A Understanding Barandes' microscopic theory of causality

[Fra]

This is hard to discuss. I admit that part of my confidence is from other directions, that happens to merge with Barandes picture at the intersection.

I'll try again in this way, not to fill in the missing parts, but to try to dress what I think are the keys

• My main concerns are sections V to VII. In this section he tries to see causal locality in a Bayesian network analogy. I would like to understand some version of it.
• His new microscopic principle of causality is defined as:

How can we understand entanglement under Barandes interpretation?

I should dig into this paper but don't have the time. I did want to say that Bayesian networks have very strong markovian properties which his unistochastic processes don't have, so I am not sure what the analogy is here.

They key lies on composition of subsystems, namely in what a constraint implicit in the composition imply.

If you consider two independent bayesian networks, but then combine them either "as is" as two independnent parts, or you combine then under some constraint, then this constraint implies a dependence between the two previously independent parts - in different ways, depending on what the constrain is of course. But the general observations has nothing todo with those details.

The magic lines in understanding the constraints, what they mean, conceptually. Barandes only has a correspondence, which via the time dependent stochastic matrices implements this constraint. But he offers no first principle explanation. This is missing, and I agree.

So I think the generalization is to consider not one bayesian network, but a system of bayesian networks that are dependent via constraints; and during certain circumstances this generalisation is a unistochastic process.

The reason for my confidence in the ideas is that that my own interpretation contains alterantive mechanisms here, that fill in the missing parts at least for me.

The most natural interpretation of the constraint is to see the two indenepdent bayesian networks as encoding predictions of the future; but from non-commutative perspectives, or different basis. And sometimes this may offer better predictive power per storage. So a global memory constraint would be a natural interpretation of a constraint. Or energy constraint if that makes more sense. I mean, now matter HOW you divide a ssytem into parts, there is some sort of conservation usually, thats implicit in the division. What that conservation is can vary.

In this sense this can all be seem as generalized inference system, where you instead of having a "simple" bayesian network, entertain parallell networks representing different encodings and consider encoding their composition. But this implies via a constraint that can mean different things in different contexts, that the parts become dependent via a top-down constraint. What properties does this system have? If its unistochastic, then Barandes showed that such systems always will exhibit quantum behaviour.

So what possible intuition do we have for such top-down constraint? There are apparently many, from a model perspectrive, but which ones would be suitable for nature and why? This is strongly related to I think information theoretic interpreations of QM, which is why i like Barandes correspondence so I feel I ought to defend the idea when some suggest that it adds nothing, which i think is not very fair.

He's view at least offers a handle to a new paradigm, to be modest. But it's up to us, what todo with this handle. Build onto it, or consider it a useless appendix

There are many other interpretations or formalisms i would consider useless before Barandes.

I would say non of this is "weird", but its rejecting realism, in the sense that it is a strong information theoretic approach. But if you take information processing as REAL, when done not by humans, but by physical subsystems, doing "stochastic" basic processing. Then it is abstract, but still "real". There is nothing surrealistic in this this. For me it is a "realistic" explanation, but not in the seense of how Bell uses the word.

/Fredrik

 

[javisot]

Barandes does not dispute Bell's theorem. He instead rejects it as a good basis for a theory of local microphysical causation, and offers an alternative (and, Barandes has remarked, more complete) theory.

Regarding Bell's theorem, Barandes comments the following in the paper shared by @pines-demon,

"There are several incorrect ways to read the stronger 1975 version of Bell’s theorem. One is that the theorem rules out hidden variables altogether. Another false reading is that one can avoid violating Bell’s principle of local causality merely by avoiding the introduction of hidden variables—but this reading confuses the weaker 1964 version of Bell’s theorem with the stronger 1975 version, which applies even to theories that do not include hidden variables at all, like textbook quantum theory itself. The correct reading of Bell’s theorem is to stay close to what Bell himself wrote and conclude that his principle of local causality is violated by all empirically adequate formulations of quantum theory, including the textbook version of the theory, again putting aside various potential loopholes.

It is far from clear, however, that the principle of local causality that Bell used to prove the stronger version of his theorem was the correct way to formulate the more basic condition of causal locality in the first place. Bell himself warned against taking his principle of local causality too seriously. Indeed, in a 1990 lecture [15], he cautioned that his principle “should be viewed with the utmost suspicion.”

Bell had good reasons for being skeptical of his own theorem’s premises, due to his history with an older theorem proved by John von Neumann decades before. That earlier theorem had been widely viewed as completely ruling out the possibility of hidden variables [34–36]. Already in 1935, Grete Hermann had determined that von Neumann’s theorem depended on an assumption about expectation values that was too narrow [37, 38]. Bell essentially discovered the same flaw in von Neumann’s proof decades later [39]. (For an excellent historical discussion of von Neumann’s theorem, its shortcomings, and its critics, see [40].)"

But I still don't understand. Barandes comments in another paper: "Systems that interact with each other start to exhibit what appears to be a nonlocal kind of stochastic dynamics."

This means that stochastic dynamics also contains nonlocality (or am I misunderstanding this?)

 

[Morbert]

This means that stochastic dynamics also contains nonlocality (or am I misunderstanding this?)

Barandes says two systems are entangled if the stochastic process describing their joint evolution cannot be factorized. (See equation 60 https://arxiv.org/pdf/2402.16935 ). However, he shows that this does not enable a violation of his proposed principle of causal locality (55, same paper) by considering observer systems Alice and Bob intervening on the entangled systems (section VIII, same paper).

 

[pines-demon]

Barandes says two systems are entangled if the stochastic process describing their joint evolution cannot be factorized. (See equation 60 https://arxiv.org/pdf/2402.16935 ). However, he shows that this does not enable a violation of his proposed principle of causal locality (55, same paper) by considering observer systems Alice and Bob intervening on the entangled systems (section VIII, same paper).

But this is kind of pointless, no entangled state in any interpretation will violate his causal locality principle right?

 

[DrChinese]

MoE Monogamy of Entanglement

But we know that's not true; not all particles are entangled.

(MoE?, what's MoE for Barandes?)

 

[javisot]

MoE Monogamy of Entanglement

I mean, we asked how Barandes understands entanglement, swapping, or delayed choice, but how does Barandes understand the monogamy of entanglement?

 

[Fra]

If there's no causal mechanism behind entanglement

I don't agree with this. It is the exact path chosen in the stochastics that has no causal mechanism, from the intrinsic perspective of transition matrix.

, why are some particles entangled and others not? If there's no causal mechanism, they could all be entangled.

But we know that's not true; not all particles are entangled.

(MoE?, what's MoE for Barandes?)

WHY we have entanglement in the first place is an interesting but deeper question. Barandes however says that the composite system’s transition matrix $$\Gamma_{AB}(t)$$ which encodes cumulative statistical information and therefore correlations to the extent that exists, will cauase fail to factorize between the two subsystems A and B.

But there is not first principle construction of why this ΓAB(t); to answer that would be the ask for an explanation of the internal structure of a system. It is similar to asking, why doe we have this particular hamiltonian operator in QM?

But I think asking these questions in the Hilbert formalism pretty much ends up with the picture that the hamiltonian is simpled inferred from an external observer via tomographic processes and statistics.

IF you seek a more evolutionary or emergent picture, rather than plain parameter fitting, I think Barandes perspective of interacting systsystems is a step in a better direction.

Personally I seek answers of these things in terms of evolutionary stability of subsystems, entanglement of parts can be conceptaully related to compressed encoding, and might be necessary for stability of physical systems. But we need a paradigm that makes these questions not look like a pure "information theoretic" picture, where "information" refers to human information in the lab. Many object to such perspectives, and i to do. I think the information encoding must be take more serious, and it is physical. Not the fiction in the brains of mathematicians. This is how I see Baranders as seeing the observer as any subsystem. This is a progress.

/Fredrik

 

[Morbert]

But this is kind of pointless, no entangled state in any interpretation will violate his causal locality principle right?

My understanding is other* interpretations would not readily have access to random variables on configuration space, and hence don't have access to his causality principle (which explicitly refers to "microphysical directed conditional probabilities"). Barandes's spectrum of magnitudes are akin to standard QM's decompositions of the identity operator on a Hilbert space, which are used to establish no-signalling between spacelike-separated systems. Barandes is using his formalism to posit a (in his view) more appropriate locality principle to conclude more than mere no-signalling.

With that said, I wish, instead of (71), he had derived $$p((q_t,a_t), t | (q_0,r_0,a_0,b_0), 0) = p((q_t,a_t), t | (q_0,r_0,a_0), 0)$$I.e. I wish he would have showed that the observer subsystem B has no causal influence on either Q or A. By focusing only on A, he might still have to worry about a no-signalling loophole. Nothing about section VIII suggests this alternative expression would not hold, but I am not that familiar with such derivations so there might be some subtle point I'm missing.

* [edit] - Bohmian mechanics presumably would. It would be interesting to know what it says about these Bayesian networks on configurations.

 

[Morbert]

I mean, we asked how Barandes understands entanglement, swapping, or delayed choice, but how does Barandes understand the monogamy of entanglement?

I have not found Barandes explicitly mentioning monogamy of entanglement in literature. But I suspect it would mean, given three subsystems A, B, C: If the unistochastic process $\Gamma_{AB}(t)$ is maximally nonfactorizable, then the unistochastic process $\Gamma_{ABC}(t)$ must factorize into $\Gamma_{AB}(t)\otimes\Gamma_C(t)$, at least when no interactions are present. Nonfactorizability would hopefully be quantifiable, in the same way bitartite entanglement is quantifiable in the Coffman–Kundu–Wootters inequality.

[edit] - Tried to get this kind of expression for the GHZ case and failed so this might not be true.

 

[Morbert]

As an aside, people might find this timestamped video relevant.

 

[pines-demon]

This post was recently created:

• Barandes's Unistochastic Refomulation Applied to Entanglement Swapping

It made me wonder, if there a way to use Barandes formalism to check which assumption of Bell's local causality is violated by Barandes interpretation? Probably it is the locality condition, but I wonder if it is statistical independence or something else.

 

[gentzen]

I finally finished watching

i.e. the last video linked in that other overly long thread which is now closed. I guess I just wanted to remove it from my "watch later" list. The reason why it got there is that I started to watch it when the other thread was still open, and I definitely got the impression that Barandes is back to earth now, and focuses more on solid stuff and his huge philosophical and physical background.

I changed my mind on this latest unistochastic paper now, but not with respect to the unistochastic part. If I read this paper as an attempt to get a better grip on causality, and see the unistochastic part just as what motivated Barandes, then it is a valid investigation which could lead to interesting learnings.

Barandes tries to present an alternative to the interventionist conception of causation. I recently saw somebody claiming "correlation + intervention = causation". It guess it was Peter Morgan, but maybe not. And somebody else explained why intervention is not required for causation (here I am quite sure that this was in Sean Carroll's mindscape episode with Barry Loewer).
I was initially underwhelmed by Barandes' enthusiasm for Bayesian networks, because I know that Judea Pearl promoted them exactly in the context of his work on causality. However, what I now learned from that latest video is than John Bell had no good grip on causality, independent of whether the work of Judea Pearl nailed causality or not. So it makes perfect sense to synthesize the current knowledge on causality and then check how well Bell's theorem holds up in that context. And if good old "no signaling" should be good enough to deny the nonlocality conclusion of Bell's theorem then, that would be an interesting learning.

 

[Morbert]

It made me wonder, if there a way to use Barandes formalism to check which assumption of Bell's local causality is violated by Barandes interpretation? Probably it is the locality condition, but I wonder if it is statistical independence or something else.

Barandes argues that Bell's principle of local causality relies on a definition of common cause that is too narrow. Specifically, Bell's principle of local causality assumes common causes must take the form of "Reichenbachian variables". E.g. If two variables A and B are correlated, but not exerting influence on one another, then there must be variables λ that exert a common causal influence on A and B.

Barandes argues there can be non-Reichenbachian common causes that establish the correlations seen in entanglement, like local interactions at a previous time, that Bell's principle miss as they do not take the form of λ, and hence you can have causally local theories that violate Bell's principle of local causality.

 

[Morbert]

I was initially underwhelmed by Barandes' enthusiam for Bayesian networks, because I know that Judea Pearl promoted them exactly in the context of his work on causality. However, what I now learned from that latest video is than John Bell had no good grip on causality, independent of whether the work of Judea Pearl nailed causality or not. So it makes perfect sense to synthesize the current knowledge on causality and then check how well Bell's theorem holds up in that context. And if good old "no signaling" should be good enough to deny the nonlocality conclusion of Bell's theorem then, that would be an interesting learning.

I'm having a hard time identifying a standard procedure for constructing appropriate Bayesian networks from his papers. E.g. Two particles that become entangled via a local interaction will therefore causally influence each other according to Barandes's principle of causal locality, but how can this be expressed via a Bayesian network, as you cannot have two nodes pointing at each other. I assume you would need to split the variables into moments 0, and t (the start and end of the unistochastic process) but I see no mention of this by Barandes so for now it is just a guess on my part.

 

[RUTA]

Quibble. The key point is here:


And that means that there is no "detailed causal mechanism" at all. It does not mean that, well, "stochastics" is good enough for a detailed causal mechanism so we don't need to look any further. It means looking any further is pointless because it is impossible to find what we're looking for. We simpl have to accept that there is no "detailed causal mechanism" there at all for us to find.

Exactly, he doesn't actually deflate Bell's theorem, he ignores it. Quantum information theorists have a way to deflate it for example. They point out that superposition and entanglement are kinematic facts about QM, not dynamical effects due to some nonlocal or superdeterministic or retro causal mechanism. They then supply two principles giving rise to the kinematic (Hilbert space) structure of QM (relativity principle justifies Information Invariance & Continuity) exactly like the relativity principle justifying the light postulate gives you the Lorentz transformations (kinematics) of special relativity. The vast majority of physicists no longer bother looking for a causal mechanism for length contraction and time dilation, they accept those are kinematic facts resulting from the observer-independence of c as justified by the relativity principle, not dynamical effects due to some causal mechanism (like the luminiferous aether). The analogy is completed by showing that Information Invariance & Continuity entails the observer-independence of Planck's constant h. Barandes could simply adopt this view and be done with it rather than engage in meaningless word plays.

 

[DrChinese]

Barandes argues there can be [1] non-Reichenbachian common causes that establish the correlations seen in entanglement, like local interactions at a [2] previous time, that Bell's principle miss as they do not take the form of λ, and hence you can have causally local theories that violate Bell's principle of local causality.

Thanks for this...

[1] This is precisely the kind of hand-waving (not on your part Morbert) that is objectionable. Barandes simply asserts that such type exists so he can "escape" Bell. How does any of this make sense? Perhaps a concrete example of what this might look like?

[2] We already know that delayed entanglement swaps don't feature a local interaction at any previous time. Ma et al 2012, etc...

 

[Morbert]

[1] This is precisely the kind of hand-waving (not on your part Morbert) that is objectionable. Barandes simply asserts that such type exists so he can "escape" Bell. How does any of this make sense? Perhaps a concrete example of what this might look like?

In section VII ( https://arxiv.org/pdf/2402.16935 ) he considers two systems $Q, R$ that interact with each other at time $t'$, such that the time evolution $U_{QR}$ no longer factorizes. Even after the interaction, when the time evolution factorizes again, the transition matrix $\Gamma_{QR}$ remains unfactorizeable. This "unfactorizeability" is entailed by the interaction. Barandes is not the first to challenge Bell's principles along these lines. Barandes quotes Unruh in section III of the same paper.

Re/ the charge of Handwaving. I don't think Barandes is handwaving, but I do think his reformualtion is quite raw, and there is plenty of homework to do to bring the project to maturity.

I'll leave entanglement swapping for the other thread.

 

[Morbert]

Perhaps a concrete example of what this might look like?

You could consider two particles entangled by the appropriate quantum gates. The unitary operator $U\ket{00} = \frac{1}{\sqrt{2}}(\ket{00} + \ket{11})$ would not factorize to operators on the individual systems.

 

[DrChinese]

You could consider two particles entangled by the appropriate quantum gates. The unitary operator $U\ket{00} = \frac{1}{\sqrt{2}}(\ket{00} + \ket{11})$ would not factorize to operators on the individual systems.

I was asking about a concrete example of what you called (while explaining Barandes) non-Reichenbachian common causes. Whatever that is, because I don’t think it is anything. It seems like hand-waving in order to deny Bell.

What you described is nonseparability of components of a normal entangled system.

 

[Morbert]

I was asking about a concrete example of what you called (while explaining Barandes) non-Reichenbachian common causes. Whatever that is, because I don’t think it is anything. It seems like hand-waving in order to deny Bell.

What you described is nonseparability of components of a normal entangled system.

The non-Reichenbachian common cause is the nonseparable $U$.

Notice that this local interaction, despite being the‘common cause’ of the correlations between Q and R, is not the sort of ‘variable’ that can be plugged into theunistochastic theory’s microphysical conditional probabilities. Reichenbach’s principle of common causes (16) therefore does not hold.

 

[pines-demon]

Barandes argues that Bell's principle of local causality relies on a definition of common cause that is too narrow. Specifically, Bell's principle of local causality assumes common causes must take the form of "Reichenbachian variables". E.g. If two variables A and B are correlated, but not exerting influence on one another, then there must be variables λ that exert a common causal influence on A and B.

Barandes argues there can be non-Reichenbachian common causes that establish the correlations seen in entanglement, like local interactions at a previous time, that Bell's principle miss as they do not take the form of λ, and hence you can have causally local theories that violate Bell's principle of local causality.

As said in post #1, Barandes admitted that he attributed a bit much of Reichenbachianism to Bell in that paper (see later podcasts). Bell seems to have drifted from that or at least Bell seems to have different definitions not all fully Reichenbachian.

 

[Fra]

The non-Reichenbachian common cause is the nonseparable $U$.

I agree with this, this is a good way of putting it that is neutral and in line with the correspondence.

And this is also why the anzats in Bell's theorem makes not sense. But you can phrase this is many different ways.

This is part of the "quantum correspondence". The remaining - unanswered question - is the obvious follow up question: What is the deeper explanation for WHY U is nonseparable in the first place?

It helps the discussion to separate things.

1) Barandes "correspondence" between the two views . This reformulates problems, not necessarily solves them in a deeper sense.

2) The core problems that exists, in both formulations.

I might be wrong, but my impression is that Dr Chinese and others have issues to see the value in the correspondence simply because there are still core problems unsolved? (which are even more foundational than the reformulation of hilbert formalism).

If we separate the issues, can we agree on what we disagree with? or what we seek?

I can answer for myself: I seek the solutions to (2), and my opinon is that while Barandes correspondece does not solve it, it offers a better perspective for formulating difficult problems. But we are not done. That Barandes thinks along these lines as well, is something I am guess due to how he speaks and elaborates the matter, and in particular how he suggests that the stochastics are some deeper improvement over the "problematic" dynamical law that is timeless. But the evolving transition matrices is indeed in where the answer to (2) must hide.. and we dont have this answer yet. And as this thread also isnt' for speculating about it, we can just look and reflect on Barandes correspondence from different angles to maybe get new ideas.

/Fredrik

 

[Morbert]

As said in post #1, Barandes admitted that he attributed a bit much of Reichenbachianism to Bell in that paper (see later podcasts). Bell seems to have drifted from that or at least Bell seems to have different definitions not all fully Reichenbachian.

Do you have any links to the relevant podcasts?

[edit] - I found a discussion at this timestamp. Is this what you are referring to?

 

[Fra]

The vast majority of physicists no longer bother

I agree - but i think it is unfortunate

looking for a causal mechanism for length contraction and time dilation, they accept those are kinematic facts resulting from the observer-independence of c as justified by the relativity principle, not dynamical effects due to some causal mechanism (like the luminiferous aether). The analogy is completed by showing that Information Invariance & Continuity entails the observer-independence of Planck's constant h. Barandes could simply adopt this view and be done with it rather than engage in meaningless word plays.

I think the heart of the matter to the core problems in (2) is precisely how to understand observer independence. Should be understand it as a "constraint" or an emergent relation? What makes this distinction more acute is exactly when one considers a part of the system as an "observer". In this case, the meaning of the constraint interpretation seems to unavoidable lead to "non-local" perspectives, if we by locality refer to the "distance" between "observers".

I think progress into open question, make need to re-questions thinks that are traditionally just seem as constraints. It is easy to understand what a constraint is from a mahtmatical model perspective, but if the model should be encoded inside a part - this get highly nontrivial, not only technically but conceptaully.

/Fredrik

 

[pines-demon]

Do you have any links to the relevant podcasts?

[edit] - I found a discussion at this timestamp. Is this what you are referring to?

He has discussed it, twice (the other time is in the Know Time podcast, about min
3:04:24), see previous discussion thread, post #563 (quoted) and #609 (link to paper).

 

[RUTA]

I agree - but i think it is unfortunate

If you look at the theoretical structure of special relativity, the kinematics follows from an empirically discovered fact (observer-independence of c) that obtains per a compelling fundamental principle (relativity principle). The (Lorentz invariant) causal mechanisms supervene on the resulting M4 spacetime. That means causal mechanisms and dynamics are not fundamental. If you think that "is unfortunate," then you're stuck in a 19th century mindset and will remain forever mystified by superposition and entanglement because any explanation of those in terms of causal mechanisms must violate locality and/or statistical independence.

I think the heart of the matter to the core problems in (2) is precisely how to understand observer independence. Should be understand it as a "constraint" or an emergent relation? What makes this distinction more acute is exactly when one considers a part of the system as an "observer". In this case, the meaning of the constraint interpretation seems to unavoidable lead to "non-local" perspectives, if we by locality refer to the "distance" between "observers".

I think progress into open question, make need to re-questions thinks that are traditionally just seem as constraints. It is easy to understand what a constraint is from a mahtmatical model perspective, but if the model should be encoded inside a part - this get highly nontrivial, not only technically but conceptaully.

/Fredrik

"Observer independence" simply means "same in all inertial reference frames" (related by boosts, spatial rotations, spatial translations, or temporal translations).

Yes, you can think of such a principle-based account as "constraints." See for example Unifying Special Relativity and Quantum Mechanics via Adynamical Global Constraints.

 

[Sambuco]

Barandes argues that Bell's principle of local causality relies on a definition of common cause that is too narrow. Specifically, Bell's principle of local causality assumes common causes must take the form of "Reichenbachian variables". E.g. If two variables A and B are correlated, but not exerting influence on one another, then there must be variables λ that exert a common causal influence on A and B.

Barandes argues there can be non-Reichenbachian common causes that establish the correlations seen in entanglement, like local interactions at a previous time, that Bell's principle miss as they do not take the form of λ, and hence you can have causally local theories that violate Bell's principle of local causality.

This is precisely what makes me skeptical of Barandes' argument. The idea that correlation is merely a consequence of the local interaction in the past is not new. For those who wish to find a "mechanism" behind entanglement, the issue is not mere correlation but the combination of correlation plus indeterminacy before measurements.

Also, Barandes argues that for two entangled subsystems Q and R, there is no causal influence from R to Q if $p(q_t,t|(q_0,r_0),0) = p(q_t,t|q_0,0)$, but I think the issue of locality is not whether there is a dependence on the initial conditions, but on space-like separated measurement outcomes. In other words, the issue is about the probability of finding a result for a measurement in Q changes when the result of a remote measurement in R is known. If the transition matrix is interpreted as mere information, as in $\Psi$-epistemic interpretations, there is no problem, but he prefers to interpret $\Gamma(t)$ as a nomological (law-like) entity.

Lucas.

 

[Fra]

If you look at the theoretical structure of special relativity, the kinematics follows from an empirically discovered fact (observer-independence of c) that obtains per a compelling fundamental principle (relativity principle). The (Lorentz invariant) causal mechanisms supervene on the resulting M4 spacetime.

Yes. I always felt ever since beeing exposed to this, that special relativity and statistical mechanics are the cleanest and most beutiful theories we have with a minimum of ad hoc stuff with a clear logical structure, and the derivation of SR is indeed very clear. And I also like your principle accounts research, that's not my point. But I do not see why we have to settle with it, because I am convinced that to make more progress we need to understand emergence in nature. In this pictures, "constraints" are rarely fundamental, but there is a causal mechanism for their emergence, and the validity of constraints may depend on the state of the emergence process.

That means causal mechanisms and dynamics are not fundamental. If you think that "is unfortunate," then you're stuck in a 19th century mindset and will remain forever mystified by superposition and entanglement because any explanation of those in terms of causal mechanisms must violate locality and/or statistical independence.

No, on the contrary to seek a deeper explanation for WHY there seems to be certain "constraints" in nature, as seen from our observational scale, is not the same path as going back to 19th century.

No need to deny empirical observations, but there are two choices.

1) Treat empirical facts about observed symmetries as fundamental mathematical constraints with perfect confidence even when extrapolating theory into new territory. (Then by new territory here I refer to ultimate unification regmies, including QG and before matter was formed)

2) We take empirical observations for what they are, but without inductive fallacies that our limited observations are fundamental hard constraints. One asks questions like: Is there a way to understand WHY, we consistently observe a max limit on signalling between parts in 3D space that is also invariant to the observer frames? And why 3D? This is remarkable enough that it is hard not to seek to understand. So we don not seek to deny, and thus invalidate, relativity, only find a deeper explanation that may also be valuable when trying to understnand how to unify spacetime dynamics with dynamics of internal structures.

"Observer independence" simply means "same in all inertial reference frames" (related by boosts, spatial rotations, spatial translations, or temporal translations).

Yes, this is what it currently means, but if we look forward. It seems a bit simplistic to think that an "observer" such as a suffiently complex subsystem in contact wit the environment, like Baranders entertains, has no other descriptors beyond it's spacetime relation. This is fine in classical picture where one consider "observations" as gedanken probes at each spacetime point, beeing inserted from an external macroworld.

In QG it seems the inter-relation between spacetime dynamics and the dynamics of internal spaces, is where the trouble lies. The solution we have today is to describe the internal dynamics in terms of the external spacetime. Then the assymmetry which supports most empirical will get shaky. To try to use constraints that have support in one limite empirical domain, into new domains is the method theoretical physicists have spent the last 100 years on.

/Fredrik

 

[Morbert]

Also, Barandes argues that for two entangled subsystems Q and R, there is no causal influence from R to Q if $p(q_t,t|(q_0,r_0),0) = p(q_t,t|q_0,0)$

What Barandes shows is two subsystems that become entangled will fail that check. I.e. $p(q_t,t|(q_0,r_0),0) \neq p(q_t,t|q_0,0)$. This failure is entailed by when their time-evolution operator did not factorize. Hence, there must be a causal relation between entangled systems.

Whether or not this account is sufficient to capture all cases of entanglement (in particular, entanglement swapping experiments) is an interesting question.

but I think the issue of locality is not whether there is a dependence on the initial conditions, but on space-like separated measurement outcomes. In other words, the issue is about the probability of finding a result for a measurement in Q changes when the result of a remote measurement in R is known. If the transition matrix is interpreted as mere information, as in $\Psi$-epistemic interpretations, there is no problem, but he prefers to interpret $\Gamma(t)$ as a nomological (law-like) entity.

The spacelike separated measurement outcomes would depend on initial conditions no? E.g. If Alice is influenced by Bob's choice of measurement, and Bob's choice of measurement is influenced by Bob's initial state, then Alice must be influence by Bob's initial state. Non-interventionist accounts of causality are uncommon in these discussions, so perhaps Barandes's reformulation will spark new interest in them.

 

[Fra]

For those who wish to find a "mechanism" behind entanglement, the issue is not mere correlation but the combination of correlation plus indeterminacy before measurements.

Are you saying that you think those seeking a "mechanism" ALSO needs to resolve the inderterminacy? This is what Bell was thinking. But its not what Barandes is thinking. Or what did you mean?

If the transition matrix is interpreted as mere information, as in $\Psi$-epistemic interpretations, there is no problem, but he prefers to interpret $\Gamma(t)$ as a nomological (law-like) entity.

If so, we may misunderstand each other. I think the indeterminacy is irreducible, but there is mechanis for the correlation. And that "mechanism" is IMO encoded in the $\Gamma(t)$, which in turn encodes how the systems "evolve". So when maximally entangled, and thus isolated from interactions, they evolve in ways that are pre-tuned. But why this is the case, is IMO encodd in the physics of the systems, the internal structor of the particles. Baranders does not "explain" this first principle; he only shows that the "description" from QM, via correspondes implies that this exists(*).

So I would see it like this, the two subsystems that are entanglet evolve independently, but their evolutions are correlated due to beeing pre-tuned. But this "mechanism" can not be put in terms of the simple global beable lambda of bells ansatz.

(*) But once we see this, maybe hte motivation for finding a first principle explanation is larger? I seems I am the only one seeing it this way in this discussion. I know I've said this now several times.

/Fredrik