The strategy of your argument here is an excellent example of inappropriate reductionism; you seek to explain frame dependence of motion and observer dependence of quantum state/properties as being mere instances of conceptual relations between thought and object. — fdrake

‘Thought and object’. It is just that instinctive division which is called. Into question by ‘the observer probllem’. Anyway - thanks for your considered criticism, I appreciate the time you have taken.

‘Thought and object’. It is just that instinctive division which is called. Into question by ‘the observer probllem’. Anyway - thanks for your considered criticism, I appreciate the time you have taken. — Wayfarer

If you are willing to collapse the distinction between the two, rather than merely and only 'inhabiting' the relation as correlationists describe, then the arche-fossil is successful; it at the very least forces a correlationist to choose between idealism and absurdity.

That there is no material reality prior to the existence of humans is certainly one way to find the argument instructive.

Anyway, was fun, even though I doubt I convinced you, I understand the arche-fossil argument in a lot more detail through rehearsing it with a willing antagonist. Thanks. :)

Yeah, that's a nice way IMO to avoid issues with relativity.

And BTW, as I said to NoAxioms a similar problem arises in Relativity, if one wants to avoid the 'block universe idea' as suggested by Rietdijk-Putnam argument(here's the link to the Wikipedia article). There is a very nice 'insight article' on Physics Forums that gives a counter-argument (which is reminiscent of the reasoning on which, for instance, RQM is based): https://www.physicsforums.com/insights/block-universe-refuting-common-argument/. — boundless

Nice find with the PF article and I fully agree with it. I was going to mention the Andromeda paradox and the idea of potentiality in relation to it in my previous post. So we seem to thinking along similar lines here.

It also reminds me of Aristotle's future sea battle example where he contrasts potential and actual:

One of the two propositions in such instances must be true and the other false, but we cannot say determinately that this or that is false, but must leave the alternative undecided. One may indeed be more likely to be true than the other, but it cannot be either actually true or actually false. It is therefore plain that it is not necessary that of an affirmation and a denial, one should be true and the other false. For in the case of that which exists potentially, but not actually, the rule which applies to that which exists actually does not hold good. — Aristotle, On Interpretation, §9

--

It seems not contradictory at all for Bob to find the state of the photon still in superposition, despite the conflict wording in the article. — noAxioms

Yes, I agree - it's just what quantum mechanics predicts will happen and so it's not contradictory (or unexpected) at all. But it does challenge objective collapse theories since they modify the standard formulation.

Had also John Horgan misattributed such a view to Wheeler? — boundless

Because pop-science writers are generally trash.

Not defining something undetectable (in SR) is fine, and I suppose the standard presentation of SR is that there isn't one. But GR, to the embarrassment of Einstein, had to admit to an apparent preferred foliation (which is not an inertial frame), so SR would actually be sort of wrong if it asserted that no preferred local frame can exist, and SR has never been shown to be wrong. — noAxioms

Do you mean that some geometries in GR require such a foliation (rather than simply allow)?

AFAIK, there are attempts to reconcile dBB and SR that use a preferred foliation (which is not prohibited by Lorentz symmetry) but I think that this does not satisfy many people because it goes against the 'spirit' of Relativity.

A preferred foliation is one thing. A preferred moment (presentism) is more of an offense to relativity — noAxioms

But is there a real difference between the two? I mean, If the structure of space-time requires such a foliation, IMO I can define a frame where all these events are present. For such a frame, there is an absolute simultaneity, which is precisely the reason why AFAIK Lorentz aether theory is criticized.

If presentism is true, what is the rate of advancement of objective time? Equivalently, by how much is say a clock that tracks GMT dilated? It isn't moving very fast, but it's the depth of the gravity well I'm interested in. I thought of this when I tried to look it up. The absolutists sort of group together like the flood geologists and put out all this propaganda against Einstein, but none of those denial sites quote this absolute dilation factor, which you think would be one of their flagship points like the absolute frame. But they evade the topic. Why is that? Must be embarrasing... — noAxioms

I'd agree with the objection you are making. But IMO what you are saying is also a clue that one cannot make an absolute simultaneity (or rather, it is possible but would be 'hidden'...).

The one from GR is not enough? — noAxioms

I don't know!

Yes, I know about the superdeterminism loophole. I also dismiss it enough to state that Bell eliminated locality and counterfactual definiteness from both being true. I see none of the listed interpretations hold both to be true, utilizing the superdeterminism loophole, so it seems the world agrees with that assessment. — noAxioms

:up:

Nice find with the PF article and I fully agree with it. I was going to mention the Andromeda paradox and the idea of potentiality in relation to it in my previous post. So we seem to thinking along similar lines here. — Andrew M

Great. Interestingly, I discovered that the same point is made by Carlo Rovelli to defend his 'relational' view, see: https://www.youtube.com/watch?v=vbYeAaCloiM. At 4:55, Valentini makes the same question that he made in the other video (namely that different observers might disagree about what happens) and at 53:52 Rovelli answers by citing the Andromeda Paradox - so we are in good company :wink: . It is a very good discussion, BTW (other than Rovelli and Valentini, also Saunders and Wallace (and others) participate in the discussion). This might also be of interest to @noAxioms.

It also reminds me of Aristotle's future sea battle example where he contrasts potential and actual: — Andrew M

Very interesting, thanks!
In fact, some time ago I read a philosophy of science paper that tried to use the potential-actual distinction in SR in order to avoid situations like Andromeda Paradox. Unfortunately, I do not remember neither the title nor the author :sad:

Yes, I agree - it's just what quantum mechanics predicts will happen and so it's not contradictory (or unexpected) at all. But it does challenge objective collapse theories since they modify the standard formulation. — Andrew M

Unfortunately, I know very little about objective collapse theories. Anyway, I agree with you. It would be interesting to see how these theories deal with this experiment.

I do not understand your point, actually.

On one hand, I agree that pop-science is not always reliable. On the other hand, in this case, it seems that you are saying that John Wheeler never proposed the idea of the 'participatory anthropic principle' (or 'participatory universe') even if there are a lot of sources that claim otherwise. Am I right?
Or you're suggesting that is their interpretation of the 'participatory anthropic principle' problematic? If so, what did he really mean?

Thanks in advance!

Yes, I agree - it's just what quantum mechanics predicts will happen and so it's not contradictory (or unexpected) at all. But it does challenge objective collapse theories since they modify the standard formulation. — Andrew M

Since none of this is new (it is demanded by QM right from the early days), how do any of the objective collapse interpretations get around this? Does this experiment change something? Did they expect a different result? I don't think so.

Do you mean that some geometries in GR require such a foliation (rather than simply allow)? — boundless

The expansion of space is uniform only under one foliation. It isn't absolutely uniform since it seems resistant to local mass, but only under one foliation does the expansion switch to accelerating everywhere at once. Essentially, only the the frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance.

AFAIK, there are attempts to reconcile dBB and SR that use a preferred foliation (which is not prohibited by Lorentz symmetry) but I think that this does not satisfy many people because it goes against the 'spirit' of Relativity.

It apparently goes against the spirit of SR, and it pained Einstein to not keep that in GR. Physics is different in other frames since non-local observations are allowed in GR.

A preferred foliation is one thing. A preferred moment (presentism) is more of an offense to relativity
— noAxioms

But is there a real difference between the two?

Of course. One objectively orders any pair of events, and other may or may not attach an ontological status to each event (has or has not yet happened). A preferred foliation has no such ontological status. There is still spacetime with all events having equal ontology. Presentism has no spacetime, only space, with only current events existing (happening) and not any of the others. That sounds like a huge difference of reality to me.

I mean, If the structure of space-time requires such a foliation, IMO I can define a frame where all these events are present. For such a frame, there is an absolute simultaneity, which is precisely the reason why AFAIK Lorentz aether theory is criticized.

I don't understand this comment. Under presentism, there is no spacetime. Only objectively current events are present, and the other events don't exist, so can't be present.

If presentism is true, what is the rate of advancement of objective time? Equivalently, by how much is say a clock that tracks GMT dilated? It isn't moving very fast, but it's the depth of the gravity well I'm interested in. I thought of this when I tried to look it up. The absolutists sort of group together like the flood geologists and put out all this propaganda against Einstein, but none of those denial sites quote this absolute dilation factor, which you think would be one of their flagship points like the absolute frame. But they evade the topic. Why is that? Must be embarrasing...
— noAxioms

I'd agree with the objection you are making. But IMO what you are saying is also a clue that one cannot make an absolute simultaneity (or rather, it is possible but would be 'hidden'...).

No, there would still be an absolute simultaneity. I can still sync remote clocks. I just find it difficult to build a clock that is designed to run in a location of known dilation and have it compensate for that in order to record the passage of absoute time. If it were possible to do that, the objective age of the universe could be known, but we only know the figure (13.8 BY) in dilated Earth time, which is obviously running slow. The universe is older than that, but by how much is the question.

Thanks for the very informative answer! I need some time to think about all of this :smile:

You might be interested in the following article that addresses this issue:

But it didn't take physicists long to realise that while the Wheeler-DeWitt equation solved one significant problem, it introduced another. The new problem was that time played no role in this equation. In effect, it says that nothing ever happens in the universe, a prediction that is clearly at odds with the observational evidence.
— Quantum Experiment Shows How Time ‘Emerges’ from Entanglement — Andrew M

I forgot to say that I actually read the article and I found it very intriguing :smile:

I did some further research on Wheeler. I found this article: https://plus.maths.org/content/it-bit - it quotes a paper by Wheeler himself.

He certainly IMHO thought that 'information' (which he believes to be 'immaterial') plays a central role and is more 'fundamental' than matter.
But he did not seem to give a 'special role' to human observers (he seemed to have a more general idea of observer).

I am still not sure about the 'participatory anthropic principle' thing.

Why not read Wheeler himself rather than derivative sources:

https://what-buddha-said.net/library/pdfs/wheeler_law_without_law.pdf

The basic idea behind the participatory universe idea is simply that what 'participates' with the universe is itself - which includes the equipment used to make a measurement (which belongs to the universe...). From the paper: "Registering equipment operating in the here and now has an undeniable part in bringing about that which appears to have happened". An 'observer' is a piece of apparatus, that's it. This, incidentally, was Bohr's position, which Wheeler understood very well.

(cf. Wheeler's comments on Bohr concept of the 'phenomenon, in the cited paper': "a phenomenon is not yet a phenomenon until it is brought to a close by an irreversible act of amplification such as the blackening of a grain of silver bromide emulsion or the triggering of a photodetector". Incidentally, this was also the point of difference between Einstein and Bohr: Einstein refused to believe the act of measurement qua equipmental intervention - or 'participation', in Wheeler's overblown vocabulary - could determine the results of a measurement, while Bohr figured this was the only consistent way to explain the results).

Thank you very much!

Actually in the article I linked, there is in it a link to a paper by Wigner himself: https://jawarchive.files.wordpress.com/2012/03/informationquantumphysics.pdf.

Since none of this is new (it is demanded by QM right from the early days), how do any of the objective collapse interpretations get around this? Does this experiment change something? Did they expect a different result? I don't think so. — noAxioms

They would predict that Wigner would not see interference for sufficiently complex friend systems. So the options are to either accept the experiment's result as falsifying their theory or else show that the experiment isn't scaled up enough to trigger a physical collapse by their criterion.

For a brief discussion of that prediction in one of the experiment's referenced papers, see https://arxiv.org/abs/1507.05255 (p18, point 1).

I actually thought about it but, unfortunately, I did not arrive at a satisfying conclusion.

The expansion of space is uniform only under one foliation. It isn't absolutely uniform since it seems resistant to local mass, but only under one foliation does the expansion switch to accelerating everywhere at once. Essentially, only the the frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance. — noAxioms

Ok, that's right. Maybe the point is that the foliation is not directly observable. As you say, we can observe only a "frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance". Just a guess. As I said, I am quite at loss.

AFAIK, there are attempts to reconcile dBB and SR that use a preferred foliation (which is not prohibited by Lorentz symmetry) but I think that this does not satisfy many people because it goes against the 'spirit' of Relativity. — boundless

It apparently goes against the spirit of SR, and it pained Einstein to not keep that in GR. Physics is different in other frames since non-local observations are allowed in GR. — noAxioms

I see...but if this does mean that non-locality is compatible with GR (as it is usually understood) why people consider non-locality problematic?

Of course. One objectively orders any pair of events, and other may or may not attach an ontological status to each event (has or has not yet happened). A preferred foliation has no such ontological status. There is still spacetime with all events having equal ontology. Presentism has no spacetime, only space, with only current events existing (happening) and not any of the others. That sounds like a huge difference of reality to me. — noAxioms

Well, yeah, you are right.
But IMO this leads either to the 'Andromeda Paradox'/Riedtjik-Putnam argument scenario or some form of retro-causality.

I'd agree with the objection you are making. But IMO what you are saying is also a clue that one cannot make an absolute simultaneity (or rather, it is possible but would be 'hidden'...). — boundless

No, there would still be an absolute simultaneity... — noAxioms

OK, I also agree with you on this.

Anyway, Antony Valentini proposed that cosmological observations might help to solve interpretational problems in QM. The de Broglie-Bohm interpretation actually makes the same predictions of QM only if the 'quantum equilibrium hypothesis' is satisfied, i.e. if the modulus square of the wave-function corresponds to the actual probability distribution (this assures that dBB satisfies the Born Rule). However, in general, this might be not true. Hence his proposal: maybe at the earliest stages of the evolution of the Universe, that hypothesis was not satisfied and - as a consequence - we should see empirical evidence against the Born Rule.

Here is the link to his talk (at the same conference): https://www.youtube.com/watch?v=XYZV9crCZM8.
Here the link to the Q&A session: https://www.youtube.com/watch?v=8qnuNLB61RA.

I suggest these videos also to @Andrew M.

According to the 'no signaling' theorem, if predictions of QM are satisfied there cannot be any direct evidence of violation of locality. Hence, it just seems that there is a sort of 'conspiracy' if there are non-local influence. This is actually one of the reasons I do not think dBB is true. But, interestingly, according to Valentini, this might be a clue that dBB is, instead, right: the fact that the world seems 'local' is due to the fact that the 'quantum equilibrium hypotesis' is true. IMO, his proposal however makes perfect sense in the light of dBB.

[Another reason for which I do not accept dBB is its 'strange' ontology. dBB is, in fact, characterized by both particles and the wave-function. In my understanding, particles have no role except moving in a way 'dictated' by the wave-function*. The wave-function seems to do all the job. Furthermore, the wave-function is not a field in real space but lives in the 3N-dimensional 'configuration space' where N is the number of particles. This prompted some proponents to adopt a 'nomological' view of the wave-function. But IMO this is still odd: laws are generally understood to not be dynamical objects and if the wave-function is merely a law, it just seems that there is no reason why particles move in that way. In fact, some think that the wave-function is better understood as representing dispositions: https://arxiv.org/abs/1406.1371.

*This is not true if one introduces the 'quantum potential' AFAIK. But even in this case, you still have a weird ontology where you have to make sense of particles living in our usual 3-dimensional world and an equally real field that lives in a 3N-dimensional world. And also some dBB supporters are critical of the 'quantum potential' formulation, see: https://plato.stanford.edu/entries/qm-bohm/#QuanPote

Also, I am a bit puzzled by the asymmetry between position and other observables. QM is perfectly 'symmetrical' with them, i.e. it treats them equally. For dBB, instead, position is somewhat 'special'. The counter-argument that is found in the SEP article on 'Bohmian mechanics' does not convince me. ]



Good find! I'll read it :smile:

Great. Interestingly, I discovered that the same point is made by Carlo Rovelli to defend his 'relational' view, see: https://www.youtube.com/watch?v=vbYeAaCloiM . At 4:55, Valentini makes the same question that he made in the other video (namely that different observers might disagree about what happens) and at 53:52 Rovelli answers by citing the Andromeda Paradox - so we are in good company :wink: . It is a very good discussion, BTW (other than Rovelli and Valentini, also Saunders and Wallace (and others) participate in the discussion). This might also be of interest to noAxioms. — boundless

Yes, another great discussion! I also liked Wallace's explanation of the wave function at 11:25.

So here's the setup and exchange between Valentini and Rovelli:

[4:55] Valentini sets up the scenario as Rovelli deciding to speak at the conference (or not) based on measuring a particle spin as spin up (or spin down). Rovelli measured spin up and so here they are talking at the conference. However a super-intelligent being in the future measures interference.

[53:52] Rovelli: Antony asks, "Carlo, some super-intelligent is believing that you are not here because in his wave function you're superimposing, there's no fact of the matter. Does this bother you?"

I think it doesn't because it's exactly the kind of thing that happens in theoretical physics all the time. I think it's very similar to what happens in special relativity. If I take Einstein's simultaneity convention, right now in Andromeda there is something which has already happened with respect to the - not the past cone but the simultaneity convention - with respect to which I haven't happened yet with respect to this.

This makes no sense whatsoever but that's the structure of the world. The relation between when things happen for who are complicated. I think with this guy in the future, I could talk if I could survive until then, I could talk to him and we would agree and the fact that now, for him, in the future before I interact with him there is a discrepancy in what we see doesn't really bother me.

Valentini: For him, there wouldn't be a fact of the matter about the past?

Rovelli: That's right.

Here's also the relevant passage from the Physics Forum Insights article that you linked to earlier: The Block Universe – Refuting a Common Argument.

(3) All events in the past light cone of a given event are real (i.e., fixed and certain) for an observer at that event.

The reason this accounts for all of our observations is that information can’t travel faster than light, so anything we observe at a given event can only give information about the past light cone of that event.

So we can see Rovelli's reasoning in the above exchange. For Alice on Andromeda, Carlo on Earth only potentially exists until a local interaction (say, a telescopic observation at light speed) brings him into her present (and then past). Similarly, for Bob the superintelligent being in the future, Carlo is only potentially at the conference until a local interaction decoheres the superposition (say, Bob talks to Carlo).

A further thought here is that I think this allows a representational interpretation of the wave function for RQM in terms of what is actual and potential for any given observer. What is locally entangled with an observer is actual (the past and present, measurements and interactions), what is not is potential (the future, spacelike separated regions, superpositions).

Thank you very much for the transcription!

So we can see Rovelli's reasoning in the above exchange. For Alice on Andromeda, Carlo on Earth only potentially exists until a local interaction (say, a telescopic observation at light speed) brings him into her present (and then past). Similarly, for Bob the superintelligent being in the future, Carlo is only potentially at the conference until a local interaction decoheres the superposition (say, Bob talks to Carlo). — Andrew M

:up:

A further thought here is that I think this allows a representational interpretation of the wave function for RQM in terms of what is actual and potential for any given observer. What is locally entangled with an observer is actual (the past and present, measurements and interactions), what is not is potential (the future, spacelike separated regions, superpositions). — Andrew M

Yeah, I'd agree. Both the representionalist and the non-representionalist views are possible. Rovelli himself wrote against a 'realistic' interpretation of the wave-function: https://arxiv.org/abs/1508.05533.

Actually, this interpretation of the wave-function is also held by some Copenaghists. For instance, Abner Shminoy wrote in the older version of the SEP on Bell's Theorem:

There may indeed be “peaceful coexistence” between Quantum nonlocality and Relativistic locality, but it may have less to do with signaling than with the ontology of the quantum state. Heisenberg's view of the mode of reality of the quantum state was briefly mentioned in Section 2 — that it is potentiality as contrasted with actuality. This distinction is successful in making a number of features of quantum mechanics intuitively plausible — indefiniteness of properties, complementarity, indeterminacy of measurement outcomes, and objective probability. But now something can be added, at least as a conjecture: that the domain governed by Relativistic locality is the domain of actuality, while potentialities have careers in space-time (if that word is appropriate) which modify and even violate the restrictions that space-time structure imposes upon actual events. The peculiar kind of causality exhibited when measurements at stations with space-like separation are correlated is a symptom of the slipperiness of the space-time behavior of potentialities. This is the point of view tentatively espoused by the present writer, but admittedly without full understanding. What is crucially missing is a rational account of the relation between potentialities and actualities — just how the wave function probabilistically controls the occurrence of outcomes. In other words, a real understanding of the position tentatively espoused depends upon a solution to another great problem in the foundations of quantum mechanics − the problem of reduction of the wave packet.

The link is to the section 'Philosophical Comments' of the article - Shimony lists other possible positions.

There are different takes. For IMHO a very interesting Neo-Kantian non-representionalist reading (among the 'Copenaghists'), check this article of Michel Bitbol (I already quoted it in this thread - I quote it again here for convenience): http://www.bourbaphy.fr/bitbol.pdf (according to him, Bohr's epistemology was close to Kant's views...). Or, if one prefers the video of the talk: https://www.youtube.com/watch?v=pYRLapWBqJY.

Another instance of interpretation of the wave-function in terms of potentiality-actuality can be found in this paper by Kastner et al: https://arxiv.org/abs/1709.03595.

Since none of this is new (it is demanded by QM right from the early days), how do any of the objective collapse interpretations get around this? Does this experiment change something? Did they expect a different result? I don't think so.
— noAxioms

They would predict that Wigner would not see interference for sufficiently complex friend systems. So the options are to either accept the experiment's result as falsifying their theory or else show that the experiment isn't scaled up enough to trigger a physical collapse by their criterion. — Andrew M

That is one thin explanation. If what Alice did wasn't complex enough to objectively collapse the wave function, she should be able to measure the subsequent superposition herself and not leave it to Bob. Of course, QM theory won't allow that, so the 'thin' explanation see to go against QM itself.
Of course maybe I just don't understand this explanation. I have not read your link and am not sure that I would find the answer there satisfactory.

Maybe the point is that the foliation is not directly observable. — boundless

It seems not to be. It would probably violate SR if it was.

As you say, we can observe only a "frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance". Just a guess. As I said, I am quite at loss.

Yes. What is: Space is expanding everywhere equally(ish) at all simultaneous points. I say 'ish' because it expands more in empty places than crowded places, but not more in any particular direction. This isn't true in other frames.
Appearance: Space appears to be expanding equally at all points at some fixed distance from any observation point. So space is expanding close by, but not expanding say 6 billion light years away. Doing these sorts of measurements is how they determined the acceleration of expansion in the first place. You can't measure what is now, but you can measure how it appears now.

I see...but if this does mean that non-locality is compatible with GR (as it is usually understood) why people consider non-locality problematic?

All of relativity seems to depend on locality, while QM interpretations might have other ideas. It is why I resist interpretations that discard locality in favor of counterfactual definiteness. I just don't see how relativity can make sense without locality. One can blatantly change the past, not just events outside one's future light cone.
That and the fact that counterfactual definiteness has all sorts of seemingly paradoxical philosophical baggage that goes away if you don't accept the principle.

Well, yeah, you are right.
But IMO this leads either to the 'Andromeda Paradox'/Riedtjik-Putnam argument scenario or some form of retro-causality.

Don't get your Dutch names wrong... I've got one myself.
The Andromeda thing and the Rietdijk-Putnam thing are pretty much the same, and are only paradoxical if you try to combine assumptions from both interpretations of time. All that proves is that they are not both correct.
Presentism demands an objective ordering of events (although no particular one), but a preferred folation does not demand a preferred moment in time.

Anyway, Antony Valentini proposed that cosmological observations might help to solve interpretational problems in QM. The de Broglie-Bohm interpretation actually makes the same predictions of QM only if the 'quantum equilibrium hypothesis' is satisfied, i.e. if the modulus square of the wave-function corresponds to the actual probability distribution (this assures that dBB satisfies the Born Rule). However, in general, this might be not true. Hence his proposal: maybe at the earliest stages of the evolution of the Universe, that hypothesis was not satisfied and - as a consequence - we should see empirical evidence against the Born Rule.

Here is the link to his talk (at the same conference): https://www.youtube.com/watch?v=XYZV9crCZM8.
Here the link to the Q&A session: https://www.youtube.com/watch?v=8qnuNLB61RA.

Way to kill an afternoon, eh? Thank you for the link. Not sure how much I'm interested in sinking an interpretation that I've already listed as low probability. I'd rather see them sink RQM. Always best to have ones own cage rattled once in a while.

It seems not to be. It would probably violate SR if it was. — noAxioms

Same impression!

Doing these sorts of measurements is how they determined the acceleration of expansion in the first place. You can't measure what is now, but you can measure how it appears now. — noAxioms

Ok, thanks! I think I'll revise GR and cosmology. I admittedly do not know very much about both.

All of relativity seems to depend on locality, while QM interpretations might have other ideas. It is why I resist interpretations that discard locality in favor of counterfactual definiteness. I just don't see how relativity can make sense without locality. One can blatantly change the past, not just events outside one's future light cone.
That and the fact that counterfactual definiteness has all sorts of seemingly paradoxical philosophical baggage that goes away if you don't accept the principle. — noAxioms

:up: I agree! I would add the 'no signaling' theorem.

Don't get your Dutch names wrong... I've got one myself. — noAxioms

Ops! Sorry!

The Andromeda thing and the Rietdijk-Putnam thing are pretty much the same, and are only paradoxical if you try to combine assumptions from both interpretations of time. All that proves is that they are not both correct. — noAxioms

Right :smile:

Presentism demands an objective ordering of events (although no particular one), but a preferred folation does not demand a preferred moment in time. — noAxioms

Maybe dBB requires a preferred moment in time and not just a preferred foliation, then! (alternatively, a preferred foliation without a preferred moment in time and retro-causality.)

Way to kill an afternoon, eh? — noAxioms

LOL, yeah!

Thank you for the link. — noAxioms

You're welcome :wink:

Not sure how much I'm interested in sinking an interpretation that I've already listed as low probability. I'd rather see them sink RQM. Always best to have ones own cage rattled once in a while. — noAxioms

I see! That's perfectly reasonable :smile:

Actually, I admit that dBB (in some forms*) is my third favorite interpretation. After all, it is still somewhat 'odd' but at the same time counterfactual definiteness is very intuitive. But as I mentioned before I find (among other things) this 'oddness' as an indication that some kind of 'paradigm change' is required. Also, it seems that, in general, there is a trend to more and more 'counter-intuitiveness' in physics...Hence, I lean towards RQM and Copenaghen.

*(I do not like the purely 'nomological' view where there is no physical explanation of the movements of the particles - I prefer the 'dispositionalist' version. Also, I think that I am in the minority but I find the 'quantum potential' formulation interesting - after all, the 'classical limit' becomes quite intuitive if the contribution of the wave-function is seen as additional force.)

That is one thin explanation. If what Alice did wasn't complex enough to objectively collapse the wave function, she should be able to measure the subsequent superposition herself and not leave it to Bob. Of course, QM theory won't allow that, so the 'thin' explanation see to go against QM itself.
Of course maybe I just don't understand this explanation. I have not read your link and am not sure that I would find the answer there satisfactory. — noAxioms

Obective collapse theories (such as GRW and Penrose's) are physically different theories to standard QM. I don't know what specific explanations they would give for this particular experiment. But they make predictions for Wigner's friend-style experiments that make them experimentally differentiable from standard QM.

As Brukner says in that link (my italics):

In my eyes, outcomes 1 and 2 would indicate fundamentally new physics. I will not consider these cases further and regard quantum theory to be a universal physical theory. This leaves us with situation 3 as the only possible outcome of Deutsch's thought experiment. The outcome is compatible with the Everett interpretation: each copy of the observer observes a definite but different outcome in different branches of the (multi)universe. The outcome is compatible with the Copenhagen interpretation too, but it is rarely discussed what the implications of this claim are for our understanding of physical reality within the interpretation. The rest of the current manuscript is devoted to this problem. — On the quantum measurement problem - Caslav Brukner

I'd rather see them sink RQM. Always best to have ones own cage rattled once in a while. — noAxioms

I'd be curious to know your thoughts about the RQM questions from my earlier exchange with boundless here.

There are different takes. For IMHO a very interesting Neo-Kantian non-representionalist reading (among the 'Copenaghists'), check this article of Michel Bitbol (I already quoted it in this thread - I quote it again here for convenience): http://www.bourbaphy.fr/bitbol.pdf (according to him, Bohr's epistemology was close to Kant's views...). Or, if one prefers the video of the talk: https://www.youtube.com/watch?v=pYRLapWBqJY.

Another instance of interpretation of the wave-function in terms of potentiality-actuality can be found in this paper by Kastner et al: https://arxiv.org/abs/1709.03595. — boundless

Thanks for the links! I had a quick skim. I find Rovelli's approach more natural than either of those. Bitbol's approach seems overly metaphysical and Kastner's approach is non-local.

Actually, this interpretation of the wave-function is also held by some Copenaghists. For instance, Abner Shminoy wrote in the older version of the SEP on Bell's Theorem:

There may indeed be “peaceful coexistence” between Quantum nonlocality and Relativistic locality, but it may have less to do with signaling than with the ontology of the quantum state. Heisenberg's view of the mode of reality of the quantum state was briefly mentioned in Section 2 — that it is potentiality as contrasted with actuality. This distinction is successful in making a number of features of quantum mechanics intuitively plausible — indefiniteness of properties, complementarity, indeterminacy of measurement outcomes, and objective probability. But now something can be added, at least as a conjecture: that the domain governed by Relativistic locality is the domain of actuality, while potentialities have careers in space-time (if that word is appropriate) which modify and even violate the restrictions that space-time structure imposes upon actual events. The peculiar kind of causality exhibited when measurements at stations with space-like separation are correlated is a symptom of the slipperiness of the space-time behavior of potentialities. This is the point of view tentatively espoused by the present writer, but admittedly without full understanding. What is crucially missing is a rational account of the relation between potentialities and actualities — just how the wave function probabilistically controls the occurrence of outcomes. In other words, a real understanding of the position tentatively espoused depends upon a solution to another great problem in the foundations of quantum mechanics − the problem of reduction of the wave packet.

The link is to the section 'Philosophical Comments' of the article - Shimony lists other possible positions. — boundless

Thanks, that was interesting. So my suggestion differs in at least two ways. First, as with Rovelli, I think that quantum mechanics is local. Second, as with Aristotle, potentialities don't "do" anything, only actual systems do.

Instead, the term "potential" provides a natural way for Wigner and his friend to describe the scenario from their own perspective and also to describe the scenario from the other's perspective.

So when the friend (Alice) measures spin up, that actualizes (i.e., realizes) the particle's spin potential for her. But she also knows that both the spin and her subsequent measurement of the spin are only potentials for Wigner until Wigner measures the friend's system in that basis.

The actual/potential terminology combined with RQM's relationalism provides an ordinary language abstraction over the underlying mechanics. That abstraction preserves locality, factual definiteness, freedom of choice and, crucially, a referent within the universe that provides a view from somewhere (i.e., the system's reference frame).

the domain governed by Relativistic locality is the domain of actuality, while potentialities have careers in space-time (if that word is appropriate) which modify and even violate the restrictions that space-time structure imposes upon actual events. — Shiminoy

There is a paragraph in the essay on Kastner's paper which says:

In particular, “real” should not be restricted to “actual” objects or events in spacetime. Reality ought also be assigned to certain possibilities, or “potential” realities, that have not yet become “actual.” These potential realities do not exist in spacetime, but nevertheless are “ontological” — that is, real components of existence.

So - they don't exist in space-time, but they're real. Here is key idea, I think - which is the idea that there can be degrees of reality, that things can be more or less real.

That intuitively maps against the idea of the probability wave also, as the probability wave is literally a distribution of possibilities or likelihoods.

The quantum concept of a “probability wave,” describing the likelihood of different possible outcomes of a measurement, was a quantitative version of Aristotle’s potential, Heisenberg wrote in his well-known 1958 book Physics and Philosophy. “It introduced something standing in the middle between the idea of an event and the actual event, a strange kind of physical reality just in the middle between possibility and reality.”

I think there reason that this is so hugely controversial is that in Western philosophy, the idea of 'degrees of reality' was abandoned by the later medievals (largely due to Duns Scotus.) So in the modern picture, something is either real, or it isn't - which maps against the classical atomist idea where a particle is 1 and the void is 0. But if things can be more or less real, then it expands the notion of ontology along a different dimension, so to speak, to include the axis from the unmanifest to the manifest. And that concept, I contend, had largely dropped out of Western discourse by the time of the Scientific Revolution.

Some more passages from Wheeler's article, Law without Law:

The dependence of what is observed upon the choice of the experimental arrangement made Einstein unhappy. It conflicts with the view that the universe exists "out there" independent of all acts of observation. In contrast, Bohr stressed that we confront here an inescapable new feature of nature, to be welcomed because of the understanding it gives us. In struggling to make clear to Einstein the central point as he saw it, Bohr found himself forced to introduce the word "phenomenon". In today's words, Bohr's point - and the central point of quantum theory - can be put into a simple sentence: "No elementary phenomenon is a phenomenon until it is a registered (observed) phenomenon".

I think this is perfectly in keeping with the regular use of the word 'phenomenon' i.e. 'what appears', however what is novel, is the distinction of the phenomenal from 'the unobserved'. Note that in Wheeler's depiction, it is not strictly speaking accurate to say that 'unobserved' means simply 'existing unperceived', as the act of observation is the very 'participation' that he introduces.

...It is wrong to think of that past [i.e. of a photon that has travelled billions of light years] as "already existing" in all detail. The "past" is theory. The past has no existence except as it is recorded in the present.

Bad news for the 'arche-fossil'!

....useful as it it is under everyday circumstances [i.e. pragmatically] to say that the world exists "out there" independent of us, that view can no longer be upheld. There is a strange sense in which this is a "participatory universe".

It is after this that the cautionary note about "consciousness" is introduced. However, here, Wheeler makes it clear that he means by "consciousness" "what is happening in the mind of the individual observer". This doesn't detract from the pivotal role of the observer in the "participatory universe".

Bad news for the 'arche-fossil'! — Wayfarer

... Really? You didn't even tag me man! And you seem to have forgotten a few things from the paper, selectively choosing what to emphasise.

Initiate close reading mode:

After your first quote, Wheeler clarifies his notion of 'recording' or 'observation':

A phenomenon is not yet a phenomenon until it has been brought to a close by an irreversible act of amplification; such as the blackening of a grain of silver bromide emulsion or the triggering of a photodetector

(my italics)

Firstly, observation is characterised as 'an irreversible act of amplification'. Secondly, he clearly ascribes the role of 'irreversible acts of amplification' to the lab equipment, rather than human consciousness. (without mentioning the previous quote @StreetlightX gave)

He also draws a large distinction between 'elementary quantum phenomenon', like the observation of a single photon dispelling its superposed histories, and macroscopic phenomena:

Anything macroscopic which happened in the past makes, we know, a rich fallout of consequences in the present. But whether we deal with the fall of the tree or the evidence for the dab of paint on the canvas or the motion of the moon through the sky, the number of quanta that come into play is so enormous that the unseen quantum individuality of the act of observation can hardly be said to influence the event observed

he goes on to clarify that rather than defining the past with respect to the present, the quantum observation determines the trajectory it took. Prior to the observation it makes no sense to speak of the route the photon took. He clarifies:

This is the sense in which, in a loose way of speaking, we decide what the photon shall have done after it has already done it. In actuality it is wrong to talk of the "route" of the photon. For a proper way of speaking we recall once more that it makes no sense to talk of a phenomenon until it has been brought to a close by an irreversible act of amplification; 'No elementary phenomenon is a phenomenon until it is a registered (observed) phenomenon'

This is much distinct from giving any sort of being, even theoretical, to the past; it is saying that for quantum states/trajectories it makes no sense to talk of their past trajectory without their observation. Moreover just after introducing his idea of a 'participatory universe', he immediately gives the clarifying note; a caution; that this should not be interpreted in terms of consciousness.

We cannot speak in these terms without a caution and a question. The caution: "consciousness" has nothing whatsoever to do with the quantum process.

He then reiterates his previous clarification between an anthropomorphic sense of 'observation' and his preferred description of it:

We are dealing with an event that makes itself known by an irreversible act of amplification, an indelible record, an act of registration. Does that record subsequently enter into the consciousness of some person, some animal or some computer?

To super-duper-mega-ultra emphasise that it is not the cognition of humans which 'creates' the 'past' of quantum phenomena, he even says of cognition/interpretation:

Is that the first step in translating the measurement into meaning?

IE, the 'measurement' is a nonconceptual thing, it is not a property of a human relating to a quantum state, it's a physical interaction which is analogised with conception or perception using perspectival vocabulary to explain it.

Of whether the requirement of observation for a quantum phenomenon to take on a determinate character renders reality some composition of ideas and perceptions. He firstly (and before the quotes we've discussed) makes an analogy with Berkeley:

Hoe does quantum mechanics today differ from what Bishop Goerge Berkeley told us two centuries ago, 'esse est percipi', to be is to be perceived'? Does the tree not exist in the forest unless someone is there to see it? Do Bohr's conclusions about the role of the observer differ from those of Berkeley? Yes, and in an important way, Bohr deals with the individual quantum process. Berkeley, like all of us under everyday circumstances, deals with multiple quantum processes

.

he concludes this analogy in a later section:

An old legend describes a dialog between Abraham and Jehovah. Jehovah chides Abraham: 'You would not even exist if it were not for me!', "Yes Lord, that I know", Abraham replies, "but also You would not be known if it were not for me"

In our time the participants in the dialog have changed. They are the universe and man. The universe, in the words of some who would aspire to speak for it, says 'I am a giant machine. I supply the space and time for your existence. There was no before before I came into being, and there will be no after after I cease to exist. You are an unimportant bit of matter located in an unimportant galaxy."

How shall we reply? Shall we say "Yes, oh universe, without you I would not have been able to come into being. Yes you, great system, are made of phenomena, and every phenomenon rests on an act of observation. You could never even exist without elementary acts of registration such as mine"?

Are elementary quantum phenomena (note not consciousness dependent - me), those untouchable, indivisible acts of creation, indeed the building material of all that is? Beyond particles, beyond fields of force, beyond geometry, beyond space and time themselves, is the ultimate constituent, the still more ethereal act of observer-participancy? For Dr. Samuel Johnson, the stone was real enough when he kicked it. The subsequent discovery that the matter in that rock is made of positive and negative electric charges and more than 99.99 per cent of empty space does not diminish the pain that it inflicts on one's toe. If that stone is someday revealed to be altogether emptiness, "reality" will be none the worse for the finding.

Are billions upon billions of acts of observer-participancy the foundation of everything? We are about as far as we can be today from knowing enough about the deeper machinery of the universe to answer that question

These theme of multiple quantum processes is exactly mirrored in his distinction between 'elementary quantum phenomena' and 'macroscopic' phenomena which he has previously discussed. Not only does Wheeler reject the dependence of observation upon consciousness, he explicitly rejects transferring the account of subjective idealism which hold in analogy for elementary quantum phenomena - which he is using to explain observer dependence to those who do not understand it - to systems of multiple quantum processes; esp. the macroscopic. How you can cite the article for support of your position when it goes to pains to refute it baffles me.

But we do certainly know that most observers are not humans, or human consciousness and so on. How can we make sense of the idea that everything is observer dependent plus the idea that observers are not human consciousnesses? (rather, recall, interpretation for Wheeler occurs after observation!) Wheeler characterises such a question as requiring more 'knowledge of the universe', IE he thinks it's something that might be true or false about nature that 'everything' is created through some system of observation. But we can say that our reality would not be transformed by such an understanding, in a similar way to Dr. Johnson's foot-pain not being alleviated from the discovery that mostly things are made of empty space.

end close reading mode.

That observer dependence isn't consciousness for Wheeler, and that he compares the discovery of the observer dependence of quantum phenomena to the discovery of that matter is largely empty space, suggest that he takes a realist stance towards observer dependence. That is, observer dependence is not an epistemic or conceptual relation toward a phenomenon; just a map; it is a mode of nature interacting with itself; observer dependence is 'in the territory' too.

Also adjoin that he thinks macroscopic phenomena are largely 'untouched' by quantum effects; ancestral statements can easily be produced. They can even be produced about the photon whose past was determined by observation; how long did it take to get here? Longer than the lifetime of human history.

All you've demonstrated is that you didn't read Wheeler's paper closely, and that you didn't actually understand the arche-fossil argument (which is my fault). Perhaps I should make a thread on it.

He clearly ascribes the role of 'irreversible acts of amplification' to the lab equipment, rather than human consciousness. — fdrake

Lab equipment, instruments, and so on, are all simply adjuncts and extensions to human sensory capabilities. An instrument can register a measurement, but it's not an observation until it is, in fact, observed:

In 1958, Schrödinger, inspired by Schopenhauer... published his lectures Mind and Matter. Here he argued that there is a difference between measuring instruments and human observation: a thermometer’s registration cannot be considered an act of observation, as it contains no meaning in itself. Thus, consciousness is needed to make physical reality meaningful. As Schrödinger concluded, "Some of you, I am sure, will call this mysticism. So with all due acknowledgement to the fact that physical theory is at all times relative, in that it depends on certain basic assumptions, we may, or so I believe, assert that physical theory in its present stage strongly suggests the indestructibility of Mind by Time." 1

Consider figure 7 in the Wheeler paper, the caption of which is 'what we call 'reality' symbolised by the letter "R" in the diagram, consists of an elaborate paper-mache construction of imagination and theory fitted between a few iron posts of observation.'

An elaborate paper mache construction!

Look at the question he asks in the very passage you've quoted:

Are elementary quantum phenomena those untouchable, indivisible acts of creation, indeed the building material of all that is? Beyond particles, beyond fields of force, beyond geometry, beyond space and time themselves, is the ultimate constituent, the still more ethereal act of observer-participancy?

Are there? He doesn't answer the question. The paper, and the footnotes, are littered with aporia, with open and unanswered questions. He compares physics to a motor vehicle, where all we've done is 'turn the starter motor over'.

All you've demonstrated is that you didn't read Wheeler's paper closely, and that you didn't actually understand the arche-fossil argument (which is my fault). Perhaps I should make a thread on it. — fdrake

You're right, I didn't read it as closely as I should have, but at the same time, I don't see how it supports anything like a realist ontology. It has many references to the 'role of the observer'.

You've quoted two passages, one from Bohr, one from Wheeler, both of which call into question the objectivity of scientific observation, as if they support the objectivity of scientific observation. So - who is not reading what? :-)

Wheeler thinks macroscopic phenomena are largely 'untouched' by quantum effects; ancestral statements can easily be produced. They can even be produced about the photon whose past was determined by observation; how long did it take to get here? Longer than the lifetime of human history. — fdrake

How can an observation that happens now, effect the path the particle has taken before being observed. That is the conundrum of the 'delayed choice experiment'.

What I am arguing is that, you take 'the world out there' as independently real, always existing, regardless of any observation by us. You assume this so naturally, that anything that appears to threaten it is treated with intense annoyance; it pushes buttons. But we know even from cognitive science that this can't be the case. Everything we see and know are after all received sensations and perceptions which are organised by the brain into a gestalt. That is what reality is, you can no more get outside it than step outside your own body. It's just that physics itself, the hardest of hard sciences, is now starting to drive this home.

You've quoted two passages, one from Bohr, one from Wheeler, both of which call into question the objectivity of scientific observation, as if they support the objectivity of scientific observation. So - who is not reading what? :-) — Wayfarer

They only 'show' this when you misinterpret the observer. Like this:

What I am arguing is that, you take 'the world out there' as independently real, always existing, regardless of any observation by us. — Wayfarer

See? Claiming observer=human again. Bohr and Wheeler have gone to pains to say that this isn't so. This is the only thing stopping you from seeing 'observers' - which recall for Wheeler are 'irreversible events of amplification' - as part of nature. Going back to the start; like a sodium atom and chlorine atom acting as observers for the electron in the outer shell of the sodium atom by constraining its distribution of trajectories in forming an ionic bond.

Claiming observer=human again. Bohr and Wheeler have gone to pains to say that this isn't so. — fdrake

But looking at the original quote from Bohr again:

We can still use the objectifying language of classical physics to make statements about observable facts. For instance, we can say that a photographic plate has been blackened, or that cloud droplets have formed. But we can say nothing about the atoms themselves. And what predictions we base on such findings depend on the way we pose our experimental question, and here the observer has freedom of choice. Naturally, it still makes no difference whether the observer is a man, an animal, or a piece of apparatus, but it is no longer possible to make predictions without reference to the observer or the means of observation. To that extent, every physical process may be said to have objective and subjective features. The objective world of nineteenth-century science was, as we know today, an ideal, limiting case, but not the whole reality.

Where Bohr says 'it doesn't make any difference what the observer is', I think this is drive home the point that the act of observation cannot be removed from the picture - no matter what you call 'observation'! - and furthermore, that 'observation' is irreducibly subjective in nature ('every physical process may be said to have objective or subjective features'). So unless you subscribe to pan-psychism, i.e. that even elementary particles are subjects of experience - then to all intents and purposes, the role of the observer is always at least implicitly a human agent.

(Why is that a problem, again?)

Which is similar to the point made by Wheeler:

The dependence of what is observed upon the choice of the experimental arrangement made Einstein unhappy. It conflicts with the view that the universe exists "out there" independent of all acts of observation.

Wheeler is known for the phrase 'participatory universe', which is what? To take it from the horse's mouth:

It from bit. Otherwise put, every "it" — every particle, every field of force, even the space-time continuum itself — derives its function, its meaning, its very existence entirely — even if in some contexts indirectly — from the apparatus-elicited answers to yes-or-no questions, binary choices, bits. It from bit symbolizes the idea that every item of the physical world has at bottom — a very deep bottom, in most instances — an immaterial source and explanation; that which we call "reality" arises in the last analysis from the posing of yes-no questions and the registering of equipment-evoked responses; in short, that all things physical are information-theoretic in origin and that this is a participatory universe.

It's exactly observation, in the human sense, which is removed in that picture. The sodium and chlorine atoms aren't having human experience of observation when the interact with each other.

Subjectivity, in other worlds, is understood as more than just being our ideas or the presence of experience. To be an observer, one does not need our ideas, our experiences, to even be consciousness at all. They just have to be a distinct point of reference compared to others.

The realisation here is not "humans experiences creates things", but rather that any interaction is a result of the particular entities involved. In other words, its always an interaction in which the participants have an effect (thus, there can be no experiment performed without our measuring equipment having an impact). We cannot set up a system of "objective rules" which push around and constrain inert objects. Those involved, whether they be our experiences, tree, equipment or atoms, always constitute the conditions of the given interaction itself.

There is an ambiguity in 'Copenaghen Interpretation' (CI) that creates endless debates like this one :smile:

In CI, measurements are explained via the 'collapse' of the wave-function. The problem is, however, that CI is simply ambiguous on it. In fact, I would say that there is no 'Copenaghen Interpretation' at all. It is rather a 'class' of very different views that are, so to speak, 'grouped' together.

But where is the ambiguity? The problem is that the formalism of the theory alone does not identify what is the 'observer'. Yet, in order to explain the wave-function collapse you need to posit an 'observer'. If not, we cannot explain why our 'everyday world' looks classical, so to speak.

Anyway, let's see the proposed solutions to this intrinsic ambiguity of CI.

Firstly, one might try to say that, indeed, there are physical objects that count as 'observers'. For instance, objects that are able to store and process 'information', like e.g. computers, registering devices, brains etc. If I am not mistaken this is the view of Wheeler. The 'universe' is 'participatory' in this view because each of these 'observers' can 'modify' reality by 'collapsing' the wave-function.

Secondly, another possible way to deal with this is to go with RQM (Relational Quantum Mechanics) as Rovelli et al do. Here, all physical systems can be 'observers' and the 'measurement' is simply a physical interaction. This is because, according to Rovelli, there is nothing special about computers, etc:

In order to prevent the reader from channeling his/her thoughts in the wrong direction, let me anticipate a few terminological remarks. By using the word “observer” I do not make any reference to conscious, animate, or computing, or in any other manner special, system. I use the word “observer” in the sense in which it is con- ventionally used in Galilean relativity when we say that an object has a velocity “with respect to a certain ob- server”. The observer can be any physical object having a definite state of motion. For instance, I say that my hand moves at a velocity v with respect to the lamp on my table. Velocity is a relational notion (in Galilean as well as in special relativistic physics), and thus it is al- ways (explicitly or implicitly) referred to something; it is traditional to denote this something as the observer, but it is important in the following discussion to keep in mind that the observer can be a table lamp. Also, I use information theory in its information-theory mean- ing (Shannon): information is a measure of the number of states in which a system can be –or in which several systems whose states are physically constrained (corre- lated) can be. Thus, a pen on my table has information because it points in this or that direction. We do not need a human being, a cat, or a computer, to make use of this notion of information.

(Source: https://arxiv.org/pdf/quant-ph/9609002.pdf ; emphasis mine)
But Rovelli's RQM is, in fact, not classified as 'CI'. Why? Rovelli claims that QM is complete, whereas for CI you still need to consider something as classical.

Or one might argue that, for instance, you cannot have a well-defined concept of information without relating it to some form of consciousness (not necessarily human, in fact). And you end up with the 'Consciousness causes collapse' interpretation

Or a Kantian-like interpretation like the one proposed by Bitbol and others (and possibly of Bohr at least for some parts of his life, if Bitbol is right...) if you do not like the idea that consciousness really 'modifies' reality (but it is nevertheless necessary to have an 'observer').

Of course, if one is really pragmatic one can simply choose to ignore the problem (but maybe this is not satisfactory for someone philosophically inclined). Finally, one can choose other interpretations of QM.

Thanks for the links! I had a quick skim. I find Rovelli's approach more natural than either of those. Bitbol's approach seems overly metaphysical and Kastner's approach is non-local. — Andrew M

You're definitely welcome.

I can understand the unease with Bitbol's approach. But note that consciousness in his interpretation does not 'do' anything, in fact. It does not affect physical reality. It simply define the 'perspective' of the 'observer'. In a way analogous to Kant, Bitbol in fact IMO says that the 'quantum world' is indeterminate. But it is not a denial of it and neither he claims that it is 'modified' by consciousness. But as I said, I can hear your unease because I share it (even if I do like Kantian-like philosophies).

Regarding Kaster's approach I am not sure to call it 'non-local'. In the paper, Kastner et al explain (page 5):

As one of us (SK) has observed (Kauffman 2016, Chapter 7), we might plan to meet tomorrow for coffee at the Downtown Coffee Shop. But suppose that, unbeknownst to us, while we are making these plans, the coffee shop (actually) closes. Instantaneously and acausally, it is no longer possible for us (or for anyone no matter where they happen to live) to have coffee at the Downtown Coffee Shop tomorrow. What is possible has been globally and acausally altered by a new actual (token of res extensa).6 In order for this to occur, no relativity-violating signal had to be sent; no physical law had to be violated. We simply allow that actual events can instantaneously and acausally affect what is next possible (given certain logical presuppositions, to be discussed presently) which, in turn, influences what can next become actual, and so on. In this way, there is an acausal ‘gap’ between res extensa and res potentia in their mutual interplay, that corresponds to a form of global nonlocality.

[Footnote 6]: While ‘acausal’ in the classical sense of efficient causality (wherein one actual state causally influences another actual state), in the quantum mechanical sense of causality wherein potentia are treated as ontologically significant, the actualized state is understood to ‘causally’ alter the probability distribution by which the next ‘possible’ state is defined. For further discussion of this distinction between classical efficient causality and quantum mechanical causality, see Epperson (2004, 92-93; 2013, 105-6). On the other hand, under certain circumstances and at the relativistic level, where decay probabilities are taken into account, the relation between an actualized state and the next QP state may itself be indeterministic (see, e.g. Kastner 2012, Section 3.4 and Chapter6).

Shimony's take, instead, seems definitely 'non-local'. But maybe he meant something like Kastner et all above (as did maybe other proponents of an 'Aristotelian-like' reading of CI).

First, as with Rovelli, I think that quantum mechanics is local. Second, as with Aristotle, potentialities don't "do" anything, only actual systems do. — Andrew M

I feel I am in agreement!

Instead, the term "potential" provides a natural way for Wigner and his friend to describe the scenario from their own perspective and also to describe the scenario from the other's perspective.

So when the friend (Alice) measures spin up, that actualizes (i.e., realizes) the particle's spin potential for her. But she also knows that both the spin and her subsequent measurement of the spin are only potentials for Wigner until Wigner measures the friend's system in that basis.

The actual/potential terminology combined with RQM's relationalism provides an ordinary language abstraction over the underlying mechanics. That abstraction preserves locality, factual definiteness, freedom of choice and, crucially, a referent within the universe that provides a view from somewhere (i.e., the system's reference frame). — Andrew M

:up:

To be more complete, in fact I lean towards RQM and CI. The problem I have with RQM is that 'information' maybe is not something well-defined in relation to all physical systems. But as I said in my previous post, this is a quite controversial point. If 'information' is something that can be defined in relation to all physical system, then RQM is IMO the best choice.

If not, maybe something like Bitbol's interpretation (with maybe some elements of 'actuality/potentiality' dualism) would be best.

I am simply undecided.