Implications of quantum foundations on interpretations of relativity

[physika]

The more accurate full comment of course is this;
Many other possibilities exist for the classical correlation subject to these side conditions, but all are characterized by sharp peaks (and valleys) at 0°, 180°, and 360°, and none has more extreme values (±0.5) at 45°, 135°, 225°, and 315°

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and the spread of superposition it is not arbitrarily large, and exist the Tsirelson bound.
QM is not so weird then.

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[stevendaryl]

But too much determinism will make it contradict Kochen-Specker Theorem.

No. Kochen-Specker shows that you can’t assume that all variables have values prior to measurement. But in the Bohm interpretation, only the position variable has definite values. A measurement of other variables such as momentum or spin doesn’t reveal a pre-existing value, but is an artifact of the measurement process.

 

[zonde]

Yeah indeed, but here's the interesting thing - what is the criteria that makes us say "that's a particle"?

Well, I don't care if we call detections events "particles". But I care that they happen in pairs.

How do those atoms react to energy, according to our theory of atoms? They react by stepping up a quantized energy level (often explained as an electron reaching the next harmonic wave mode - exactly the hypothesis behind Planck's Law).

So if atoms already are rigged to be only capable of storing quantized energy steps, how exactly do we purport to differentiate between "a particle causing that quantized reaction", vs "a wave causing that quantized reaction"? Either way, what we see is an atom stepping up one energy level.

If both models agree with observations then we can't discard one of them if favor of the other. Well, of course it's possible that one is more practical.

Put this together with the fact that the system acts as a wave until that quantized interaction occurs (that's the moment when we say "we saw a particle"), and put it together with the fact that plain wave mechanics predict a simple cosine correlation for a Bell experiment (because you are simply filtering a direction component out from a vector when you offset a filter from the actual wave polarization - this is part of basic wave mechanics)

It's pretty silly to claim that classical mechanics predict a linear correlation in Bell experiment - they only do so if we assume there really are particles, or that energy absorption mechanisms are continuous, neither of which is really supported by evidence.

Sorry, but I still don't see an argument why would wave produce paired detections. Actually I see exactly the opposite argument: "because you are simply filtering a direction component out from a vector when you offset a filter from the actual wave polarization" - replace polarizer with polarization beam splitter and you will have two beams with respective direction components, and then why don't you see double detection in both arms at least time by time?

 

[jedishrfu]

I’ve been reading this thread for a while now and realize how little I know of Quantum Mechanics.

I think it’s still safe to agree with Prof Feynman that no one really understands Quantum Mechanics and so we Let the Mystery Be (title of an Iris Dement song).

One observation I will make here are that some of us are prone to posting long detailed posts that take a long time to read and understand.

I would ask that posters stay more focused and limit the size of their posts to one or two pages of commentary.

Our time here is limited and long posts are guaranteed to turn off some readers and make it very difficult for moderators to moderate without deleting the whole post.

Also remember while we do discuss all aspects of STEM, we are not a pure academic environment.

Our members are quite diverse from students to professionals sprinkled with some Phd folks and we simply don’t have the bandwidth to handle heated academic debate.

Lastly, when references are asked for, it means reputable peer reviewed references not some pop sci book, personal blog, Wikipedia article or cool YouTube video. (There are exceptions of course)

We are looking for peer reviewed articles from reputable journals. Wikipedia articles for some instances are okay especially if there are further references in the article and sometimes rarely a YouTube video from a reputable channel.

However, for more cutting edge stuff we’ll likely need peer reviewed articles only, and rarely arxiv but never vixra.

Please keep these thoughts in mind as you post here Now and in future.

And now back to our regularly scheduled thread…

Thank you.

The Moderators.

 

[physika]

One observation I will make here are that some of us are prone to posting long detailed posts that take a long time to read and understand.

I would ask that posters stay more focused and limit the size of their posts.

Please keep these thoughts in mind as you post here Now and in future.
Thank you.
The Moderators.

Thanks.

Yes, concise and succinct.

 

[Demystifier]

Thanks.

Yes, concise and succinct.

Nobody on this forum is more concise and succinct than you. At the beginning it was irritating me, then I got used to it, and finally I started to praise and appreciate that.

 

[physika]

Nobody on this forum is more concise and succinct than you. At the beginning it was irritating me, then I got used to it, and finally I started to praise and appreciate that.

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...sort of autistic

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[Sunil]

What cannot be accommodated by any interpretation involving classical spacetime is superposition. For example, suppose we set up a "Schrödinger's cat" type experiment where, instead of a random quantum event like a radioactive decay determining whether a cat is alive or dead, have it determine whether or not a significant change in the distribution of matter occurs--for example, whether a ball with enough mass to register in a Cavendish-type experiment goes to the left or to the right. No classical spacetime model can describe this experiment, because it involves a superposition of different spacetime geometries (more precisely, it involves the entanglement of the spacetime geometry with other degrees of freedom). In a classical spacetime model, there is only one spacetime geometry. The geometry can be determined dynamically by the distribution of matter, but there is no way to model a superposition of different matter distributions being entangled with the spacetime geometry and causing a superposition of different spacetime geometries.

A possibility to circumvent this would be to give up the spacetime interpretation. Space and time can remain, in this case, absolute and classical, while the gravitational field distorts only attempts to measure absolute spatial distances or absolute time. Then superpositions of different gravitational fields become unproblematic because they have no direct connection with space and time.

 

[PeterDonis]

A possibility to circumvent this would be to give up the spacetime interpretation. Space and time can remain, in this case, absolute and classical, while the gravitational field distorts only attempts to measure absolute spatial distances or absolute time. Then superpositions of different gravitational fields become unproblematic because they have no direct connection with space and time.

Do you have a reference for any actual theories along these lines?

 

[PeterDonis]

A possibility to circumvent this would be to give up the spacetime interpretation.

That's not what you're describing.

Space and time can remain, in this case, absolute and classical

This is not giving up the spacetime interpretation; it's just saying spacetime geometry is not a quantum degree of freedom and can't participate in quantum dynamics.

the gravitational field distorts only attempts to measure absolute spatial distances or absolute time

This is an additional, separate restriction on the spacetime geometry: basically in such a model the spacetime geometry would be flat Minkowski spacetime, but this geometry would be unobservable because gravitational fields would distort the measurements so it looked like the spacetime geometry was curved. This is, of course, just the "spin-2 field on flat spacetime" interpretation of GR, and it has been known for decades that it is mathematically equivalent to the usual curved spacetime interpretation (except possibly for issues of global topology, which I don't think we need to go into for this discussion).

The issue I see for using a model like this with the Transactional Interpretation would be that, as it currently stands, the TI expects to use the actual, physical light cones--the ones that we actually measure--but in the kind of model you're describing, it wouldn't, it would have to use the unobservable light cones of the background Minkowski spacetime. For example, in an experiment with entangled photons, where we have a superposition of different gravitational fields due to, say, a quantum event making a heavy ball go left or right, the actual events where the photons are emitted and detected would be the ones determined by the actual, observable light cones of whichever curved spacetime (aka flat spacetime with gravitational field) corresponded to the measured outcome of where the ball went, whereas the TI would be using different events for the "transaction", the ones corresponding to the background (unobservable) flat spacetime. But that contradicts the whole reason for using the TI in the first place, that the "transaction" occurs between the actual emission and detection events.

 

[Sunil]

Do you have a reference for any actual theories along these lines?

Logunov, A.A. (1990). The relativistic theory of gravitation. Theor Math Phys 85(1)
Logunov, A.A. (2002). The Theory of Gravity. arxiv:gr-qc/0210005

Schmelzer, I. (2012). A Generalization of the Lorentz Ether to Gravity with General-Relativistic Limit. Advances in Applied Clifford Algebras 22(1), 203-242, resp. arxiv:gr-qc/0205035.

Schmelzer has considered your problem with superpositions of different spacetimes to, in (unpublished, but may be interesting in this context)

Schmelzer, I. (2009). The background as a quantum observable: Einstein's hole argument in a quasiclassical context, arXiv:0909.1408.

This is not giving up the spacetime interpretation; it's just saying spacetime geometry is not a quantum degree of freedom and can't participate in quantum dynamics.

It gives up the spacetime interpretation of the gravitational field. This allows the gravitational field to be handled like other matter fields and to become a quantum degree of freedom. Then, indeed, space and time can't participate in quantum dynamics, but classical space and time don't participate in dynamics anyway.

This is an additional, separate restriction on the spacetime geometry: basically in such a model the spacetime geometry would be flat Minkowski spacetime, but this geometry would be unobservable because gravitational fields would distort the measurements so it looked like the spacetime geometry was curved. This is, of course, just the "spin-2 field on flat spacetime" interpretation of GR, and it has been known for decades that it is mathematically equivalent to the usual curved spacetime interpretation (except possibly for issues of global topology, which I don't think we need to go into for this discussion).

Correct. I don't like to refer to the field-theoretic interpretation of GR because I have no good reference which clarifies the conceptual questions (like what destroys covariance, the status of the gauge condition). Whatever, it can be quantized (as an effective theory) without problems, see

Donoghue, J.F. (1994). General relativity as an effective field theory: The leading quantum corrections. Phys Rev D 50(6), 3874-3888

Instead, to quantize GR in the spacetime interpretation leads to topological foam and similar ...

The issue I see for using a model like this with the Transactional Interpretation would be that, as it currently stands, the TI expects to use the actual, physical light cones--the ones that we actually measure--but in the kind of model you're describing, it wouldn't, it would have to use the unobservable light cones of the background Minkowski spacetime. For example, in an experiment with entangled photons, where we have a superposition of different gravitational fields due to, say, a quantum event making a heavy ball go left or right, the actual events where the photons are emitted and detected would be the ones determined by the actual, observable light cones of whichever curved spacetime (aka flat spacetime with gravitational field) corresponded to the measured outcome of where the ball went, whereas the TI would be using different events for the "transaction", the ones corresponding to the background (unobservable) flat spacetime. But that contradicts the whole reason for using the TI in the first place, that the "transaction" occurs between the actual emission and detection events.

Both theories allow to solve this problem, because they both have also some causality condition which requires that the actual light cones are inside the background Minkowski light cone (RTG) resp. inside absolute future (Schmelzer). So, once the Bell violation experiment requires, in TI, some "transaction" inside the observable lightcone, the corresponding "transaction" would be possible in the background structure too.

 

[PeterDonis]

Logunov

Schmelzer

Both of these authors have been discussed extensively in past PF threads. I don't think there's anything useful to say about their work that hasn't already been said on PF many times. A search on PF should easily turn up past threads on both of them.

 

[PeterDonis]

classical space and time don't participate in dynamics anyway.

They do in standard GR, via the Einstein Field Equation.

I don't like to refer to the field-theoretic interpretation of GR because I have no good reference which clarifies the conceptual questions (like what destroys covariance, the status of the gauge condition).

You don't consider the many papers published by Deser, Feynman, Weinberg and others in the 1960s and 1970s that developed the spin-2 field theory in detail (IIRC Weinberg's 1972 textbook also discusses this) to address these questions?

The main issue I'm aware of with the field-theoretic interpretation of GR is that the spin-2 field theory is not renormalizable. But if you consider it as just an effective field theory, that's not really an issue.

 

[Demystifier]

Do you have a reference for any actual theories along these lines?

A little contribution to nongeometrical interpretation of gravity by me:
https://arxiv.org/abs/gr-qc/9901057

 

[Sunil]

They do in standard GR, via the Einstein Field Equation.

Of course. With "classical space and time" I tried to refer to the pre-relativistic notions.

You don't consider the many papers published by Deser, Feynman, Weinberg and others in the 1960s and 1970s that developed the spin-2 field theory in detail (IIRC Weinberg's 1972 textbook also discusses this) to address these questions?

Do you have a source which addresses it? I have not seen one. But I have not studied them in much detail. In particular, because the main technical question, if the spin-2 field theory really gives the Einstein equations, did not interest me.

The main issue I'm aware of with the field-theoretic interpretation of GR is that the spin-2 field theory is not renormalizable. But if you consider it as just an effective field theory, that's not really an issue.

Agreement.

 

[martinbn]

A little contribution to nongeometrical interpretation of gravity by me:
https://arxiv.org/abs/gr-qc/9901057

I find these (not just this one, but many similar) a bit strange. Or may be I don't understand them. It seems that the idea is that the metric is split as $g=\eta+h$, where $\eta$ is Minkowski. The Minkowski part is taken to be the "real" space-time metric, and the rest $h$ to be the gravitational field, which is also "real" just like the other matter fields. The motivation seems to be to treat gravity just as another field theory and be able to avoid some difficulties, say quantizing. My problems are: 1) it is completely arbitray. One can split it as $g=g_0+F$, where $g_0$ is any fixed solution. And obtain an equally "useful" theory. This is not even mentioned! 2) All non gravitational fields see and live on the goemetry of $g$, not $\eta$, but the gravitational field $h$ is somehow very different because it alone sees and lives on the Minkowski geometry. But the point (one point) was to treat it the same way as anything else! All observations also see only the full metric. The whole constranction could only be a usefull mathemtical tool, except that there are never applications, but not anything fundamental. 3) A theory/intepretation like this would predict that there are no black holes, and other of the GR conciquences, which seems to be in conflict with all the evidence so far. Doesn't this imidiatly disprove these attempts?

 

[Sunil]

Both of these authors have been discussed extensively in past PF threads. I don't think there's anything useful to say about their work that hasn't already been said on PF many times. A search on PF should easily turn up past threads on both of them.

Hm, may be the search function does not show me all of them, but I would not name what I have seen "discussed extensively". For example, I have found such a claim:

You might be missing a crucial point: what this paper calls the "Relativistic Theory of Gravitation" is not General Relativity. See here for some background (and bear in mind that Wikipedia cannot be relied on to give an accurate picture of the actual status of a theory--the article conspicuously fails to mention any issues with Logunov's theory, of which there are plenty, but most importantly it makes predictions that do not agree with experiment)

but not even information which of the predictions do not agree with experiment.

 

[Demystifier]

A theory/intepretation like this would predict that there are no black holes, and other of the GR conciquences, which seems to be in conflict with all the evidence so far.

I would interpret it differently. Such an interpretation suggests that the Schwarzschild
singularity is a true physical singularity and questions the existence of black hole interior. It doesn't conflict any experimental evidence and seems compatible with some proposals to resolve the black hole information paradox.

 

[martinbn]

I would interpret it differently. Such an interpretation suggests that the horizon singularity is a true physical singularity and questions the existence of black hole interior. It doesn't conflict any experimental evidence and seems compatible with some proposals to resolve the black hole information paradox.

How! If the interior of the black holes do not exist, your space-time is not Minkowski, which is what you start with.

 

[Demystifier]

How! If the interior of the black holes do not exist, your space-time is not Minkowski, which is what you start with.

Interior spacetime exists, but perhaps physical matter living on it doesn't exist.

 

[martinbn]

Interior spacetime exists, but perhaps physical matter living on it doesn't exist.

You said it didn't. I guess part of the interpretation is to change it as you go .

What about cosmology? You cannot have a big bang, right?

 

[stevendaryl]

Interior spacetime exists, but perhaps physical matter living on it doesn't exist.

Well, in the gravitational collapse of a spherically symmetric distribution of matter, there is already in the interior, isn’t there?

 

[Demystifier]

You said it didn't. I guess part of the interpretation is to change it as you go .

“If we knew what it is we were doing, it would not be called research. Would it?”
- Albert Einstein

What about cosmology? You cannot have a big bang, right?

If you mean the initial singularity, it's a problem even in standard GR, so I don't know what's your point.

 

[Demystifier]

Well, in the gravitational collapse of a spherically symmetric distribution of matter, there is already in the interior, isn’t there?

Good point! That could be a challenge for firewall/fuzzball proponents.

 

[martinbn]

If you mean the initial singularity, it's a problem even in standard GR, so I don't know what's your point.

The point is, that you don't have solutions like that and the observations support them, so your interpretation is in conflict with observations. And, no, it is not a problem in GR.

 

[Demystifier]

you don't have solutions like that

Why?

 

[martinbn]

Why?

Are there solutions like those?

 

[PeterDonis]

Do you have a source which addresses it?

I learned about it from the Feynman Lectures on Gravitation, which has references to some early papers on the topic. Weinberg's textbook is from 1972. MTW (1973) also contains references to papers on the topic, including, IIRC, one by Deser in about 1970 which is probably the most comprehensive treatment.

 

[PeterDonis]

may be the search function does not show me all of them

Unless you're seeing threads going back to the period 2005-2009 or so, no, it isn't. That was the time frame when the main discussions I'm aware of occurred.

 

[PeterDonis]

Such an interpretation suggests that the Schwarzschild
singularity is a true physical singularity

In which case you don't have a different interpretation of GR, you have a different theory. In standard GR the locus $r = 2m$ in Schwarzschild coordinates is not a physical singularity, since all curvature invariants are finite.