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.