. Neumaier said:When viewed in the large ##N## limit, does your many-particle relativistic quantum mechanics reproduce macroscopic continuum mechanics?
I was answering a direct question by the official Bohmian around here.Either the question is on topic and then the answer is, or the question is off topic and then you should make your comment addressing the question.A. Neumaier said:This is not a thread to discuss and correct notions of ''real'' but one on Bohmian mechanics. Please keep your remarks on topic.
In which way, then?Demystifier said:Yes (but not in a way you naively expect).
I did it already: https://www.physicsforums.com/posts/5665529/ and posts #95-#97. But you didn't listen.RockyMarciano said:I was answering a direct question by the official Bohmian around here. Either the question is on topic and then the answer is, or the question is off topic and then you should make your comment addressing the question.
This is just playing semantically with the distinction between inferences and assumptions. The premise of BI that measurements in the same direction determines perfect anticorrelation measurements pressumes simultaneous existence of the spin measurement angles at certain initial time t, therefore determinism despite of how common sense this premise might appear. The fact is that this premise is implied by "no action at a distance" i.e. classical locality principle when applied to spacelike separated regions. So here the classical notion of locality based on simultaneity is used, i.e. the classical determinism with an initial state at time t=0 with a Cauchy surface of simultaneous measurements outcomes.zonde said:Ok, then here are some of Bell's own words:
"It is important to note that to the limited degree that determinism plays a role in the EPR argument, it is not assumed but inferred. What is held sacred is the principle of “local causality” or “no action at a distance”. Of course, mere correlation between distant events does not itself imply action at a distance, but only correlation between the signals reaching the two places. These signals, in the idealized example of Bohm, must be sufficient to determine whether the particles would go up or down. For any residual undeterminism could only spoil the perfect correlation. It is remarkably difficult to get this point across, that determinism is not a presupposition of the analysis."
In the context of EPR, EPR realism is clearly well defined, so why not use it? The meaning "not solipsism" is the broadest philosophical meaning and this is indeed confusing in the quantum context of EPR.And please try not to use "realism" in QM context unless you mean "not solipsism" because it's very confusing what you mean with it. (is it determinism here? or causality? or particles having spin at all times?)
Classical fluid consists of many classical mutually non-entangled particles. Quantum mechanically, each of these particles can be considered to have it's own wave function, the width of which is of the order of Bohr radius. By Ehrenfest theorem, the "center" of each of these wave packets moves by classical laws. In BM, each of these wave packets is filled with a few pointlike particle (depending on the kind of atom one talks about). Within packet the Bohmian motion of the particles is highly non-classical. Nevertheless, since each particle is confined within the packet (the center of which moves classically), this non-classical motion looks pretty classical at large macroscopic distances.A. Neumaier said:In which way, then?
And then in #99 you asked a question as off-topic from the OP as the ones Demystifier have been asking me.A. Neumaier said:I did it already: https://www.physicsforums.com/posts/5665529/ and posts #95-#97. But you didn't listen.
It is my thread and my question in #99 was about an aspect of Bohmian mechanics quite related to the title. But you answered in #131 again an offtopic post by zonde to one of your off-topic posts and contribute in this way to the pollution of the thread.RockyMarciano said:And then in #99 you asked a question as off-topic from the OP as the ones Demystifier have been asking me.
I don't see how starting from your relativistic multiparticle version, this gives macroscopic continuum mechanics. Reference?Demystifier said:Classical fluid consists of many classical mutually non-entangled particles. Quantum mechanically, each of these particles can be considered to have it's own wave function, the width of which is of the order of Bohr radius. By Ehrenfest theorem, the "center" of each of these wave packets moves by classical laws. In BM, each of these wave packets is filled with a few pointlike particle (depending on the kind of atom one talks about). Within packet the Bohmian motion of the particles is highly non-classical. Nevertheless, since each particle is confined within the packet (the center of which moves classically), this non-classical motion looks pretty classical at large macroscopic distances.
Ok, if it comes down to this I'm out.A. Neumaier said:It is my thread
I've just explained it in the post above, but in a sketchy way. If you don't see it I would need to write a long article with all details for you, which I don't plan to do. There is no reference because it is considered obvious, not only in the BM community, but also in the clasicallity-from-decoherence community.A. Neumaier said:I don't see how starting from your relativistic multiparticle version, this gives macroscopic continuum mechanics. Reference?
Strange. In statistical mechanics, it is considered nontrivial to derive macroscopic continuum mechanics from microscopic multiparticle theory, but apparently in BM everything trivializes so that none of the difficult things must be done. It is this attitude that was criticised by Reinhard Werner in the article quoted in post #1,Demystifier said:There is no reference because it is considered obvious, not only in the BM community, but also in the clasicallity-from-decoherence community.
Reinhard Werner said:The Bohmian perspective seems to be the opposite. You don’t care about the hard problem, but only about that last, utterly trivial bit.
It is of course non-trivial (either with or without BM) to do it rigorously. But it is trivial if you don't insist on rigor.A. Neumaier said:In statistical mechnaics, it is considered nontrivial to derive macroscopic continuum mechanics from microscopic multiparticle theory, but apparently in BM everything trivializes so that none of the difficult things must be done.
I have noticed that many of your questions about BM totally miss the point. To exaggerate a bit, many of your questions sound to me like: OK, string theory is the theory of everything, so how string theory explains the protein folding? Reference?A. Neumaier said:I don't see how starting from your relativistic multiparticle version, this gives macroscopic continuum mechanics. Reference?