Consensus about Non-Locality & Spacetime

[stglyde]

What's the present most popular consensus about non-locality and spacetime? Is it since the wave function is not something physical, there is nothing there in spacetime to be non-local about. So let's just extinguish the concept of physicality this means we just treat wave function and spacetime as just equations and don't try to have physical picture of it, and this thinking is enough to put it under the rug?

To get in the mood. The following is interesting stuff from March 2009 Scientific American article called "Was Einstein Wrong? Quantum Threat to Special Relativity":

And it is the wave function that lies at the heart of puzzles about the nonlocal effects of quantum mechanics. But what is it, exactly? Investigators of the foundations of physics are now vigorously debating that question. Is the wave function a concrete physical object, or is it something like a law of motion or an internal property of particles or a relation among spatial points? Or is it merely our current information about the particles? Or what?

Quantum-mechanical wave functions cannot be represented mathematically in anything smaller
than a mind-bogglingly high-dimensional space called a configuration space. If, as some argue,
wave functions need to be thought of as concrete physical objects, then we need to take seriously the idea that the world’s history plays itself out not in the three-dimensional space of our everyday experience or the four-dimensional spacetime of special relativity but rather this gigantic and unfamiliar configuration space, out of which the illusion of three-dimensionality somehow emerges. Our three-dimensional idea of locality would need to be understood as emergent as well. The nonlocality of quantum physics might be our window into this deeper level of reality.

 

[bohm2]

What's the present most popular consensus about non-locality and spacetime? Is it since the wave function is not something physical, there is nothing there in spacetime to be non-local about. So let's just extinguish the concept of physicality this means we just treat wave function and spacetime as just equations and don't try to have physical picture of it, and this thinking is enough to put it under the rug?

I never understood that. I mean, if we take that stance, then what do the equations refer to?

 

[Demystifier]

There is no consensus. Some argue that nature is nonlocal, while others argue it is local. For a very brief list of local interpretations see
https://www.physicsforums.com/blog.php?b=3622
which you can use for further googling.

 

[Demystifier]

I never understood that. I mean, if we take that stance, then what do the equations refer to?

Wave functions are, of course, "physical", but the question is whether they are ontological or merely epistemological. If they are only epistemological, then the ontological may or may not be local, depending on what the ontological, if anything, is.

For example, ontology may refer to hidden variables which describe only the observer and not the observed objects, in which case ontology may be local:
http://xxx.lanl.gov/abs/1112.2034

 

[Ken G]

I can't at present see any real difference between CI and the solipsistic hidden variables. Nikolic appears to associate the hidden variables as being part of the observer, but that is also what Bohr always said-- physics is what an observer can say about his/her surroundings, so what is unknown about physics is what is unknown about the observer. Perhaps Bohr felt it was unknowable, whereas Nikolic might attribute it to potentially knowable internal "hidden variables" in the observer, but the latter claim is so wholly unsubstantiated I cannot see any real difference. One superficial difference appears to be whether or not the existence of an "objective reality" is postulated, but all Bohr was doing was noting the fact that the word "objective" implies some kind of mutually agreed-on consistencies, which of course depend on the observers to be able to arrive at. Claiming that there's no such thing as an objective reality is thus the same thing as saying that we cannot know how the observer perceptions are altering that reality, which is also the same thing as saying that the variables needed to describe those perceptions are "hidden". Until someone can suggest a way to "unhide" those variables, I see no scientific difference at all.

 

[Demystifier]

I can't at present see any real difference between CI and the solipsistic hidden variables. Nikolic appears to associate the hidden variables as being part of the observer, but that is also what Bohr always said-- physics is what an observer can say about his/her surroundings, so what is unknown about physics is what is unknown about the observer. Perhaps Bohr felt it was unknowable, whereas Nikolic might attribute it to potentially knowable internal "hidden variables" in the observer, but the latter claim is so wholly unsubstantiated I cannot see any real difference. One superficial difference appears to be whether or not the existence of an "objective reality" is postulated, but all Bohr was doing was noting the fact that the word "objective" implies some kind of mutually agreed-on consistencies, which of course depend on the observers to be able to arrive at. Claiming that there's no such thing as an objective reality is thus the same thing as saying that we cannot know how the observer perceptions are altering that reality, which is also the same thing as saying that the variables needed to describe those perceptions are "hidden". Until someone can suggest a way to "unhide" those variables, I see no scientific difference at all.

To a certain extent, you are right. Still, there are some differences between Copenhagen Interpretation (CI) and Solipsistic Hidden Variables (SHV). You may feel that the differences are not important, and I will not insist that they are, but still they exist. Some of them are:

- While CI is rather vague on the concept of observer and its role, SHV provides an explicit quantitative model of the "observer" in terms of particle trajectories satisfying definite equations of motion.

- Some people prefer Bohmian interpretation over CI because they find CI rather unintuitive. SHV can be viewed as a variant of CI which will be much more intuitive to adherents of the Bohmian interpretation.

- Some people dislike Bohmian interpretation because they feel that all these Bohmian particle trajectories are not really needed to explain the quantum phenomena. SHV explains more clearly why all these trajectories are indeed not necessarily needed, but at the same time why at least some radically restricted set of trajectories seems to be needed.

- SHV provides an explicit counterexample to the wide belief that it is simply impossible to have local hidden variables compatible with QM. Perhaps the price is very big, but it's possible. By having such a counterexample one can better understand what REALLY is impossible.

- Perhaps the most interesting or most important value of SHV is to demonstrate that Copenhagen interpretation and Bohmian interpretation are not really so different as most physicists think they are. SHV interpolates between them, i.e., they can be viewed as two different limits of one "unifying" interpretation - SHV interpretation.

 

[Ken G]

Yes, I can accept that SHV navigates the differences between CI and deBB, indeed I would say its greatest value is in helping to show why these two interpretations are not necessarily any different either (even though they seem as ontologically different as F=ma and least action). When "many worlds" is similarly unified, we can finally see that all the interpretations are simply barking up the same tree, which is the question "what does the observer do?" To me, the main purpose of CI is to draw attention to this question, without actually answering it, so any approach that also draws attention to that question is a close cousin to CI. Just what the differences between the interpretations actually are, in my opinion, is an issue that must await the answer to that question, if it is even answerable at all.

 

[bohm2]

Wave functions are, of course, "physical", but the question is whether they are ontological or merely epistemological. If they are only epistemological, then the ontological may or may not be local, depending on what the ontological, if anything, is.

But I still don't understand. I mean, typically "physical" meant something spatial/extensible or existing in space-time/field. I don't think there's a problem with treating the wave function as something that defies this explanation (e.g. evolves in configuration space, etc.) and yet still being "physical" but in that case, what would the difference between ontological or epistemological mean? Something is physical and epistemological versus something that is physical (in this novel non-local/holistic way) and ontological? This is confusing. Also, I don't see how a model could be both non-local and local, unless one somehow emerges from the other? It seems weird that there would be 2 different types of "spaces"/ontologies (objects in 3-dimensional space and the wave function in 3-N dimensional configuration space) with both being "physical" and yet they interact, in some way.

 

[Ken G]

One possible meaning for "physical" is simply "of use in physics." That's actually the most defensible meaning for the term, and the wavefunction is certainly that, but I agree that often people imagine a much more highly extrapolated version of the term-- but it's not clear that such extrapolations really mean anything. If one leaves the realm of simply what is useful in physics, then what does one have?

 

[Demystifier]

Yes, I can accept that SHV navigates the differences between CI and deBB, indeed I would say its greatest value is in helping to show why these two interpretations are not necessarily any different either (even though they seem as ontologically different as F=ma and least action). When "many worlds" is similarly unified, we can finally see that all the interpretations are simply barking up the same tree, which is the question "what does the observer do?" To me, the main purpose of CI is to draw attention to this question, without actually answering it, so any approach that also draws attention to that question is a close cousin to CI. Just what the differences between the interpretations actually are, in my opinion, is an issue that must await the answer to that question, if it is even answerable at all.

Yes, I can more-or-less agree with that. I only don't agree that we must necessarily await the answer to that question. We should at least try to answer it, because if we don't, the answer will not pop out spontaneously without our assistance.

 

[Ken G]

The question is, what does "our assistance" look like? I think it looks like clever insights into the next set of observations that will guide us. Any inquiry into questions like which is more real, configuration space or real space, can help if they focus the question in a way that can lead to that kind of observation. It is certainly a noble effort, and the next big theory might rely on it, I just don't know if we are ever really going to be able to understand what the observer is doing-- the question is just so intimately intertwined with our efforts to answer it.

 

[stglyde]

The question is, what does "our assistance" look like? I think it looks like clever insights into the next set of observations that will guide us. Any inquiry into questions like which is more real, configuration space or real space, can help if they focus the question in a way that can lead to that kind of observation. It is certainly a noble effort, and the next big theory might rely on it, I just don't know if we are ever really going to be able to understand what the observer is doing-- the question is just so intimately intertwined with our efforts to answer it.

Hi Ken, For weeks we have struggled in another thread in uncovering physics of Preferred Foliations courtesy of Maudlin paper on "Non-Local Correlations in Quantum Theory: How the Trick Might Be Done", part of it mentioned:

"It has been a constant complaint against Bohmian mechanics, from its inception, that it “has no Relativistic version”. The reason that the theory is hard to reconcile with Relativity is clear: it is because of the way the non-locality of theory is implemented. In fact, the easiest way to extend that implementation to a space-time with a Lorentzian metric is to add a foliation, as we have seen. There may be some other way, but no one has discovered it yet."

http://xxx.lanl.gov/abs/1002.3226

I guess Maudlin was wrong because he has not known about Demystifier paper on "Making nonlocal reality compatible with relativity" at http://xxx.lanl.gov/abs/1002.3226 which is based on peer reviewed Physical Review Journal paper. Can you please read it to see if it is viable enough or is there possible flaw that we still can't determine in the other thread and it is giving us sleepless nights?

Part of the paper quote:

"O: Isn’t it shown that the Bohmian interpretation requires a preferred Lorentz frame?
R: That is true in the usual formulation of the Bohmian interpretation based on the usual formulation of QM in which time and space are not treated on an equal footing. When QM is generalized as outlined in 2) above, then the corresponding Bohmian interpretation does not longer require a preferred Lorentz frame.
O: I think I’ve got a general idea now. But I’ll not be convinced until I see the technical
details."

Need your valuable comment Ken and others who can grasp the math of the paper. Thanks.

 

[Ken G]

That might take a little time, but they do look like interesting questions. Can you link in the Maudlin paper as well? Personally, it doesn't bother me whether the Bohm approach can be made relativistic, because I view the standard version of Bohm as an interpretation of nonrelativistic quantum mechanics. It doesn't matter to me if an interpretation of nonrelativistic quantum mechanics can also be an interpretation of relativistic quantum mechanics, because it would not be unusual for a nonrelativistic theory to call for a different interpretation than a relativistic one. Certainly that is true of ordinary classical physics as it is taught to this day.

 

[Demystifier]

Hi Ken, For weeks we have struggled in another thread in uncovering physics of Preferred Foliations courtesy of Maudlin paper on "Non-Local Correlations in Quantum Theory: How the Trick Might Be Done", part of it mentioned:

The reference is:
Maudlin, T., “Non-Local Correlations in Quantum Theory: Some Ways the Trick Might
be Done”, Einstein, Relativity, and Absolute Simultaneity, ed. Quentin Smith and
William Lane Craig, Routledge 2007, 186-209.

I guess Maudlin was wrong because he has not known about Demystifier paper on "Making nonlocal reality compatible with relativity" at http://xxx.lanl.gov/abs/1002.3226 which is based on peer reviewed Physical Review Journal paper.

My paper above did not yet exist in 2007 when the Maudlin's paper was published.

 

[stglyde]

The reference is:
Maudlin, T., “Non-Local Correlations in Quantum Theory: Some Ways the Trick Might
be Done”, Einstein, Relativity, and Absolute Simultaneity, ed. Quentin Smith and
William Lane Craig, Routledge 2007, 186-209.


My paper above did not yet exist in 2007 when the Maudlin's paper was published.

When I put "http://xxx.lanl.gov/abs/1002.3226" in the search window at Physicsforum. It doesn't exactly give the threads with the url being discussed.. it only returned threads with any of the words gov, lan, 1002... this seems to be a flaw the the website design.. unless there is really a way to search only exactly for that phase? Anyway, if you remember the thread where this was discussed before. Let me know so I can see the comments of others. Thanks.

 

[jtbell]

there is really a way to search only exactly for that phase?

Use the "Search PF via Google" option and enclose the string in quotes ("").

 

[stglyde]

That might take a little time, but they do look like interesting questions. Can you link in the Maudlin paper as well? Personally, it doesn't bother me whether the Bohm approach can be made relativistic, because I view the standard version of Bohm as an interpretation of nonrelativistic quantum mechanics. It doesn't matter to me if an interpretation of nonrelativistic quantum mechanics can also be an interpretation of relativistic quantum mechanics, because it would not be unusual for a nonrelativistic theory to call for a different interpretation than a relativistic one. Certainly that is true of ordinary classical physics as it is taught to this day.

Ken, are you a Quantum Mechanic, or a Relativistic Geometry Surveyor? If you are well verse in the latter too.. hope you can comment on at least the following paragraph in Demystifier paper.


"By 2) I mean that time and space should be treated on an equal footing. Note that in the usual formulation of QM, time and space are not treated on an equal footing. First, for one particle described by the wave function psi(x,t), the infinitesimal probability in the usual formulation is |psi|^2d^3 x, while from a symmetric treatment of time and space one expects |psi|^2 d^3 x dt. Second, for n particles the wave function in the usual formulation takes the form (x1, . . . , xn, t), while from a symmetric treatment of time and space one expects (x1, t1, . . . , xn, tn). I formulate QM such that fundamental axioms involve the expressions above in which time and space are treated symmetrically, and show that the usual formulation corresponds to a special case."

What do you make of it where he said time and space should be treated on an equal footing? Don't we treat space and time as equal footing now? Time is in imaginary axis while space is in real axis. Perhaps what he did is make time another space too? (what don't we and if not why do we not do it in the first place?)

If Demystifier could only make presentation like Brian Greene where laymen can understood everything, much better.. but it looks like Demystifier only speak to physicists.

 

[Ken G]

What do you make of it where he said time and space should be treated on an equal footing? Don't we treat space and time as equal footing now? Time is in imaginary axis while space is in real axis.

This is how it works in special relativity, but not in nonrelativistic quantum mechanics (and even relativistic quantum mechanics is often a kind of cluge, it doesn't always seem very natural). I am not an expert in relativistic quantum mechanics, but I think what Demystifier is doing in that paragraph is casting regular old nonrelativistic quantum mechanics in a framework that treats time and space symmetrically, so that a later extension to relativistic quantum mechanics will seem more natural. The problem that I see is that the asymmetry between space and time in quantum mechanics goes deeper than just the way we intepret probability measures. It seems to me that the way he is altering the probability measures is pretty natural but by itself isn't really saying anything all that new (I haven't yet gone further to see where he goes with it though), it's pretty straightforward. It's not clear that it yet addresses the deeper issue, which is that time is not an observable in quantum mechanics-- there is no global "time operator", although there can be operators in each situation that function like a time operator in the sense of being instantaneously complementary to the energy operator. I just mean there's an energy/time uncertainty principle, similar to the position/momentum one, but it is actually a bit different because we don't actually have a time operator and we don't talk about time bases, we think of a particle as being in a superposition of different energy states but not as being in a superposition of different "time states." Maybe we should, I don't know.

What I mean here is that we don't do time measurements on systems, we simply use clock readings as a kind of bookkeeping tool to tell us which predictions apply to the actual measurements that we are making on the system. We can measure the location of a particle, or the momentum of a particle, or the energy of a particle-- but the time is still just what the clock on the wall reads, to tell us when to stop the unitary evolution in our calculation. This is particularly clear in the Heisenberg representation, where there isn't the usual separation between the state of the system and the measurement operators on the system, there is just the fixed measurement basis, and the time-dependent expectation value of a measurement in that basis. A truly time/space symmetric treatment would need to include a concept of destroying the coherences between different times, as if when an observation was made had to be a key element of the docoherences generated by any measurement. We could contrast that with measurements whose time of application was inherently indeterminate, to begin to understanding the meaning of a superposition of events occurring at different times. We're not really used to thinking about quantum mechanics that way, but maybe that's just what is needed to make it relativistic.

Perhaps what he did is make time another space too? (what don't we and if not why do we not do it in the first place?)

The symmetry of time and space in relativity was always a bit of a shock, because we don't perceive them as symmetric or similar in any way. But that doesn't make time "just another space", because the signature of the metric is different with regard to space and time (like you said, the time axis is in some sense imaginary compared to the spatial axes), so the two will always be juxtaposed as much as opposites as they are cousins. Spacelike and timelike separation are really quite different animals in relativity. But at least they are opposite faces of the same coin-- in quantum mechanics, we tend to think of them as having totally different places, as if they appeared on different coins altogether, since location is an observation that can be performed on a particle, whereas we never perform time measurements on particles-- we just look up at the clock on the wall when we are doing whatever measurement on the particle we are actually doing. This is just yet another difficulty in unifying relativity and quantum mechanics, and I haven't yet gone far enough into Demystifier's paper to see if he is really able to address it.

If Demystifier could only make presentation like Brian Greene where laymen can understood everything, much better.. but it looks like Demystifier only speak to physicists.

There are tradeoffs there. Brian Greene is considered to be highly successful at making complex ideas accessible to nonphysicists, but is he really conveying a true understanding, or just a kind of illusion of understanding? I won't take a position there because it would require more specifics, but as a teacher, I've seen the pitfalls-- students are often happiest when they are allowed to believe that they understand better than they actually do, whereas if they are challenged to really dig into their understanding and find the inconsistencies, it might make them feel dissatisfied and frustrated. It's a very delicate balance to walk, because we only turn people off if we make them feel stupid, but we do them no service if we make them feel like something makes sense when it actually falls apart like a cheap suit when put to the test.

 

[stglyde]

This is how it works in special relativity, but not in nonrelativistic quantum mechanics (and even relativistic quantum mechanics is often a kind of cluge, it doesn't always seem very natural). I am not an expert in relativistic quantum mechanics, but I think what Demystifier is doing in that paragraph is casting regular old nonrelativistic quantum mechanics in a framework that treats time and space symmetrically, so that a later extension to relativistic quantum mechanics will seem more natural. The problem that I see is that the asymmetry between space and time in quantum mechanics goes deeper than just the way we intepret probability measures. It seems to me that the way he is altering the probability measures is pretty natural but by itself isn't really saying anything all that new (I haven't yet gone further to see where he goes with it though), it's pretty straightforward. It's not clear that it yet addresses the deeper issue, which is that time is not an observable in quantum mechanics-- there is no global "time operator", although there can be operators in each situation that function like a time operator in the sense of being instantaneously complementary to the energy operator. I just mean there's an energy/time uncertainty principle, similar to the position/momentum one, but it is actually a bit different because we don't actually have a time operator and we don't talk about time bases, we think of a particle as being in a superposition of different energy states but not as being in a superposition of different "time states." Maybe we should, I don't know.

What I mean here is that we don't do time measurements on systems, we simply use clock readings as a kind of bookkeeping tool to tell us which predictions apply to the actual measurements that we are making on the system. We can measure the location of a particle, or the momentum of a particle, or the energy of a particle-- but the time is still just what the clock on the wall reads, to tell us when to stop the unitary evolution in our calculation. This is particularly clear in the Heisenberg representation, where there isn't the usual separation between the state of the system and the measurement operators on the system, there is just the fixed measurement basis, and the time-dependent expectation value of a measurement in that basis. A truly time/space symmetric treatment would need to include a concept of destroying the coherences between different times, as if when an observation was made had to be a key element of the docoherences generated by any measurement. We could contrast that with measurements whose time of application was inherently indeterminate, to begin to understanding the meaning of a superposition of events occurring at different times. We're not really used to thinking about quantum mechanics that way, but maybe that's just what is needed to make it relativistic.
The symmetry of time and space in relativity was always a bit of a shock, because we don't perceive them as symmetric or similar in any way. But that doesn't make time "just another space", because the signature of the metric is different with regard to space and time (like you said, the time axis is in some sense imaginary compared to the spatial axes), so the two will always be juxtaposed as much as opposites as they are cousins. Spacelike and timelike separation are really quite different animals in relativity. But at least they are opposite faces of the same coin-- in quantum mechanics, we tend to think of them as having totally different places, as if they appeared on different coins altogether, since location is an observation that can be performed on a particle, whereas we never perform time measurements on particles-- we just look up at the clock on the wall when we are doing whatever measurement on the particle we are actually doing. This is just yet another difficulty in unifying relativity and quantum mechanics, and I haven't yet gone far enough into Demystifier's paper to see if he is really able to address it.

Do you agree with the following comment by the author of "Physics Meets Philo at the Planck Scale"?

Despite the variety of programmes, and of controversies, in quantum gravity, most workers would agree on the following, admittedly very general, diagnosis of what is at the root of most of the conceptual problems of quantum gravity. Namely: general relativity is not just a theory of gravity – in an appropriate sense, it is also a theory of spacetime itself; and hence a theory of quantum gravity must have something to say about the quantum nature of space and time.

Meaning all these can be resolved by a theory of quantum gravity.. which is not just about Planck scale physics but the nature of space and time itself and how they are connected to matter. If it were true that both general relativity and quantum theory emerge from a theory very different from both, then we have to rethink about space and time. Therefore Ken, you must be a quantum gravitist to handle both problems. What do you think of the following statement by the same author above:

For these reasons, a good case can be made that a complete theory of quantum
gravity may require a revision of quantum theory itself in a way that removes the a priori use of continuum numbers in its mathematical formalism.

Finally, we note that (from time to time) a few hardy souls have suggested that a full theory of quantum gravity may require changing the foundations of mathematics itself. A typical argument is that standard mathematics is based on set theory, and certain aspects of the latter (for example, the notion of the continuum) are grounded ultimately in our spatial perceptions. However, our perceptions probe only the world of classical physics – and hence we feed into the mathematical structures currently used in all domains of physics, ideas that are essentially classical in nature. The ensuing category error can be remedied only by thinking quantum theoretically from the very outset – in other words, we must look for ‘quantum analogues’ of the categories of standard mathematics.

How this might be done is by no means obvious.51 One approach is to claim that, since classical logic and set theory are so closely linked (a proposition P determines – and is determined by – the class of all entities for which P can be rightly asserted), one should start instead with the formal structure of quantum logic and try to derive an analogous ‘non-Boolean set theory’. Such ideas are related to the exciting subject of topos theory, which can be viewed as a far-reaching generalization of standard set theory. This is why, as mentioned in Section 2.5.3, topos theory is a natural arena within which to develop speculative schemes in which
‘regions’ of spacetime (or space, or time) are more important than ‘points’ (which may not exist at all).

What do you think?

 

[bohm2]

"By 2) I mean that time and space should be treated on an equal footing. Note that in the usual formulation of QM, time and space are not treated on an equal footing. First, for one particle described by the wave function psi(x,t), the infinitesimal probability in the usual formulation is |psi|^2d^3 x, while from a symmetric treatment of time and space one expects |psi|^2 d^3 x dt. Second, for n particles the wave function in the usual formulation takes the form (x1, . . . , xn, t), while from a symmetric treatment of time and space one expects (x1, t1, . . . , xn, tn). I formulate QM such that fundamental axioms involve the expressions above in which time and space are treated symmetrically, and show that the usual formulation corresponds to a special case."

What do you make of it where he said time and space should be treated on an equal footing? Don't we treat space and time as equal footing now? Time is in imaginary axis while space is in real axis. Perhaps what he did is make time another space too? (what don't we and if not why do we not do it in the first place?)

I think Maudlin would probably argue against treating space and time on an equal footing. In fact he does defend the difference between space ant time in this paper:

Remarks on the passing of Time
http://www.jstor.org/pss/4545373

So, I'm guessing he would probably question any attempt (like Demystifier's) to treat space and time as the same? But maybe I'm mistaken?:

Consider the theory of relativity: one could think that this theory brings about the lesson that space and time are not fundamentally distinct because they appear into the laws in the same manner. But what is the explanation of the fact that we perceive them differently? Einstein warned us that we will never be able to explain, in physics, our sensations, included the one concerning the passing of time. In any case, on the one hand relativity suggests that space and time are of the same kind, on the other it does not explain why we do not perceive them equally. A analogy can be drawn again with quantum mechanics: on one hand it suggests that physical space is R^3N, on the other hand it does not explain why we perceive it as R³. If one accepts the position that in relativity physical space is R⁴ and not R³, then why not accept that in quantum mechanics physical space is R^3N? A possible position is the one of Tim Maudlin in his Remarks on the Passing of Time (Maudlin 2002), that rejects both positions: space is three-dimensional and it is fundamentally different from time.

Fundamental Physical Theories: Mathematical Structures Grounded on a Primitive Ontology
http://www.niu.edu/~vallori/thesis4.pdf

 

[Ken G]

Do you agree with the following comment by the author of "Physics Meets Philo at the Planck Scale"?

That seems like a generally true remark, but I think there is a subtext that might be even more important-- the goals of GR were actually somewhat different from the goals of quantum mechanics, so it's not that obvious that they should be unified by treating gravity like just more quantum mechanics. Quantum mechanics works by quantizing action, which is a quantization that plays out in phase space, not in either configuration space or spacetime. So when people say "let's quantize gravity next", they immediately think "quantize spacetime", but spacetime doesn't seem like the same thing as action, so I'm not sure that quantizing it is really the unification that is needed here. But people who know more about relativistic quantum mechanics than I do.

What do you think of the following statement by the same author above:

I can't say it's right or wrong, but it makes a lot of sense. I also feel that the unification of QM and GR is not going to look like QM+gravitons, and maybe not even like string theory (there I have no idea), but maybe like a very different theory altogether. Perhaps new mathematical insights are indeed needed, similar to what Riemannian geometry did for GR or complex analysis did for QM.

 

[Ken G]

Fundamental Physical Theories: Mathematical Structures Grounded on a Primitive Ontology
http://www.niu.edu/~vallori/thesis4.pdf

Personally, I reject the whole idea of grounding a theory on an ontology, I think that is backwards logic. The theory comes first, and has a much closer connection to reality (it predicts it to some degree of accuracy)-- the ontology comes later, and is just a way to think about the theory, and as such has a rather subjective and tenuous connection to reality. I don't think physics advances when we marry our past ontologies, I think it is obstructed by that.

 

[bohm2]

Personally, I reject the whole idea of grounding a theory on an ontology, I think that is backwards logic. The theory comes first, and has a much closer connection to reality (it predicts it to some degree of accuracy)-- the ontology comes later, and is just a way to think about the theory, and as such has a rather subjective and tenuous connection to reality. I don't think physics advances when we marry our past ontologies, I think it is obstructed by that.

Actually, I'm not personally a fan of those models for other reasons, but that's my biases toward's Valentini's and Bohm's/Hiley's interpretations of the wave function but let's assume that Allori is mistaken and "the theory comes first and has a much closer connection to reality" as you argue. Then where did that theory come from? I mean, how did we develop that particular theory/model versus some other one? What is the theory about? What was the evidence that led us to this road and how do we test it with respect to its truthfulness? Here are some justifications they present:

Many scientists maintain that the purely technical, formal and logical aspects of a theory represent all what deserves attention. We share with J S Bell and many others the opinion that further requirements must be imposed to any theoretical scheme to be considered as a fundamental account of natural processes. We do not want to spend many words on this point; for a deep analysis we refer the reader to a recent lucid paper (see second link below) in which the demand for a richer elaboration of the meaning of the formal scheme one is considering has been put forward. The authors of this paper have stressed the necessity of equipping any theory with what they call ‘the Primitive Ontology’ (PO) of the formalism. In brief, the PO consists in the clear and precise specification of what the theory is fundamentally about.

The interpretation of quantum mechanics: where do we stand?
http://lanl.arxiv.org/PS_cache/arxiv/pdf/0904/0904.0958v1.pdf

The PO of a theory—and its behavior—is what the theory is fundamentally about. It is closely connected with what Bell called the ‘local beables’:
n the words of Bohr, ‘it is decisive to recognize that, however far the phenomena transcend the scope of classical physical explanation, the account of all evidence must be expressed in classical terms.’ It is the ambition of the theory of local beables to bring these ‘classical terms’ into the equations, and not relegate them entirely to the surrounding talk. (Bell [1976])

On the Common Structure of Bohmian Mechanics and the Ghirardi–Rimini–Weber Theory
http://lanl.arxiv.org/PS_cache/quant-ph/pdf/0603/0603027v4.pdf

 

[Ken G]

Then where did that theory come from? I mean, how did we develop that particular theory/model versus some other one? What is the theory about?

Let's take a simple example-- theories of gravity. Like most theories, all our theories of gravity began as an inductive process of collecting similar behaviors and noticing a pattern-- things fall. Quantitative tests explore the regularities further: things fall at the same rate when air resistance is unimportant. Unifications bring additional phenomena under the same umbrella, and allow a more powerful and general theory to be developed: planets and apples act under the same gravity. Some sort of functional dependence is inferred, and included in a mathematical structure of some kind, which is parsimonious and testable, and we have a mature theory at this point. Where in all that did we need any ontology of gravity? When we imagined that there is mass and there are forces, at what point did it seem obvious that masses should generate attractive forces? Never, at no point did our ontology tell us anything new, we certainly didn't build the theory from its ontological elements-- at every step of the way, our ontology only gave us a way of understanding or picturing what we had already found to be true, to put it into words. This is a double-edged sword-- the good part is, we get a language with which to communicate to others and to ourselves, what lessons we interpret the theory as conveying to us. The bad part is, we tend to go too far, and imagine that the ontology is itself the reality, rather than just provisional and convenient claims made on the reality for instructive purposes. Ontology is pedagogy, so it is the path to understanding, but epistemology is the path to knowing.

Note all this doesn't necessarily contradict either Bohm's desire to speak in terms of "beables" or Bohr's desire to frame any theory in terms of its implications on classically knowable reality. I can agree with both of them that this can be one fruitful path in seeking useful ontologies for our theory. I simply say that there are two important things to bear in mind about the ontologies of a theory:
1) they should never be expected to be unique, or even widely preferred in some absolute or time-honored way, and
2) since the role of an ontology is to achieve understanding of a theory, we should not imagine that the ontology is actually informative about the theory itself, because the theory itself functions the same way whether we understand it or not, or whether we understand it in the same way or not-- which we very clearly generally do not. For example, it is simply not true that the great classical theories of physics converged on widely agreed-upon ontologies over time-- if anything, the ontologies of the great theories diverge more and more with time from their original inception, as we probe them more deeply and encounter new theories to replace them. We keep having to reassess prior ontologies when new ones prove useful, and this is what we should expect. It suddenly seems so much less important to be able to say "what a theory is about" when it is no longer considered the current best theory, yet that is the natural fate of all physics theories.

 

[bohm2]

Let's take a simple example-- theories of gravity. Like most theories, all our theories of gravity began as an inductive process of collecting similar behaviors and noticing a pattern-- things fall.

A little off topic but some argue that scienctific theories and progress doesn't occur by induction or even falsification. In fact, one can point to many examples in the history of science, where it is clear, that selection of theories was largely undetermined by the experimental evidence; internal aesthetic criteria (i.e. beauty, simplicity, symmetry, etc.) often prevailed over empirical criteria in directing theory formulation:

Time after time, people have been able to construct remarkable explanatory theories on the basis of very limited evidence, often rejecting much of the available evidence on obscure intuitive grounds...we are led to inquire into the innate structures of mind that make this achievement possible...Our knowledge...even in science and mathematics is not derived by induction, by applying reliable procedures, and so on; it is not grounded or based on ‘good reasons’ in any sense of these notions. Rather, it grows in the mind, on the basis of our biological nature, triggered by appropriate experience, and in a limited way shaped by experience that settles options left open by the innate structure of mind

Just my innatist/Kantian/rationalist rant.

 

[Demystifier]

I think Maudlin would probably argue against treating space and time on an equal footing. In fact he does defend the difference between space ant time in this paper:

Remarks on the passing of Time
http://www.jstor.org/pss/4545373

So, I'm guessing he would probably question any attempt (like Demystifier's) to treat space and time as the same? But maybe I'm mistaken?:

Yes, many physicists, even relativists, think of time as something completely different from space. But I believe that's because they do not distinguish two very different meanings of the word "time":
http://fqxi.org/data/essay-contest-files/Nikolic_FQXi_time.pdf

 

[stglyde]

Yes, many physicists, even relativists, think of time as something completely different from space. But I believe that's because they do not distinguish two very different meanings of the word "time":
http://fqxi.org/data/essay-contest-files/Nikolic_FQXi_time.pdf

So you divide the concept of time into two forms: physical time which you call "pime", and just regular experienced time. And the physics concept of pime is just a coordinate in a grid. As such there's no way to have a "pime paradox" any more than there is a way to have a "space paradox". In such a concept of time, going back in time would be no more weird than stepping to your side, or stepping backward.

Now regular experienced time.. do you equate this with the nonlocal s parameter that you claimed nonlocal correlations in Bohmian Mechanics also employed making it relativistic?

 

[Ken G]

A little off topic but some argue that scienctific theories and progress doesn't occur by induction or even falsification. In fact, one can point to many examples in the history of science, where it is clear, that selection of theories was largely undetermined by the experimental evidence; internal aesthetic criteria (i.e. beauty, simplicity, symmetry, etc.) often prevailed over empirical criteria in directing theory formulation:

In my opinion, most situations where it is claimed that people used "intuition" rather than experimental experience to formulate some theory, all that is happening is that many types of experimental experience that went into the theory are being overlooked. In particular, is it all the experiences and lessons of the individual that breeds their intuition, it's not instinct. The inductive process begins essentially at birth, not just after graduating from university. It's true that we feel to some degree that "the truth must be aesthetically simple" at some level, but that's more a constraint on the truth we are looking for-- we are looking for the truth that is aesthetically simple. What is the actual truth is a wholly different matter-- I have little doubt that the actual truth is appallingly complex, how could it not be?

 

[Demystifier]

So you divide the concept of time into two forms: physical time which you call "pime", and just regular experienced time. And the physics concept of pime is just a coordinate in a grid. As such there's no way to have a "pime paradox" any more than there is a way to have a "space paradox". In such a concept of time, going back in time would be no more weird than stepping to your side, or stepping backward.

That is correct.

Now regular experienced time.. do you equate this with the nonlocal s parameter that you claimed nonlocal correlations in Bohmian Mechanics also employed making it relativistic?

No I don't. The experienced time is subjective time that has to do with consciousness. I have almost no idea how consciousness arises from the laws of physics.

 

[Ken G]

I have almost no idea how consciousness arises from the laws of physics.

Indeed, I find it curious how often that basic assumption is made-- that consciousness (or any aspect of reality) arises from the laws of physics. To me, that is essentially backward thinking-- it must instead be true that the laws of physics arise from consciousness (and any other aspects of reality). In other words, laws explain phenomena, but they don't create or cause phenomena, because laws are inside our heads. To hold that laws create reality, or that reality arises from laws (including consciousness), is essentially the philosophy of "idealism", where reality is subordinate to our minds. Yet most physicists claim to be realists, who hold that our minds are subordinate to reality. So it would be a fundamental mistake to place the laws in the reality rather than the place where they demonstrably exist-- in our minds. This point gets underscored every time a well-loved set of "laws" gets replaced by some new one!

The connection to x,t in quantum mechanics is that these parameters have to be connected to observations to be useful, and observations require participation by our minds to decide what constitutes an x measurement or a t measurement. The laws of physics escape the need to have clear definitions of what x or t are, we just know how to use these concepts correctly in our theory. That's an aspect that is not strictly related to pime or pace.

 

[stglyde]

Indeed, I find it curious how often that basic assumption is made-- that consciousness (or any aspect of reality) arises from the laws of physics. To me, that is essentially backward thinking-- it must instead be true that the laws of physics arise from consciousness (and any other aspects of reality). In other words, laws explain phenomena, but they don't create or cause phenomena, because laws are inside our heads. To hold that laws create reality, or that reality arises from laws (including consciousness), is essentially the philosophy of "idealism", where reality is subordinate to our minds. Yet most physicists claim to be realists, who hold that our minds are subordinate to reality. So it would be a fundamental mistake to place the laws in the reality rather than the place where they demonstrably exist-- in our minds. This point gets underscored every time a well-loved set of "laws" gets replaced by some new one!

The connection to x,t in quantum mechanics is that these parameters have to be connected to observations to be useful, and observations require participation by our minds to decide what constitutes an x measurement or a t measurement. The laws of physics escape the need to have clear definitions of what x or t are, we just know how to use these concepts correctly in our theory. That's an aspect that is not strictly related to pime or pace.

Ken, Can you please critique the following concepts made by Demystifier regard nonlocality and the its compatibility with the minkowski metric structure (do you believe they are compatible?). These are taken partially from from a June 2010 thread exchange between Demystifier and Maaneli in the thread "Re: Pilot wave theory, fundamental forces" at https://www.physicsforums.com/showthread.php?t=366994&page=6. Please see attached paper shared by Demystifier in that thread for summary of the ideas.

Maaneli: the relativity of simultaneity is nevertheless a consequence of the metrical structure of Minkowski spacetime

Demystifier: No, this is not true. What is true is that the metrical structure of Minkowski spacetime implies relativity of simultaneity IF THERE IS NO ANY OTHER STRUCTURE. But in the case we are considering there is another structure. And this additional structure is not the parameter s (as you might naively think), but the non-local wave function. (Or the scalar potential in the classical setting discussed in http://xxx.lanl.gov/abs/1006.1986.)

And yet, you can see that this nonlocal wave function (or the scalar potential) is compatible with the metrical structure of Minkowski spacetime and does not introduce a foliation-like structure.

So, does it mean that you agree that WITH example of my theory there IS a known dynamical structure that is consistent with the metrical structure of Minkowski spacetime, and yet violates the relativity of simultaneity?

By the way, one can introduce such a structure even in classical local relativistic mechanics. Consider two twins who initially have the same velocity and same position, and their clocks show the same time. After that, they split apart, and each has a different trajectory, independent of each other. Yet, one can consider pairs of points on two trajectories which have THE SAME VALUE OF PROPER TIME (showed by a local clock on each trajectory). Such a structure (defined at least mathematically, if not experimentally) also can be said to violate relativity of simultaneity, in a way very similar to that of my theory. Of course, there is a difference, but the similarity may be illuminating too.

Demystifier: Or let me use an analogy with nonrelativistic BM. A point is space is denoted as r=(x,y,z). Consider two particles with space positions {\bf r}_1 and {\bf r}_2 at a given time t. There is a Cartesian frame (given by a rotation of the original Cartesian frame) in which {\bf r}_1 and {\bf r}_2 have the same value of z. In this frame, we say that the interaction between these two particles is z-taneous. Does it lead to any paradoxes? Does it mean there is a preferred z-coordinate? Does it mean there is a preferred foliation of space into 2-surfaces? Whatever your answer is, the same answer applies to analogous questions in relativistic-covariant BM. And if you still don't get it, then look at the equations of relativistic-covariant BM again.


Maaneli: ... by virtue of the fact that you have to synchronize the initial (spacetime) positions of the particles at a common time s,

Demystifier: The parameter s is not time.

Maaneli: But as a "joint parameter", it plays precisely the role of a universal time parameter for the evolution of the particle spacetime coordinates. Yes, I realize that the wavefunction on configuration spacetime doesn't depend on s, but that doesn't mean that s cannot also be interpreted as a time parameter (even if it is a fictitious one).

Demystifier: You are right. The parameter s can be interpreted as a sort of time. However, this is more like Newton absolute time, note like Einstein relativistic time [which I already implied by saying it is a UNIVERSAL time parameter]. OK, that's clear enough. And you are right, nonlocal signaling violates the relativity of simultaneity. Yet, in the next post I explain why it is NOT in contradiction with metrical structure of Minkowski spacetime.

(Maaneli in other message mentioned Nikolic theory has preferred foliation like structure)

Demystifer: No, there is no foliation-like structure. The synchronization parameter is NOT something additional to the SR metrical structure, just as time in nonrelativistic BM is NOT something additional to the 3-space rotational-symmetry structure.

My point is that relativistic-covariant BM in 4-dimensional spacetime is ANALOGOUS to nonrelativistic BM in 3-dimensional space. I am just trying to make you understand this ANALOGY, because when you do, you will suddenly say: "Oh, THAT is what you meant. Now I get it. In fact, it is trivial." But it is essential that you see this analogy by yourself, while I can only guide you in the right direction. And at the moment, it seems to me that you don't have a clue what I am talking about, because you are not able to see the analogy. And that is probably because you are unable to think of time as just another "space" coordinate.

To help you think in the correct way, let me suggest you a mental trick. For a moment, FORGET that the spacetime metric has the form (+---). Instead , think of metric as just any metric, which can be (++++), (++--), or whatever. In fact, simply don't think about metric at all. Just pretend that you have a 4-dimensional space with some unspecified metric. Or if it is easier for you, just pretend that the metric is (++++). And forget that one of the coordinates is called "time". (Who cares about names, anyway?) And NOW try to understand again what equations of relativistic-covariant BM are actually saying. This trick works for many physicists, so it could work for you as well.

(Note: the last exchange between Demystifer and Maaneli occurred in Jun 22, 2010)

Maaneli: Of course, by covariant, you must mean "fundamentally covariant", because anyone can construct a covariant particle dynamics on a preferred foliation. I think it might be best for us to resume our discussion on the old thread, "Pilot waves, fundamental forces, etc.", regarding whether your proposal of using a synchronization parameter and treating time and space on equal footing is truly fundamentally covariant or not, and whether or not it does have the condition of equivariance. We never got to finish that discussion, mainly because I became too overwhelmed with deadlines and work and kept forgetting to reply to the thread. My apologies about that.

Demystifier: I would like to continue the discussion there. But I will wait for your first step.

(But they never continued. And since June, 2010. There is no other challenger to Demystifier. And he continued to share his papers which are referenced in peer reviewed journals but unfortunately, no one read it much. Therefore let us continue and settle it once and for all whether Demystifier is fundamentally correct.)

References:

http://xxx.lanl.gov/PS_cache/arxiv/pdf/1002/1002.3226v2.pdf
http://xxx.lanl.gov/PS_cache/arxiv/pdf/1007/1007.4946v1.pdf (see section 2.1)

 

[Ken G]

I'm not enough of an expert to be brought up to speed on the details of the argument without investing a lot of time, but I can give my general impressions:

1) I don't see why Bohmian nonlocality contradicts relativity, unless there is something "more nonlocal" in Bohmian mechanics than what is already in the predictions of quantum mechanics. I wouldn't expect that to be true, for as near as I can tell, BM is constructed to make all the same predictions as quantum mechanics in the same types of idealized situations in which physics is generally applicable. Extending BM to relativistic quantum mechanics should not be any harder than so extending any of the other interpretations.

2) In my opinion, strict global simultaneity is always a coordinate issue, which is never demonstrably essential to any of the physics. Demystifier seems to be advocating a coordinate s which is to be viewed as a physically real version of global simultaneity. I don't think it is wrong to inject a concept of global simultaneity into one's interpretation of physics, but I do think it is unnecessary to do so. That is my general beef against Bohmian approaches: they are invariably rife with unnecessary injections that allow a particular view of how reality works to be maintained, when it seems more natural to me to not cling to any preconceptions about how reality behaves and just let it teach us its lessons. To me, one key lesson of relativity is that there simply is no such thing as absolute global simultaneity, that is merely mistaking a subjective coordinate for something objectively real. But that doesn't make it wrong to interpret global simultaneity, any more than the standard rejection of preferred reference frames makes the aether wrong. For example, it is actually not a principle of relativity that there must be no preferred reference frames, it is merely a principle that there be no requirement for a preferred reference frame. The requirement refers to the theory itself, not any given interpretation of that theory. It is not at all uncommon for intepretations to create elements that are not required in the theory-- for example, most interpretations of Newtonian mechanics create a concept of a force, yet other interpretations (like the principle of least action) require no such ontological entities as forces. I view all ontology as the arena of interpretation, not of physical theory itself. For the theories themselves, the only ontology is the epistemology-- what exists is the theory, and all its interpretaitons, and their value to us. It is only in the interpretations that we encounter the various ontologies, and we need not expect them to be unique.

3) So I'm generally sympathetic to Demystifier's position that relativity does not refute BM. I view BM as a way to allow classical notions like trajectories and global simultaneity to survive quantum mechanics, just as Lorentz aether theory was a way to let those notions survive relativity. I just don't see the point in doing that-- but it doesn't make it wrong. It's important to recognize the difference between what is ruled out by observation, and what is simply regarded as a preferred lesson of the observations. Demystifier is arguing that BM need not be ruled out by the observations that support the need for a covariant formulation of quantum mechanics, and I can find no flaw in that position, though Maaneli may be seeing deeper than I am.

 

[stglyde]

I'm not enough of an expert to be brought up to speed on the details of the argument without investing a lot of time, but I can give my general impressions:

1) I don't see why Bohmian nonlocality contradicts relativity, unless there is something "more nonlocal" in Bohmian mechanics than what is already in the predictions of quantum mechanics. I wouldn't expect that to be true, for as near as I can tell, BM is constructed to make all the same predictions as quantum mechanics in the same types of idealized situations in which physics is generally applicable. Extending BM to relativistic quantum mechanics should not be any harder than so extending any of the other interpretations.

2) In my opinion, strict global simultaneity is always a coordinate issue, which is never demonstrably essential to any of the physics. Demystifier seems to be advocating a coordinate s which is to be viewed as a physically real version of global simultaneity. I don't think it is wrong to inject a concept of global simultaneity into one's interpretation of physics, but I do think it is unnecessary to do so. That is my general beef against Bohmian approaches: they are invariably rife with unnecessary injections that allow a particular view of how reality works to be maintained, when it seems more natural to me to not cling to any preconceptions about how reality behaves and just let it teach us its lessons. To me, one key lesson of relativity is that there simply is no such thing as absolute global simultaneity, that is merely mistaking a subjective coordinate for something objectively real. But that doesn't make it wrong to interpret global simultaneity, any more than the standard rejection of preferred reference frames makes the aether wrong. For example, it is actually not a principle of relativity that there must be no preferred reference frames, it is merely a principle that there be no requirement for a preferred reference frame. The requirement refers to the theory itself, not any given interpretation of that theory. It is not at all uncommon for intepretations to create elements that are not required in the theory-- for example, most interpretations of Newtonian mechanics create a concept of a force, yet other interpretations (like the principle of least action) require no such ontological entities as forces. I view all ontology as the arena of interpretation, not of physical theory itself. For the theories themselves, the only ontology is the epistemology-- what exists is the theory, and all its interpretaitons, and their value to us. It is only in the interpretations that we encounter the various ontologies, and we need not expect them to be unique.

3) So I'm generally sympathetic to Demystifier's position that relativity does not refute BM. I view BM as a way to allow classical notions like trajectories and global simultaneity to survive quantum mechanics, just as Lorentz aether theory was a way to let those notions survive relativity. I just don't see the point in doing that-- but it doesn't make it wrong. It's important to recognize the difference between what is ruled out by observation, and what is simply regarded as a preferred lesson of the observations. Demystifier is arguing that BM need not be ruled out by the observations that support the need for a covariant formulation of quantum mechanics, and I can find no flaw in that position, though Maaneli may be seeing deeper than I am.

Thanks.. I'll reflect on what you said. For now I have only one question (at the bottom sentence).
Nikolic mentioned in the attached paper in my prior message:

"1.1 Relativistic Bohmian interpretation

- Nonlocality in BM requires superluminal (faster than light)
communication between particles.
- The most frequent argument that it is not compatible with relativity:

Superluminal communication
⇒ there is a Lorentz frame in which communication is instantaneous
⇒ there is a preferred Lorentz frame
⇒ the principle of relativity is violated.
- However, this is not a valid argument, because
this is like using the following argument on subluminal communication:

Subluminal communication
⇒ there is a Lorentz frame in which particle is at rest
⇒ there is a preferred Lorentz frame
⇒ the principle of relativity is violated.

The argument on subluminal communication is wrong:
- It is the general law of motion that must have the same form
in any Lorentz frame.
- A particular solution (a particle at rest with respect to some particular
Lorentz frame) does not need to have the same form
in all Lorentz frames.
But the argument on superluminal communication is
completely analogous.
⇒ It is wrong for exactly the same reason:
- A particular solution (communication instantaneous with respect to
some particular Lorentz frame) does not need to have the same form
in all Lorentz frames.

This analogy works if one exchanges the roles of time and space."

My only question is how come this analogy only works if one exchanges the roles of time and space? If you don't know, Hope Nikolic himself can share. Thanks.

 

[Ken G]

I'm not sure about the point of exchanging time and space either, but it seems to me that Demystifier is making a fairly simple argument that instantaneous communication is not ruled out by relativity as long as no FTL information can be extracted from that "communication," analagous to how phase velocity can be > c as long as group velocity is < c. This is commonplace, even Feynman path integrals include processes that one might regard as FTL "communication" if one wanted, but the point is, at the end of the calculation when all the amplitudes are added up, there can be no transfer of classical information that is FTL. This can be viewed as a kind of explanation for the principle of least action-- the path of least action is the path of constructive interference, so what actually happens emerges from a sea of possibilities that we don't expect to happen. Relativity is only about what actually happens, not about the sea of possibilities we include in our interpretation of what actually happens.

But this brings up a different problem for BM, which I think is a valid criticism of it. There is no need to interpret quantum mechanical nonlocality as a form of FTL communication between parts, because parts don't communicate-- intelligences do. So adopting the term "communication" here is just an awkward anthropomorphism. Nor should we say that parts "influence" other parts, because if the message is that QM is nonlocal, then I say we should ditch the whole concept of "local parts" that could "communicate" with each other in the first place, and simply talk about the complete system as if it was a whole, not a bunch of entangled parts. But again, this doesn't mean BM is wrong, it just means it may miss a key lesson of QM, choosing to instead replace that new lesson with old lessons from classical thinking. But whether or not this is actually a good or bad thing to do depends more on the next theory that we don't have yet, than it does on either quantum mechanics or relativity.

 

[stglyde]

I'm not sure about the point of exchanging time and space either, but it seems to me that Demystifier is making a fairly simple argument that instantaneous communication is not ruled out by relativity as long as no FTL information can be extracted from that "communication," analagous to how phase velocity can be > c as long as group velocity is < c. This is commonplace, even Feynman path integrals include processes that one might regard as FTL "communication" if one wanted, but the point is, at the end of the calculation when all the amplitudes are added up, there can be no transfer of classical information that is FTL. This can be viewed as a kind of explanation for the principle of least action-- the path of least action is the path of constructive interference, so what actually happens emerges from a sea of possibilities that we don't expect to happen. Relativity is only about what actually happens, not about the sea of possibilities we include in our interpretation of what actually happens.

But this brings up a different problem for BM, which I think is a valid criticism of it. There is no need to interpret quantum mechanical nonlocality as a form of FTL communication between parts, because parts don't communicate-- intelligences do. So adopting the term "communication" here is just an awkward anthropomorphism. Nor should we say that parts "influence" other parts, because if the message is that QM is nonlocal, then I say we should ditch the whole concept of "local parts" that could "communicate" with each other in the first place, and simply talk about the complete system as if it was a whole, not a bunch of entangled parts. But again, this doesn't mean BM is wrong, it just means it may miss a key lesson of QM, choosing to instead replace that new lesson with old lessons from classical thinking. But whether or not this is actually a good or bad thing to do depends more on the next theory that we don't have yet, than it does on either quantum mechanics or relativity.

I've spent about 4 hours now just reading and rereading the old thread between Demystifer and Manelli and I think I can see it clearer now (we need to scrutinize Demystifier approach so that we can become conversant in dealing with exotic spacetime formulation in our search for ultimate physics of Quantum Gravity). The following message tells about Demystifier position that his theory is not lorentz invariance as we and Maudlin understood it.

message #78 of https://www.physicsforums.com/showthread.php?t=366994&page=5

Maaneli, you are correct that I use a different definition of "fundamental" Lorentz invariance than you (and Maudlin) do. Let me refer to this (your and Maudlin's) definition as CAUSAL Lorentz invariance.

You are also correct that my theory is not causal Lorentz invariant.

However, my point is that I do not see any particular motivation for retaining causal Lorentz invariance. For me, the only reason why I want Lorentz invariance is SYMMETRY, so for me the covariance with respect to coordinate transformations and the absence of a preferred frame is enough. Let me refer to it as SYMMETRY Lorentz invariance.

Let us also not use the unfair and vague expression "fundamental" Lorentz invariance any more.

Now let me answer you questions, having the definitions above in mind.

"So will the superluminal signaling occur along all of those hypersurfaces?"
- Yes.

"And would you still regard superluminal signaling in your theory as consistent with your definition of fundamental Lorentz invariance?"
- I would regard it consistent with symmetry Lorentz invariance.

Now in other message in that thread. Demystifier admitted that his theory depended wholly on making space and time equal. Therefore if we can argue correctly that it isn't so. Then his whole castle collapses.

Demystifer. First please explain why your example of subluminal and superluminal and how "a particular solution does not need to have the same form in all Lorentz frames" statement has everything to do with exchanging space and time. Me and Ken (perhaps) still don't understand this, so please explain. Thanks.

 

[Ken G]

What I'd like to know is whether Demystifier is claiming that treating x and t symmetrically results in a theory that says it is possible to send classical information superluminally. Since there is no experimental evidence that this is possible, that would sound like going too far to treat x and t symmetrically. After all, the main reason for treating x and t symmetrically, despite our experience to the contrary, is that doing so supports the concept of a universal speed limit. Remove that constraint, and much of the reason to want to treat x and t symmetrically also vanishes. I'm not one of those who believes that we should embed symmetries into our theories even if nature does not give us reason to, just for the sake of having a more symmetric theory. Symmetry is often associated with parsimony, but there is more than just Occam's Razor to think about when constructing theories, there are also advantages to theories that support interpretations that retain our general experiential notions.

 

[Demystifier]

My only question is how come this analogy only works if one exchanges the roles of time and space? If you don't know, Hope Nikolic himself can share. Thanks.

The argument compares two very similar arguments, one referring to a superluminal velocity
dx/dt > 1 .. (1)
the other to a subluminal velocity
dx/dt < 1 .. (2)
But note that (1) can be written as
dt/dx < 1 .. (1')
while (2) can be written as
dt/dx > 1 .. (2')
So, if we exchange the roles of space and time, i.e., if we interpret t as "space" and x as "time", then it is natural to define the velocity as dt/dx, rather than dx/dt. In this way (1') is interpreted as "subluminal" velocity, while (2') is interpreted as "superluminal" velocity. In other words, by exchanging the roles of space and time, subluminal velocities transform to superluminal velocities, and vice versa. Thus, if space and time are treated on an equal footing, then their exchange should be allowed, and then there is no fundamental difference between superluminal and subluminal velocities. In particular, if subluminal velocities are compatible with relativity, then so are superluminal ones.

I hope it's clearer now.

 

[Demystifier]

What I'd like to know is whether Demystifier is claiming that treating x and t symmetrically results in a theory that says it is possible to send classical information superluminally. Since there is no experimental evidence that this is possible, that would sound like going too far to treat x and t symmetrically.

I would put it this way. If x and t are treated symmetrically, then there is nothing paradoxical about sending classical information superluminally. But it does not yet mean that sending classical information superluminally is possible. We apparently cannot send classical information superluminally because the dynamics is described by a particular Lagrangian which does not allow that. If the dynamics has been described by a somewhat different relativistic-covariant Lagrangian as in
http://xxx.lanl.gov/abs/1006.1986
then sending classical information superluminally would be possible.

 

[stglyde]

The argument compares two very similar arguments, one referring to a superluminal velocity
dx/dt > 1 .. (1)
the other to a subluminal velocity
dx/dt < 1 .. (2)
But note that (1) can be written as
dt/dx < 1 .. (1')
while (2) can be written as
dt/dx > 1 .. (2')
So, if we exchange the roles of space and time, i.e., if we interpret t as "space" and x as "time", then it is natural to define the velocity as dt/dx, rather than dx/dt. In this way (1') is interpreted as "subluminal" velocity, while (2') is interpreted as "superluminal" velocity. In other words, by exchanging the roles of space and time, subluminal velocities transform to superluminal velocities, and vice versa. Thus, if space and time are treated on an equal footing, then their exchange should be allowed, and then there is no fundamental difference between superluminal and subluminal velocities. In particular, if subluminal velocities are compatible with relativity, then so are superluminal ones.

I hope it's clearer now.

Ok, clearer now. But you also give as one of the conditions that there should be no free will. Why. Why would your model collapse if there is free will? And what is the relation of free will to treating space and time as equal and these views seemingly dependent on each other? Maybe something to do with the fact that you believe in block spacetime and nothing can ever influence it. Everything is already written from past to future? This is what can falsify your theory. We don't have to discuss what is free will (to avoid off topic and it's not necessary), but the fact whether there is free will or not can either vadliate or invalidate your theory right?
So 50 yeasr from now. If it would be proven there was really free will, then your model completely collapse.

 

[Demystifier]

Why would your model collapse if there is free will?

I have explained it in the paper, but let me repeat. If one has free will, then one can choose to send a signal one wishes to. But in my theory, that signal may travel faster than light. This means that a signal can be sent to the past. But sending a signal to the past one wishes to may be logically inconsistent (grandfather paradox).

If free will would be proven to exist, then all currently known fundamental physical theories, either deterministic or probabilistic, would collapse. That's because free will is incompatible with fundamental deterministic laws, as well as with fundamental probabilistic laws.

 

[stglyde]

I have explained it in the paper, but let me repeat. If one has free will, then one can choose to send a signal one wishes to. But in my theory, that signal may travel faster than light. This means that a signal can be sent to the past. But sending a signal to the past one wishes to may be logically inconsistent (grandfather paradox).

But it's easy to get over it. Whenever free will was used, then Preferred Foliation (Maudlin context) is invoked. There you won't have any grandfather paradox. What's so difficult about this? Note Preferred Foliation is even simpler or equally likely than your treating space and time as equal. Or you can have them both anyway with preferred foliation only used for free will.

 

[Demystifier]

But it's easy to get over it. Whenever free will was used, then Preferred Foliation (Maudlin context) is invoked. There you won't have any grandfather paradox. What's so difficult about this? Note Preferred Foliation is even simpler or equally likely than your treating space and time as equal. Or you can have them both anyway with preferred foliation only used for free will.

Yes, that's also a logical possibility, but I wouldn't call it "simpler" or "equally likely".

 

[stglyde]

Yes, that's also a logical possibility, but I wouldn't call it "simpler" or "equally likely".

How come in Copenhagen, free will can coexist with nonlocal correlations such that the randomness can't be used to send information because quantum randomness doesn't have order. Yet in Bohmian, nonlocal correlations automatically can be used to send information and cause causality paradox. Remember it is the wave function that do the trick in both so why can't we say the wave function in bohmian acts like in Copenhagen preventing the sending of sginal. I can't quite verbalize it although the reason is just on the surface of my mind. When mentioning Bohmian, please specify whether you are talking of old fashioned BM or your BM.

 

[stglyde]

How come in Copenhagen, free will can coexist with nonlocal correlations such that the randomness can't be used to send information because quantum randomness doesn't have order. Yet in Bohmian, nonlocal correlations automatically can be used to send information and cause causality paradox. Remember it is the wave function that do the trick in both so why can't we say the wave function in bohmian acts like in Copenhagen preventing the sending of sginal. I can't quite verbalize it although the reason is just on the surface of my mind. When mentioning Bohmian, please specify whether you are talking of old fashioned BM or your BM.

Oh I think I remember. Copenhagen has randomness scrambler built in so Alice and Bob wouldn't know what is really sent. So you mean if Bohmian would have randomness scrambler added, then will free and nonlocality won't imply sending information, agree with these arguments?

 

[stglyde]

Oh I think I remember. Copenhagen has randomness scrambler built in so Alice and Bob wouldn't know what is really sent. So you mean if Bohmian would have randomness scrambler added, then will free and nonlocality won't imply sending information, agree with these arguments?

Oh I remember the contextuality part. In Copenhagen, in the absence of measurement to measure its position, the particle has no position.. so with randomness scrambler built in, there was no way to affect the past because the past won't know what to measure. In Bohmian, a particle always has position, so even if you send random 1 and 0 nonlocally and superluminal, it can still affect the past by the value regardless of 1 or 0 existing... but note this only occurs in a relativistic BM. But convensional BM has no relativistic counterpart (except yours) so this causality won't even be a problem because convensional BM uses Newtonian spacetime.

Now in your time and space equal formulation of BM which you made relativistic. You have to invoke it to avoid causality effect. But you have do away with free will.

Is is impossible to create relativistic BM (with changing reference frame) without using any of your device of treating space and time as equal?

 

[Ken G]

Thus, if space and time are treated on an equal footing, then their exchange should be allowed, and then there is no fundamental difference between superluminal and subluminal velocities. In particular, if subluminal velocities are compatible with relativity, then so are superluminal ones.

The usual statement made about relativity is not that superluminal velocities are categorically impossible, but rather that crossing from subluminal to superluminal is impossible. So if there was some population of superluminal particles (tachyons), they would always be superluminal. This preserves the symmetry, yet still holds that superluminal communication is impossible, unless you get access to tachyons. So that doesn't refute BM, because BM can invoke some tachyon-like connection and still be consistent with relativity, but it's not clear that invoking new physics is justified simply to allow BM to give a consistent rendition of what is happening.

 

[Ken G]

Not to get the thread too embroiled in free will, but I should point out that I can think of at least two ways that free will is not challenged by any highly successful deterministic (or random, for that matter) theory of physics:

1) physics theories are used by intelligences to understand reality, but the understanding it generates is never complete. If we observe something that we don't understand, and other things that we do understand, we do not say that the things we do understand make impossible those we don't. The only solid definition of an "illusion" is something that can be better understood in a different way, not something that simply isn't understood at all. Arguments that successful deterministic theories require a self-delusion of free will do not offer us any better understanding of delusions of free will than they do of actual free will.

2) the nature of free will is not well defined, and certain versions of the concept are fully compatible with determinism. Determinism is about predictability, and free will can be viewed as being about the absence of constraints that would tend to influence an agent to feel forced to do something against their nature. That is certainly close to the legal definition of someone's "will", after all. In those terms, anyone who argues that deterministic theories preclude free will is arguing that people being allowed to act according to their nature must not have free will if their nature is predictable. That argument does not follow, because if someone's behavior is predictable based on their nature, and they are allowed to perform according to their nature, then we can say that acting according to their nature is what acting according to free will is actually about.

Personally, I hold to the first argument of those, so find the second argument to be unnecessary. I think we don't know enough about free will to even give it a definition that makes any contact with fundamental physics at all.

 

[Demystifier]

Is is impossible to create relativistic BM (with changing reference frame) without using any of your device of treating space and time as equal?

Perhaps it is, but probably not in such a simple (whatever that means) way.

 

[Demystifier]

The usual statement made about relativity is not that superluminal velocities are categorically impossible, but rather that crossing from subluminal to superluminal is impossible.

That's true if the mass of the particle is constant. But if mass can change, or more precisely if the sign of m^2 can change, then the particle can change its velocity from a subluminal to a superluminal one. See
http://xxx.lanl.gov/abs/1006.1986

... but it's not clear that invoking new physics is justified simply to allow BM to give a consistent rendition of what is happening.

Quite the opposite, I think it is more than justified to introduce some new physics in order to explain what is happening behind the standard "shut up and calculate" rules of QM.

 

[stglyde]

That's true if the mass of the particle is constant. But if mass can change, or more precisely if the sign of m^2 can change, then the particle can change its velocity from a subluminal to a superluminal one. See
http://xxx.lanl.gov/abs/1006.1986

Here's the problem of normal matters using tachyons and sending them which not even be possible.. anyone know any workaround for it?

By PeterDonis:

Well, there's the obvious point that the theory would violate Lorentz invariance. You would also have to work out whether it is even possible for your version of tachyons to interact with ordinary matter, and if so how. Theorists have tried to construct theories of tachyons and have found issues with doing that; for example, the straightforward way of constructing a theory of tachyons interacting with normal matter violates conservation of energy. Also, when you start bringing in quantum field theory, it turns out that you can't really use tachyons to transmit information faster than light anyway; in other words, a quantum field theory that would allow a "tachyon pistol" is not really possible. See here:

http://www.desy.de/user/projects/Physics/ParticleAndNuclear/tachyons.html

I don't know whether an "aether" theory of tachyons could overcome the above issues, because if tachyons interact with normal matter, the interaction has to be Lorentz invariant even if the tachyons by themselves could violate Lorentz invariance (because normal matter is still Lorentz invariant, at least to a very good approximation).