The Time Symmetry Debate in Quantum Theory

[stevendaryl]

Bill, I agree with the quoted part.
Non-contextuality is a strong assumption IMO. But yes it makes the Hilbert formalism "ugly" not to adopt it. But Gleason's theorem assumes non-contextuality and that was the sense of my comment about lack of generality of the theorem as there are QM interpretations that don't assume non-contextuality (you mentioned BM but there are also the modal interpretations and others).

I did a Google search on the phrase "non-contextuality" and although it gets many hits, I still don't really understand what it means. Can someone give a real definition, and briefly explain why it's relevant in interpretations of quantum mechanics?

 

[audioloop]

I did a Google search on the phrase "non-contextuality" and although it gets many hits, I still don't really understand what it means. Can someone give a real definition, and briefly explain why it's relevant in interpretations of quantum mechanics?

conjugates values that does not depend on the context, that is independent of its antecedents.

http://plato.stanford.edu/entries/kochen-specker/https://www.physicsforums.com/showpost.php?p=4401195&postcount=12

really, you have to define locality/non-locality just like subsets of contextuality/noncontextuality,
contextuality is broader, subsumes locality/nonlocality.
that every state that is contextual with respect to the defined test of contextuality is nonlocal as per the CHSH (Clauser, Horne, Shimony, Holt test) but the converse is not true, or as i like to ask:

Every state that is contextual is nonlocal.
...and the inverse, is every state that is nonlocal is contextual ?-----
measured values (atributtes, characteristics, properties) in context, just is related to that, "context", be real goes beyond properties, the possibility of values requires pre-existent objects or process, without objects, there is no possibility of properties (values).

 

[stevendaryl]

conjugates values that does not depend on the context, that is independent of its antecedents.

http://plato.stanford.edu/entries/kochen-specker/


https://www.physicsforums.com/showpost.php?p=4401195&postcount=12

That leaves me a little puzzled, still. Maybe somebody can give examples of a toy model that is contextual?

What I do understand is this: The argument that it is impossible for a hidden-variables theory that reproduces the predictions of quantum mechanics in an EPR-type twin particle experiment assumes that the hidden variable is unaffected by choices made at the measuring devices. But such an effect is ruled out by locality, so I don't see why "contextuality" matters in that case.

 

[DrChinese]

That leaves me a little puzzled, still. Maybe somebody can give examples of a toy model that is contextual?

What I do understand is this: The argument that it is impossible for a hidden-variables theory that reproduces the predictions of quantum mechanics in an EPR-type twin particle experiment assumes that the hidden variable is unaffected by choices made at the measuring devices. But such an effect is ruled out by locality, so I don't see why "contextuality" matters in that case.

An example of a contextual model can be seen if a context is considered to reside in the future. If Alice and Bob can signal from the future to the past as to what they are planning to measure, then entangled state correlations are easier to explain. Nothing needs to propagate faster than c for such mechanism to operate (and to properly describe any existing experiments).

So here we have locality respected while non-contextuality is not, which is essentially what you are looking for. Most contextual models seem "strange" as in counter-intuitive. I personally don't see them as any stranger than non-local ones.

 

[DevilsAvocado]

That leaves me a little puzzled, still. Maybe somebody can give examples of a toy model that is contextual?

Spekkens Toy Model take the epistemic view and has local and non-contextual variables (= fails to reproduce violations of Bell inequalities), here’s a short introduction and here’s the arXiv paper.

Jan-Åke Larsson has made a contextual extension of this toy model:

http://arxiv.org/abs/1111.3561

Quantum systems show contextuality. More precisely, it is impossible to reproduce the quantum-mechanical predictions using a non-contextual realist model, i.e., a model where the outcome of one measurement is independent of the choice of compatible measurements performed in the measurement context. There has been several attempts to quantify the amount of contextuality for specific quantum systems, for example, in the number of rays needed in a KS proof, or the number of terms in certain inequalities, or in the violation, noise sensitivity, and other measures. This paper is about another approach: to use a simple contextual model that reproduces the quantum-mechanical contextual behaviour, but not necessarily all quantum predictions. The amount of contextuality can then be quantified in terms of additional resources needed as compared with a similar model without contextuality. In this case the contextual model needs to keep track of the context used, so the appropriate measure would be memory. Another way to view this is as a memory requirement to be able to reproduce quantum contextuality in a realist model. The model we will use can be viewed as an extension of Spekkens' toy model [Phys. Rev. A 75, 032110 (2007)], and the relation is studied in some detail. To reproduce the quantum predictions for the Peres-Mermin square, the memory requirement is more than one bit in addition to the memory used for the individual outcomes in the corresponding noncontextual model.

What I do understand is this: The argument that it is impossible for a hidden-variables theory that reproduces the predictions of quantum mechanics in an EPR-type twin particle experiment assumes that the hidden variable is unaffected by choices made at the measuring devices. But such an effect is ruled out by locality, so I don't see why "contextuality" matters in that case.

I agree, I always thought that contextuality means that the entire measurement setup has to be taken in consideration for the context of outcome, i.e. if Alice put her polarizer orthogonal to Bob this will have an effect on the outcome of photon B = non-locality...

 

[DevilsAvocado]

An example of a contextual model can be seen if a context is considered to reside in the future. If Alice and Bob can signal from the future to the past as to what they are planning to measure, then entangled state correlations are easier to explain. Nothing needs to propagate faster than c for such mechanism to operate (and to properly describe any existing experiments).

I’m lost DrC... how could “Alice and Bob signal from the future” without an FTL-mechanism that is forbidden by both QM and SR?

 

[bhobba]

I am looking forward to it. However, the argument was about something different: that deterministic theory is a special kind of probabilistic theory. I am quite interested what others think about this.

Yea - but in discussing that you raised the issue. I still believe it is. Indeed if it isn't then Kochen-Sprecker is in deep trouble because that's what it assumes - namely for QM to be deterministic you need to be able to define a measure of only 0 and 1.

I have started a thread over in that sub-forum about it and already their are some interesting replies.

Thanks
Bill

 

[Charles Wilson]

Here I go again...
From Age of Entanglement:

"...But what if we let relativity enter the game even deeper? What if the detectors are in relative motion such that each detector in its own reference frame analyzes its photon before the other?...

"...once one assumes that the collapse is a real phenomenon, and once one considers specific models, then the conflict is real and testable"...if both measurements happen before the other, then the quantum correlation should disappear, however large the speed of the spooky action!

"Once the engineering was made feasible, "this experiment was also performed in Geneva in the spring of 1999", reported Gisin. "The two-photon interferences were still visible, independently of the relative velocity between Alice and Bob's reference frames." Alice, in her reference frame, measures her photon first; from Bob's point of view, he has measured his photon first; yet, the correlation is still present..."

 

[DevilsAvocado]

From Age of Entanglement:

Ah! :!) Thank you for reminding me. I must get that book, NOW!

 

[bhobba]

I did a Google search on the phrase "non-contextuality" and although it gets many hits, I still don't really understand what it means. Can someone give a real definition, and briefly explain why it's relevant in interpretations of quantum mechanics?

Conceptually its very simple. Suppose you have some observable A = sum y1|b1><b1| + y2|b2><b2| + y3 |b3><b3| where |b3> means outcome |b1> or |b2> did not occur. Outcome |b1> occurs with probability |<u|b1>|^2 from the Born rule. Now consider the observable C = y1 |b1><b1| + c2|c2><c2| + c3|c3><c3|. Now from the Born rule outcome |b1> will occur with exactly the same probability even though the second outcome is different. This is known as non-contextuality because a property does not depend on what else you happen to be measuring with it. It allows a probability measure to be uniquely defined regardless of what basis it is part of ie the other possible outcomes of an observation. Now it turns out, due to Gleason's theorem, that the assumption of non-contextuality all by itself is enough to prove Born's rule. In fact it would be a pretty silly choice of Hilbert space as the formalism for the states of QM if it wasn't true. This is what's meant by non-contextuality being unnatural and counter-intuitive.

But now look at it physically and forgetting the Hilbert space formalism. We have zero reason to believe that changing what else you measure will not affect other things you measure at the same time - after all you have a different apparatus. This is what's meant by the physical basis is unclear. And indeed interpretations of QM such as Bohmian Mechanics exist that are contextual.

Thanks
Bill

 

[bhobba]

I agree, I always thought that contextuality means that the entire measurement setup has to be taken in consideration for the context of outcome, i.e. if Alice put her polarizer orthogonal to Bob this will have an effect on the outcome of photon B = non-locality...

It means measurements are not affected by what else you happen to be measuring at the same time. If you have an observable A = sum ai |bi><bi| the probability of outcome |b1> does not depend on the other |bi>. What you mention is just one example.

Thanks
Bill

 

[bhobba]

"...once one assumes that the collapse is a real phenomenon, and once one considers specific models, then the conflict is real and testable"...if both measurements happen before the other, then the quantum correlation should disappear, however large the speed of the spooky action!

But that is precisely what many interpretations such as the ensemble interpretation specifically deny ie its a real phenomena. In that interpretation the state is simply something that tells us about the probabilistic behavior of a conceptual ensemble of systems. Collapse is simply selecting an element of the ensemble - nothing in a real sense occurred. Since such is possible I am at a loss to understand stuff like the above - all you are arguing for is interpretations where its not real - not that QM has any issues.

Thanks
Bill

 

[Charles Wilson]

Yeesh!
I'll admit the pull quote is not rigorous. I hate using the word "collapse" because I think it's loaded from Bohr's Metaphysics. "But everybody else uses it..."
"So if everybody sez they're going to jump off a cliff, are you going to follow 'em?"

Well...ummm...no. I thought it was valuable to add into the discussion, however, since it pushed the tension between SR and QM. I thought that it was interesting that the Naive Realist position (Not necessarily G E Moore's NR) would state that the interference patterns should disappear and they do not. QM wins again!

But SR still believes, in their reference frame, that they won.

That's why I posted.

CW

 

[T0mr]

... but electromagnetism is 10^39 times stronger than gravitation ...

I think the Bohr model is pretty dead, there are incompatibilities to empirical spectral lines, and it also violates the uncertainty principle, and even if you magically could fix all that – where is your single localized particle in the double-slit experiment?

It doesn’t work...

How does the Bohr model violate the uncertainty principle? The Bohr model does correctly predict spectral lines for atomic hydrogen. That is something at least. I get the impression that we feel very confident we have exhausted all mechanical analogies for things like the double slit experiment when we cannot possibly have. There are an infinitude of possible mechanical analogies we could use to model a particle like an electron (and all but one will be wrong). I don't know if anyone has seen the experiments with silicon droplets but I saw these a while back and found them very interesting:

http://www.youtube.com/watch?v=nmC0ygr08tE

Also Morgan Freeman narrates:
http://www.youtube.com/watch?v=sGCtMKthRh4

 

[audioloop]

*"...But what if we let relativity enter the game even deeper? What if the detectors are in relative motion such that each detector in its own reference frame analyzes its photon before the other?...

*"...once one assumes that the collapse is a real phenomenon, and once one considers specific models, then the conflict is real and testable"

*it will be done

Fundamental quantum optics experiments conceivable with satellites -- reaching relativistic distances and velocities
http://arxiv.org/abs/1206.4949
the line up:
David Rideout, Thomas Jennewein, Giovanni Amelino-Camelia, Tommaso F. Demarie, Brendon L. Higgins, Achim Kempf, Adrian Kent, Raymond Laflamme, Xian Ma, Robert B. Mann, Eduardo Martin-Martinez, Nicolas C. Menicucci, John Moffat, Christoph Simon, Rafael Sorkin, Lee Smolin, Daniel R. Terno.

Super Physics Smackdown: Relativity vs Quantum Mechanics...In Space

Read more: http://www.technologyreview.com/view/428328/super-physics-smackdown-relativity-v-quantum-mechanicsin-space/#ixzz2UyZfdG1L
From MIT Technology Review

*it will be done
(objective reduction models)

Observation of a kilogram-scale oscillator near its quantum ground state
http://iopscience.iop.org/1367-2630/11/7/073032/pdf/1367-2630_11_7_073032.pdf

http://eprints.gla.ac.uk/32707/1/ID32707.pdf

the line up:
B Abbott, R Abbott, R Adhikari, P Ajith, B Allen, G Allen, R Amin, S B Anderson, W G Anderson,
, M A Arain, , M Araya, H Armandula, P Armor, Y Aso, S Aston, P Aufmuth...

 

[audioloop]

That leaves me a little puzzled, still. Maybe somebody can give examples of a toy model that is contextual?

What I do understand is this: The argument that it is impossible for a hidden-variables theory that reproduces the predictions of quantum mechanics in an EPR-type twin particle experiment assumes that the hidden variable is unaffected by choices made at the measuring devices. But such an effect is ruled out by locality, so I don't see why "contextuality" matters in that case.

http://digital.library.pitt.edu/u/ulsmanuscripts/pdf/31735033440391.pdf

 

[TrickyDicky]

I’m lost DrC... how could “Alice and Bob signal from the future” without an FTL-mechanism that is forbidden by both QM and SR?

I thought the same, I still don't know what to make of that answer.

 

[stevendaryl]

I’m lost DrC... how could “Alice and Bob signal from the future” without an FTL-mechanism that is forbidden by both QM and SR?

I'm not sure if this is what he meant, but there are "time-symmetric" formulations of wave propagation in which the future affects the present in the same way the past does. It's not FTL, in the sense that propagation speed is always <= c, although the propagation can be into the past as well as into the future. This is consistent with SR in the weak sense that there is no violation of lorentz invariance.

 

[TrickyDicky]

Conceptually its very simple. Suppose you have some observable A = sum y1|b1><b1| + y2|b2><b2| + y3 |b3><b3| where |b3> means outcome |b1> or |b2> did not occur. Outcome |b1> occurs with probability |<u|b1>|^2 from the Born rule. Now consider the observable C = y1 |b1><b1| + c2|c2><c2| + c3|c3><c3|. Now from the Born rule outcome |b1> will occur with exactly the same probability even though the second outcome is different. This is known as non-contextuality because a property does not depend on what else you happen to be measuring with it. It allows a probability measure to be uniquely defined regardless of what basis it is part of ie the other possible outcomes of an observation. Now it turns out, due to Gleason's theorem, that the assumption of non-contextuality all by itself is enough to prove Born's rule. In fact it would be a pretty silly choice of Hilbert space as the formalism for the states of QM if it wasn't true. This is what's meant by non-contextuality being unnatural and counter-intuitive.

But now look at it physically and forgetting the Hilbert space formalism. We have zero reason to believe that changing what else you measure will not affect other things you measure at the same time - after all you have a different apparatus. This is what's meant by the physical basis is unclear. And indeed interpretations of QM such as Bohmian Mechanics exist that are contextual.

Thanks
Bill

I guess you meant "This is what's meant by contextuality being unnatural and counter-intuitive."

Bill, I find this answer quite reasonable.
Maybe you can help me understand this better. Especially the part where the physical basis is unclear which connects with the QM completeness/incompleteness issue.
When you say that the Hilbert formalism is silly if we don't assume non-contextuality I interpret you mean that non-contextuality brings an independent probabilistic picture and that independence fits well with the superposition principle and therefore vector spaces.
Going back to Gleason's theorem and why I was associating a point-particle model to the Born rule, the theorem proves that the Born rule for the probability of obtaining specific results to a given measurement, follows naturally from the structure formed by the lattice of events in a real or complex Hilbert space. Now lattices are discrete subgroups and are formed by points (zero-dimensional discrete topology) that can be physically interpreted as point particles. but the key starting point is the Hilbert space, its linearity allows the Born rule to be interpreted as following naturally from the points-events lattice.

As you rightly say forgetting for a moment the Hilbert formalism we don't have compelling reasons to rule out contextuality, but the only popular contextual interpretation seems to be BM, probably because the hilbert formalism tightly limits what one can make with a contextual interpretation.

 

[TrickyDicky]

I'm not sure if this is what he meant, but there are "time-symmetric" formulations of wave propagation in which the future affects the present in the same way the past does. It's not FTL, in the sense that propagation speed is always <= c, although the propagation can be into the past as well as into the future. This is consistent with SR in the weak sense that there is no violation of lorentz invariance.

Something like Feynman-Wheeler absorber theory? but that was refuted many years ago, among other things assumed no self-interaction of particles.

 

[DrChinese]

Something like Feynman-Wheeler absorber theory? but that was refuted many years ago, among other things assumed no self-interaction of particles.

There are others:

Relational Blockworld:
http://arxiv.org/abs/0908.4348

Yakir Aharonov and Jeff Tollaksen's take on Time Symmetry:
http://arxiv.org/abs/0706.1232

 

[Jano L.]

but that was refuted many years ago, among other things assumed no self-interaction of particles.

The F-W theory consists of the basic equations (action principle) and a peculiar boundary condition, which is not the only one possible.

Which part do you think was refuted?

 

[audioloop]

I'm not sure if this is what he meant, but there are "time-symmetric" formulations of wave propagation in which the future affects the present in the same way the past does. It's not FTL, in the sense that propagation speed is always <= c, although the propagation can be into the past as well as into the future. This is consistent with SR in the weak sense that there is no violation of lorentz invariance.

http://prl.aps.org/abstract/PRL/v110/i21/e210403
"The role of the timing and order of quantum measurements is not just a fundamental question of quantum mechanics"
"we entangle one photon from the first pair with another photon from the second pair. The first photon was detected even before the other was created. The observed two-photon state demonstrates that entanglement can be shared between timelike separated quantum systems"the two vector formalism fit neatly with that process.

Can a Future Choice Affect a Past Measurement's Outcome?
http://arxiv.org/ftp/arxiv/papers/1206/1206.6224.pdf

https://www.physicsforums.com/showpost.php?p=4053068&postcount=31
https://www.physicsforums.com/showpost.php?p=4053118&postcount=32
https://www.physicsforums.com/showpost.php?p=4056855&postcount=36-------
but there is the possibility that the photons interchange information at the time of the monogamy creation or like i prefer to say heterogamy (one up, one down) or is an inherent symmetrical process, we need more experimental testing to know.

https://www.physicsforums.com/showpost.php?p=4402245&postcount=135
http://arxiv.org/pdf/1206.4949v2.pdf
"Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an eective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters. In contrast, quantum theory provides an eective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, 10^-20 meters, up to that of hundreds of kilometers. Yet, such tests fall short of the scales required to investigate potentially signicant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena"
"The tests have the potential to determine the applicability of quantum theory at larger length scales"

Super Physics Smackdown: Relativity vs Quantum Mechanics...In Space
http://www.technologyreview.com/view/428328/super-physics-smackdown-relativity-v-quantum-mechanicsin-space/#ixzz2UyZfdG1L
.

 

[DevilsAvocado]

Here I go again...
From Age of Entanglement:

"...But what if we let relativity enter the game even deeper? What if the detectors are in relative motion such that each detector in its own reference frame analyzes its photon before the other?...

"...once one assumes that the collapse is a real phenomenon, and once one considers specific models, then the conflict is real and testable"...if both measurements happen before the other, then the quantum correlation should disappear, however large the speed of the spooky action!

"Once the engineering was made feasible, "this experiment was also performed in Geneva in the spring of 1999", reported Gisin. "The two-photon interferences were still visible, independently of the relative velocity between Alice and Bob's reference frames." Alice, in her reference frame, measures her photon first; from Bob's point of view, he has measured his photon first; yet, the correlation is still present..."

The paper is very interesting. Though there seems to be a tiny ‘issue’...

However, it is possible that it is not the detector that triggers the collapse. The photons could take the decision already at the beamsplitter and go out through one output port, like in the Bohm-de-Bloglie pilot wave picture [26] (which much inspired Suarez). With the beam-splitter as choice-device superluminal signaling is not possible (to our knowledge). A corresponding experimental test would be more demanding, a beam-splitter would have to be in motion. A clever way-out could be the use of an acousto-optical modulator representing a beam-splitter moving with the speed of the acoustic wave. We are working on such an experiment.

[my bolding]

My absolutely unscientifically guess is that the “stuff” happens at the polarizer/beam-splitter...

(Does anyone know if they proceeded with that new experiment?)


P.S: I'll get back on PM.

 

[DevilsAvocado]

How does the Bohr model violate the uncertainty principle?

Angular momentum depends on both the radius of the orbit and the velocity of the electron in that orbit. The uncertainty principle stipulates that the radius OR velocity MUST be uncertain = angular momentum can NOT be quantized, because it can NOT be known.

The Bohr model does correctly predict spectral lines for atomic hydrogen.

Yup

That is something at least.

Something is not everything...

I get the impression that we feel very confident we have exhausted all mechanical analogies for things like the double slit experiment when we cannot possibly have.

We shall never ‘give up’, but I think it was Feynman who said that it’s proven that an alternative/succeeding theory has to be at least as ‘weird’ as QM. So, there is not much hope for a classical fruit with a big nut inside...

There are an infinitude of possible mechanical analogies we could use to model a particle like an electron (and all but one will be wrong). I don't know if anyone has seen the experiments with silicon droplets but I saw these a while back and found them very interesting:

Droplets are sweet, but they do nothing. I could put a rubber duck there instead, with same result. Medium is everything... w ∙ a ∙ v ∙ e ∙ s

 

[DevilsAvocado]

There are others:

Relational Blockworld:
http://arxiv.org/abs/0908.4348

Ah! Captain RUTA & RBW! But how do we signal from the future in RBW with 'only' spacetimematter?

“past, present and future are co-constructed as well, there are no dynamical entities or dynamical laws in our fundamental formalism [...] accordingly, all dynamical explanation supervenes on, and is secondary to, non-dynamical topological facts about the graph world”

Yakir Aharonov and Jeff Tollaksen's take on Time Symmetry:
http://arxiv.org/abs/0706.1232

Ouch... but wait... conservation of the CPT symmetry requires time reversal to rename particles as antiparticles and vice versa... tachyonic antitelephone anyone??


(sorry, DrC hysterical lame jokes )

 

[bhobba]

the structure formed by the lattice of events in a real or complex Hilbert space.

The technical meaning of lattice used here is different to what you are interpreting it as. Its an algebraic structure used in Quantum Logic:
https://www.physicsforums.com/newreply.php?do=newreply&p=4403159

Just to elaborate a bit on contextuality being unnatural in the Hilbert Space formalism.

If you choose that as your formalism you would expect the states to tell us something as far as the results of experiment are concerned so you can make predictions. Technically that means defining some kind of measure on the states. If contextuality was true you couldn't do that because it would depend on the basis you expand the state out as. Not only that but modern physics has taught us coordinates (and basis are a generalization of coordinates), being an arbitrary man made thing, are independent of the physics - this is one of key insights of Einstein in GR with his principle of covariance (as Kretchmann pointed out to Einstein, and Einstein eventually accepted, it's a principle devoid of physical content, but is of great heuristic importance - however that is another story).

Victor Stenger wrote a nice book on this a few years ago now:
http://www.colorado.edu/philosophy/vstenger/nothing.html

It quite amusing actually. Some people interpreted this as Stenger was saying the Laws of Nature came from nothing. That wasn't the case at all - they came from symmetries which are hardly nothing. The thing is symmetries are so appealing to our intuition it seems to come from nothing. For example that momentum exists and is conserved in an inertial frame comes from the space translation symmetry of an inertial frame and since that is the definition of an intertal frame you think its pulled out of a hat and comes from nowhere. First definitions contain no physics - the import of an inertial frame is that out there in interstellar space frames exist that are to a very high degree inertial which is an observational matter - the universe doesn't have to be like that - it just is. And secondly you need something to be symmetrical in - in this case its the laws of QM - and their validity is an experimental/observational matter - they may or may not be true. Its just that this symmetry stuff is so appealing and all pervasive in modern physics it seems like magic and beautiful beyond compare - which it is - when you understand it.

Thanks
Bill

 

[bhobba]

Which part do you think was refuted?

I am pretty sure the FW theory has never been refuted - in fact I think that would be pretty hard to do since it was deliberately cooked up to be equivalent to ordinary EM but without fields. The issue with it is no-one has been able to figure out a quantum version - to the best of my knowledge anyway.

Thanks
Bill

 

[DevilsAvocado]

I am pretty sure the FW theory has never been refuted - in fact I think that would be pretty hard to do since it was deliberately cooked up to be equivalent to ordinary EM but without fields. The issue with it is no-one has been able to figure out a quantum version - to the best of my knowledge anyway.

The expansion of the universe is not time symmetric in the thermodynamic limit.
Feynman himself stated that self-interaction is needed to correctly account for the Lamb shift.

 

[Jano L.]

The expansion of the universe is not time symmetric in the thermodynamic limit.

I am not sure what you mean. How do you check whether expansion is time-symmetric? How does it connect to the FW theory?

Feynman himself stated that self-interaction is needed to correctly account for the Lamb shift.

Can you give a reference? People often state many things without convincing arguments. The Lamb shift was measured originally for hydrogen, whose atom consists of two particles. It is hard to show that self-action is necessary when the main forces in play are those of the interaction between different particles, and their effect is hard to evaluate.

The Lamb shift can be explained in other ways, one among which is the interaction of the atom with other particles in the surroundings (their EM field). Self-interaction of one particle on itself is not necessary.