> On 22 Nov 2019, at 08:35, Bruce Kellett <bhke...@optusnet.com.au> wrote:
>
> I have been reading Sean Carroll's book "Something Deeply Hidden". It is more reasonable than some of the commentary had led me to believe. The issue at the moment is whether or not all things happen in the quantum multiverse. I argued that just because I might turn left at some point, it does not follow from Many-Worlds QM that in some other world I turn right.
Absolutely. That follows directly from the Schroedinger equation. That is why we take life instead of jumping out of the window! On the contrary the linearity and decoherence assures us that when we take a decision, we acts similarly in all universe, unless the decision use a quantum coin of course.
> Carroll agrees with this, despite some reports to the contrary. On page 214 he says "No, you do not cause the wave function to branch by making a decision.... Branching is the result of a microscopic process amplified to macroscopic scales: a system in a quantum superposition becomes entangled with the environment, leading to decoherence. A decision, on the other hand, is a purely macroscopic phenomenon. There are no decisions being made by the electrons and atoms inside your brain; they're just obeying the laws of physics.”
OK. Of course, we can branch if we desire to do so, like deciding to take the holiday in the North or in the south by untangling that decision with a quantum coin.
>
> So there is not a coy of me in some other branch that is typing a completely different email at this moment.....
>
> Carroll also says sensible things about quantum suicide and other moral issues.
>
> I was, as Brent also reported, a little surprised by his argument that it didn't really matter whether you thought of the splitting of the wave function/universe on a decohered quantum event as spreading at light speed, or as instantaneous throughout the entire universe. (pp. 170-171). I think this reflects the fact that Carroll does not seem to be as opposed to the idea of non-locality as are other advocates of many worlds. However, he does seem to think that the fact that outcomes of experiments are not unique in many-worlds does deflect the impact of Bell's theorem in that theory. "That doesn't mean that Bell's theorem is wrong in Many-Worlds; mathematical theorems are unambiguously right. It just means that the theorem doesn't apply. Bell's result does not imply that we have to include spooky action at a distance in Everettian quantum mechanics, as it does for boring old single-world theories. The correlations don't come about because of any kind of influence being transmitted faster than light, but because of branching of the wave function into different worlds, in which correlated things happen." (p. 105)
I agree with Carroll. I guess you don’t ...
>
> I think this is wrong, of course.
… as you say.
> The trouble with this argument is that deflecting Bell's theorem does not automatically mean that your theory is, in fact, local.
I agree on this. But why would it be non local?
> And, as is usual for many-worlders, Carroll does not go on the actually spell out how the magic of world branching actually gives rise to the observed correlations. (He can't, of course, and that is why the issue is glossed over.) Maudlin, on the other hand, is so pissed off with people thinking that they can subvert Bell's theorem, that he simply states baldly that the quantum mechanical wave function is intrinsically non-local (Philosophy of Quantum Theory, 2019).
I will wait for a proof of this statement.
On 25 Nov 2019, at 22:53, Bruce Kellett <bhkel...@gmail.com> wrote:On Tue, Nov 26, 2019 at 1:31 AM Bruno Marchal <mar...@ulb.ac.be> wrote:> On 22 Nov 2019, at 08:35, Bruce Kellett <bhke...@optusnet.com.au> wrote:
>
> I have been reading Sean Carroll's book "Something Deeply Hidden". It is more reasonable than some of the commentary had led me to believe. The issue at the moment is whether or not all things happen in the quantum multiverse. I argued that just because I might turn left at some point, it does not follow from Many-Worlds QM that in some other world I turn right.
Absolutely. That follows directly from the Schroedinger equation. That is why we take life instead of jumping out of the window! On the contrary the linearity and decoherence assures us that when we take a decision, we acts similarly in all universe, unless the decision use a quantum coin of course.
> Carroll agrees with this, despite some reports to the contrary. On page 214 he says "No, you do not cause the wave function to branch by making a decision.... Branching is the result of a microscopic process amplified to macroscopic scales: a system in a quantum superposition becomes entangled with the environment, leading to decoherence. A decision, on the other hand, is a purely macroscopic phenomenon. There are no decisions being made by the electrons and atoms inside your brain; they're just obeying the laws of physics.”
OK. Of course, we can branch if we desire to do so, like deciding to take the holiday in the North or in the south by untangling that decision with a quantum coin.
>
> So there is not a coy of me in some other branch that is typing a completely different email at this moment.....
>
> Carroll also says sensible things about quantum suicide and other moral issues.
>
> I was, as Brent also reported, a little surprised by his argument that it didn't really matter whether you thought of the splitting of the wave function/universe on a decohered quantum event as spreading at light speed, or as instantaneous throughout the entire universe. (pp. 170-171). I think this reflects the fact that Carroll does not seem to be as opposed to the idea of non-locality as are other advocates of many worlds. However, he does seem to think that the fact that outcomes of experiments are not unique in many-worlds does deflect the impact of Bell's theorem in that theory. "That doesn't mean that Bell's theorem is wrong in Many-Worlds; mathematical theorems are unambiguously right. It just means that the theorem doesn't apply. Bell's result does not imply that we have to include spooky action at a distance in Everettian quantum mechanics, as it does for boring old single-world theories. The correlations don't come about because of any kind of influence being transmitted faster than light, but because of branching of the wave function into different worlds, in which correlated things happen." (p. 105)
I agree with Carroll. I guess you don’t ...No, as I say. One problem is that his stance on decoherence spreading instantaneously is at variance with his rejection of Bell non-locality.
Actually, Carroll's ambivalence towards non-locality is even more evident in the latter part of his book, where he attempts to find space-time emerging from entanglement. He has to acknowledge that entanglement is intrinsically non-local, in that it mixes the wave function at one point with that at another. And the points that are entangled act as a unit, even though widely separated -- with no intervening physical processes.On page 233, he distinguishes between two senses of "locality": what we might call 'measurement locality' and 'dynamical locality'. The EPR thought experiment shows that there is something that seems non-local about quantum measurement. ... Whether many-worlds is non-local in this sense depends on how we choose to define our branches of the wave function: we're allowed to make either local or non-local choices, where branching happens only nearby or immediately throughout space.Dynamical locality, on the other hand, refers to the smooth evolution of the quantum state when no measurement or branching is happening....This kind of locality is enforced by the rule in special relativity that nothing can travel faster than light. And it's this dynamical locality that we're concerned with at the moment as we study the nature and emergence of space itself." (p. 233)
I think this whole section is rather confused and this is little more than sophistry. Sean is trying to cover up what is really a glaring inconsistency in his approach. Maybe more work will enable one to make a bit more sense of this……
>
> I think this is wrong, of course.
… as you say.
> The trouble with this argument is that deflecting Bell's theorem does not automatically mean that your theory is, in fact, local.
I agree on this. But why would it be non local?Because, the wave-function itself is non-local -- it contains entangled particles that are widely separated in space. That is the definition of non-locality!
> And, as is usual for many-worlders, Carroll does not go on the actually spell out how the magic of world branching actually gives rise to the observed correlations. (He can't, of course, and that is why the issue is glossed over.) Maudlin, on the other hand, is so pissed off with people thinking that they can subvert Bell's theorem, that he simply states baldly that the quantum mechanical wave function is intrinsically non-local (Philosophy of Quantum Theory, 2019).
I will wait for a proof of this statement.I suggest you read Maudlin's new book, or even the second edition (2011) of his earlier book on Quantum Non-Locality and Relativity. As I have often said, the singlet state of two entangled spin-half particles is intrinsically non-local because it is a single quantum state that refers to two distinct spatial locations. This is true for any entangled state -- it refers to two or more spatial locations simultaneously, which is the definition of non-local.
Bruce--
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On 25 Nov 2019, at 22:53, Bruce Kellett <bhkel...@gmail.com> wrote:Because, the wave-function itself is non-local -- it contains entangled particles that are widely separated in space. That is the definition of non-locality!I am not sure. I use “non-locality” for “FTL physical influence”.
In the MWI, some particles can be entangled but without implying any possible FTL when we do measurement on them, except from the local point of view, due to our ignorance of all terms of the wave. It means simply that Alice and Bob belongs to the same branch of history/reality.
On 26 Nov 2019, at 22:39, Bruce Kellett <bhkel...@gmail.com> wrote:On Wed, Nov 27, 2019 at 12:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 25 Nov 2019, at 22:53, Bruce Kellett <bhkel...@gmail.com> wrote:Because, the wave-function itself is non-local -- it contains entangled particles that are widely separated in space. That is the definition of non-locality!I am not sure. I use “non-locality” for “FTL physical influence”.That is just an abuse of language. Non-local means "not local", i.e., not all in one place.
Some attempt has been made to replace the term "non-local" with the term "non-seperable”.
I think we can all agree that the singlet wave function is non-separable -- it cannot be written as a simple product of two terms, one referring to each particle.
I maintain that it is also non-local, in that the two particles are at different locations (locales). Non-local can have no other meaning in ordinary linguistic usage.
In the MWI, some particles can be entangled but without implying any possible FTL when we do measurement on them, except from the local point of view, due to our ignorance of all terms of the wave. It means simply that Alice and Bob belongs to the same branch of history/reality.The trouble with this hope is that it no local account of the EPR correlations been realised in any coherent mathematics. Bell's theorem rules it out: no local hidden variable account of the EPR correlations is possible in any theory, whatsoever. It is a no-go theorem; it proves a negative -- something is impossible. Many-worlds does not subvert Bell's theorem.
I think it is becoming generally accepted in the physics community that the entangled state is intrinsically non-local: acting on one part of it affects the rest, even across the entire universe.
Bruce--
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On 26 Nov 2019, at 22:39, Bruce Kellett <bhkel...@gmail.com> wrote:On Wed, Nov 27, 2019 at 12:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 25 Nov 2019, at 22:53, Bruce Kellett <bhkel...@gmail.com> wrote:Because, the wave-function itself is non-local -- it contains entangled particles that are widely separated in space. That is the definition of non-locality!I am not sure. I use “non-locality” for “FTL physical influence”.That is just an abuse of language. Non-local means "not local", i.e., not all in one place.Then even Newton Universe is non local.
Some attempt has been made to replace the term "non-local" with the term "non-seperable”.Yes, notably d’Espagnat. It avoids the confusion with the Eisnsteinian non-locality, which requires FTL (cf the “spooky action at a distance”), which must exist in QM + the assumption of a unique universe.I think we can all agree that the singlet wave function is non-separable -- it cannot be written as a simple product of two terms, one referring to each particle.Yes, we agree on this.I maintain that it is also non-local, in that the two particles are at different locations (locales). Non-local can have no other meaning in ordinary linguistic usage.I invite you, and Alice, and I give you an envelop to each of you. You are told that one contain a piece of paper with O inscribed on it, and the other with one. Then you go in different galaxies, say, and open it. Once you see 0 (res. 1) you know that Alice will see 1 (res. 0). This seems non local in your sense, where most would agree that in this case, there is no “non-locality” issue. What I claim is that in the Everett theory, all non-locality are of that type.
In the MWI, some particles can be entangled but without implying any possible FTL when we do measurement on them, except from the local point of view, due to our ignorance of all terms of the wave. It means simply that Alice and Bob belongs to the same branch of history/reality.The trouble with this hope is that it no local account of the EPR correlations been realised in any coherent mathematics. Bell's theorem rules it out: no local hidden variable account of the EPR correlations is possible in any theory, whatsoever. It is a no-go theorem; it proves a negative -- something is impossible. Many-worlds does not subvert Bell's theorem.That is right. But the violation of Bell’s inequality entails FTL only when one world is assumed, with well defined outcome for all measurement, or put in another way, assuming a unique reality, with one Bob and one Alice, but Bell’s reasoning does not prove FTL influence in The many-worlds, where all outcomes are obtained, and propagate between diverse Alice and Bob locally, leading to the apparent violation of Bell’s inequality, but without FTL.
I think it is becoming generally accepted in the physics community that the entangled state is intrinsically non-local: acting on one part of it affects the rest, even across the entire universe.That would mean some FTL actions, but I very much doubt this.
On 26 Nov 2019, at 22:39, Bruce Kellett <bhkel...@gmail.com> wrote:I think it is becoming generally accepted in the physics community that the entangled state is intrinsically non-local: acting on one part of it affects the rest, even across the entire universe.That would mean some FTL actions, but I very much doubt this.Bruno
On Thursday, November 28, 2019 at 5:50:18 PM UTC-6, Bruce wrote:
On Fri, Nov 29, 2019 at 1:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:
On 26 Nov 2019, at 22:39, Bruce Kellett <bhkel...@gmail.com> wrote:I think it is becoming generally accepted in the physics community that the entangled state is intrinsically non-local: acting on one part of it affects the rest, even across the entire universe.That would mean some FTL actions, but I very much doubt this.
No, there is no need of FTL. For example, in the third (2011) edition of his book 'Quantum Non-Locality and Relativity', Maudlin shows that Flash GRW theory, as developed by Tumulka, gives a perfectly relativistic account of the EPR correlations without any FTL action.Bruce
The GRW flash theory: a relativistic quantum ontology of matter in space-time?whenever there is a spontaneous localization of the wave-function in configuration space, that development of the wave-function in configuration space represents an event occurring in physical space, namely there being a flash centred around a space-time point. The flashes are all there is in space-time. That is to say, apart from when it spontaneously localizes, the temporal development of the wave-function in configuration space does not represent the distribution of matter in physical space. It represents the objective probabilities for the occurrence of further flashes, given an initial configuration of flashes. As in BM, there hence are no superpositions of anything existing in physical space. However, by contrast to BM, GRWf does not admit a continuous distribution of matter: there are only flashes beingsparsely distributed in space-time, but no trajectories or worldlines of anythingOver and above the flashes being the primitive stuff in physical space, the initial configuration of flashes instantiates a dispositional property – more precisely a propensity – that fixes probabilities for the occurrence of further flashes. The occurrence of such further flashes is the manifestation of that propensity. The propensity of any given configuration of flashes to manifest itself in the occurrence of further flashes is represented by the wave-function. The GRW law supervenes on that propensity in the sense that whenever such a propensity is instantiated in a possible world, the GRW law holds in that world. By contrast to what is admitted by Humeanism, that disposition or propensity hence is a modal property....In conclusion, one may go for an event ontology instead of a particle ontology. But theflash ontology is too sparse an ontology: since it does not provide for anything likecontinuous sequences of events, it does not have the means at its disposal to account forinteractions that are supposed to trigger the occurrence of further flashes (such as e.g.measurements). In the end, therefore, it seems that the flash ontology hardly is a convincinganswer to the question of what quantum mechanics tells us about what there is in space-time.
On 29 Nov 2019, at 00:50, Bruce Kellett <bhkel...@gmail.com> wrote:On Fri, Nov 29, 2019 at 1:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 26 Nov 2019, at 22:39, Bruce Kellett <bhkel...@gmail.com> wrote:On Wed, Nov 27, 2019 at 12:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 25 Nov 2019, at 22:53, Bruce Kellett <bhkel...@gmail.com> wrote:Because, the wave-function itself is non-local -- it contains entangled particles that are widely separated in space. That is the definition of non-locality!I am not sure. I use “non-locality” for “FTL physical influence”.That is just an abuse of language. Non-local means "not local", i.e., not all in one place.Then even Newton Universe is non local.Yes Newton was aware of this.Some attempt has been made to replace the term "non-local" with the term "non-seperable”.Yes, notably d’Espagnat. It avoids the confusion with the Eisnsteinian non-locality, which requires FTL (cf the “spooky action at a distance”), which must exist in QM + the assumption of a unique universe.I think we can all agree that the singlet wave function is non-separable -- it cannot be written as a simple product of two terms, one referring to each particle.Yes, we agree on this.I maintain that it is also non-local, in that the two particles are at different locations (locales). Non-local can have no other meaning in ordinary linguistic usage.I invite you, and Alice, and I give you an envelop to each of you. You are told that one contain a piece of paper with O inscribed on it, and the other with one. Then you go in different galaxies, say, and open it. Once you see 0 (res. 1) you know that Alice will see 1 (res. 0). This seems non local in your sense, where most would agree that in this case, there is no “non-locality” issue. What I claim is that in the Everett theory, all non-locality are of that type.That non-loclality has a common cause explanation. Like Bertlmann's socks, there is no mystery here. The problem is with entangled systems, where non-separability means non-locality that has no common cause explanation, even in many-worlds theory.
In the MWI, some particles can be entangled but without implying any possible FTL when we do measurement on them, except from the local point of view, due to our ignorance of all terms of the wave. It means simply that Alice and Bob belongs to the same branch of history/reality.The trouble with this hope is that it no local account of the EPR correlations been realised in any coherent mathematics. Bell's theorem rules it out: no local hidden variable account of the EPR correlations is possible in any theory, whatsoever. It is a no-go theorem; it proves a negative -- something is impossible. Many-worlds does not subvert Bell's theorem.That is right. But the violation of Bell’s inequality entails FTL only when one world is assumed, with well defined outcome for all measurement, or put in another way, assuming a unique reality, with one Bob and one Alice, but Bell’s reasoning does not prove FTL influence in The many-worlds, where all outcomes are obtained, and propagate between diverse Alice and Bob locally, leading to the apparent violation of Bell’s inequality, but without FTL.Bell did not assume a collapse. His is a mathematical result, where the only assumption is locality. As usual, if you think there is a local explanation of the EPR correlations in many-worlds, then produce it.
I think it is becoming generally accepted in the physics community that the entangled state is intrinsically non-local: acting on one part of it affects the rest, even across the entire universe.That would mean some FTL actions, but I very much doubt this.No, there is no need of FTL. For example, in the third (2011) edition of his book 'Quantum Non-Locality and Relativity', Maudlin shows that Flash GRW theory, as developed by Temulka, gives a perfectly relativistic account of the EPR correlations without any FTL action.
Bruce--
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On 29 Nov 2019, at 00:50, Bruce Kellett <bhkel...@gmail.com> wrote:On Fri, Nov 29, 2019 at 1:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 26 Nov 2019, at 22:39, Bruce Kellett <bhkel...@gmail.com> wrote:On Wed, Nov 27, 2019 at 12:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 25 Nov 2019, at 22:53, Bruce Kellett <bhkel...@gmail.com> wrote:Because, the wave-function itself is non-local -- it contains entangled particles that are widely separated in space. That is the definition of non-locality!I am not sure. I use “non-locality” for “FTL physical influence”.That is just an abuse of language. Non-local means "not local", i.e., not all in one place.Then even Newton Universe is non local.Yes Newton was aware of this.Some attempt has been made to replace the term "non-local" with the term "non-seperable”.Yes, notably d’Espagnat. It avoids the confusion with the Eisnsteinian non-locality, which requires FTL (cf the “spooky action at a distance”), which must exist in QM + the assumption of a unique universe.I think we can all agree that the singlet wave function is non-separable -- it cannot be written as a simple product of two terms, one referring to each particle.Yes, we agree on this.I maintain that it is also non-local, in that the two particles are at different locations (locales). Non-local can have no other meaning in ordinary linguistic usage.I invite you, and Alice, and I give you an envelop to each of you. You are told that one contain a piece of paper with O inscribed on it, and the other with one. Then you go in different galaxies, say, and open it. Once you see 0 (res. 1) you know that Alice will see 1 (res. 0). This seems non local in your sense, where most would agree that in this case, there is no “non-locality” issue. What I claim is that in the Everett theory, all non-locality are of that type.That non-loclality has a common cause explanation. Like Bertlmann's socks, there is no mystery here. The problem is with entangled systems, where non-separability means non-locality that has no common cause explanation, even in many-worlds theory.I doubt this. The MWI reduces the non-separability of the probabilities into an equivalent with Bertlmann’s socks, still keeping the violation of Bell’s inequality justifying the appearance of non-locality.
In the MWI, some particles can be entangled but without implying any possible FTL when we do measurement on them, except from the local point of view, due to our ignorance of all terms of the wave. It means simply that Alice and Bob belongs to the same branch of history/reality.The trouble with this hope is that it no local account of the EPR correlations been realised in any coherent mathematics. Bell's theorem rules it out: no local hidden variable account of the EPR correlations is possible in any theory, whatsoever. It is a no-go theorem; it proves a negative -- something is impossible. Many-worlds does not subvert Bell's theorem.That is right. But the violation of Bell’s inequality entails FTL only when one world is assumed, with well defined outcome for all measurement, or put in another way, assuming a unique reality, with one Bob and one Alice, but Bell’s reasoning does not prove FTL influence in The many-worlds, where all outcomes are obtained, and propagate between diverse Alice and Bob locally, leading to the apparent violation of Bell’s inequality, but without FTL.Bell did not assume a collapse. His is a mathematical result, where the only assumption is locality. As usual, if you think there is a local explanation of the EPR correlations in many-worlds, then produce it.We differ only on the way we interpreted the wave and the worlds. The singlet state is … local! It does not entail any correlation between the Alices and the Bobs. It enforces only that the Alices and Bobs can meet only their corresponding correlated partners, among the infinitely many Alices and Bobs (most of them being not accessible from each others).
I think it is becoming generally accepted in the physics community that the entangled state is intrinsically non-local: acting on one part of it affects the rest, even across the entire universe.That would mean some FTL actions, but I very much doubt this.No, there is no need of FTL. For example, in the third (2011) edition of his book 'Quantum Non-Locality and Relativity', Maudlin shows that Flash GRW theory, as developed by Temulka, gives a perfectly relativistic account of the EPR correlations without any FTL action.This astonishes me. If you have a link I could try to see if this makes sense, but, to be sure, I am not enthusiast at all on the GRW theory, which is new QM theory. If some measurement affects the rest of the Universe instantaneously, I think that imply FTL (without signals, but still with a physical influence).
Carroll then says that since many-worlds does not assume that experiments have single outcomes, Bell's theorem doesn't apply. His unspoken assumption here is that if many-worlds evades Bell's result, then it can give a local account of the EPR correlations -- they happen "because of branching of the wave function into different worlds, in which correlated things happen." (p. 105) This is similar to your claim above, but it is not an explanation. And even if Bell's theorem doesn't apply, it does not follow that the theory can provide a local account of the correlations.You still have to provide that account.
The other major source I can refer to is the book "The Emergent Multiverse" by David Wallace (Oxford, 2012). This book is the most comprehensive account of Everettian ideas currently available. Wallace also ducks the issue. In sections 8.5-8.7 (pages 302-312) he gives a detailed account of the branching structure that arises if Alice and Bob do independent spin measurements at space-like separations. Then on page 310 he gives a general entangled wave-function and points out that Alice's and Bob's measurements again lead to splitting. But he then says: "In this case, the amplitudes of the four sets of branches into which C [a central, neutral observer] eventually branches are not determined simply by the separate weights of the branchings at A and B. Nor is this to be expected: as I stressed previously, in Everettian quantum mechanics interactions are local but states are nonlocal. The entanglement between the particle at A and the particle at B is a nonlocal property of the forward light cone of A and that of B. Only in their intersection can it have locally determinable effects---and it does, giving rise to the branch weights which, in turn, give rise to the sorts of statistical results recorded in Aspect's experiments."
This might sound good, but again, there is no detail. What exactly is supposed to happen at the intersection of the forward light cones from A and B?
There is no interaction there -- any information that is made locally present there was already present in the only relevant interactions, which are the original measurements made by A and B; any branch weights that are around are set there, exactly as in the case of non-entangled particles. Wallace started out well, but ducked out at the last minute, and he failed to give any comprehensible account that does not rely on simple magic.
So the best authorities available fail to give a local account of the EPR correlations in a many-worlds setting -- they all simply duck the issue when the rubber hits the road. Just as you routinely do.
Bruce
--
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Counterfactual definiteness is that unmeasured variables have definite values...something QM denies.
Brent
On 2 Dec 2019, at 12:06, Bruce Kellett <bhkel...@gmail.com> wrote:On Mon, Dec 2, 2019 at 8:08 PM Bruno Marchal <mar...@ulb.ac.be> wrote:On 29 Nov 2019, at 00:50, Bruce Kellett <bhkel...@gmail.com> wrote:On Fri, Nov 29, 2019 at 1:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 26 Nov 2019, at 22:39, Bruce Kellett <bhkel...@gmail.com> wrote:On Wed, Nov 27, 2019 at 12:27 AM Bruno Marchal <mar...@ulb.ac.be> wrote:On 25 Nov 2019, at 22:53, Bruce Kellett <bhkel...@gmail.com> wrote:Because, the wave-function itself is non-local -- it contains entangled particles that are widely separated in space. That is the definition of non-locality!I am not sure. I use “non-locality” for “FTL physical influence”.That is just an abuse of language. Non-local means "not local", i.e., not all in one place.Then even Newton Universe is non local.Yes Newton was aware of this.Some attempt has been made to replace the term "non-local" with the term "non-seperable”.Yes, notably d’Espagnat. It avoids the confusion with the Eisnsteinian non-locality, which requires FTL (cf the “spooky action at a distance”), which must exist in QM + the assumption of a unique universe.I think we can all agree that the singlet wave function is non-separable -- it cannot be written as a simple product of two terms, one referring to each particle.Yes, we agree on this.I maintain that it is also non-local, in that the two particles are at different locations (locales). Non-local can have no other meaning in ordinary linguistic usage.I invite you, and Alice, and I give you an envelop to each of you. You are told that one contain a piece of paper with O inscribed on it, and the other with one. Then you go in different galaxies, say, and open it. Once you see 0 (res. 1) you know that Alice will see 1 (res. 0). This seems non local in your sense, where most would agree that in this case, there is no “non-locality” issue. What I claim is that in the Everett theory, all non-locality are of that type.That non-loclality has a common cause explanation. Like Bertlmann's socks, there is no mystery here. The problem is with entangled systems, where non-separability means non-locality that has no common cause explanation, even in many-worlds theory.I doubt this. The MWI reduces the non-separability of the probabilities into an equivalent with Bertlmann’s socks, still keeping the violation of Bell’s inequality justifying the appearance of non-locality.The devil is in the detail. And you have still not provided any detail.
In the MWI, some particles can be entangled but without implying any possible FTL when we do measurement on them, except from the local point of view, due to our ignorance of all terms of the wave. It means simply that Alice and Bob belongs to the same branch of history/reality.The trouble with this hope is that it no local account of the EPR correlations been realised in any coherent mathematics. Bell's theorem rules it out: no local hidden variable account of the EPR correlations is possible in any theory, whatsoever. It is a no-go theorem; it proves a negative -- something is impossible. Many-worlds does not subvert Bell's theorem.That is right. But the violation of Bell’s inequality entails FTL only when one world is assumed, with well defined outcome for all measurement, or put in another way, assuming a unique reality, with one Bob and one Alice, but Bell’s reasoning does not prove FTL influence in The many-worlds, where all outcomes are obtained, and propagate between diverse Alice and Bob locally, leading to the apparent violation of Bell’s inequality, but without FTL.Bell did not assume a collapse. His is a mathematical result, where the only assumption is locality. As usual, if you think there is a local explanation of the EPR correlations in many-worlds, then produce it.We differ only on the way we interpreted the wave and the worlds. The singlet state is … local! It does not entail any correlation between the Alices and the Bobs. It enforces only that the Alices and Bobs can meet only their corresponding correlated partners, among the infinitely many Alices and Bobs (most of them being not accessible from each others).The singlet state is non-separable, and hence non-local when Alice and Bob are separated.
The rest of you comment here is without meaning.
You have to flesh it out, and your reluctance to do so convinces me that you cannot. You are just hoping for a miracle.
I think it is becoming generally accepted in the physics community that the entangled state is intrinsically non-local: acting on one part of it affects the rest, even across the entire universe.That would mean some FTL actions, but I very much doubt this.No, there is no need of FTL. For example, in the third (2011) edition of his book 'Quantum Non-Locality and Relativity', Maudlin shows that Flash GRW theory, as developed by Temulka, gives a perfectly relativistic account of the EPR correlations without any FTL action.This astonishes me. If you have a link I could try to see if this makes sense, but, to be sure, I am not enthusiast at all on the GRW theory, which is new QM theory. If some measurement affects the rest of the Universe instantaneously, I think that imply FTL (without signals, but still with a physical influence).I only know this from Maudlin's books. There is a detailed account in his recent book, "Philosophy of Physics: Quantum Theory" (Princeton, 2019).
The paper that Phil referenced: Esfeld and Gisin (arXiv:1310.5308) contains a summary and discussion, even though those authors are not convinced by the theory.I must admit that Flash GRW is not an approach that I find convincing either. The ontology of this theory is the flashes themselves, the wave-function is not part of the ontology, so the collapse is entirely epistemic, and just like the "collapse" in classical probability theory. It works, but may not be convincing to everyone, since the ontology is remarkable thin!The real problem is, as ever, that despite many promises, many-worlds theory does even less well in that it offers nothing in the way of an explanation.
Maudlin's recent book discusses many worlds, but he concentrates on the problems with this idea, and essentially is not convinced that many-worlds makes sufficient sense in its own terms to provide an explanation for anything. Sean Carroll, in his recent book "Something Deeply Hidden", also evades the question. His discussion is on pages 104-105. He states that Bell assumed "that measurements have definite outcomes”.
Essentially, this is the assumption of counterfactual definiteness that has often been proposed. Carroll then says that since many-worlds does not assume that experiments have single outcomes, Bell's theorem doesn't apply. His unspoken assumption here is that if many-worlds evades Bell's result, then it can give a local account of the EPR correlations -- they happen "because of branching of the wave function into different worlds, in which correlated things happen." (p. 105) This is similar to your claim above, but it is not an explanation. And even if Bell's theorem doesn't apply, it does not follow that the theory can provide a local account of the correlations.You still have to provide that account.
The other major source I can refer to is the book "The Emergent Multiverse" by David Wallace (Oxford, 2012). This book is the most comprehensive account of Everettian ideas currently available. Wallace also ducks the issue. In sections 8.5-8.7 (pages 302-312) he gives a detailed account of the branching structure that arises if Alice and Bob do independent spin measurements at space-like separations. Then on page 310 he gives a general entangled wave-function and points out that Alice's and Bob's measurements again lead to splitting. But he then says: "In this case, the amplitudes of the four sets of branches into which C [a central, neutral observer] eventually branches are not determined simply by the separate weights of the branchings at A and B. Nor is this to be expected: as I stressed previously, in Everettian quantum mechanics interactions are local but states are nonlocal. The entanglement between the particle at A and the particle at B is a nonlocal property of the forward light cone of A and that of B. Only in their intersection can it have locally determinable effects---and it does, giving rise to the branch weights which, in turn, give rise to the sorts of statistical results recorded in Aspect's experiments."This might sound good, but again, there is no detail. What exactly is supposed to happen at the intersection of the forward light cones from A and B? There is no interaction there -- any information that is made locally present there was already present in the only relevant interactions, which are the original measurements made by A and B; any branch weights that are around are set there, exactly as in the case of non-entangled particles. Wallace started out well, but ducked out at the last minute, and he failed to give any comprehensible account that does not rely on simple magic.
So the best authorities available fail to give a local account of the EPR correlations in a many-worlds setting -- they all simply duck the issue when the rubber hits the road. Just as you routinely do.Bruce
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