A Implications of quantum foundations on interpretations of relativity

[zonde]

No, that's not what the basic math of QM says. The basic math of QM only says that your state (1) is the one you use to predict the probabilities for various results of the measurement, and state (2) is the one you use to predict the probabilities for future measurements once you know the result of this one.

Any other claim is interpretation dependent.

It does not matter. From the text I quoted I read Cramer as saying that (1) never represents physical reality i.e. there is no superposition of entangled particle states.

 

[PeterDonis]

It does not matter.

Yes, it does. Saying that a particular aspect of the math, in this case superposition, is not "in reality" is one thing. Saying that it is simply not there at all is another. The latter claim is the one I was arguing against (not against you, but against the poster who originally made the claim in this thread). If all you are asserting is the former claim, we are in agreement.

I quoted I read Cramer as saying that (1) never represents physical reality

Yes, that's what the TI says.

i.e. there is no superposition of entangled particle states.

"In reality", yes. But the superposition is still there in the math, because the math is the same as the standard math of QM. As I have already said, to what extent the things that happen in the math also happen "in reality" is interpretation-dependent; the TI is one interpretation. But the math is still the same for all interpretations.

 

[PeterDonis]

It does not matter.

I would argue that what does not matter is the differing claims that different interpretations make about "reality". None of those claims are experimentally testable, since all interpretations of QM make the same predictions for actual experimental results. They just tell different stories about why the results are what they are. To me, such differences do not matter. The TI tells one story; other interpretations tell other story. In the TI story, "superpositions" never exist "in reality"--but the TI still says there is a random, unpredictable choice among different alternatives, just as the math of standard QM does. It gives us no help at all in explaining why one particular result happens instead of another.

What does matter is when such differences are used to construct different theories, that make different predictions about actual experimental results. For example, the GRW stochastic collapse model is a different theory; it makes different predictions from standard QM about the results of certain (very hard to do) experiments. So far, as I understand it, what experiments we can do along these lines make the model seem unlikely; but at least it's testable vs. standard QM. TI, in its current form, is not. Perhaps a different theory drawing inspiration from TI will come along one day, and then we can test it.

 

[zonde]

I would argue that what does not matter is the differing claims that different interpretations make about "reality". None of those claims are experimentally testable, since all interpretations of QM make the same predictions for actual experimental results. They just tell different stories about why the results are what they are. To me, such differences do not matter.

Yes, good point. I recognize your position as quite rational.
However I have different take on interpretations. As I see it is possible to find flaws in interpretations even if they declare that they agree with all the predictions of QM.
It is possible that they can't predict outcomes of some experiments even if they have the same math for some other experiments.
And they can be inconsistent and they can be unscientific. Say if interpretation is inconsistent it can't make unequivocal predictions - it's a fail. And if it is unscientific it will never ever give us any knowledge (say I tend to consider TI as unscientific because it seems as equivalent to superdeterminism - eternally-global consistency rule that determines what combinations of outcomes are valid).

But if we would get rid of all the trash it might just happen that it would be clearer where to look for a new theory not just interpretation.

 

[PeterDonis]

It is possible that they can't predict outcomes of some experiments even if they have the same math for some other experiments.

This doesn't make sense. All interpretations use the same math. If something only uses the same math for some experiments, but different math (or no math at all, so it can't even make a prediction) for others, it isn't an interpretation of QM; it's a different theory.

they can be inconsistent

This doesn't make sense either. The math of QM is consistent, so any interpretation based on it should also be consistent.

and they can be unscientific

This is a purely subjective criterion which comes down to personal opinion.

f we would get rid of all the trash it might just happen that it would be clearer where to look for a new theory not just interpretation.

If you really believe this you should not be posting about it here. You should be publishing a new paper that "gets rid of all the trash" and shows how that points the way to a new theory.

 

[zonde]

This doesn't make sense. All interpretations use the same math. If something only uses the same math for some experiments, but different math (or no math at all, so it can't even make a prediction) for others, it isn't an interpretation of QM; it's a different theory.

This doesn't make sense either. The math of QM is consistent, so any interpretation based on it should also be consistent.

Interpretations can use quite different math. They just have to demonstrate that it can be reduced to standard QM math. But it is conceivable that it reduces nicely to QM math in some cases, but in other cases it doesn't.
For example Bohmian Interpretation is claimed to be no collapse interpretation, but I can't wrap my head around how it then predicts BI violations. As I remember in one thread Demystifier tried to explain that but was not very successful at that. But of course it might be that he have found a way, however I will remain rather skeptical until I see such explanation.

This is a purely subjective criterion which comes down to personal opinion.

Well, would you call Poppers falsifiability subjective too?

If you really believe this you should not be posting about it here. You should be publishing a new paper that "gets rid of all the trash" and shows how that points the way to a new theory.

Sorry but why? You shared your opinion, I shared mine. How did you arrived at such farfetched suggestion?

 

[PeterDonis]

Interpretations can use quite different math. They just have to demonstrate that it can be reduced to standard QM math. But it is conceivable that it reduces nicely to QM math in some cases, but in other cases it doesn't.

In the latter case, again, it's not an interpretation; it's a different theory, which just happens to have standard QM as one approximation under certain conditions.

You might not want to use "interpretation" that way, but in this forum, that is how that term is used.

Bohmian Interpretation is claimed to be no collapse interpretation, but I can't wrap my head around how it then predicts BI violations.

It's a no collapse interpretation because the actual, physical state of the system includes the unobservable particle positions, so the results of actual, physical measurements are not due to any random choice among alternatives, they are due to whichever branch of the wave function happens to contain the unobservable particle positions.

It predicts BI violations because it is explicitly nonlocal: the equation of motion for the unobservable particle positions includes the quantum potential, which allows an interaction anywhere in the universe to instantaneously affect the motion of the unobservable particles anywhere else in the universe. (Yes, "instantaneously" means we are violating relativity; AFAIK there is no generally accepted relativistic version of the Bohmian interpretation.)

 

[zonde]

It's a no collapse interpretation because the actual, physical state of the system includes the unobservable particle positions, so the results of actual, physical measurements are not due to any random choice among alternatives, they are due to whichever branch of the wave function happens to contain the unobservable particle positions.

You describe the situation after beamsplitter, where there are two separate branches. But even at beamsplitter particle is not behaving randomly. In which branch particle will end up is determined by pilotwave and initial position of particle.
But too much determinism will make it contradict Kochen-Specker Theorem.

It predicts BI violations because it is explicitly nonlocal: the equation of motion for the unobservable particle positions includes the quantum potential, which allows an interaction anywhere in the universe to instantaneously affect the motion of the unobservable particles anywhere else in the universe. (Yes, "instantaneously" means we are violating relativity; AFAIK there is no generally accepted relativistic version of the Bohmian interpretation.)

Yes quantum potential is nonlocal and it allows an interaction anywhere in the universe to instantaneously affect the motion of the particles anywhere else in the universe. But will it affect the right particle at the right time in the right way? That's the question that requires the answer. Otherwise it's just handwaving.

 

[PeterDonis]

You describe the situation after beamsplitter

No, I describe the situation at all times according to the Bohmian interpretation. You even agree with me:

In which branch particle will end up is determined by pilotwave and initial position of particle.

Exactly; that's what I'm saying. Which means there is no collapse in this interpretation because, given the initial position of the particle, one single measurement result is determined to occur. There is no random choice between alternatives; the "alternatives" in the wave function (pilot wave) are there in the math but not in reality according to this interpretation.

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

I don't know what you mean here. The Bohmian interpretation's predictions are exactly the same as standard QM, so it doesn't contradict the theorem.

will it affect the right particle at the right time in the right way?

Of course. Why wouldn't it?

That's the question that requires the answer.

It already has an answer. See above.

 

[Fra]

This is a purely subjective criterion which comes down to personal opinion.

Well, would you call Poppers falsifiability subjective too?

I think the distinction is between hypothesis/conjecture generation and falsification of candidates.

The hypothesis generation may well be subjective, but the falsification is not. Popper tried to deny the fuzzy inductive part of science, by sweeping the process of conjecture generation under the rug, and instead focus on falsification to make science seems like a clean deductive reasoning (which it clearly isn't).

For a theorist, the hypothesis-building part seems to be the big and important part, but unfortunately the problem of PREMATURELY judging a hypothesis (without actually making falsifiable predictions), is not falsifable, because while while a theory can be "wrong", a hypothesis generator can not be "wrong" as it can learn and correct! It can perhaps be more or less efficient in learning. So one must judge a theory for optimal hypothesis generation, in a different way - which way? but this is way beyond Poppers description which i find simplistic. I read his book long time ago and it left me unsatisfied and frustrated.

/Fredrik

 

[PeterDonis]

would you call Poppers falsifiability subjective too?

To the extent that it is equivalent to "experimentally testable", no. But the term "unscientific" is not the same as "not falsifiable". If you meant the latter, that's what you should have said.

 

[PeterDonis]

I think the distinction is between hypothesis/conjecture generation and falsification of candidates.

As far as Popper's criterion goes, yes, I think this distinction is key. Popper's criterion can usually be applied reasonably if you already have a hypothesis in hand. But it offers no help at all in finding a hypothesis.

However, the term "unscientific", as I just remarked to @zonde in my previous post, is not the same as "not falsifiable". The latter is a reasonably precise term that can be referenced to something specific (Popper's criterion). The former is not.

 

[AnssiH]

Yes, it does. The superposition is in the multiple "offer waves" that get sent out, and the multiple "response waves" that get sent back. One of those offer-response pairs is randomly selected to become the actual result; that corresponds to collapse.

Also, in my post #65, which was where I brought up superposition in the context of this thread, I did not refer to superposition in general, but to superposition of different spacetime geometries. No interpretation of QM has a way to deal with that, including the TI. TI says that offer and response waves travel along light cones; but if we have a superposition of different spacetime geometries, we have a superposition of different light cone structures, and TI cannot handle that.

Hey Peter :)

I'm afraid that is your personal interpretation of TI, not in any way required or useful in the actual framework of TI. The idea of retarded and advanced waves operate exclusively in a static spacetime structure, which means you can think of them as static shapes where correlations merely appear to exist between space-like separated events. The whole idea hinges on Minkowski's notion of time being an illusion to conscious observers (which is why I don't really think of it as realistic... But that of course is an opinion only)

You seem to possibly interpret that mechanism as if "spacetime itself evolves over time" - that would just mean you add a redundant time evolution to time evolution - which cannot be observed. So why include it into an interpretation? There is no need since you already can posit any possible correlation as occurring due to the emission event already having feedback "from the static future". It's pretty simple idea really.

The idea that there would be multiple spacetimes (multiple universes) in superposition is completely redundant component in this interpretation - it yields no effect to the outcome.

I can only repeat - you seem to have little bit confused view of what superposition is. It's an explanation to Bell experiment correlations. An explanation. Others exist. We've seen at least three concepts already that don't contain superposition, since Ruta brought up the concept of relativistic measurement of Planck constant:

Here is a shorter layperson's version in ScienceX: Einstein's missed opportunity to rid us of 'spooky actions at a distance' (https://sciencex.com/news/2020-10-einstein-opportunity-spooky-actions-distance.html).

Pretty interesting idea Ruta! There's actually more interesting facets to Planck constant when applied to relativity (such as the idea of "relativistic black holes" via extreme doppler shifts), those would be interesting to discuss in some other thread perhaps I'm afraid I don't know any publications that would have brought that up though, so maybe not on this forum.

Cheers everyone!
-Anssi

 

[PeterDonis]

I'm afraid that is your personal interpretation of TI

The first part, about superposition in general, is a simple statement of how TI works mathematically. It's taken straight from the Cramer paper you yourself linked to.

For the second part, about curved spacetime, see below.

The idea of retarded and advanced waves operate exclusively in a static spacetime structure

Sure, and that's fine as long as we are assuming spacetime is classical, so there is only one spacetime structure.

But the whole premise of the search for a theory of quantum gravity is that spacetime structure should not be classical--that it should work like everything else does, where you have amplitudes for different spacetime structures, and where the spacetime structure can get entangled with other quantum degrees of freedom via interactions. Any such entangled state will not have well-defined light cones and so the TI would not work, at least not in its current form. I have not seen Cramer or anyone else advocating TI propose a way for the TI to work in such a case.

If your position is that spacetime structure should not be quantum, that it should remain as a classical entity even though everything else is quantum, then you would not be alone; I believe Freeman Dyson, among others, proposed a similar viewpoint. But I have not seen Cramer or anyone else advocating TI propose such a viewpoint.

You seem to possibly interpret that mechanism as if "spacetime itself evolves over time"

No, that is not at all what I'm saying. See above.

 

[AnssiH]

It just does not work. Detection events are paired up like particles. You can't throw away that because it's just experimental fact (I believe experimental limit for efficiency of pairing up downconverted photons is around 99%).

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

It's a discrete reaction on a detection plane - a piece of matter - made of discrete collection of atoms, right?

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).

Before someone asks for a reference to this claim:
https://en.wikipedia.org/wiki/Planck's_law
Yes I know Wikipedia is not considered a valid reference but come on boys, if you really doubt the validity of Planck's Law, there's hundreds of references right at the bottom of that page for you to investigate.

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.

(And how exactly do you reconcile for the fact that particle may have more energy content than the next wave mode of an electron can absorb? But that's a bonus question)

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.

Have fun,
-Anssi

 

[PeterDonis]

Before someone asks for a reference to this claim

We don't need a reference for Planck's Law itself in an "A" level thread on QM. Anyone with the requisite background knowledge for an "A" level thread on QM should already be familiar with Planck's Law.

The same does not apply to other claims you have been making in this thread, which is why you got asked for references for those other claims.

how exactly do we purport to differentiate between "a particle causing that quantized reaction", vs "a wave causing that quantized reaction"?

By constructing models for each alternative, looking for experimental scenarios where the models make different predictions, and running the experiments to see which way nature votes. If the predictions of both models are the same, then we have no way of distinguishing between them by experiment, at least not that particular experiment.

So what models are you using for "particle causing that quantized reaction" and "wave causing that quantized reaction" that lead you to claim that they make the same predictions for an "atom absorbing energy" experiment? And will that also be true for any experiment whatever? Or are there other experiments we could use to distinguish between these two models (because they make different predictions for those other experiments)?

It's pretty silly to claim that classical mechanics predict a linear correlation in Bell experiment

What classical mechanics model makes this prediction? The class of models Bell considered didn't make such a prediction; the only common feature that class of models has is that it can't produce correlations that violate the Bell inequalities.

 

[AnssiH]

There is a time when there is wavefunction (which can be represented as superposition dependent on the choice of basis) and later there is collapse and result of measurement. Cramer on the other hand says it is "atemporal process" (actually seems like an oxymoron), so it should mean that "offer waves" actually do not exist at any moment in time. So there is no temporal process of wavefuntion collapse.

Yeah, it seems like an oxymoron because TI only works if you literally assume the existence of static Minkowski spacetime

So "there is no dynamic time" in it.

One way to look at it is to realize that the problem with Bell experiment correlations - if we view them as coming out from measuring a property of particles that literally flew from emitter to detector - is that once we have measured the outcomes, we can no longer go back to influence the emission because it has already happened.

So that's where the idea of superposition comes to play - as one explanation to those correlations (and it can in itself be interpreted in multitude of ways of course).

But just think about a static spacetime - of course it could have correlations going which ever way - if someone wants to posit that as an interpretation, it can always be done. And that is TI. To think about TI in terms of time evolution and superposition that dynamically evolves and at some point collapses, is to think in oxymoronic / redundant terms.

The fact that a static spacetime interpretation can always be done seems so trivially obvious to me that I can't believe Einstein would have missed that opportunity - I suspect he did not. He probably just didn't care much about it. (Much like we don't care to seriously posit the possibility of solipsism, just as an example)

-Anssi

 

[AnssiH]

We don't need a reference for Planck's Law itself in an "A" level thread on QM. Anyone with the requisite background knowledge for an "A" level thread on QM should already be familiar with Planck's Law.

Thanks, that's a relief

By constructing models for each alternative, looking for experimental scenarios where the models make different predictions, and running the experiments to see which way nature votes. If the predictions of both models are the same, then we have no way of distinguishing between them by experiment, at least not that particular experiment.

Yuup, and that's where we enter the wonderful world of interpretations and philosophy.

So what models are you using for "particle causing that quantized reaction" and "wave causing that quantized reaction" that lead you to claim that they make the same predictions for an "atom absorbing energy" experiment? And will that also be true for any experiment whatever? Or are there other experiments we could use to distinguish between these two models (because they make different predictions for those other experiments)?

Good question. At least I struggle to think of experiments to differentiate between these possibilities, because they appear similar in such a fundamental level of our observational limits (because we just can't directly "just see energies" without using a piece of matter that reacts to it). That's why the difference is fundamentally a matter of interpretation.

Basically if you view any type of "orientation wave filter" classically, the expected "energy dampening" is of course just basic trigonometry since you are removing a direction component from a wave, so it's cos^2(angle). In terms of QM, that exact idea (and math) represents the dampening of the probability of detecting a particle after the filter. Basically exactly this:


(Not intended as a reference, just an example of the mathematical concept)

In terms of an "atom absorbing quantized energy" idea, by dampening wave energy with a filter you would still be literally making it less probable for any atom to be able to react to that energy (as you are approaching the lowest possible energy limits, you would start seeing sparse reactions). The only difference is that in the latter case you "interpret" the situation as if there is low energy wave energy present - which you cannot detect with matter unless certain energy threshold is reached. And in the former case you "interpret" the situation as if there's a superposition (of your flavor) present in the system for the particles that are "making a journey" (as per your assumption that they indeed exist)

So, while I don't know about a published paper that would discuss this sort of treatment (I'd imagine some might exist, I just don't know about them), but on the other hand I'm really talking about trigonometry and very basic wave mechanics. And I do struggle to find a case where an actual observational difference could be found - looks like an interpretation to me.

What classical mechanics model makes this prediction? The class of models Bell considered didn't make such a prediction; the only common feature that class of models has is that it can't produce correlations that violate the Bell inequalities.

That I don't know - I was merely referring to the comment made with the correlation picture at the end of the Overview section here:
https://en.wikipedia.org/wiki/Bell's_theorem#Overview

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°

In order to have sharp peaks and valleys, you must be assuming the possibility of detecting arbitrarily small energies after the filters - but that is already excluded by our model of an atom.

Where-as the QM correlation as pictured is - as I'm sure you know - exactly cosine correlation. The important part of course being that the QM correlation does not represent an actual detection, but the probability of a detection. So another way to put it is to simply say - in the classical views (as purported by that Wikipedia article) everyone assumes any and every energy level can detected - even though we are using atoms to do so

-Anssi

 

[PeterDonis]

in the classical views (as purported by that Wikipedia article)

I don't see how what you quoted from the Wikipedia article appears anywhere in the actual literature I've read about Bell's Theorem and related theorems.

More generally, I don't think that Wikipedia article is a good reference for a discussion of Bell's Theorem. The very first sentence in the "Overview" is false:

"The theorem is usually proved by consideration of a quantum system of two entangled qubits with the original tests as stated above done on photons."

No, the theorem is proved using math that has nothing whatsoever to do with quantum mechanics. Once the theorem is proved, then the obvious fact that the predictions of QM violate the Bell inequalities means that QM must violate at least one of the premises of the theorem. But the actual proof of the theorem has nothing to do with QM. It's just a proof that any theory satisfying the premises must make predictions that satisfy the Bell inequalities.

The important part of course being that the QM correlation does not represent an actual detection, but the probability of a detection.

No, the "QM correlation" is a prediction of what the correlation will be after the measurements are made and the results are known. It is not a prediction of a probability of anything.

It is true that QM cannot predict what the individual measurement results will be, it can only predict probabilities. But that does not mean its prediction of the correlation between results is probabilistic. It isn't. QM predicts that the correlation will be exactly $\cos \theta$. It does not predict that the correlation has probability $p$ of being one value and probability $q$ of being another value.

 

[PeterDonis]

I struggle to think of experiments to differentiate between these possibilities

I wasn't just asking for experiments, I was asking for models. Before you can even think about doing an experiment to compare the predictions of models, you have to have models to compare.

if you view any type of "orientation wave filter" classically

Why would absorption of light by an atom have anything to do with an "orientation wave filter"? What model of light leads you to this?

Basically, it looks to me like you don't have a well-defined model in mind at all; you're just waving your hands. Without a well-defined model of "light as a wave" and "light as a particle", you have no basis for making any claims at all about what we should see in experiments and whether it should be different depending on whether light is a wave or a particle.

(Note, btw, that in our current best theory of light, quantum electrodynamics, light is neither a wave nor a particle, it is a quantum field.)

 

[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°

.

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

.

 

[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.

.

...sort of autistic

.

 

[Sunil]

What cannot be accommodated by any interpretation involving classical spacetime is superposition. For example, suppose we set up a "Schrodinger'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.