Is Quantum Uncertainty Related to Dynamic Instability?

[akashdgr8]

please tell me if the uncertainity arising in the quantum mechanics is related to the uncertainity due to the dynamic instability
and whether we can calculate the quantum uncertainity using the mathematical equations used in the dynamics

 

[inha]

It's not related to dynamical instability. Incompatible observables just can't have a common (complete) set of eigenfunctions.

 

[Juan R.]

please tell me if the uncertainity arising in the quantum mechanics is related to the uncertainity due to the dynamic instability
and whether we can calculate the quantum uncertainity using the mathematical equations used in the dynamics

Both are related in a specific sense: from microworld to macroworld.

Quantum uncertainty is amplified by dynamical instability generating chaos. In the usual interpretation of chaos, uncertainty is associated to initial conditions, but is not correctly said that phase space (x, p) cannot be defined with total precision due to quantum uncertainty.

In a non chaotic system, quantum uncertainty is microscopic and cannot be detected at macroscopic scale. However, microscopic uncertainty is amplified by nonlinear instable systems and then macroscopic chaos observed.

 

[El Hombre Invisible]

There is one intepretation of QM which suggests that a particle is 'guided' by it's wave functions which describes the 'quantum potential' acting on it. In this hidden variables theory, the particle does have an exact position and momentum, but the slightest change in either leads the particle being guided along a different path, which basically means any particle is itself a chaotic system. Such theories aren't that popular, presumably because they propose the existence of something that cannot be verified and yet do not alter existing mathematical formulation that works quite happily without these variables.

 

[Juan R.]

There is one intepretation of QM which suggests that a particle is 'guided' by it's wave functions which describes the 'quantum potential' acting on it. In this hidden variables theory, the particle does have an exact position and momentum, but the slightest change in either leads the particle being guided along a different path, which basically means any particle is itself a chaotic system. Such theories aren't that popular, presumably because they propose the existence of something that cannot be verified and yet do not alter existing mathematical formulation that works quite happily without these variables.

The very old Bohm interpretation of QM is rather discredited.

In the "hidden variables" theory, the particle "does have" an exact position and momentum that is unphysical, cannot be computed and cannot be measured, therefore they do not exist, just like standard QM states. The Bohm interpretation "solves" quantum misteries via the introduction of new misteries like the pilot wave, the undetectable misterious quantum Bohm potential, etc.

Moreover, the Bohm interpretation is only valid in the old position-formulation phy(x,t). It is not applicable to the general dirac formulation, |phy(t)>, of QM and cannot say nothing of others properties like spin. Bohm formulation is incompatible with special relativity, of course cannot explain pair creation and annihilation, etc.

An do not forget that interpretation of phy(x, t) like a "real" wave is only valid for ONE body systems where dimension of Hilbert space is 4 (no spin), since that already phy(x1, x2, t) lives in a different Hilbert space of 7D.

Moreover, Bohmian interpretation asummes that is physically undemostrable: that universe is deterministic.

This is even false at the classical level, how the theory of stochastic systems shows. Even at classical level, Bohm simply ignores all experimental data on fluctuations and indeterminism beyond the classical mechanics of one body.


P.S: The magician Uri Geller has convinced David Bohm that has supernatural abilities which may be explained via Bohm potential.

No comment!

 

[El Hombre Invisible]

The very old Bohm interpretation of QM is rather discredited.

In the "hidden variables" theory, the particle "does have" an exact position and momentum that is unphysical, cannot be computed and cannot be measured, therefore they do not exist, just like standard QM states. The Bohm interpretation "solves" quantum misteries via the introduction of new misteries like the pilot wave, the undetectable misterious quantum Bohm potential, etc.

The notion that if it "cannot be computed and cannot be measured, it doesn't exist" seems to be in line with the Coppenhagen way of thinking - obviously the Bohm interpretation is the antithesis of this so I'm not sure that argument holds. And, yes, the mystery of the wavefunction becomes the mystery of the quantum potential... six of one, half a dozen of the other.

Bohm formulation is incompatible with special relativity, of course cannot explain pair creation and annihilation, etc.

Standard QM isn't compatible with SR anyway, is it? The Bohm interpretation doesn't "solve" the non-locality problem, but it didn't introduce it.

Moreover, Bohmian interpretation asummes that is physically undemostrable: that universe is deterministic.

Again, no worse than the undemonstrability that quantum systems are in superposition (as in, we do not observe such systems in superposition).

P.S: The magician Uri Geller has convinced David Bohm that has supernatural abilities which may be explained via Bohm potential.

Ha ha! A quantum theory of spoon-bending is what the world really needs!

Not that I subscribe to the Bohm interpretation at all. I don't know enough about it or QM in general to decide for myself whether it is inherently worse or better than other interpretations, but I've yet to hear one (that is, a physical one) that seems any less flawed (MWI, Penrose's). I just assume Bohm is wrong because everyone else does!

 

[Juan R.]

The notion that if it "cannot be computed and cannot be measured, it doesn't exist" seems to be in line with the Coppenhagen way of thinking - obviously the Bohm interpretation is the antithesis of this so I'm not sure that argument holds. And, yes, the mystery of the wavefunction becomes the mystery of the quantum potential... six of one, half a dozen of the other.

In science, a theory is a proved scientific hyphotesis. A scientific hyphotesis is any hyphotesis that can be falsified by scientific method.

If you claim that at infinitum -i.e. beyond the observed universe- there is a "Saloon" with pink elephants dancing "Macarena" song, that is not a scientific hyphotesis. Bohm claims existence of undetectable things, therefore is not a scientific hyphotesis.

As explained the quantum potential is not equivalent to wave function. Bohm focused only on single particles where phy(x, y, z, t) and therefore can be interpreted like a kind of "standard" wave. For two body systems, there is not a potential in usual space that mimics the wavefunction behavior.

Standard QM isn't compatible with SR anyway, is it? The Bohm interpretation doesn't "solve" the non-locality problem, but it didn't introduce it.

Whereas a relativistic quantum field theory has been developed, Bohm mechanics is still at level of pre-relativstic quantum physics. Nobody has generalized Bohm mechanics. Another reason which is not taken seriously.

Again, no worse than the undemonstrability that quantum systems are in superposition (as in, we do not observe such systems in superposition).

We observe systems in superposition. If you take two electrons to behave classically you cannot explain we observe in experiments with atoms and molecules. Precisely, chemical reactivity of a molecule is computed from superposition of charges. If you take electrons to be not in supersposition your theoretical prediction is experimentally incorrect.

The existence of superpositions already was predicted by chemist G. N. Lewis years before formulation of QM. From purely chemical reasoning Lewis obtained that electron in a bond cannot be in atom A or atom B is in both togheter.

We observe superpositions in laboratory experiments, even with today thecnology we van create superposition of big systems (e.g. macromolecules) during some instants and see like are destroyed by decoherence.

What is not observed are macroscopic superpositions, and this is the problem of incompatibility of QM with macroscopic phenomena.

 

[El Hombre Invisible]

In science, a theory is a proved scientific hyphotesis. A scientific hyphotesis is any hyphotesis that can be falsified by scientific method.

I'm not saying B.I. (henceforth) is proven or even provable - I'm just saying that the notion that if something cannot be directly observed it cannot be said to exist is a philosophy of an alternative interpretation of QM.

If you claim that at infinitum -i.e. beyond the observed universe- there is a "Saloon" with pink elephants dancing "Macarena" song, that is not a scientific hyphotesis. Bohm claims existence of undetectable things, therefore is not a scientific hyphotesis.

Again, all physical intepretations of QM that I've heard of are like this. I think that attitude is a little harsh. B.I. does attempt to explain observable phenomena - dancing/singing pink elephants beyond the observable universe does not. Funny, but not comparable. And now I have that tune stuck in my head. Below-the-belt tactics on your part, I think.

As explained the quantum potential is not equivalent to wave function. Bohm focused only on single particles where phy(x, y, z, t) and therefore can be interpreted like a kind of "standard" wave. For two body systems, there is not a potential in usual space that mimics the wavefunction behavior.

True, that was kind of an argument twice removed. The de Broglie wave (also for a single particle) is intepreted as the pilot wave (in fact, I'm sure I read that this was the direction de Broglie himself was headed), and the de Broglie wave is the wave function of a free particle. I was using words interchangeably.

Whereas a relativistic quantum field theory has been developed, Bohm mechanics is still at level of pre-relativstic quantum physics. Nobody has generalized Bohm mechanics. Another reason which is not taken seriously.

To my knowledge, the QM formulation generally used day-to-day is not relativistic. I only know this from other threads where newbies like myself were trying to mix SR and QM - the standard answer was "QM is non-SR". I know next to nothing about relativistic QM, but would I be right in saying this is something outside standard QM?

We observe systems in superposition. If you take two electrons to behave classically you cannot explain we observe in experiments with atoms and molecules. Precisely, chemical reactivity of a molecule is computed from superposition of charges. If you take electrons to be not in supersposition your theoretical prediction is experimentally incorrect.

Exactly. Key word being computed. Obviously QM works, but we don't physically see the superposition that makes it work any more than we could, were B.I. correct, see the position & momentum of a particle. I don't know if it is possible to derive the same experimental data with B.I. or modifications thereof - if not, you're of course right. But then I would have thought B.I. would have been "disproved" rather than "discredited". Surely no-one's hammered that last nail yet?

We observe superpositions in laboratory experiments, even with today thecnology we van create superposition of big systems (e.g. macromolecules) during some instants and see like are destroyed by decoherence.

We see the effects of superposition and are able to predict them using the maths that, as far as I can tell, have largely been advised by such observations. Maybe I'm out of date (I've been reading Feynman Lectures vol. III where he discusses the math of QM and repeats often "We don't know why it is like this, but it is"). But the results of experiments such as diffraction experiments that are explained by superposition can presumable be explained by B.I. And decoherence in B.I. would presumably be due to the quantum potential of whatever is causing the decoherence effecting the particle(s) under observation. In fact, such experiments are the examples used in explaining B.I. that I have read (and yield very pretty diagrams, btw).

What is not observed are macroscopic superpositions, and this is the problem of incompatibility of QM with macroscopic phenomena.

Must be wrong then.

 

[HallsofIvy]

In science, a theory is a proved scientific hyphotesis. A scientific hyphotesis is any hyphotesis that can be falsified by scientific method.

Then you are saying that there are no theories in science! NO scientific hypothesis (or theory) can be proven- they can only be disproven.

 

[Juan R.]

I'm not saying B.I. (henceforth) is proven or even provable - I'm just saying that the notion that if something cannot be directly observed it cannot be said to exist is a philosophy of an alternative interpretation of QM.

Science is about things that can be detected/measured. Bohm is metaphysics.

Again, all physical intepretations of QM that I've heard of are like this. I think that attitude is a little harsh. B.I. does attempt to explain observable phenomena - dancing/singing pink elephants beyond the observable universe does not. Funny, but not comparable. And now I have that tune stuck in my head. Below-the-belt tactics on your part, I think.

I do not think so.

True, that was kind of an argument twice removed. The de Broglie wave (also for a single particle) is intepreted as the pilot wave (in fact, I'm sure I read that this was the direction de Broglie himself was headed), and the de Broglie wave is the wave function of a free particle. I was using words interchangeably.

Pilot wave does not work for multiparticle states.

To my knowledge, the QM formulation generally used day-to-day is not relativistic. I only know this from other threads where newbies like myself were trying to mix SR and QM - the standard answer was "QM is non-SR". I know next to nothing about relativistic QM, but would I be right in saying this is something outside standard QM?

Relativistic QFT is based in QM combined with SR (at least partially). Bohm theory ignores relativity.

Exactly. Key word being computed. Obviously QM works, but we don't physically see the superposition that makes it work any more than we could, were B.I. correct, see the position & momentum of a particle. I don't know if it is possible to derive the same experimental data with B.I. or modifications thereof - if not, you're of course right. But then I would have thought B.I. would have been "disproved" rather than "discredited". Surely no-one's hammered that last nail yet?

Well, We "see" it. Bohm potential is unobservable.

QM is not applicable to macrocosmos.

 

[Juan R.]

Then you are saying that there are no theories in science! NO scientific hypothesis (or theory) can be proven- they can only be disproven.

No i did not say that!

 

[El Hombre Invisible]

Science is about things that can be detected/measured. Bohm is metaphysics.

Then the graviton is equally discredited, as is the Higgs boson, and, in fact, even the electron, proton, all quarks, gluons, virtual particles... As per the copenhagen intepretation, none of these can be said to actually exist. All that can be said is the experimental apparatus appears to change as if these particles exist. Everything concerned with such particles is a model, and the physicality of these models is inferred. Experiments tell you about nothing other than the experimental apparatus. Mathematical models tell you nothing other than how to predict the outcomes observed in this apparatus. All physical descriptions are philosophical.

Relativistic QFT is based in QM combined with SR (at least partially). Bohm theory ignores relativity.

Yes, but STANDARD QM is non-SR. That does not 'discredit' it, it just places a limit on its accuracy in certain applications.

Well, We "see" it. Bohm potential is unobservable.

Wavefunctions are unobservable too. In both cases, the effects of them are observable.

QM is not applicable to macrocosmos.

Well, how 'macro' are you talking? Very large molecules have been observed to exhibit quantum properties. When does QM stop being applicable? Have you found the elusive cut-off point?

 

[Juan R.]

Then the graviton is equally discredited, as is the Higgs boson, and, in fact, even the electron, proton, all quarks, gluons, virtual particles... As per the copenhagen intepretation, none of these can be said to actually exist. All that can be said is the experimental apparatus appears to change as if these particles exist. Everything concerned with such particles is a model, and the physicality of these models is inferred. Experiments tell you about nothing other than the experimental apparatus. Mathematical models tell you nothing other than how to predict the outcomes observed in this apparatus. All physical descriptions are philosophical.

Electrons, protons etc. are detected. Quarks are not and some people doubt of its existence. Even Gell-Mann initially claimed that quarks were not real precisely because cannot be isolated. The Higgs has been not measured and, therefore, is just a hypothesis (scientific one because can be falsified).

Virtual particles are presuntely detected -indirectly- and the graviton, yes it is a hyphotesis. Scientific one? Some people, like Nobel Prize Dyson, claims that gravitons cannot be detected and, therefore, do not exist for physicists. For Dyson, the supposed existence of gravitons is a non scientific hypothesis.

Need of experimental proof is the reason for searching Black holes and, also, for searching gravitational waves, and for extra dimensions, etc. In fact, if experimental proof/detectio/measure were unnecessary, nobody would waste his/her time on costly experiments for detecting the Higgs, or the gravitational waves predicted by GR but undetected still.

Yes, but STANDARD QM is non-SR. That does not 'discredit' it, it just places a limit on its accuracy in certain applications.

Yes I agree, but Bohm theory is incompatible with SR and, therefore, nobody has constructed a version of Bohm theory explaining relativistic quantum effects.

Wavefunctions are unobservable too. In both cases, the effects of them are observable.

Well I partially agree. "Wavefunctions" -really the norm- are observed from maps of electronic density in some simple cases. The problem of Bohm is that introduce more unobserved things for obtaining a poor result that with standard quantum theory. Moreover do not forget the very important fact that wavefuntions have more mathematical than physical sense in standard interpretation of QM. None textbook on QM will attempt to convince to you that |1s> orbital of Hydrogen atom is a real wave in an "EM sense", only norm <1s|1s> derived from it and observables (e.g. energy) have full physical sense. However, Bohm claims full physical sense for his postulated unobserved (and impossible to be observed) things.

Well, how 'macro' are you talking? Very large molecules have been observed to exhibit quantum properties. When does QM stop being applicable? Have you found the elusive cut-off point?

Nobody can reply with certainty this still but the decoherence time is a good parameter for the transition quantum/classical.

Note that a C2H2 molecule is already big enough

 

[El Hombre Invisible]

Electrons, protons etc. are detected.

Electrons, protons, etc. are detected indirectly. Mathematical models are based on their existence and properties that yield the correct experimental results. That is as far as they are detected, hence my reference to the Copenhagen interpretation; that is, an electron cannot be said to exist, but the results of a particular experimental set-up can be predicted on the basis that such postulated objects have properties described by the model. Likewise, the Bohm potential cannot be directly detected, but the formulation underlying it, i.e. wave mechanics, can predict experimental results. You can have a mathematical concept of an electron and, if you prefer, refer to this rather than the physical concept. Likewise you have wave mechanics and can (and do) refer to this rather than any physical interpretation. But if you WANT a physical interpretation you have to accept that it is just that - an interpretation.

Quarks are not and some people doubt of its existence. Even Gell-Mann initially claimed that quarks were not real precisely because cannot be isolated.

And do you consider quarks discredited based on their undetectability?

The Higgs has been not measured and, therefore, is just a hypothesis (scientific one because can be falsified).

Any physical intepretation of QM is only as falsifiable as the mathematical model underlying it, as long as the interpretation is consistent with that model. The exact position and momentum of particles is not necessarily inconsistent with QM so long as the apparent manifestation of uncertainty is consistent. The maths doesn't care why the HUP holds, only that it does. The apparent uncertainty in the Bohm model is explained by the effects of the quantum potential, both the potential of the particle itself and its environment.

Virtual particles are presuntely detected -indirectly- and the graviton, yes it is a hyphotesis. Scientific one? Some people, like Nobel Prize Dyson, claims that gravitons cannot be detected and, therefore, do not exist for physicists. For Dyson, the supposed existence of gravitons is a non scientific hypothesis.

But, again, not discredited. Virtual particles cannot be detected. Experiments can, however, confirm the predictions of formulations based on their existence.

Yes I agree, but Bohm theory is incompatible with SR and, therefore, nobody has constructed a version of Bohm theory explaining relativistic quantum effects.

But prior to the formulation of relativistic QM, would you deem QM discredited? Again, the Bohm interpretation is a physical intepretation of QM (or not). If it is in any way inconsistent then it must be modified or abandoned.

It took a good few stabs to get a quantum model of conductivity established. Would you sound the death knell for QM of matter after Pauli's electron gas theory was found to be flawed? No - physics is a process.

However, Bohm claims full physical sense for his postulated unobserved (and impossible to be observed) things.

The quantum potential? But this is a physical interpretation of the wave function. What are you saying? That ANY physical interpretation of QM is invalid on the basis that the wavefunction is not observable? I don't get why you insist that the wavefunction is plausible but a physical interpretation of it is not because it cannot be observed. Especially since you're comfortable with electrons, etc. Everything is observed by its impact on experimental apparatus.

Note that a C2H2 molecule is already big enough

Larger molecules than that have exhibited QM effects. The buckyball, for one.

 

[Juan R.]

Electrons, protons, etc. are detected indirectly. Mathematical models are based on their existence and properties that yield the correct experimental results. That is as far as they are detected, hence my reference to the Copenhagen interpretation; that is, an electron cannot be said to exist, but the results of a particular experimental set-up can be predicted on the basis that such postulated objects have properties described by the model. Likewise, the Bohm potential cannot be directly detected, but the formulation underlying it, i.e. wave mechanics, can predict experimental results. You can have a mathematical concept of an electron and, if you prefer, refer to this rather than the physical concept. Likewise you have wave mechanics and can (and do) refer to this rather than any physical interpretation. But if you WANT a physical interpretation you have to accept that it is just that - an interpretation.

Everything is detected indirectly. Even when i am reading now your post i am detecting words indirectly due to light between the monitor and my eyes.

I think that are confusing ontological concept of existence with epistemological one. Electron exists in science.

Bohm theory is based in things cannot be detected either direct or indirectly. This is one of reasons why Bohm theory is not popular between physicists. It is not more physical than standard QM.

And do you consider quarks discredited based on their undetectability?

I am saying that evidence of quarks are real particles is not the same that for electrons. In fact, there is no isolated quarks like there is other isolated particles.

Any physical intepretation of QM is only as falsifiable as the mathematical model underlying it, as long as the interpretation is consistent with that model. The exact position and momentum of particles is not necessarily inconsistent with QM so long as the apparent manifestation of uncertainty is consistent. The maths doesn't care why the HUP holds, only that it does. The apparent uncertainty in the Bohm model is explained by the effects of the quantum potential, both the potential of the particle itself and its environment.

I think that you are mistaken about Bohm theory. Bohm theory is childish in many ways. QM says that there is not such one thing like exact position and momentum togheter. This is verified by experience. Then, obviously Bohm cannot say that there is such one thing like measured exact position and momentum. He say that there is such one thing like hidden exact position and momentum, therefore that hypotesis cannot be experimentally verified (Therein hidden).

Then, the basic question (that Bohm and others ignore) is if it cannot be detected and the supposed deterministic underlying formulation cannot be detected by anyway, how do you prove that it exists?

You words are a reflect of an incorrect epistemological attitude

You talk of "aparent uncertainty" but talk of "Bohm quantum potential". The problem is that uncertainty is detected experimentally but Bohm potential and guiding waves and hidden variables cannot be detected anyway.

From experiments one may talk of uncertainty (measured) and "apparent Bohm potential" (newer measured) since there is not direct or indirect proof of its existence. Moreover, the best theoretical interpretation of Bohm potential was given by Bohm (1980)

rather strange and arbitrary

Moreover, i do not know like Bohm explains that crucial step from pure determinism to QM probabilities. Do you know? Average over ignorance? When properly interpreted, that does not work in statistical mechanics (coarse grained is very popular from a practical point of view but is inconsistent when difficult questions are asked doing that still today nobody has shown like probabilities of SM arise from a deterministic asumed formulation: ergodic hyphotesis and all that is incorrect) and one obtains the same problem in Bohm theory. Since that variables are hidden Bohm asumes an initial distribution that when averaged on it is "compatible" with experimental results.

But, again, not discredited. Virtual particles cannot be detected. Experiments can, however, confirm the predictions of formulations based on their existence.

Again incorrect, if Dyson is correct, then any scientific theory of gravitons is useless. He already explained that and said (last year?) that if really gravitons cannot be observed then string theory is an useless theory since that cannot provide experimental predictions that can be different from others theories without gravitons. If Dyson is correct, the gravitons will be discredited.

But prior to the formulation of relativistic QM, would you deem QM discredited? Again, the Bohm interpretation is a physical intepretation of QM (or not). If it is in any way inconsistent then it must be modified or abandoned.

No you are wrong here. Bohm theory is not a physical interpretation of QM. See http://arxiv.org/abs/quant-ph/0206196.

Moreover, people reject Bohm formulation like a substitute to QM because incompatibilities with SR. Non-relativistic QM is not incompatible with SR, thereis it was generalized to relativistic domain. But nobody has formulated a consistent relativistic Bohm theory.

The quantum potential? But this is a physical interpretation of the wave function. What are you saying? That ANY physical interpretation of QM is invalid on the basis that the wavefunction is not observable? I don't get why you insist that the wavefunction is plausible but a physical interpretation of it is not because it cannot be observed. Especially since you're comfortable with electrons, etc. Everything is observed by its impact on experimental apparatus.

I am saying that "Hidden variables" mean hidden. As already explained the wavefunction is not physically interpreted in QM. Take a textbook.

But Bohm claims that his theory is purely physical one, even when "hidden things" cannot NEWER be measured.

Larger molecules than that have exhibited QM effects. The buckyball, for one.

Hum i think that you are wrong. In the proper definition of buckyball there is classical description. Are you confounding the full molecule with his electronic structure?

Let me a question. Chemical reactions are not deterministic. The chemical forces are thus.

F_total = F_determ + F_random

Now you claims that universe is determinist

F_total = F'_determ

How do you demonstrate it?

 

[El Hombre Invisible]

I can't understand everything in your response because of typos and grammatical weirdness so forgive me if I don't reply to all your points.

Everything is detected indirectly.

So that's direct observation out of the question.

Even when i am reading now your post i am detecting words indirectly due to light between the monitor and my eyes.

Are you? How do you know the light was "between" the monitor and your eyes. All you can say is your eyes are detecting light emitted by your monitor. Anything in between is speculation.

I think that are confusing ontological concept of existence with epistemological one. Electron exists in science.

Not at all, I'm trying to make your argument stick to well accepted notions. The criteria you cite for dismissing the Bohm intepretation would also render other notions dead that clearly aren't. All I'm saying is that everything should be judged bu the same criteria.

Bohm theory is based in things cannot be detected either direct or indirectly. This is one of reasons why Bohm theory is not popular between physicists. It is not more physical than standard QM.

I am saying that evidence of quarks are real particles is not the same that for electrons. In fact, there is no isolated quarks like there is other isolated particles.

My question, Juan, was: is the inability to observe a quark grounds the dismiss it?

I think that you are mistaken about Bohm theory. Bohm theory is childish in many ways. QM says that there is not such one thing like exact position and momentum togheter. This is verified by experience. Then, obviously Bohm cannot say that there is such one thing like measured exact position and momentum.

This is a bogus argument. The manifestation of uncertainty in position and momentum is observed. Does this mean the particle HAS no exact position or momentum, or does it mean that no precise position or momentum can be OBSERVED? One does not mean the other. Uncertainty in position and momentum is explained in the Bohm interpretation, while the actual position and momentum themselves are precise. The reason why position and momentum cannot be known together is not a physical one - it is a mathematical one. The wave model of a particle with precise momentum is infinite in space along the direction of momentum. The wave model of a particle with precise position is a superposition of an infinite number of deBroglie waves. This does not itself rule out the particle having a physical exact position and momentum - it speaks only for the model.

He say that there is such one thing like hidden exact position and momentum, therefore that hypotesis cannot be experimentally verified (Therein hidden).

I find a huge contradiction in this argument as a whole. You tell me the Bohm interpretation cannot be experimentally verified then, to prove it is wrong, you link a paper recording the results of an experiment to test the Bohm interpretation against standard QM. Either the B.I. can be experimental verified or that experiment means nothing. One part of your argument is wrong.

Then, the basic question (that Bohm and others ignore) is if it cannot be detected and the supposed deterministic underlying formulation cannot be detected by anyway, how do you prove that it exists?

Let me use an analogy - the electromagnetic field. What was that? It was a hypothesised physical thing that emanated from charged particles so that the field of one charge can act directly on the other charge itself without the two meeting. So what was being observed here? Not the field, but the effects of the proximity of one charge to another - i.e. motion due to that proximity. The electric field could not be directly observed. Even fluctuations in it could not be seen directly, only their hypothesised existence correlated to the supposed effects on electrons in measuring apparatus (such as eyes). Now replace electric field with quantum potential. Likewise, the quantum potential itself cannot be observed. Nonetheless, the Bohm interpretation does tell us that the potential of one particle will act on the other, so there will be an observable difference between an electron passing through a double-slit untouched and one doing so in the presence of a light source. The difference, of course, is that the results of this experiment were known and predictable before the Bohm interpretation existed - i.e. the mechanics of QM were well known before anyone postulated why they were as they were - while the postulate of the electric field was less after the fact. What lended credance to the electric field hypothesis was the success with experimental verification. In the case of the Bohm interpretation, the experimental predictions can be made without it - we have the mathematical (non-physical) model and know it works. By your argument, while the mathematical model of an electric field (like QM) was obviously successful, the physical notion of a field should have been discredit based on its invisibility. This wasn't the case - the model was overthrown by experimental observation, not the fact that the field was hidden.

You talk of "aparent uncertainty" but talk of "Bohm quantum potential". The problem is that uncertainty is detected experimentally but Bohm potential and guiding waves and hidden variables cannot be detected anyway.

Okay, let's make a crowbar separation between the potential/pilot wave and the position/momentum of the particle. The reason being is that, if you start by accepting the Bohm interpretation, the potential IS observed by its correlation to the wavefunction of the particle, that is - observed to kind of the same extent as the electric field, for instance. That's the whole point - it's supposed to be a physical interpretation of the wave nature of matter as described by the wave function. The position/momentum thing IS hidden, as far as I understand, whatever happens. It can only be infered from accepting the Bohm intepretation, just like the fact that the gluon carries colour charge can only be infered from accepting QCD - that is, the only reason they must be accepted is that the model breaks down without their inclusion. They're both products not of observation, but of necessity for the success of the model.

Again incorrect, if Dyson is correct, then any scientific theory of gravitons is useless. He already explained that and said (last year?) that if really gravitons cannot be observed then string theory is an useless theory since that cannot provide experimental predictions that can be different from others theories without gravitons. If Dyson is correct, the gravitons will be discredited.

There's two things here. There's the graviton as a mathematical model to explain gravity on the quantum scale, and there's the physicality of the graviton, i.e. the physical interpretation of the graviton as a particle. What is being argued against here is the mathematical graviton as something that does not add anything to the ability to predict and analysis observations. What you are dismissing in the Bohm intepretation is (what is supposed to be) a physical intepretation of an already-existing and accepted mathematical model. Two different things. The graviton would be accepted if the mathematical model of it was subject to experimental verification. You still won't be able to 'see' a graviton any more than you may see the Bohm potential. All that matters is that it works, experimentally. The Bohm interpretation may not work as a physical interpretation of QM, like I said earlier, in which case it must be AMENDED or DISCARDED.

No you are wrong here. Bohm theory is not a physical interpretation of QM. See http://arxiv.org/abs/quant-ph/0206196.

Okay, what I meant was "an attempt at a physical intepretation of QM." This just goes back to what I said a few posts ago: if the physical model does not fully correspond to QM, it must be amended or discarded. Discrepancies between theory and evidence does not necessarily lead to the instant dismissal of that theory, though. Like I said, QM was not abandoned just because Pauli's electron gas model didn't fully work - you just fix it (if possible).

Moreover, people reject Bohm formulation like a substitute to QM because incompatibilities with SR. Non-relativistic QM is not incompatible with SR

I thought it was.

thereis it was generalized to relativistic domain. But nobody has formulated a consistent relativistic Bohm theory.

And up until the advent of relativistic QM, nobody had formulated it. Do you not see what I'm getting at here? There was a long period when QM and SR were incompatible. This did not mean QM had to be abandoned. The Bohm intepretation and SR are incompatible. Why does this mean the Bohm interpretation must be abandoned, rather than just formulating an SR-consistent Bohm model? Note, QM now is not consistent with GR, hence the postulated graviton. Don't see anyone abandoning QM on that basis.

I am saying that "Hidden variables" mean hidden. As already explained the wavefunction is not physically interpreted in QM. Take a textbook.

Don't need to. I have never said the wavefunction is physically explained in QM. You just keep telling me it's not. You're arguing against yourself. That's just crazy.

In the proper definition of buckyball there is classical description. Are you confounding the full molecule with his electronic structure?

Nope, the molecule itself has been diffracted. You'll have no trouble finding articles on it.

Now you claims that universe is determinist

No, I don't. I never said that.

 

[Juan R.]

I can't understand everything in your response because of typos and grammatical weirdness so forgive me if I don't reply to all your points.

You are open to ask

So that's direct observation out of the question.

Always. One thing is the epistemological level (science) and other is the ontological one (phylosophy). QM works at epistemological level. Bohm theory works at the ontological level, asuming the existence of an underlying structure which cannot be observed, either directly or indirectly, as already said. Bohm theory is strictly speaking metaphysics.

Are you? How do you know the light was "between" the monitor and your eyes. All you can say is your eyes are detecting light emitted by your monitor. Anything in between is speculation.

Speculation? The engineers of my GoldStar 17'' do not think the same

Not at all, I'm trying to make your argument stick to well accepted notions. The criteria you cite for dismissing the Bohm intepretation would also render other notions dead that clearly aren't. All I'm saying is that everything should be judged bu the same criteria.

Under the same criteria, QM is physics and Bohm theory is

artificial metaphysics

Pauli 1952.​

My question, Juan, was: is the inability to observe a quark grounds the dismiss it?

If you cannot detect quarks, the theoretical interpretation is not, rigorously speaking, sound. Quark theory explains several things, but how do you know that the mathematical concept of quark is just an illusion? This is the reason that Gell-Mann initially claimed that quarks was not real particles. Perhaps are strings or spacetime knoks or the collective behavior of underlying particles still to be discovered, etc.

It appears very probable that quarks are real. But today, in the limits of my knowledge, are not unambiguously detected.

This is a bogus argument. The manifestation of uncertainty in position and momentum is observed. Does this mean the particle HAS no exact position or momentum, or does it mean that no precise position or momentum can be OBSERVED? One does not mean the other. Uncertainty in position and momentum is explained in the Bohm interpretation, while the actual position and momentum themselves are precise. The reason why position and momentum cannot be known together is not a physical one - it is a mathematical one. The wave model of a particle with precise momentum is infinite in space along the direction of momentum. The wave model of a particle with precise position is a superposition of an infinite number of deBroglie waves. This does not itself rule out the particle having a physical exact position and momentum - it speaks only for the model.

Is the point!

The manifestation of uncertainty mean that position and momentum cannot be defined togheter due to complementarity, and this IS verified by experience. If you apply classical mechanics you fail.

You cannot claim that particle HAS exact position or momentum if you cannot measure it NEWER. Precisely, the main hipothesis of Bohm theory is that there is an underlyng dynamical structure is HIDDEN. But if is HIDDEN cannot be OBSERVED and if cannot be OBSERVED then does not exist for SCIENCE.

Again i remark that Bohm theory belongs to metaphysics

It is not true that uncertainty in position and momentum is explained in the Bohm interpretation from actual precise position and momentum.

Because 1) those supposed precise position and momentum are HIDDEN in the "real" world accesible to science -belonging just to a world of "ideas"-. 2) Bohm does not explain how probabilities arise from an underlying deterministic HIDDEN structure.

The reason why position and momentum cannot be known together IS physical one. It is the principle of complementarity.

I think that you are again confusing epistemological with ontological models. You claim that QM is a model and that particles have both momentum and position. Well, the only "alternative" model of REALITY that I know is Bohm theory which claims that position and momentum are precise definite values BUT cannot be measured, even in principle! Then Bohm cannot shows that those precise values EXIST. It is just a phylosophical model.

You appears interested in substituting a well-proven physical model of reality by a methaphysical one, which, moreover, is less sucessful than QM for laboratory predictions.

I find a huge contradiction in this argument as a whole. You tell me the Bohm interpretation cannot be experimentally verified then, to prove it is wrong, you link a paper recording the results of an experiment to test the Bohm interpretation against standard QM. Either the B.I. can be experimental verified or that experiment means nothing. One part of your argument is wrong.

I think that "Wrong" is not the correct word at least in a first insight; "metaphysical" is more accurate.

The contradiction is just in your head.

QM says A = 2 p

where p is a probability.

Bohm says that there are not real probabilities and that p = 96 X where X is a hidden variable that cannot be detected/measured even in principle.

If you cannot experimentally verify p is 96 X because X is HIDDEN (perhaps is p = 34564576598705938567457 B where B is a hidden temperature ), then you cannot test Bohm theory (nor my theory about hidden temperatures), just QM which says what is p.

Let me use an analogy - the electromagnetic field. What was that? It was a hypothesised physical thing that emanated from charged particles so that the field of one charge can act directly on the other charge itself without the two meeting. So what was being observed here? Not the field, but the effects of the proximity of one charge to another - i.e. motion due to that proximity. The electric field could not be directly observed. Even fluctuations in it could not be seen directly, only their hypothesised existence correlated to the supposed effects on electrons in measuring apparatus (such as eyes). Now replace electric field with quantum potential. Likewise, the quantum potential itself cannot be observed. Nonetheless, the Bohm interpretation does tell us that the potential of one particle will act on the other, so there will be an observable difference between an electron passing through a double-slit untouched and one doing so in the presence of a light source. The difference, of course, is that the results of this experiment were known and predictable before the Bohm interpretation existed - i.e. the mechanics of QM were well known before anyone postulated why they were as they were - while the postulate of the electric field was less after the fact. What lended credance to the electric field hypothesis was the success with experimental verification. In the case of the Bohm interpretation, the experimental predictions can be made without it - we have the mathematical (non-physical) model and know it works. By your argument, while the mathematical model of an electric field (like QM) was obviously successful, the physical notion of a field should have been discredit based on its invisibility. This wasn't the case - the model was overthrown by experimental observation, not the fact that the field was hidden.

But 1) EM fields can be indirectly measured in some situations. For example in absence of magnetic effects

E = (1/e) dp/dt

from Lorentz force. Both e and dp/dt can be measured.

2) Precisely many authors reject the existence of fields. There are EM theories without fields, for example Feynman/Wheeler one. Really fields are not eliminated. Instead of being real physical objects by themselves, the fields in the FW formulation are identities arising from particle trajectories.

3) The quantum potential is different. In FW formulation of EM, fields are functions of particle trajectories, which are observable

E = E(x y z)

In Bohm theory, the Quantum potential is function of unobserved things and does not appear to be very convenient even ignoring nonlinearities nonlocality, etc. Precisely some modern schools of Bohm theory (so called Bohmian school) say that is an unuseful artifact. For example D. Dürr, et al claim that the quantum potential may be ignored.

You have a very wrong conception of physical and mathematical models. QM is not a mathematical model and Bohm interpretation physical one.

Precisely is the inverse status. QM is physical (is a part of physics), and Bohm theory is methaphysical -or even if you prefer mathematical- model because has no link with measured reality.

Okay, let's make a crowbar separation between the potential/pilot wave and the position/momentum of the particle. The reason being is that, if you start by accepting the Bohm interpretation, the potential IS observed by its correlation to the wavefunction of the particle, that is - observed to kind of the same extent as the electric field, for instance. That's the whole point - it's supposed to be a physical interpretation of the wave nature of matter as described by the wave function. The position/momentum thing IS hidden, as far as I understand, whatever happens. It can only be infered from accepting the Bohm intepretation, just like the fact that the gluon carries colour charge can only be infered from accepting QCD - that is, the only reason they must be accepted is that the model breaks down without their inclusion. They're both products not of observation, but of necessity for the success of the model.

No, the potential is NOT observed, therefore is avoided by modern Bohmian School. No, it is not a physical interpretation because is based in unphysical postulates. Bohm model is not sucessful and QCD is not based in hidden variables.

There's two things here. There's the graviton as a mathematical model to explain gravity on the quantum scale, and there's the physicality of the graviton, i.e. the physical interpretation of the graviton as a particle. What is being argued against here is the mathematical graviton as something that does not add anything to the ability to predict and analysis observations. What you are dismissing in the Bohm intepretation is (what is supposed to be) a physical intepretation of an already-existing and accepted mathematical model. Two different things. The graviton would be accepted if the mathematical model of it was subject to experimental verification. You still won't be able to 'see' a graviton any more than you may see the Bohm potential. All that matters is that it works, experimentally. The Bohm interpretation may not work as a physical interpretation of QM, like I said earlier, in which case it must be AMENDED or DISCARDED.

Well, as brilliantly explained by Dyson, there are reasons for believing that graviton cannot be detected then the term quantum gravity is useless. I think that you are ignoring this very important point of Dyson discussion. Wthout posibility for detecting quantums of gravity there is no posibility for testing different versions of quantum gravity theories. Then Dyson claim there is not physical reason for formulating a quantum theory of gravity based in gravitons.

What you are dismissing in the Bohm interpretation is that is NOT a physical interpretation of an already-existing and accepted mathematical model.

QM is a theoretical model, is not just math. And Bohm theory is not a physical model is a metaphysical model.

Okay, what I meant was "an attempt at a physical intepretation of QM." This just goes back to what I said a few posts ago: if the physical model does not fully correspond to QM, it must be amended or discarded. Discrepancies between theory and evidence does not necessarily lead to the instant dismissal of that theory, though. Like I said, QM was not abandoned just because Pauli's electron gas model didn't fully work - you just fix it (if possible).

The physical interpretation of QM is just the standard one. Read a book!

There is no reason for doing not search a better physical intepretation but Bohm methaphysical one is not suitable like a substitute. This is reason that is rejected by almost all physicists.

I thought it was.

No it is not, because there is not direct contradiction between SR for low velocities (reduces to Newtonian mechanics) and non relativistic QM (e.g correspondence principle). Non relativistic QM is not applicable to high velocities and this is reason that exists a relativistic quantum theory. However nobody has formulated still a consistent relativistic generalization of Bohm theory precisely due to his strong incompatibility with SR.

And up until the advent of relativistic QM, nobody had formulated it. Do you not see what I'm getting at here? There was a long period when QM and SR were incompatible. This did not mean QM had to be abandoned. The Bohm intepretation and SR are incompatible. Why does this mean the Bohm interpretation must be abandoned, rather than just formulating an SR-consistent Bohm model? Note, QM now is not consistent with GR, hence the postulated graviton. Don't see anyone abandoning QM on that basis.

First part already replied. Second part:

It is not true that QM is not consistent with GR. QM applies to some problems and GR to others. That people is doing is searching an extended theory that can be applied to both sides there in the name quantum gravity (QG).

QG = quantum mechanics + gravity

You are very wrong in epistemological issues. QM does not need to be abandoned because any realistic QG theory may reduce to standard QM when G constant ---> 0.

Don't need to. I have never said the wavefunction is physically explained in QM. You just keep telling me it's not. You're arguing against yourself. That's just crazy.

No. i am not arguing myself. The wavefunction has no direct physical sense but indirect one as ALREADY explained -if you prefer we can talk about rays in Hilbert space-. Therefore, there is no problem with usual interpretation beyond usual ones of measurement problem. However, Bohm theory claim full physical sense for hidden variables, potential, etc. This is the reason that is not seriously taken.

Nope, the molecule itself has been diffracted. You'll have no trouble finding articles on it.

I think that you do not know that a molecule is. Precisely, the nuclear framework of the molecule cannot be purely quantum because then there is not molecule just a bundle of atoms.

No, I don't. I never said that.

 

[El Hombre Invisible]

I'm not going to respond point-by-point; if I did, these posts will just get larger and larger. I'll just categorise my points instead.

On my beliefs: I (personally) do not believe a particle has an exact position and momentum. BOHM believes this. I am not he. He is not me. Furthermore, I do not subscribe to the Bohm model, so your argument:

You appears interested in substituting a well-proven physical model of reality by a methaphysical one, which, moreover, is less sucessful than QM for laboratory predictions.

is bogus. My argument is not that Bohm is correct, but that the criteria you cite for its failure would also spell doom for other theories.

Your main argument is that position and momentum are unobservable due to being hidden, and this makes it metaphysics. You seem to agree there are other variables in other physical models that are similarly unobservable, but you do not seem to notice the dual standards you're applying as a consequence. I guess I cannot spell it out any clearer.

Also, I think you are confused about my usage of the words 'physical' and 'mathematics'. You seem take take them to mean schools of thought, which they do, but that's not what I meant. I don't mean 'part of physics', I mean 'has physicality'. The afore-mentioned electric field was a 'physical' explanation for the physics it sought to give physicality - however, while the notion of the physical field may have been incorrect, the physics were not. You see?

None of which makes any difference when you notice the fact that on the one hand you are dismissing the Bohm model as being metaphysics due to its untestability, then on the other you link a paper testing it against standard QM. ?

As for Bohm not being compatible with SR, I can't spell it out any clearer. You keep saying relativistic QM IS SR-compatible but don't seem to get that someone had to formulate it from a non-SR-compatible theory. Bohm is inherently non-SR. That's kind of the point - it is a non-local theory. I don't know much (well, anything really) about QFT, but I thought the EPR argument still held.

As for this:

I think that you do not know that a molecule is. Precisely, the nuclear framework of the molecule cannot be purely quantum because then there is not molecule just a bundle of atoms.

I can only say... wha? You stated that QM is not applicable to anything bigger than C2H2. The buckyball is waaaaay bigger than this, and diffraction experiments have been carried out with a positive thumbs up for QM effects. I can only assume you've changed the argument somewhere along the line.

 

[Juan R.]

is bogus.

bogus? i remember you said. It was

The reason why position and momentum cannot be known together is not a physical one - it is a mathematical one.

Your main argument is that position and momentum are unobservable due to being hidden, and this makes it metaphysics.

Mine?

Even Einstein rejected Bohm mechanics.

Bohm theory is "artificial methaphysics" in own words of Pauli.

You seem to agree there are other variables in other physical models that are similarly unobservable, but you do not seem to notice the dual standards you're applying as a consequence.

Please explain when I applied a "dual standard". It is well known in this forum that i do not follow the standard field approach of EM, also is well known that i do not accept the spacetime curvature of GR because newer was measured. You may unknow my hot debates in the gravitation forum because i said that gravitational waves were no real even if GR predicts because had been still undetected. If tomorrow gravitational waves or gravitons are detected i will accept them.

Thanks by clarification of your own definition of the words 'physical' and 'mathematics'. However is not true that physics underlying the field concept is "correct". If were, people would not discuss "aberration" in the sci.physics.

None of which makes any difference when you notice the fact that on the one hand you are dismissing the Bohm model as being metaphysics due to its untestability, then on the other you link a paper testing it against standard QM. ?

Touché!...

No, wait a moment... You may unaware that there exist several versions of Bohm theory. Initially was claimed by the own Bohm that both theories would be equivalent. But recent work shows that are not always. Still there is different versions: one using Bohm potential, other do not using it and claiming that is unphysical, etc.

As for Bohm not being compatible with SR, I can't spell it out any clearer. You keep saying relativistic QM IS SR-compatible but don't seem to get that someone had to formulate it from a non-SR-compatible theory. Bohm is inherently non-SR. That's kind of the point - it is a non-local theory. I don't know much (well, anything really) about QFT, but I thought the EPR argument still held.

Bohm theory always has been claimed to be inherently incompatible with SR. This is well-known. I do not know any consistent relativistic generalization of Bohm theory today. But QM was not inherently incompatible with SR this is reason that relativistic quantum field theory can be obtained "easily". The problem of Bohm and relativity is not "EPR" or locality, it is more fundamental. Bohm does not know that position is. the problem is in what is x or x_op in a relativistic framework. Do you know what is the relativistic uncertainty relation for x?

I can only say... wha? You stated that QM is not applicable to anything bigger than C2H2. The buckyball is waaaaay bigger than this, and diffraction experiments have been carried out with a positive thumbs up for QM effects. I can only assume you've changed the argument somewhere along the line.

don't worry, I will explain to you slooowly.

QM (all) is not applicable to a (entire) molecule in his full sense in the same form how you cannot apply QM (all) to a cat.

In fact i do not know absolutely none application of full QM to molecules. Quantum chemists split molecules into two parts: electrons more nuclei. Electrons are studied via full QM. Nuclei are studied classically or semiclassically. Newer large molecules are studied using total QM because that does not work.

In fact, none pure quantum wave describes any full molecule higgher than C2H2. I only know pure electronic wavefunctions.

Handbook of molecular physics and quantum chemistry. Volume 1 Whiley 2003, p624.

in general, eigenstates of the full molecular Hamiltonian do not describe chemical species.

Emphasis is on the original.

Full QM do not apply to "large" molecules. Curiously molecules are described via canonical science.