Status of deBroglie-Bohm pilot wave theory

[zenith8]

Oh fantastic, I made a racey joke thinking you were male. This is what too little sleep gets you. *facepalm* I am truly sorry. As for the difference between SQM and deBB, I do undertand, although I think I've been arguing with people who have a perspective unlike yours in this area.

So no phone number then? Ah well..

You bring up the issue of seeing the atom with the naked eye, and here I have single decent rebuttal. Daniel Rugar at IBM continues to look at the magnetic fields of single electrons, and if you want to talk about something looking as predicted... wow. It really DOES appear to be clouds of probability in almost exactly the configuration expected. You can't have two lobes of an electron "field" in a model where electrons and atoms exist continually.

Attached is a picture of a calculated spin-dependent electron trajectory in a hydrogen 2p_x state (Colijn + Vrscay, Phys. Lett. A, 300, 334). Admire the nice double lobed structure..

You believe that marker belongs to deBB, and arguably you've done a better job in defending your position than I have mine.

Mmm... I love it when you say things like that..

 

[gmax137]

Well I appreciated the discussion above, having just read Bohm's biography "Infinite Potential." This book is certainly *not* a scientific biog or a history of Bohm's work, but it tries to describe his ideas in non mathematical terms. I was wondering about the current standing of his work & ideas, and here comes this thread !

As far as teaching Copenhagen vs Bohm, I didn't get as far in physics as you guys (switching to engineering after my bachelor's) but I don't think I heard about Bohm in my 3 or 4 undergrad classes on 'modern physics' / quantum mech. That was back in the early 1970s.

 

[zenith8]

As far as teaching Copenhagen vs Bohm, I didn't get as far in physics as you guys (switching to engineering after my bachelor's) but I don't think I heard about Bohm in my 3 or 4 undergrad classes on 'modern physics' / quantum mech. That was back in the early 1970s.

Back in the early 1970s it was illegal..

''In recent years the debate on these ideas has reopened, and there are some who question what they call 'the Copenhagen interpretation of quantum mechanics' - as if there existed more than one possible interpretation of quantum mechanics.'' [Rudolf Peierls, 1979]

 

[Frame Dragger]

So no phone number then? Ah well..


Attached is a picture of a calculated spin-dependent electron trajectory in a hydrogen 2p_x state (Colijn + Vrscay, Phys. Lett. A, 300, 334). Admire the nice double lobed structure..


Mmm... I love it when you say things like that..

*looks at picture of electron trajectories... curses*. Ok... On the bright side I feel I've gone a long way towards proving my point that I've done a poor job defending my position lol. So... this time I'm going to ask... Do the calculations that produced the double lobed structure predict a single lobed structure as well? Both were found in IBM's work, but I'm guessing of the dual lobe can be formulated, the single was as well.

You know, these unsolved issues in physics really can become dangerously annoying! On the bright side I've come out of this with less certainty in the state of SQM than I did coming in. I see that as a good thing, if not the most comfortable. I think I need to do a great deal more reading along the lines you've described. Maybe if I get an opposing reading list from Dr. Chinese I can REALLY experience some cognitive dissonance lol.

How that will turn out... who knows.

 

[Demystifier]

I think I need to do a great deal more reading along the lines you've described. Maybe if I get an opposing reading list from Dr. Chinese I can REALLY experience some cognitive dissonance lol.

If you need a neutral review of de Broglie-Bohm theory with both pro and contra arguments at one place, I recommend
http://xxx.lanl.gov/abs/quant-ph/0412119

 

[Frame Dragger]

If you need a neutral review of de Broglie-Bohm theory with both pro and contra arguments at one place, I recommend
http://xxx.lanl.gov/abs/quant-ph/0412119

Thank you very much Demystifier. I like the look of it already! Considering how I took a similarly harsh approach in your deBB thread, I appreciate the gesture as well.

 

[Dmitry67]

I think Interpretations form not a list, but rather a tree.

If we exclude "Shut up or calculate", and SM we have 2 groups: random/collapse (CI, TI + flavors) and deterministic/no collapse (dBB, MWI + flavors)

I think it would be useful to separate a choice of collapse/no collapse (based on the discussion of the measurement process and quantum decoherence) from much more granular choice (dBB vs MWI for example).

 

[Demystifier]

I think Interpretations form not a list, but rather a tree.

If we exclude "Shut up or calculate", and SM we have 2 groups: random/collapse (CI, TI + flavors) and deterministic/no collapse (dBB, MWI + flavors)

I think it would be useful to separate a choice of collapse/no collapse (based on the discussion of the measurement process and quantum decoherence) from much more granular choice (dBB vs MWI for example).

I like your idea of the branching structure of interpretations. I would like to add that before random vs deterministic branching, there is also reality vs no reality branching. According to no reality interpretations, quantum mechanics does not describe objective reality existing out there, but only the statistics of measurement outcomes.

 

[Dmitry67]

Hm... May be I am wrong, but isn't "quantum mechanics does not describe objective reality existing out there, but only the statistics of measurement outcomes" called a "macroscopic realism" ?

 

[Frame Dragger]

I don't know if dBB, as much as I remain unconvinced by it thus far (see previous post and my need to read), but it seems to be more than simply an interpretation of the consequences of decoherence. Zenith already made the case that deBB can be formulated as either deterministic or not, which is in a completely different league than MWI. It seems to be SQM interpreted as String Theories and Brane Cosmology, random collapse as you said such as The CI, and "Other" theories which don't accept that the mathematics of probabilistic distribution is reflected in nature as implied by the math alone (dBB). MWI, consistent Histories... these all strike me as metaphysical interpretations using the vast loopholes in current knowledge.

 

[Frame Dragger]

Hm... May be I am wrong, but isn't "quantum mechanics does not describe objective reality existing out there, but only the statistics of measurement outcomes" called a "macroscopic realism" ?

Yes, but that is for people who believe that SQM is a real description at any point. dBB formulates the effects of SQM in more Classical terms... well.. actually that's putting the cart before the horse, but you get my drift.

As an adherent of SQM I'd say that the notion that a threshold exists at which quantum effects give way to the macroscopic effects we percieve as reality presupposes that you DO accept SQM. dBB is a different description entirely.

 

[Demystifier]

Hm... May be I am wrong, but isn't "quantum mechanics does not describe objective reality existing out there, but only the statistics of measurement outcomes" called a "macroscopic realism" ?

I wouldn't say so. Some physicists think that objective reality does not exist at all, neither microscopic nor macroscopic. According to them, there are only observations (or only information) and nothing else. Such a view is close to solipsism, though they claim that it is not the same as solipsism.

 

[Frame Dragger]

I wouldn't say so. Some physicists think that objective reality does not exist at all, neither microscopic nor macroscopic. According to them, there are only observations (or only information) and nothing else. Such a view is close to solipsism, though they claim that it is not the same as solipsism.

Now that is not entirely fair. While some may believe that for lack of a creative or inquisitive spirit, I think many use the notion of "information" as a generalization. It's a bit misleading to take a militnantly mathematacal description and render it as metaphysics. The generally accepted view is that there is a threshold at which quantum interactions give way to the macrocosm we experience. It may be that quantum behaviour exists regardless of scale, but our ability to percieve it is limited by our scale relative to the observed interactions.

SQM has a bevy of theories to explain how "reality" emerges from the quantum world, but they are hardly complete. deBB and other Classicist theories obviously avoid some of those pitfalls, but at the cost of unverified assumptions... just like SQM. *sigh* that's a little annoying.

 

[zenith8]

I wouldn't say so. Some physicists think that objective reality does not exist at all, neither microscopic nor macroscopic. According to them, there are only observations (or only information) and nothing else. Such a view is close to solipsism, though they claim that it is not the same as solipsism.

Now that is not entirely fair. While some may believe that for lack of a creative or inquisitive spirit, I think many use the notion of "information" as a generalization. It's a bit misleading to take a militnantly mathematacal description and render it as metaphysics.

I'm afraid Demystifier is right, and it is entirely fair. Seriously, I've met many of these people. They really do believe that the universe consists of 'information'.

Even if you don't make 'information' part of the ontology, and you just say that QM is about information, you have to ask yourself:

* Information about what? \Psi somehow captures or contains information about, but does not directly describe, whatever is physically real. But then it should be possible to formulate the theory without even mentioning \Psi - which, after all, according to the theory, doesn't actually exist.

* How can the terms of a quantum superposition interfere with each other, producing an observable interference pattern, if such superpositions are just an expression of our ignorance? There is a whole field of experimental physics called 'matter wave optics' where the wave field is directly manipulated by essentially optical instruments, which is tricky if its just information.

* Why then does the very form of the Hamiltonian and wave function strongly point to a microscopic level of description. Why else \Psi(\bx_1,\bx_2,\ldots,\bx_N)? As de Broglie himself said at the 1927 Solvay conference: "It seems a little paradoxical to construct a configuration space with the coordinates of points that do not exist."

 

[Frame Dragger]

I'm afraid Demystifier is right, and it is entirely fair. Seriously, I've met many of these people. They really do believe that the universe consists of 'information'.

Even if you don't make 'information' part of the ontology, and you just say that QM is about information, you have to ask yourself:

* Information about what? \Psi somehow captures or contains information about, but does not directly describe, whatever is physically real. But then it should be possible to formulate the theory without even mentioning \Psi - which, after all, according to the theory, doesn't actually exist.

* How can the terms of a quantum superposition interfere with each other, producing an observable interference pattern, if such superpositions are just an expression of our ignorance? There is a whole field of experimental physics called 'matter wave optics' where the wave field is directly manipulated by essentially optical instruments, which is tricky if its just information.

* Why then does the very form of the Hamiltonian and wave function strongly point to a microscopic level of description. Why else \Psi(\bx_1,\bx_2,\ldots,\bx_N)? As de Broglie himself said at the 1927 Solvay conference: "It seems a little paradoxical to construct a configuration space with the coordinates of points that do not exist."

Well there are people who don't care to consider a world beyond mathematics, or believe that only a mathematical description of the world is valid, but there are people who like to shag sheep. Neither is really representative of the norm.

As for quantum superpositions being a result of the ignorance of the observer, that is the result of SQM being an incomplete theory. We don't ignore all of GR because at some points you find sigularities, do we? Well... some do, but thus far with little success compared to GR. It's also not quite fair to say that human ignorance = an interaction that isn't observed. There are very acceptable (in my view) models which allow for the propagation of influence in more than one direction in time. That's no more contrived than the assumptions made by SQM or deBB in my view. For each theory you are required to make assumptions, but SQM has been far more productive than any other theory at predicting and describing the behaviour of the microscopic world.

As for arguments that SQM seems unrealistic as in your examples regarding the generalizatin of "information", that can be easily explained by the notion that a theory doesn't have to make sense for it to work, and doesn't have to work for it to make sense. Now, you might say that deBB hasn't received a fair shake, or that 2-channel tests are mechanically biased against it, and while that's still impossible to confirm or refute, I just find the arguments used less appealing.

You said at one point that perception shapes thinking, and as the general perception is that of SQM, he general thinking should be as well to some degree or another. That thinking has produced a LOT more since de Broglie talked in 1927 than any of the Bohmian theories. If that is a simple result of academic infighting, so be it, and as I've said before SQM will fail to deliver and people will eventually move to alternate (or predecessing) theories. I think that before that happens the LHC will produce data that helps to confirm or modify the standard model and allow some form of unification with GR.

I have question for you; If quantum computations can be performed, even on a small scale in line with SQM's prediction of superpositioned states, then what would the reaction be from the Bohmian percpective?

 

[Dmitry67]

Well there are people who don't care to consider a world beyond mathematics, or believe that only a mathematical description of the world is valid, but there are people who like to shag sheep. Neither is really representative of the norm.

Max Tegmark should consider it as a personal insult :)
Me too :)

 

[Frame Dragger]

I wouldn't say so. Some physicists think that objective reality does not exist at all, neither microscopic nor macroscopic. According to them, there are only observations (or only information) and nothing else. Such a view is close to solipsism, though they claim that it is not the same as solipsism.

I've done some thinking on this, and I find the analogy with solopism a little off base. These are not people who believe that nothing outside of their own minds and experience exists. I think a lifetime of trimming variables and reductionistic thinking may make for less than stellar views on life, but not to the point of being a mental hermit.

In fact, I think any physicist who made a knowledgeable argument about the undertainty of objective reality would first have to question their subjective experiences. Solopism would stop you cold at that point, as nothing beyond that would matter, and objective reality and one's experiences would be all that exist. In fact, that same person would probably argue for the unreliablity of one's internal world above all else. Anyway, people with that kind of limited thinking aren't going to be forging new trails based on any theory. People without the curiosity to at least speculate as to what the possible real-world implications are of the equations being manipulated is a drudge. Maybe a really REALLY talented and intelligent drudge, but alas. That is only an argument against a particular mindset, and not the theory that spawns them.

 

[Frame Dragger]

Max Tegmark should consider it as a personal insult :)
Me too :)

What would you think of someone who viewed the world without even a rudimentary understanding of mathematics? Anyway, you apparanlty subscribe to the MWI, which is hardly a purely mathematical construct without any curiosity as to the nature of reality is it? Is someone playing the devil's advocate? ;)

EDIT: Is it just me, or do these inflated ontologies rely on the same arguments? I think the only reason dBB and SQM are still around is (they still fall in line with most experimental evidence) and they are doing roughly the same dance on the edge of Occam's Razor. It's not that one can't apply it to dBB, it's just that by dBB's (fair in this case) tu quoque argument renders SQM down to the same choppy mess. Very upsetting.

 

[Dmitry67]

What would you think of someone who viewed the world without even a rudimentary understanding of mathematics? Anyway, you apparanlty subscribe to the MWI, which is hardly a purely mathematical construct without any curiosity as to the nature of reality is it? Is someone playing the devil's advocate? ;)

MWI is in fact *the only* interpretation which is compatible with MUH (for that very reason Max Tegmark is a proponent of MWI) - as I discussed for example here:
https://www.physicsforums.com/showthread.php?t=365313
- other interpretations have some non-mathematical axioms ("word baggage" (c) Max Tegmark)

 

[Dmitry67]

Frame Dragger, I *do* believe that the TOE will look like

some_function(omnium) = 0

And all other properties (number of dimensions, particles, forces) will emerge from that equation. No words will be needed.

 

[Frame Dragger]

Frame Dragger, I *do* believe that the TOE will look like

some_function(omnium) = 0

And all other properties (number of dimensions, particles, forces) will emerge from that equation. No words will be needed.

I think that it's fair to say that a theory which purports to describe or refute objective reality in favour in infinite mathematical constructs as REAL has a lot of explaining to do... in words. We're human after all, and short of this being a divine insight (me=agnostic, so sarcasm) I'm unimpressed by one man's ability to believe that every mathematical construct exists. As for MWI, I see your point, but why bother with an attempt to describe an objective reality that is unreachable and indescribable?!

EDIT: Don't take this the wrong way, but to postulate that everything emerges from an infinite mathematical soup is as religious a statement as any devotee of creationism has uttered. There is no proof, and no hope of proof or benefit. From a phenomenological and human point of view Tegmark's view is borderline absurdist when it's not an expression of faith.

 

[Dmitry67]

MUH is a *HYPOTESIS*

So if it s right then it will be possible to write such equation and to get rid of the word baggage completely. It does not postulate "that everything emerges from an infinite mathematical soup". In such case it would be called MUA (Mathematical universe Axiom), not MUH.

Words can be useful to simplify the explanation. But if MUH is true they are just "pure labels without any meaning". MUH allows to get rid of all questions like "what is TRUE meaning of time?" or "what space consists of?" or "is curveed spacetime embedded or not?" and all similar questions. As soon as theories mathematically isomorphic they are the same. And most of these questions are as absurd as "what number 1 is made of?"

 

[Dmitry67]

But again, returning to the subject, BM is *not* compatible with MUH

 

[Frame Dragger]

MUH is a *HYPOTESIS*

So if it s right then it will be possible to write such equation and to get rid of the word baggage completely. It does not postulate "that everything emerges from an infinite mathematical soup". In such case it would be called MUA (Mathematical universe Axiom), not MUH.

Words can be useful to simplify the explanation. But if MUH is true they are just "pure labels without any meaning". MUH allows to get rid of all questions like "what is TRUE meaning of time?" or "what space consists of?" or "is curveed spacetime embedded or not?" and all similar questions. As soon as theories mathematically isomorphic they are the same. And most of these questions are as absurd as "what number 1 is made of?"

I suppose my primary objection is that the hypothesis is baseless expcept that to some people it appears elegant. In the way that SQM offends the sensabilities of many (Bohmians especially ;) ) I find these kind of hypothetical inflated ontologies... ponderous. I'm not trying to piss on your viewpoint, but I can't pretend to see it as anything but counteruintive and counterexperiential and experimental evidence!

I see the notion that people will find a "single equation to rule them all" if you'll pardon the reference, to be as likely as religious people seeing the face of god. In fact, it strikes me as perfectly analogous, except that smart people only are drawn to one of them (and I'm not talking about religion lol).

 

[Frame Dragger]

Oh, an MUH isn't a hypothesis, it's a conjecture. One might just say it's one man's fantasy, or a reflection of what one man's reality has become... and that propogated like a faith amongst a small and dedicated community. I alwise find that physics is a field full of cognitive dissonance, and the unique solutions to that most uncomfortable of states.

 

[Dmitry67]

I suppose my primary objection is that the hypothesis is baseless expcept that to some people it appears elegant.

It is not baseless.
Check Max arguments
http://arxiv.org/abs/arXiv:0704.0646
page 2.

I read the article 1.5y ago and I have to admit it was the most shoking thing I've read during the whole life, so 2 weeks after that I could think only about MUH.

I see the same trend everywhere: Universe is simple and elegant, and people are always try to drag some notions they got use to into the mathematical description: either, absolte time, "wavefunction collapse"... The history with the collapse is one of the most ridiculous: after almost 60 years with the collapse and endless discussions it was discovered that... collapse can be replaced by QM and is not required at all!

The same with "local realism" some people can't give up in parralel threads, or with these Newtonian billiard balls we all like (BM particles :) )..

And yes, MWI and MUH are both crazy enough, and MUH+MWI is so crazy that I sense a smell of truth, it is so crazy that it MUST be true.. Yes, it is lyrics, not physics, but we are discussing the interpretations here...

 

[Frame Dragger]

It is not baseless.
Check Max arguments
http://arxiv.org/abs/arXiv:0704.0646
page 2.

I read the article 1.5y ago and I have to admit it was the most shoking thing I've read during the whole life, so 2 weeks after that I could think only about MUH.

I see the same trend everywhere: Universe is simple and elegant, and people are always try to drag some notions they got use to into the mathematical description: either, absolte time, "wavefunction collapse"... The history with the collapse is one of the most ridiculous: after almost 60 years with the collapse and endless discussions it was discovered that... collapse can be replaced by QM and is not required at all!

The same with "local realism" some people can't give up in parralel threads, or with these Newtonian billiard balls we all like (BM particles :) )..

And yes, MWI and MUH are both crazy enough, and MUH+MWI is so crazy that I sense a smell of truth, it is so crazy that it MUST be true.. Yes, it is lyrics, not physics, but we are discussing the interpretations here...

First let me just say that I appreciate your sense of humour and spirited debate. I get what you're aiming at, in that MUH, MWI, TI, CI... etc... are all pretty ad hoc and messy. I don't necessarily expect elegance from the universe, but I wish that people were more willing to live with the discomfort of dissonance and accept that we have to forge ahead with anything as comforting as a truly useful conjecture or interpretation.

Collapse is absurd, but only if you believe that is the end of the story. MWI could be true, but then lots of things could be. Collapse is simple, if not elegant. F(ominium)=0 is a wonderful notion, but to me it seems less an attempt to interpret existing data, and more an attempt to justify one man's nearly autistic (not in the medical sense) world of math.

I've stated it before, that I believe wave-particle duality represents something neither wave nor particle, but a true duality. I don't think we'll have material with which to make a palatable conjecture until/unless SQM can be rectified (or another theory) with the predictions and experimental results of GR. Until then, it's fun, but ultimately of little consequence except insofar as Zenith's argument re: shaping perspective is valid.