Quantum Entanglement and time travel

[Careful]

I just noticed the time arrow - space arrow thing a couple of messages back. It would seem to me that if there is a discernable arrow of time such as isotropic expansion on both local and universal scales, then might not this also be called the arrow of space (ie., the universe is expanding outwardly, omnidirectionally from its point(s) of origin -- just like a disturbance in air or water or other familiar local media)?

No, because the expansion is not only isotropic but also homogeneous. If you inflate a balloon there is no way to tell in which direction it is expanding globally. If you put a bug on it (an operation which distroys homogeneity) you can define an arrow of space locally relative to the bug (in a closed universe, you get into trouble). But again, such concept would be emergent and not fundamental, you believe the existence of a universal clock to be of fundamental nature.

 

[mgelfan]

No, because the expansion is not only isotropic but also homogeneous. If you inflate a balloon there is no way to tell in which direction it is expanding globally. If you put a bug on it (an operation which distroys homogeneity) you can define an arrow of space locally relative to the bug (in a closed universe, you get into trouble). But again, such concept would be emergent and not fundamental, you believe the existence of a universal clock to be of fundamental nature.

I'm not sure I'm following you here. If something is expanding globally then doesn't that mean it's expanding ... everywhere? So, in that case, wouldn't the expansion be omnidirectional, and therefore the arrow of space is outward from every point?

Isn't the fundamental motion of the universe isotropic expansion? If not, then what?

In other words, there is an arrow of time precisely because there is an arrow of space. Or no?

 

[Careful]

I'm not sure I'm following you here. If something is expanding globally then doesn't that mean it's expanding ... everywhere? So, in that case, wouldn't the expansion be omnidirectional, and therefore the arrow of space is outward from every point?

Definition of an arrow field : a function from the points of the (spatial) manifold to its tangent space. As you might know a function can have only one image. The arrow of time means that there exists a globally well defined timelike vectorfield such that the motion of every particle is timelike and has positive projection on the field (for signature +---). In your example there is no direction in which space moves as seen from any point, space just moves outwards from it. So, you might wonder whether expansion somehow relates to an arrow of time. No, it doesn't, a Friedmann universe which recollapses again also contains an arrow of time, likewise does a Schwarzschild universe which neither expands nor contracts.

 

[RandallB]

Good old Albert certainly intended a determinstic universe !

No I don’t think that is fair.
Einstein expected a Determinate Local reality; determinate is not the same thing as deterministic. Determinate can be best understood by his expectation of a hidden not yet known variable that must exist as part of each of the two entities used in EPR type experiments. These HUV are determined, fixed, and unchanging parts of the photons, or particles. This “determinate” character of the variable is established at the creation of the photon or particle, and would remain only until it sufficiently interacted with something, such as a detector.

Expecting, even finding, such a variable would not require any ability to acquire sufficient knowledge to predict precisely what that and other variables will be prior to the generation of the “entangled pair”. Nor does it demand the possibility accruing enough information to precisely forecast exactly what kind of interaction and results the two separate photons / particles futures.
That kind of expectation of our current state as being predetermined from our past and our future is uncontrollable in a predestined future of a “Deterministic Universe” is not at all what Einstein implied.

Even though to date the evidence has not found such a hidden variable, and indicates Einstein was wrong to demand that such a variable even exists, that’s fine. But it is not fair to stick him with claiming a deterministic universe, that is not the same as his stubborn demand for Local Realism.

 

[Careful]

No I don’t think that is fair.
Einstein expected a Determinate Local reality; determinate is not the same thing as deterministic. Determinate can be best understood by his expectation of a hidden not yet known variable that must exist as part of each of the two entities used in EPR type experiments. These HUV are determined, fixed, and unchanging parts of the photons, or particles. This “determinate” character of the variable is established at the creation of the photon or particle, and would remain only until it sufficiently interacted with something, such as a detector.

Expecting, even finding, such a variable would not require any ability to acquire sufficient knowledge to predict precisely what that and other variables will be prior to the generation of the “entangled pair”. Nor does it demand the possibility accruing enough information to precisely forecast exactly what kind of interaction and results the two separate photons / particles futures.
That kind of expectation of our current state as being predetermined from our past and our future is uncontrollable in a predestined future of a “Deterministic Universe” is not at all what Einstein implied.

Even though to date the evidence has not found such a hidden variable, and indicates Einstein was wrong to demand that such a variable even exists, that’s fine. But it is not fair to stick him with claiming a deterministic universe, that is not the same as his stubborn demand for Local Realism.

Ok, can you give me a source for that ?! And how is this compatible with his sentence ``God does not play dice ?''. I mean, you seem to suggest for example that he would content himself with a locally stochastic universe, this also seems to be at odds with the following citation from Chapter 1 of Holland's Quantum Theory of Motion, p. 13 :

"In his (i.e., Einstein's) view, the indeterministic aspect of quantum
mechanics follows from the failure to provide a complete description
and not because it is an intrinsic characteristic of matter. In a
letter to Schrodinger in 1950 he says (Prizbram, 1967, p. 40) it seems
certain to me that the fundamentally statistical character of the
theory is simply a consequence of the incompleteness of the
description. In Einstein's programme, resolving the difficulty of
describing a determinate reality entails constructing a causal
(determinist) description, because he felt that this is a basic
requirement of a complete physical theory. (cf. Fine (1986, p. 103)).
That is, in the process of making microphysics determinate, it would
cease to be intrinsically statistical."

Anyway, I am sure he held many different opinions at different times, it was also debated on http://www.lepp.cornell.edu/spr/2001-12/msg0037413.html

 

[RandallB]

Ok, can you give me a source for that ?! And how is this compatible with his sentence ``God does not play dice ?''.

I do not know how to provide a source to establish something that Einstein did not say.
What he did say; “God does not play dice'' and authors descriptions of things as “indeterministic” when the item being considered only need be indeterminate to make the point in the discussion, are addressing the Non-Local vs. Local issue. Not the idea that we live in a predetermined life and world.

I don’t understand your use of “stochastic”.
Einstein believed that the results of an EPR should not be dependent upon an uncertain probability but a determinate HV, that is Local Realism.
If you have a source that is specific in showing how Einstein ever extended Local Realism to a deterministic predestined universe, I’d like to see it.

 

[Careful]

Ok, can you give me a source for that ?! And how is this compatible with his sentence ``God does not play dice ?''.

I do not know how to provide a source to establish something that Einstein did not say.

I was clearly asking for a source to establish your claim for a determinate instead of deterministic universe.

I don’t understand your use of “stochastic”.
Einstein believed that the results of an EPR should not be dependent upon an uncertain probability but a determinate HV, that is Local Realism.
If you have a source that is specific in showing how Einstein ever extended Local Realism to a deterministic predestined universe, I’d like to see it.

Well, by stochastic here I meant something like a random walk, a stochastic field theory (particle coupled to a fundamentally stochastic field) or so. I just provided you with a reference, where his use of the word statistical strongly suggests a deterministic universe.

 

[vanesch]

You seem to underestimate global problems. By the way, you miss the point of my previous comment : if you allow for CTC's in general you have to show that they do not occur on timescales of seconds, minutes, days.

I don't see why ? We're discussing the theoretical possibility of CTC's as allowed in principle by Einstein's local equations of GR. Now, there are variations on GR which would not allow for them, I understand, but that doesn't mean that the original view of a spacetime manifold + fields which respects everywhere the Einstein equations cannot allow for them. Whether this view is an appropriate description of *our universe* is to be seen. But also, it is not because the fundamental equations of GR allow in principle for CTCs, that they have to occur - and moreover occur in all kinds of flavors - in our specific universe, and "near" to us. The usual reason to reject CTCs is because of the "paradoxes" that they would generate, but I'm trying to argue that if you take GR seriously all the way, that these paradoxes do not occur, even on CTCs.

Certainly one would notice that if one assumes memory indeed not to influence the physical state ( which I guess you as a ``consciousness fan'' do not protest against ).

Of course memory influences the physical state: it is part of it ! You never understood exactly what I meant with those consciousness things, it is not some kind of ghostly figure floating around in ectoplasm world living his life of his own (and maybe even with little wings and eating sweet deserts with golden spoons)! A conscious observer has no "hidden memory" disconnected from physical reality (as would have, I take it, such a ghostly creature).

If, on the other hand your memory is wiped away, then you would be in trouble with the observation that since millions of years a rectilinear evolution occurs : every minut/second of eigentime our information increases.

Well, that's for sure something that cannot (and will not) happen along a CTC, and it is the essence of my argument: if you are "living on a CTC", then the laws physics along that line will have to induce such an evolution, that when you cross "again" the same event, that your memory state must be exactly as it was, the "first time" you crossed it. If all the other fields are also defined over the spacetime manifold, they must (because they are single-valued) take on exactly the same values too, and because they respect their evolution equations over the manifold too, this evolution must come about "naturally" along the CTC. Along a CTC, there can't be anything else but a "whiped-away" memory from the "previous passage". A creature living on a CTC will remember a part of the CTC, and call that "his past". The amount of information, along the CTC, must be a periodic function.

All this doesn't mean that CTCs have to exist in our world. Only, the often-cited argument that they can't exist because leading to paradoxes, is IMO, wrong. I don't think that if you take GR exactly litterally, that there is any form of paradox. And given that CTCs are a theoretical possibility in a certain way (the original way) of formulating GR, it is interesting to think about them up to a point.

But much more interesting is the topic of quantum mechanics in such universe.

Yes, but given that we don't even know how to do QM with even much simpler geometries, I think that one simply can't answer that question as of now.

 

[Jheriko]

This thread makes for a great read whilst bored at work. I did see a couple of things that bothered me though:

No personal intuitions, just the mere fact that nobody has observed it yet in human recorded history. Is that not enough for you ?! I don't need quantum mechanics to understand that.

This kind of 'logic' always bugs me so I will say my piece:

Not having observed something doesn't even qualify as good evidence that nobody has observed something... let alone being a valid way to discredit a theory. All of recorded human history isn't exactly a significant span of time either. All we can say is that during the course of our history we /think/ that nobody has observed X. All that is evidence for, is that nobody has observed X... and don't forget that history is selective and recorded by the few, so we don't know with any useful certainty if *anything* has never been observed, much less knowing that something does not exist.

It is somewhat akin to taking a bathtub full of Smarties, Skittles or (insert multicolored sweets here), picking out 5 or 6 with a biased selection process and then saying that that no blue sweets in your hand is evidence that there are no blue sweets in the bathtub...

This is probably part of why we develop self-consistent theories based on observations, it allows us to rapidly disprove them, constrain them and improve them by making small numbers of observations. This is why we talk of the lower-bound for the proton half-life for instance... even though nobody has observed a proton decay. Non-observation isn't useful in the same way, all it let's us do is speculate with a false sense of security.

So what you are saying is actually a personal intuition... or is, at least, motivated by experience or personal opinion. Either way it has no logical or theoretical value.

No I don’t think that is fair.
Einstein expected a Determinate Local reality; determinate is not the same thing as deterministic. Determinate can be best understood by his expectation of a hidden not yet known variable that ...

I have to disagree, I have read quite a few quotes from Einstein that imply that he believed that everything is pre-determined. More importantly what does a hidden variable theory have to do with determinism?

AFAIK, hidden variable theories are just about explaining the distributions from quantum mechanics in terms of a deterministic theory. e.g. If I fire a gun at a target there is a distribution to where the shots land, however, given sufficiently good instruments we can measure the causes of this distribution and predict the correct result given sufficient information and time to calculate, in practice however it is easier to just model the distribution. This is how I think Einstein viewed quantum mechanics and why he expected a hidden variable theory to provide a more accurate description of nature, and what's more if this was his opinion he didn't just believe in determinism.

I will see if I can find a specific quote I am thinking of, but Google is failing me

It went something like this, but with more elegant wording: "I find it easier to forgive people for their mistakes, and not to dwell on my own, since all of our actions are simply the results of the laws of nature".

Anyone know of the exact quote I am thinking of? If I find it I will edit this post...

 

[GUS]

Quote:
Originally Posted by JesseM
Backwards time travel has nothing to do with "rewinding" anything, it has to do with a worldline that loops around and revisits a portion of spacetime it's already crossed through. It's important to think of these things in terms of relativity's view of spacetime as a 4-dimensional continuum in which past, present and future events all coexist, rather than the intuitive view that there is a single objective "present" and that things in the past have "ceased to exist" or that things in the future "don't yet exist".

That is exactly my point too.

Well that clears that up then

 

[GUS]

I disagree. The intuitive view is better for understanding some things.

If you want to translate some data from one reference frame to another, then, yes, the definitions and conventions of relativity theory facilitate this in an unambiguous manner.

But, if you want to understand why backward time travel is a nonsensical idea, then using notions of a four-dimensional spacetime, etc., is not the most promising way to proceed..

yet its also supposedly impossible for nonlocality to occur yet we know it happens. Perhaps it is not the fact that we need to recreate past configurations but rather that these configurations of past , present and future all exist simoultaneously

 

[GUS]

I think you're still not understanding how the geometrical view sheds light on closed timelike curves in GR--nothing is being rewound or repositioned! To see how the geometric "block time" view works, imagine spacetime as a literal block of ice, with some pieces of string embedded in it to represent worldlines. Now imagine slicing this block up into a stack of very thin cross-sections, like slicing meat at a deli counter. Each cross-section of the block will contain cross-sections of all the strings, which will just look like dots embedded in a 2D sheet. If we were to take pictures of each cross-section in succession, and then run them together as frames in a movie, we'd see the dots moving around over time, corresponding to particles moving around in space.

Now, time travel in GR does not mean that the configuration of dots in the movie must return to a copy of their configuration in an earlier frame of the movie. Equivalently, it does not mean that a later cross-section of the ice looks identical to an earlier cross-section. Instead, returning to thinking about the whole block of ice before it was sliced into sections, a CTC should be thought of as a piece of string that loops around and intersects an "earlier" part of itself. From our perspective viewing the ice as a whole, nothing is changing, it's just a static configuration of strings embedded in the ice with one of them happening to form a loop. You could even imagine the block of ice being cone-shaped, so that successive cross-sections would be larger and larger, representing the expansion of space; contrary to what you suggested above, there is no notion of a past state having to be recreated when the universe is larger, since again, it's just a string which loops around and revisits a section of the cone closer to the tip where the cross-section is smaller.

Similarly, if you can vaguely imagine standing outside spacetime as a whole, it would just look like a static curved 4D surface with various worldlines embedded in it, and CTCs would just be worldlines that form a loop. This picture really only makes sense in terms of the "block time" view, thinking in terms of the view that time "really flows" will just get you confused. Well, the intuitive view has caused you to misunderstand the idea of CTCs in GR, so at least in this situation it doesn't seem very helpful. Backwards time travel might be problematic for other reasons, but it's definitely allowed in GR (though a theory of quantum gravity may change this), and your arguments for why it's nonsensical don't work, for the reasons I tried to explain above.

Would that not imply in effect that our destiny is fixed and we can do nothing to change it ? What about the possibility of an infinite amount of different versions of the static bits of string ? (im trying to avoid the word timiline)

 

[RandallB]

RB: "Einstein expected a Determinate Local reality; determinate is not the same thing as deterministic. Determinate can be best understood by his expectation of a hidden not yet known variable that ..."

I have to disagree, I have read quite a few quotes from Einstein that imply that he believed that everything is pre-determined. More importantly what does a hidden variable theory have to do with determinism?

AFAIK, hidden variable theories are just about explaining the distributions from quantum mechanics in terms of a deterministic theory ………

As I said HVT has nothing to do with the determinism of a deterministic theory of the universe, as you proceed to claim that it does. This was not Einstein’s view and twisting some obscure quote or two from him, into his believing that he had no choice or control of the achievements in his life won’t do. It will need to be direct and specific enough to counter his religion not of a individual Jewish God, but a religion of science, where humanistic free choice does allow for, and I suspect in his opinion call for, moral choices for ‘good’. An extended debate on Einstein’s Philosophy belongs in the Philosophy Forum. I just don’t think it fair to allow miss representations of it to go un-rebutted here. To the extent one can claim a deterministic universe as a legit theory (I do not) – it was not one accepted by Einstein.

 

[ueit]

yet its also supposedly impossible for nonlocality to occur yet we know it happens.

No, we don't know that. In fact, there are good reasons to think that non-locality (understood as an interaction taking place faster than c) is indeed forbidden in our universe.

 

[GUS]

No, we don't know that. In fact, there are good reasons to think that non-locality (understood as an interaction taking place faster than c) is indeed forbidden in our universe.

I thought Quantum entanglement was something we were pretty sure about ? Isnt quantum entanglement itself pretty much impossible from a common sense point of view ?

 

[RandallB]

I was clearly asking for a source to establish your claim for a determinate instead of deterministic universe.

Well, by stochastic here I meant something like a random walk, a stochastic field theory (particle coupled to a fundamentally stochastic field) or so. I just provided you with a reference, where his use of the word statistical strongly suggests a deterministic universe.

I never made a claim for a determinate universe! Just a determinate solution to EPR issues in that at the point of creation of two “entangled” particles determinate HV’s could provide a Local Realist solution to “entanglement” not a problematic (stochastic) one.
That’s why I couldn’t understand your use of stochastic in post #55 or what “a locally stochastic universe” could even mean. Einstein’s HVT takes the view that the problematic (stochastic) solutions to EPR are incomplete and deal with microphysics not the whole or even 'local' universe.

The quote you gave me (from Prizbram, not Einstein) refers to establishing a determinate explanation to a microphysics problem with very limited boundaries, not the question of a deterministic universe. That is an unfounded extrapolation to the large scope of the whole universe, unjustified by only any conclusions from a limited EPR test. Even if HV’s were to be proven as real, Determinate Microphysics by itself would not be able to establish a requirement for a Determinate/Deterministic universe.

 

[ueit]

I thought Quantum entanglement was something we were pretty sure about ? Isnt quantum entanglement itself pretty much impossible from a common sense point of view ?

Entanglement requires that there exist correlations between parts of a quantum system, regardless of the distance between the parts (as seen in the EPR experiments). Nothing is said, however, about the mechanism by which those correlation are enforced and there is no reason to believe this mechanism to be non-local.

 

[RandallB]

Entanglement requires that there exist correlations between parts of a quantum system, regardless of the distance between the parts (as seen in the EPR experiments). Nothing is said, however, about the mechanism by which those correlation are enforced and there is no reason to believe this mechanism to be non-local.

Every reputable experiment so far on EPR/entanglement indicates that only non-local solutions will work and strong imply that no truly Local HVT can be possible. So, there is a huge reason to believe this mechanism is non-local.

But there are several different ways to reach a non-local solution, including some that do not require physical interactions taking place faster than the speed of light. Some with a form of extra dimensional part of the items being tested remaining connected even as they separate in our three dimensions. So with so many alternatives like BM MWI etc. in addition to QM theories and no conclusive result on A correct one, just that it does seem to work “Non-Locally”, the issue is NOT something we are "pretty sure about" as GUS may have thought.

Although the evidence is strong for non-local, I would agree that there is no reason to stop those that wish to look for a Local solution if they wish. They just need to understand they are going against the majority view, and there is nothing automatically wrong with that. And they need to accept the risk of not making any real progress – and I do accept that risk myself.

 

[vanesch]

But there are several different ways to reach a non-local solution, including some that do not require physical interactions taking place faster than the speed of light. Some with a form of extra dimensional part of the items being tested remaining connected even as they separate in our three dimensions. So with so many alternatives like BM MWI etc. in addition to QM theories and no conclusive result on A correct one, just that it does seem to work “Non-Locally”, the issue is NOT something we are "pretty sure about" as GUS may have thought.

I hate to repeat this for the 100th time or so, but in MWI, there is no genuine non-locality in the EPR situation. In fact, MWI kills Bell's theorem for the simple reason that there is no unique outcome at Bob and Alice (which is of course a requirement in Bell's theorem). Given that both outcomes exist simultaneously, the observed correlations when the "results come together" are then nothing else but a local interference pattern of these different outcomes which only occur upon their coming together.
In other words, in this view, the "correlations between Alice and Bob" are not more surprising than the interference pattern of a lightbeam that has been split, got far away, and then came together again, to interfere.

 

[Careful]

I don't see why ? We're discussing the theoretical possibility of CTC's as allowed in principle by Einstein's local equations of GR. Now, there are variations on GR which would not allow for them, I understand, but that doesn't mean that the original view of a spacetime manifold + fields which respects everywhere the Einstein equations cannot allow for them. Whether this view is an appropriate description of *our universe* is to be seen. But also, it is not because the fundamental equations of GR allow in principle for CTCs, that they have to occur - and moreover occur in all kinds of flavors - in our specific universe, and "near" to us.

You miss my point again, when I spoke about universes with CTC's having a large probability (and saying that the action does not surpress them), I was clearly referring to problems you should have in quantum gravity where each universe is represented democratically at least if we take the Feynman path integral seriously. Moreover, each time you allow for extra variables in a physical theory, you have more and more a problem of finetuning initial data.

Of course memory influences the physical state: it is part of it ! You never understood exactly what I meant with those consciousness things, it is not some kind of ghostly figure floating around in ectoplasm world living his life of his own (and maybe even with little wings and eating sweet deserts with golden spoons)! A conscious observer has no "hidden memory" disconnected from physical reality (as would have, I take it, such a ghostly creature).

Sure, I know this, I was merely teasing you. But admit it, it is kind of unbelievable that this wonderful consciousness of yours is so important in order for your brain to make observations, that it cannot do anything else but that !

Well, that's for sure something that cannot (and will not) happen along a CTC, and it is the essence of my argument: if you are "living on a CTC", then the laws physics along that line will have to induce such an evolution, that when you cross "again" the same event, that your memory state must be exactly as it was, the "first time" you crossed it. If all the other fields are also defined over the spacetime manifold, they must (because they are single-valued) take on exactly the same values too, and because they respect their evolution equations over the manifold too, this evolution must come about "naturally" along the CTC.

Sigh, my argument was that we measure information to increase in function of eigentime, so the mere ability to do that as well as the fact that it happens excludes CTC's by the mere argument you just repeated. The mere fact that we have authentic books dating before Jezus Christ means that there was no CTC going back to a later moment than that date.

 

[RandallB]

I hate to repeat this for the 100th time or so, but in MWI, there is no genuine non-locality in the EPR situation.

And to reply again for almost as many times: A collection of Multiple Worlds to account for the various outcomes to provide a solution certainly is NOT Local to our classical 3D sense of reality or what is meant by Einstein / Bell Local. As I’ve said before it is acceptable to think of a Non-Local version of “Local” for theories such as MWI, BM, etc.
BUT, The mere idea of Multiple Dimensions or Multiple Worlds converted into a Theory is not sufficient to claim something like MWI or BM kills Bell's theorem. Not without producing some real way of demonstrating that an additional dimension, or in your case at least one of the Many Worlds, actually exists.

I happen to believe in a HVT as did Einsein, but I do not accept those that believe the same so much so, they simply declare Bell to be invalid for some silly reason because they don’t like its results denying a HVT.
Neither of us has the right to declare themselves as Right or that Bell results can be ignored as meaningless; unless verifiable proof is provided.
So do us a favor and identify your MWI theory as a Theory and what it might mean IF it is ever proven, and stop representing it as a given fact.
I’m betting I’ll find a HVT before you can find even one additional “World”. But till one of us does, neither is even a main stream theory let alone worthy of being put forward as fact.

 

[Careful]

I never made a claim for a determinate universe!

Ok, I should have asked in full that I would like to have a reference from Einstein where he explains his position about determinate versus deterministic. Was this so hard to understand from the sentence ``I was clearly asking for a source to establish your claim of a determinate instead of a deterministic universe'' given that just before that we were discussing whether Einstein said determinate in the sense you imply instead of deterministic ?

Just a determinate solution to EPR issues in that at the point of creation of two “entangled” particles determinate HV’s could provide a Local Realist solution to “entanglement” not a problematic (stochastic) one.
That’s why I couldn’t understand your use of stochastic in post #55 or what “a locally stochastic universe” could even mean. Einstein’s HVT takes the view that the problematic (stochastic) solutions to EPR are incomplete and deal with microphysics not the whole or even 'local' universe.

Euh it seems to me that if a determinate theory can cover microphyiscs , it should cover for macrophysics as well. So, for good understanding (because this was not clear from your previous post) : with determinate you mean that the outcome of an experiment is fixed once the HV's are assigned after creation of the entangled pair ?

The quote you gave me (from Prizbram, not Einstein) refers to establishing a determinate explanation to a microphysics problem with very limited boundaries, not the question of a deterministic universe. That is an unfounded extrapolation to the large scope of the whole universe, unjustified by only any conclusions from a limited EPR test.

Why, why would you even want to look for an EPR solution if you cannot extend the same laws to the universe ? This makes no sense at all, since the mere motivation for hidden variables originates from the way macroscopic physics works - given the desire to have one unifying dynamics.

 

[ueit]

Every reputable experiment so far on EPR/entanglement indicates that only non-local solutions will work and strong imply that no truly Local HVT can be possible. So, there is a huge reason to believe this mechanism is non-local.

Bell's theorem states that if the hidden variables do not depend on the detectors' settings the inequality must hold.

There are ways in which this dependence can be enforced in a perfectly local manner, without postulating other dimensions, holograms, backwards causality, etc. I'll give you an example.

We have a source producing entangled particles and two detectors. By "detector" I mean everything that is related to the polarizer, including the device selecting its orientation (randomizer, human, monkey pressing buttons, gamma rays together with the quasar they come from, etc.)

If the proposed LHV theory is deterministic, the orientation of the detectors at any time can be inferred from their state at any previous time.

We have to make the following two assumptions:

1. The state of the detectors is made available at the source location by means of a local field (probably classical EM field would do)

2. The entangled particles are generated as a result of this field (which contains all the information regarding both the time of detection and detector orientation) in accordance with the Malus law.

But there are several different ways to reach a non-local solution, including some that do not require physical interactions taking place faster than the speed of light. Some with a form of extra dimensional part of the items being tested remaining connected even as they separate in our three dimensions. So with so many alternatives like BM MWI etc. in addition to QM theories and no conclusive result on A correct one, just that it does seem to work “Non-Locally”, the issue is NOT something we are "pretty sure about" as GUS may have thought.

I have some doubts regarding the non-locality of Bohm's interpretation. As far as I understand it, the particles are guided by a wave which evolves on its own since big-bang. There is no need for particle A to receive information about what particle B is doing. They both move according to the universal wavefunction and the known local fields.

Although the evidence is strong for non-local, I would agree that there is no reason to stop those that wish to look for a Local solution if they wish. They just need to understand they are going against the majority view, and there is nothing automatically wrong with that. And they need to accept the risk of not making any real progress – and I do accept that risk myself.

I'm not a physicist and I don't know exactly what is the "majority view" but I agree with you that LHV theories are not very high in the physicists' preferences. I'm still puzzled by the wrong interpretation ascribed by many to the EPR experiments.

 

[mgelfan]

Definition of an arrow field : a function from the points of the (spatial) manifold to its tangent space. As you might know a function can have only one image. The arrow of time means that there exists a globally well defined timelike vectorfield such that the motion of every particle is timelike and has positive projection on the field (for signature +---).

I'm not using this model ... rather, just wondering about the connection between expanding wavefronts (local and cosmological) and an arrow of time. In many of the physical problems that I'm confronted with, I've found it useful to begin by thinking in terms of the physical phenomena themselves, rather than using some mathematical model or other at the outset.

In your example there is no direction in which space moves as seen from any point, space just moves outwards from it.

The direction of the arrow of space is away from points of interaction.
In homogenous 3D media, disturbances propagate pretty much isotropically.

Expanding water wavefronts (moving outward from, eg., the interaction of a pool of water with a stone dropped into it) are frequently used as a local example of the radiative arrow of time, aren't they?

In this case the arrow of space is the arrow of time.

So, you might wonder whether expansion somehow relates to an arrow of time. No, it doesn't, ...

I guess I'll have to disagree with you on this then ... at least for the time being.

The fundamental motion of our universe is isotropic expansion, and the fundamental force is the kinetic energy (imparted via the Big Bang) of the expansion. This isotropic expansion on cosmological scales is obviously connected to the radiative arrow of time observed locally. Don't you think so?

... a Friedmann universe which recollapses again also contains an arrow of time, likewise does a Schwarzschild universe which neither expands nor contracts.

But these are just models -- neither of which describes our universe.

 

[Careful]

Expanding water wavefronts (moving outward from, eg., the interaction of a pool of water with a stone dropped into it) are frequently used as a local example of the radiative arrow of time, aren't they?

In this case the arrow of space is the arrow of time.

Your analogy is useless since by throwing in ONE stone you break homogeneity : I have commented on that already and said you can define an arrow of space in this case, but nevertheless this has nothing to do with the arrow of time). One of my objections is about your abuse of the word ``arrow of space'', an arrow is a vector, outwards expansion is a scalar : that is the eigentime derivative of the expansion of a geodesic congruence.

But these are just models -- neither of which describes our universe.

Euh, (a) it is no known wheter a big crunch is excluded or not (b) a Schwarzschild universe is quite a good approximation to a non rotating black hole in the center of some galaxy.

 

[RandallB]

Ok, I should have asked in full that I would like to have a reference from Einstein where he explains his position about determinate versus deterministic. Was this so hard to understand from the sentence ``I was clearly asking for a source to establish your claim of a determinate instead of a deterministic universe'' given that just before that we were discussing whether Einstein said determinate in the sense you imply instead of deterministic ?

Again Einstein did not speak to a “deterministic universe'' but determinate variables. He was certainly smart enough to not jump to global conclusions from a small local event until he at least had the details of how a HV worked to decide if or how it might be applied to a larger perspective. Why would he even consider making such a leap with no information?

I have some doubts regarding the non-locality of Bohm's interpretation. As far as I understand it, the particles are guided by a wave which evolves on its own since big-bang. There is no need for particle A to receive information about what particle B is doing. They both move according to the universal wavefunction and the known local fields.

Until you can show what and exactly where a “BM universal wavefunction” is in strictly Local Terms and how it provides its guide wave function, I’ll consider it NON-Local as do most.

 

[Careful]

Again Einstein did not speak to a “deterministic universe'' but determinate variables. He was certainly smart enough to not jump to global conclusions from a small local event until he at least had the details of how a HV worked to decide if or how it might be applied to a larger perspective. Why would he even consider making such a leap with no information?

You basically did not answer neither my request, nor some questions I had. Euh, Einstein himself made the biggest extrapolation in history on virtually no grounds : he created with GR a theory of the universe. So, why would he refrain himself here (while the logic in both cases appears to be the same to me) ?

 

[RandallB]

You basically did not answer neither my request, nor some questions I had. Euh, Einstein himself made the biggest extrapolation in history on virtually no grounds : he created with GR a theory of the universe. So, why would he refrain himself here (while the logic in both cases appears to be the same to me) ?

The logic is clear to me that it is not the same. GR even has tests to support it, while the HV hasn't even been documented to even consider what it may show related to the larger universe, use a bit of common sense.

And for the third time I do not know how to provide you a referance to something Einstein did not say, by what logic do you think that could be done.
Why haven't you shown a specific Einstein reference to a “deterministic universe'' that is not someones convenient reinterpretation of a determent HV EPR comment, to support something he did not really mean or say.
Without that I see no point in extending this pointless fencing.

 

[Careful]

The logic is clear to me that it is not the same. GR even has tests to support it, while the HV hasn't even been documented to even consider what it may show related to the larger universe, use a bit of common sense.

Things become only real when predictions are supporting some part of a theory, nobody has seen gravitational waves so far, no one knows whether there is a singularity behind the event horizon of a black hole. Oh yes, and let's not forget that our universe seems to square uneasily with it, given the issues of dark matter and energy - GR has only been properly tested in the solar system, seems a tiny place in comparison with our universe. Moreover, I was not saying that any hidden variable theory (suitable for microphysics) immediately needed to be extrapolated to the entire universe ! I said that I would not consider a hidden variable theory which could not.

And for the third time I do not know how to provide you a referance to something Einstein did not say, by what logic do you think that could be done.

You said: ``Einstein said determinate which did not imply deterministic (in his mind)'' while many of us do think he did imply deterministic, so where is your source ? It exists not, fine, so he basically only said that the universe is determinate (in the sense you more or less explained), but my point was that he also saw statistical theories as inadequate (which you acknowledged). So, then I suggested the possibility of a locally stochastic universe (like a random walk, Sorkin and Rideout have made (non local) random walk causal set models). Here, you did not know what I meant (you might want to look up the latter papers - GRW is an example of a non local stochastic collapse theory) ; that caused lot's of confusion with me - since in my mind - only determinstic models are left as a *reasonable* option. But the latter is the very thing you are pointing out to me as being an unnecessary restriction. Therefore, it seems you are talking merely semantics here (which is totally useless); perhaps it would be better if you would present a realistic example of a determinate, but not deterministic hidden variable theory for - say - EPR.

Why haven't you shown a specific Einstein reference to a “deterministic universe'' that is not someones convenient reinterpretation of a determent HV EPR comment, to support something he did not really mean or say.
Without that I see no point in extending this pointless fencing.

Well, you know, I did not make an issue about this one tiny sentence ! Moreover, at one moment I said that Einstein probably considered many options in his life, something which is well known about him. Wolfgang Pauli once made more or less the remark that ``usually a scientist sticks to a direction he chooses for a few years, but Einstein can come up with an entirely new theory in half a year! ´´.

 

[vanesch]

And to reply again for almost as many times: A collection of Multiple Worlds to account for the various outcomes to provide a solution certainly is NOT Local to our classical 3D sense of reality or what is meant by Einstein / Bell Local. As I’ve said before it is acceptable to think of a Non-Local version of “Local” for theories such as MWI, BM, etc.

If you can formulate the theory in a geometrical way (in other words, if its formulation is Lorentz-invariant), then it is "local" enough to me. This is not the case for BM, but it is for MWI. Any genuine projection cannot be written in such a Lorentz-invariant way, and hence violates locality. However, the unitary dynamics can.

BUT, The mere idea of Multiple Dimensions or Multiple Worlds converted into a Theory is not sufficient to claim something like MWI or BM kills Bell's theorem.

What you need, for Bell's theorem to apply, is that there are definite outcomes at Alice and at Bob, because we are talking about probabilities for them to be realized, and it is this probability measure which cannot be set up without simultaneous knowledge of the two polarizer settings. But in MWI, there is no such thing as the unique outcome at Alice and a unique outcome at Bob, so there is no probability measure to be set up in the first place. Hence, Bell's theorem doesn't apply to this case.

Not without producing some real way of demonstrating that an additional dimension, or in your case at least one of the Many Worlds, actually exists.

No, it is a matter of logic. One cannot say that a certain conclusion holds in all cases, when there is demonstrably a counter example - independent of whether that counter example is actually true or not in reality. The conclusion here would be that "physics is non-local", while there is a clear logical construction which reproduces the *observed* probabilities, and which doesn't suffer an explicit non-locality. Even if in the end, this logical construction doesn't correspond to reality, its logical existence proves that the reasoning that lead to the "non-locality" conclusion is erroneous. In the same way as the very construction of BM proves that there CAN be a hidden-variable construction that makes the same predictions as QM, contrary to the "theorem" by von Neumann. The very logical existence of BM makes that the theorem by von Neumann must be false. In the same way, the logical existence of MWI proves that the conclusion of non-locality from EPR is erroneous.

Neither of us has the right to declare themselves as Right or that Bell results can be ignored as meaningless; unless verifiable proof is provided.

Of course Bell's result is not meaningless. Only, his theorem doesn't apply to those cases where his premisses are not valid. Now it seems like such an evident premisse that Alice and Bob "have" a result, but in MWI, that's simply not the case: they both have both results. So Bell's theorem doesn't apply to MWI.

So do us a favor and identify your MWI theory as a Theory and what it might mean IF it is ever proven, and stop representing it as a given fact.
I’m betting I’ll find a HVT before you can find even one additional “World”. But till one of us does, neither is even a main stream theory let alone worthy of being put forward as fact.

MWI, as a logical construction, exists, for a fact. Whether it corresponds to reality is a totally different matter. The same can be said about BM.
Now, MWI is entirely formulated in a lorentz invariant way (which means it is local, to me). So there clearly exists a logical construction which 1) is lorentz-invariant (hence local) and 2) has all the observable predictions of standard QM.
As such, one cannot claim, that ALL thinkable schemes which obey 2) must violate 1), because there's a logical counter example.

 

[Demystifier]

Would that not imply in effect that our destiny is fixed and we can do nothing to change it ?

Not necessarily. It is possible that free will exists, but that it does not act at a specific time. For example, you may decide that tomorrow you will eat ham. But the act of decision does not occur today, nor tomorrow, nor a day after tomorrow. You simply decide it, without attributing a moment of time at which this decision occurs. This is not how this decision is subjectively perceived by your brain, but this is how it really is (in a block universe with a free will).

 

[Demystifier]

Now, MWI is entirely formulated in a lorentz invariant way (which means it is local, to me).

OK, it is local for you. But is it local for itself? Is the whole Universe (the collection of All worlds of mwi) local? Is the split/branching of the Universe in a number of different copies a local event? And if you say that this question is irrelevant, isn't such a view of nature quite antropomorphic?

 

[RandallB]

….., fine, so he basically only said that the universe is determinate (in the sense you more or less explained),

You miss quote me again; I did not explain a “determinate” vs. “deterministic” universe! I said Einstein expected the HV in an EPR to provide “determinate” not problematic solution, and that is all he said. Without actually finding a HV, I’ve seen nothing to suggest that he jumped to the conclusion or opinion that the entire universe was “deterministic” or "determinate", and that all his discoveries and every thought had been predestined from the Big Bang or even earlier. I do not accept that all these posts we fuss over here are meaningless events already set by a predetermined deterministic universe and the idea that Einstein did is balderdash! I don’t care if such a view comes from a PHD, they need to do much better than their interpretation of what Einstein’s comments on EPR might mean for a full universe view of causality. That is their extrapolation not Einstein’s.

…perhaps it would be better if you would present a realistic example of a determinate, but not deterministic hidden variable theory for - say - EPR.

Easy
A photon approaches a PDC at some point (unknown & undeterminable to the photon) ahead. Likewise the PDC cannot know or determine exactly when or it what specific condition all the variables that makeup the EM details of that photon. But when they do interact, all these unknown variables combine to produce two photons. The random direction of one photon within a well defined “cone” of options is perfectly matched by the direction of the second based on conservation laws. Likewise, the polarity of the two photons is set one V the H. These parameters are set at the LOCAL creation of the two photons and remain determinate and unchanging until there interact with something else in each of there unknowable paths. PLUS, going with them on that path is the HV also determinate and unchanging and provides the fixed and unchanging information required to account for “entanglement” correlations.
Now if you can show the exact & complete details of such a HV; only then can you make meaningful judgments to speculate on an interpretation that could define with precision all the unknown details about the PDC and the Photon as it approached, to ultimately generate the two photons. Until that can be done you cannot, and I do not believe Einstein ever presumed, that all the events in the universe that lead up to the conversion of that one photon turning into 2 photons was preset in a “deterministic universe”.
That is an unfair, self-serving, and unsupported claim on Einstein’s real work.
And I do not consider that a small point.

 

[RandallB]

If you can formulate the theory in a geometrical way (in other words, if its formulation is Lorentz-invariant), then it is "local" enough to me.

That only means you have a lower standard for "local" than I do and IMO it is lower than the Einstein/Bell standard.
Also IMO you cannot solve a problem by simply lowering the standards.
AFAIC local to the Einstein/Bell standard is required to confirm a “Local” theory, and adding the need for even one additional “world” beyond the 2D Classical one we seem to see ourselves in, means a Non-Local reality.

As evidence indicates reality is expected to be Non-Local I don’t understand why you don’t want to define MWI a Non-Local. The idea that by playing some game to define a theory as “Local” is enough to presume it as correct is just silly.

As I’ve said you are entitled to your opinion, but please respect the integrity of this forum and stop declaring it as a fact. I do not care to debate the details, of MWI.

 

[vanesch]

That only means you have a lower standard for "local" than I do and IMO it is lower than the Einstein/Bell standard.

What does it mean, local ? Local means that things that are associated with a spacetime point are determined as much as can be by all things that are associated to the past light cone of that spacetime point, and that, once this past lightcone is given, adding or not, any part of the state description outside this lightcone doesn't alter this. A theory which can be written down in a Lorentz-invariant way automatically satisfies this requirement (which is why you cannot write down BM in a Lorentz-invariant way).
The Schroedinger equation (the unitary evolution) satisfies this requirement. As this is the only physical ingredient of MWI, one can say that this version of quantum theory is local in this sense. What makes quantum theory with an explicit projection non-local, is the projection postulate. If you apply a projection on one component, you automatically alter the contributions (by eliminating some of them) of spacelike connected physical systems.

AFAIC local to the Einstein/Bell standard is required to confirm a “Local” theory, and adding the need for even one additional “world” beyond the 2D Classical one we seem to see ourselves in, means a Non-Local reality.

That's a random requirement you postulate. As I said, the Bell requirement is satisfied for MWI: at no point, there is an influence on the part of the state description at event A, by whatever goes on at event B, if B is outside of the past lightcone of A - this is exactly Bell's requirement for locality.
However, in MWI, there are no "outcomes" of experiments independent of the observer that makes them (and for every combination of possible outcomes, there exist observers that have "seen" them). So, what ruins Bell's logic, is that THE observation at A is influenced by THE setting and/or outcome at B, given that at A, both observations take place, in an uninfluenced way by the settings/outcomes at B.

As evidence indicates reality is expected to be Non-Local I don’t understand why you don’t want to define MWI a Non-Local. The idea that by playing some game to define a theory as “Local” is enough to presume it as correct is just silly.

Because the evidence DOESN'T indicate that reality is non-local. It is only if you impose extra conditions on reality that it must turn out to be non-local, and the very logical existence of MWI proves that.

As I’ve said you are entitled to your opinion, but please respect the integrity of this forum and stop declaring it as a fact. I do not care to debate the details, of MWI.

Well, I can understand that you do not want to discuss the logical counter example to the "theorem" you postulate. Again, I'm not claiming that reality corresponds to MWI. I'm only pointing out that there exists a logical counter example to the claim you are making, namely that "evidence indicates that reality is non-local". I have a local theory in every sense of the word (ontological state related to spacetime point A is uninfluenced by whatever is the ontological state related to a spacetime point B which is spacelike connected to A, if we have the ontological state description related to the past light cone of A). It complies with the usual observational predictions of QM. Hence, the usual observational predictions of QM cannot lead logically to the conclusion that nature MUST BE non-local, given the existence of this counter example.

I'm not lowering the standards of "locality" by doing this. If you think I'm doing this, then point out what aspect of the unitary time evolution is NOT respecting locality.

 

[ueit]

Until you can show what and exactly where a “BM universal wavefunction” is in strictly Local Terms and how it provides its guide wave function, I’ll consider it NON-Local as do most.

Think of the universal wave function as a field existing in space or as a curvature of space that particles follow. If the universe is in a stationary state this curvature just is, it doesn't change with time. If not, it changes in a deterministic manner. Either way, no information of any sort is exchanged between the source and detectors in an EPR experiment.

 

[ueit]

As evidence indicates reality is expected to be Non-Local.

I think it doesn't. I've presented you a local mechanism for EPR without any requirement for new dimensions/worlds/etc. I'd like to see what your objections against this mechanism are.

 

[skippedstate]

I am not in the same league as you all, but I do share an interest in your topics. I am humbled by your intellects, and am looking for more understanding. I love reading about this stuff!

One thing I am sure you can correct my logic on, is that, in your post, speaking on memories, you felt that the memories likely would not be there had we gone back to kill our grandpa. Call me naive, but how would our physical body be able to traverse backwards (or to parallels) without our memories, along with every other cell? (praying that it is an answer NOT so elementary... :) )

 

[RandallB]

RB: “ Until you can show what and exactly where a “BM universal wavefunction” is in strictly Local Terms and how it provides its guide wave function, I’ll consider it NON-Local as do most.

Think of the universal wave function as a field existing in space or as a curvature of space that particles follow. If the universe is in a stationary state this curvature just is, it doesn't change with time. If not, it changes in a deterministic manner. Either way, no information of any sort is exchanged between the source and detectors in an EPR experiment.

RB … evidence indicates reality is expected to be Non-Local.

I think it doesn't. I've presented you a local mechanism for EPR without any requirement for new dimensions/worlds/etc. I'd like to see what your objections against this mechanism are.

To just what EVIDENCE do you refer?
Your provided “mechanism” (?) is no evidence. Also, the WHAT, WHERE, AND HOW it gives it well short of being exact in any detail. Plus, as you describe the “state of the universe” (whatever that may be) as stationary or changing deterministically; that “state” you require is well outside the bounds of the “Local” part of EPR. That Non-Local character is similar to MWI selecting an appropriate “world” with its entire surrounding non-local character configured appropriately to justify EPR correlations. I do not ask that you two abandon your opinions as being wrong, just stop demanding that everyone accept you opinion(s) as the correct one!

The two of you cannot both be right, so at least present convincing evidence to each other to demonstrate which is correct BM or MWI. They maybe you will save the entire scientific community that is wasting so much time and effort pursuing so many different things that do not agree with either of you.

I’ll disengage from this debate until I see ueit & vanesch concur on which is correct MWI or BM.
Until then I choose to continue my own individual search for a true Local Theory (I agree, a long shot), without the distraction of these two Non-Local theories claiming to be local.

 

[mgelfan]

Your analogy is useless since by throwing in ONE stone you break homogeneity : I have commented on that already and said you can define an arrow of space in this case, but nevertheless this has nothing to do with the arrow of time). One of my objections is about your abuse of the word ``arrow of space'', an arrow is a vector, outwards expansion is a scalar : that is the eigentime derivative of the expansion of a geodesic congruence.

Maybe we should call it the arrow of motion.
The arrow of motion, any motion (including expansion), has direction and magnitude. My point in addressing this arrow of space and arrow of time thing was that it didn't make much sense to me to talk about an arrow of space as being independent of an arrow of time if space is taken to refer to the material universe, and time is taken to refer to the material universe in motion.

Whether you want to put it in terms of space or in terms of time, there is a fundamental motion underlying all phenomena -- the expansion of the universe. The radiative arrow is fundamental.

... (a) it is no known wheter a big crunch is excluded or not (b) a Schwarzschild universe is quite a good approximation to a non rotating black hole in the center of some galaxy.

The universe is expanding and the energy imparted via the Big Bang is dispersing and dissipating. A Big Crunch would require more energy, not less. So, Big Crunch models can be excluded.

 

[ueit]

Your provided “mechanism” (?) is no evidence. Also, the WHAT, WHERE, AND HOW it gives it well short of being exact in any detail.

It is good evidence against your interpretation of EPR. I only need a logically consistent counterexample, not a TOE.

Plus, as you describe the “state of the universe” (whatever that may be) as stationary or changing deterministically; that “state” you require is well outside the bounds of the “Local” part of EPR.

The experiment is a part of that state and, as a result, it displays the symmetries embedded in that state.

That Non-Local character is similar to MWI selecting an appropriate “world” with its entire surrounding non-local character configured appropriately to justify EPR correlations. I do not ask that you two abandon your opinions as being wrong, just stop demanding that everyone accept you opinion(s) as the correct one!

Look, I think you are redefining the word "local" here. The sea level at your place being similar with the one at my place is hardly a proof for our ftl communication.

I don't demand anything from you but I expect you to back up your claims.
You reject my counterexample for not being detailed enough but this is hardly a reason. What you need to show is that it is either logically inconsistent or it violates accepted physics.

The two of you cannot both be right, so at least present convincing evidence to each other to demonstrate which is correct BM or MWI. They maybe you will save the entire scientific community that is wasting so much time and effort pursuing so many different things that do not agree with either of you.

In fact we are probably both wrong. This doesn't make you right, though.

I’ll disengage from this debate until I see ueit & vanesch concur on which is correct MWI or BM.

I cannot compete with vanesch on this, I'm only trying to understand this stuff.

Until then I choose to continue my own individual search for a true Local Theory (I agree, a long shot), without the distraction of these two Non-Local theories claiming to be local.

Can you provide us with some insight about what you are looking for? Does any of the existing theories/interpretations/hypotheses present any resemblance with your "true Local Theory"?

As far as I remember, your position is that both QM and GR are non-local. Given the fact that these theories are the best we have, can I ask you for what reason do you look for a theory that necessarily denies both of them?

 

[Careful]

You miss quote me again; I did not explain a “determinate” vs. “deterministic” universe! I said Einstein expected the HV in an EPR to provide “determinate” not problematic solution, and that is all he said. Without actually finding a HV, I’ve seen nothing to suggest that he jumped to the conclusion or opinion that the entire universe was “deterministic” or "determinate", and that all his discoveries and every thought had been predestined from the Big Bang or even earlier. I do not accept that all these posts we fuss over here are meaningless events already set by a predetermined deterministic universe and the idea that Einstein did is balderdash!

GR is a determinate theory, and are we not all using it for the entire universe as a good approximation ? It seems YOU are pretty religious about not having determinism.

Easy
A photon approaches a PDC at some point (unknown & undeterminable to the photon) ahead. Likewise the PDC cannot know or determine exactly when or it what specific condition all the variables that makeup the EM details of that photon. But when they do interact, all these unknown variables combine to produce two photons. The random direction of one photon within a well defined “cone” of options is perfectly matched by the direction of the second based on conservation laws. Likewise, the polarity of the two photons is set one V the H. These parameters are set at the LOCAL creation of the two photons and remain determinate and unchanging until there interact with something else in each of there unknowable paths. PLUS, going with them on that path is the HV also determinate and unchanging and provides the fixed and unchanging information required to account for “entanglement” correlations.

Sure that is more or less the most general scenario (in which you could account for conspiration, stochastic theories, as well as faster than light). I asked you for a specific non-deterministic, but determinate example and you did no such thing at all.

Now if you can show the exact & complete details of such a HV; only then can you make meaningful judgments to speculate on an interpretation that could define with precision all the unknown details about the PDC and the Photon as it approached, to ultimately generate the two photons. Until that can be done you cannot, and I do not believe Einstein ever presumed, that all the events in the universe that lead up to the conversion of that one photon turning into 2 photons was preset in a “deterministic universe”.

Why would I need an HV theory of entanglement prior to figuring out a model for a photon ; the latter could very well be found by relying upon well known physics. But again you say, I do not *believe* that Einstein ever presumed a deterministic universe (many people must misread Einstein then, including me, 't Hooft, ..).

That is an unfair, self-serving, and unsupported claim on Einstein’s real work.
And I do not consider that a small point.

Sure, sure, but the point so far is that you did not do anything but pointing out to others what some famous physicist did not say according to you. By the way, what observation is concerned, I guess determinstic theories are indistinguishable from determinate ones; so all this discussion seems to turn around religious tastes.

 

[RandallB]

I don't demand anything from you but I expect you to back up your claims.
In fact we are probably both wrong. This doesn't make you right, though.

Fine that means you think I’m probably right as the ONLY claim I made was it was wrong to consider BM Local or as haven been accepted as “correct”.

GR is a determinate theory, and are we not all using it for the entire universe as a good approximation? It seems YOU are pretty religious about not having determinism.

No not until someone resolves Lee Smolin’s points about GR being background independent. His new book is an OK read but his papers on the subject are easily found and should be understandable by most on this forum.

And I don’t know about religious, but I’m very well convinced that you and I have free will and are not just going though the motions of responding here in accord with some predetermined “deterministic universe”.
The rest of your comments are still so far off the point for me they are “not even wrong” so I can even comment.

Look guys as far as I’m concerned between careful ueit & vanesch I’m seeing three different versions of Non-local theories, each claiming to be “local” and as far as I can see by little more than that claim of being “local” as being the correct theory of reality. None of that has been shown as “accepted physics” in the view of the majority of prominent scientist.

Even at three against one I’ve not changed my mind, as the only thing I think I can agree with you guys on is that showing AND PROVING a local solution would disprove both “entanglement” and “superposition” and “time travel” as well. And that such a proof would displace all non-local theories. BUT AFAIC to do that, the standard for local needs to be much higher that any of you seem to be willing to accept. So allow me to depart this and I’ll stick with my standard for local, even if it might be impossible to satisfy - - that’s my problem.

 

[Careful]

No not until someone resolves Lee Smolin’s points about GR being background independent.

Euhhh, background independence has nothing to do with GR being determinate ! And neither do I consider it to be a crucial ingredient for a future theory of quantum gravity.

And I don’t know about religious, but I’m very well convinced that you and I have free will and are not just going though the motions of responding here in accord with some predetermined “deterministic universe”.

So, that confirms my point.

The rest of your comments are still so far off the point for me they are “not even wrong” so I can even comment.

Look guys as far as I’m concerned between careful ueit & vanesch I’m seeing three different versions of Non-local theories, each claiming to be “local” and as far as I can see by little more than that claim of being “local” as being the correct theory of reality. None of that has been shown as “accepted physics” in the view of the majority of prominent scientist.

You confuse since as long as I am here locality with causality, that's all there is to it. Bell didn't invent the terminology ``local causality'' for nothing you know.

Even at three against one I’ve not changed my mind

Bravo, an heroic act.

BUT AFAIC to do that, the standard for local needs to be much higher that any of you seem to be willing to accept. So allow me to depart this and I’ll stick with my standard for local, even if it might be impossible to satisfy - - that’s my problem.

Perhaps, you should ask wether you can find a local, determinate, realistic theory of photons first, using your notion of locality, such that Maxwell theory is recovered in a suitable limit. You might end up very dissapointed soon.

Careful

 

[vanesch]

That Non-Local character is similar to MWI selecting an appropriate “world” with its entire surrounding non-local character configured appropriately to justify EPR correlations. I do not ask that you two abandon your opinions as being wrong, just stop demanding that everyone accept you opinion(s) as the correct one!

The two of you cannot both be right, so at least present convincing evidence to each other to demonstrate which is correct BM or MWI. They maybe you will save the entire scientific community that is wasting so much time and effort pursuing so many different things that do not agree with either of you.

Both, MWI and BM are "correct" theories in the sense that they set up a logically coherent construction (at least to a level of informal rigor which is usual with physical theories). That's what I'm trying to tell you: logically, these theories exist. Whether they correspond to our universe is another matter of course (probably not !), but that's not the point. The point is that they exist, as theories, and they both agree with the experimental results which are under discussion here (EPR correlations). So their logical existence means that one cannot deduce logically, from these experimental predictions, any property which BM or MWI would not have, given that they logically exist.

von Neumann already committed this error with BM: he claimed that certain predictions of QM could never be obtained with a deterministic HV theory. BM does exactly that, so von Neumann's reasoning must have been wrong, irrespective of whether BM is or isn't "true" in nature.

In exactly the same way, MWI has an entirely local dynamics, and makes the same predictions of observation as does standard QM. As such, any claim that one can deduce, from these observations, that the dynamics must be non-local, is just as erroneous as von Neumann was in his case. Again, irrespective of whether MWI is "true" in nature or not.

So, logically, BM and MWI are both "correct", as is any well-constructed theory. This has nothing to do with whether it is the correct description of nature. Newtonian mechanics is also "correct".

 

[Demystifier]

Vanesch, I would very appreciate if you could answer to my post #82.
Thanks!

 

[vanesch]

OK, it is local for you. But is it local for itself? Is the whole Universe (the collection of All worlds of mwi) local? Is the split/branching of the Universe in a number of different copies a local event? And if you say that this question is irrelevant, isn't such a view of nature quite antropomorphic?

"The whole universe" in MWI is nothing else but the state vector, which evolves under unitary evolution. So the question of locality is related to this unitary evolution. It doesn't need to be so. For instance, the unitary evolution induced by, say, the Coulomb hamiltonian in NR QM certainly doesn't induce a local unitary evolution (in the same way as the Coulomb force in classical phase space doesn't induce a local phase flow, given that there is "action at a distance"). But if the interactions in the hamiltonian (which is the generator of unitary evolution) are local, then the unitary flow in Hilbert space is just as local as the phase space flow in classical mechanics, if the interactions are local. This can easily be verified by the fact that this unitary evolution can be written out in a Lorentz-invariant way.

The "splittings in worlds" in MWI is a pure observer-dependent concept: not for all observers, the universe is "split" in the same way. In fact, this splitting is simply the projection on the different "subspaces of awareness" by the observer (that is, those subspaces of hilbert space which correspond to different "states of awareness", which you can grossly imagine to correspond to different memory states which correspond to "observations"). "Worlds" do not have any objective ontological existence in MWI, independent of an observer.

Look at the wavefunction, where Alice has done a measurement and Bob has done a measurement, but they didn't talk to each other yet:

|psi> = |alice+> (u |bob+> + v|bob->) + |alice->(w |bob+> + x |bob->)

For Alice, there are 2 worlds, one in which she has seen the + outcome, and one in which she has seen the - outcome. Her local state description is |alice+> in one world, and |alice-> in another, and the |alice+> state has an overall weight of u^2 + v^2, while the |alice-> world has an overall weight of w^2 + x^2.
Note that these elements are in no way affected by what happens at Bob, as long as this is a local, unitary evolution. Whatever happens to the "bob" states, the weight of the Alice+ state will always remain u^2 + v^2.

We can re-write the SAME state vector from Bob's PoV:
|psi> = |bob+>(u |alice+> + w |alice-> + |bob-> (v |alice+> + x |alice->)

For Bob, there are also 2 worlds, one in which he has seen the + outcome, and one in which he has seen the - outcome. The bob+ state has an overall weight of u^2 + w^2 and the bob- state has an overall weight of v^2 + x^2.
Again, this local state description of Bob is independent of what happens at Alice: the weights of these two states will remain the same under any unitary transformation at Alice's place.

Note also that Alice's worlds have nothing to do with Bob's worlds.

Now, imagine they come together, and exchange their information. This alters of course the "state of awareness" for both alice and bob, but can only occur when they are in local contact.

We now have an evolved state:
|psi2> = u|bob++> |alice++> + w |bob+->|alice-+> + v|bob-+>|alice+-> + x |bob-->|alice-->

We now have an altered state for alice, which can be in 4 different states:
alice++, alice+-, alice-+ and alice--, with weights respectively u^2, v^2, w^2 and x^2.

This modification of alice's state description came about because of her LOCAL interaction with Bob, when he came to tell her his results. The unitary evolution which did this was local to the place of meeting.

Alice now lives in 4 worlds (and so does bob), and this time the worlds coincide between alice and bob (because they are in local interaction).

Notice the difference with a projection-based (and hence non-local) explanation of this story:
Before Alice or Bob performs a measurement, the state is:
|psi> = |alice0> (|a+>(u |b+> + v|b->) + |a->(w |b+> + x |b->)) |bob0>

(where we introduced the a-states, of the particle at Alice's place,and the b-states, of the particle at Bob's place).

Alice's weight is 1 for her state alice0.
However, the weight for the a+ state (at Alice's place) is (u^2 + v^2) while the weight for the a- state (at Alice's place) is (w^2 + x^2)

Let us first say that Bob performs a measurement, and his outcome is +:
this MODIFIES the statevector by projection:
|psi'> = |alice0> (|a+>(u |bob+>) + |a->(w |bob+>))/sqrt(u^2 + w^2)

and note that this CHANGES the weights of the a-states at Alice:
instead of a weight u^2 + v^2, we now have a weight of u/sqrt(u^2 + w^2) for the a+ state, and a weight w/(sqrt(u^2 + w^2) instead of (w^2+x^2) for the a- state.

So we see here that a state description of something at ALICE has been changed by a remote interaction (Bob's measurement). This is what is non-local in the projection postulate. It is the essence of the EPR effect.

Alice's state description has not been altered however. But of course, as Alice is going to interact locally with a, she will find a different state now than if Bob wouldn't have measured (with projection) on his side.

Alice's measurement will do nothing special to Bob's: imagine she finds +:
|psi"> = |alice+>|bob+>

This interaction doesn't do anything "non-local". Bob's state was +1 with weight 1, and this remains so. The culprit was the first measurement by bob, who ALTERED the state description of the a-particle remotely, by projection. This is the explicit non-local mechanism in "standard" projection-based quantum mechanics. Mind you that what introduces the alteration of the local state description is the projection: the fact of throwing away some terms in the wavefunction for ALL constituents, local or remote. The unitary evolution cannot do such a thing (if the interactions in it are local), because there is conservation of hilbert norm.

 

[Demystifier]

"The whole universe" in MWI is nothing else but the state vector, which evolves under unitary evolution. So the question of locality is related to this unitary evolution. It doesn't need to be so. For instance, the unitary evolution induced by, say, the Coulomb hamiltonian in NR QM certainly doesn't induce a local unitary evolution (in the same way as the Coulomb force in classical phase space doesn't induce a local phase flow, given that there is "action at a distance"). But if the interactions in the hamiltonian (which is the generator of unitary evolution) are local, then the unitary flow in Hilbert space is just as local as the phase space flow in classical mechanics, if the interactions are local. This can easily be verified by the fact that this unitary evolution can be written out in a Lorentz-invariant way.

The "splittings in worlds" in MWI is a pure observer-dependent concept: not for all observers, the universe is "split" in the same way. In fact, this splitting is simply the projection on the different "subspaces of awareness" by the observer (that is, those subspaces of hilbert space which correspond to different "states of awareness", which you can grossly imagine to correspond to different memory states which correspond to "observations"). "Worlds" do not have any objective ontological existence in MWI, independent of an observer.

OK, I am satisfied with the first part in which you explain why it is local.

But I still do not understand the second part, so I will ask you additional questions:
What is "observer"?
Is it necessarily a conscious being?
Can one electron be an observer?
Do observers have objective ontological existence in MWI?
Is the MWI interpretation above essentially the same as Rovelli's relational interpretation?
Is the projection on the different "subspaces of awareness" by the observer - nonlocal at least for that observer (even if there is no objective nonlocality)?
Does MWI misses a satisfying theory of the observer? If yes, does it mean that quantum mechanics is not complete? If yes, could that mean that a satisfying completion would require a sort of nonlocality?

 

[vanesch]

But I still do not understand the second part, so I will ask you additional questions:
What is "observer"?

This is going to turn philosophical again
The ultimate "reason of existence" of physics, and of all studying of nature, and even of all our thinking, is to explain our subjective experiences. Probably
you're not thinking of it that way, but if you give it some reflection, you will find out that all of our intellectual activity comes ultimately down to understanding our subjective experience.

Now, usually we think of that as a secondary problem, because deep down, we are somehow convinced that our subjective experiences are directly derived from our sensory inputs, which correspond to a unique "reality" in an obvious and evident way, and that we can put "ourselves" out of play in the business of describing that outside reality. But this is nothing but hypothesis. It is also possible that the relationship between "reality" and our subjective experience is far more complex than we imagine. (and then maybe not) This is the viewpoint of MWI, and it is essentially inspired by the clash between the obvious quantum description of, say, a human being (which can then be in several places at once, the superposition principle applying to him as well as to anything else), and our daily perception which doesn't allow for such phantasies. There are two ways out: 1) quantum theory doesn't apply to human bodies or 2) our daily perception doesn't correspond to "reality" as a whole. MWI takes on the last stance.

So what's an observer ? It is something having subjective experiences which tries to relate it to an objective world "outside" in this viewpoint. Otherwise, it is just a physical construction as any other.

You might also say: an observer is something which cannot accept being in a quantum superposition because it is convinced that his subjective experiences do not correspond to that.

Is it necessarily a conscious being?

In as far as consciousness is related to "the existence of subjective experience", yes.

Can one electron be an observer?

In as far as an electron has subjective experiences...

It is maybe necessary to make a distinction between "an observer" and a "measuring device". A measuring device is a thing that interacts with a system, and has memory states that correspond to "outcomes of measurement". If you apply quantum theory to a measurement device, there is not really a problem: you will find that the device will end up in a quantum state which is a superposition of "outcomes", in a way which mimicks the original quantum superposition of the system at hand. Nothing goes wrong here. What goes wrong is when we *subjectively observe* such a measurement device, that we only see it in one state. Now, this can be because it truly is in one state (in which case the entire quantum description goes wrong at this level), or, and that is the MWI viewpoint, it is because we are only subjectively aware of one of the states.

Do observers have objective ontological existence in MWI?

The physical structure related to an observer has objective existence in MWI (the "body"). However, the "observer" itself, not really: it are specific body states which "act as observer". You cannot know if a physical structure is "an observer" or not: you just declare it to be so or not. (in fact, in exactly the same way as you cannot really know if a person is conscious or is a zombie) This is the ill-defined part (but as subjective observation is ill-defined in any case, that's not a problem FAPP, but only in principle).

Is the MWI interpretation above essentially the same as Rovelli's relational interpretation?

Personally, I think so ! But others do not agree with me on that point.

Is the projection on the different "subspaces of awareness" by the observer - nonlocal at least for that observer (even if there is no objective nonlocality)?

No, because these subspaces (which identify clearly different bodystates, corresponding to clearly different experiences) are only related to a local bodystate. What an "observer" observes, are his bodystates, and nothing else. So this bodystate is of course local to the body, and observers attached to this body are only "aware" of this bodystate (actually, of components of it). It are bodystate conglomerates which define "different states of awareness" and the corresponding subspaces.

Does MWI misses a satisfying theory of the observer?

yes, on a level of principle. No, FAPP (for all practical purposes). That is to say, our differentiated "states of awareness" are so terribly coarse grained, that their precise definition doesn't really matter. But we bump here into the same difficulty as in Copenhagen QM, with the "quantum-classical" transition. Only, we removed the problem totally out of the "objective physics" part and entirely in the link between objective physics and subjective experience, which is in any case a very fuzzy domain (in principle, but not FAPP).

If yes, does it mean that quantum mechanics is not complete? If yes, could that mean that a satisfying completion would require a sort of nonlocality?

This has nothing to do with it. Concepts such as locality and so on are supposed to reign in the domain of pure physics, which is entirely well-defined in MWI (namely, the Schroedinger equation, period). What is fuzzy, is simply the details of the link between physical reality and subjective experience - which is in any case fuzzy on a very detaillistic level, but which is more than sufficient to talk about observations which have such a clear influence on our "state of awareness" that there is not much discussion - this is what is usually considered as "macroscopic observations".

 

[Demystifier]

Thanks vanesch, now I think I understand MWI (or at least your view of MWI) much better.

But let me also present a critical "summary" of MWI. In MWI, the conscious observer plays an important role. On the other hand, MWI does not contain a theory for that conscious observer.

In comparison, the Bohmian interpretation also does not contain a theory of conscious observers, but they do not play an important role in that interpretation. (Of course, the Bohmian interpretation contains other disadvantages.)

Do you agree?