Strings and Non-Locality

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  • #1
Canute
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If particles are made out of strings then it seems to follow that strings are, or can be, both local and non-local. Is this correct? I haven't seen any discussion of the wave-particle nature of strings (or the property of strings that allows particles to be also waves) so I assume I'm wrong about this. Can somebody explain how the ambivalent nature of particle/waves arises from strings, or haven't we got that far yet?
 

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  • #2
Berislav
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If I'm not mistaken, the "wave-particle" (using that term as loosely as possible) arises simply from applying the quantization formalism to strings themselves.
 
  • #3
Canute
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Sorry but I don't understand that answer. Can you clarify it a little.
 
  • #4
selfAdjoint
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He means that in quantization, the dynamic variables of a classical theory, such as position and momentum, are replaced by "operators" acting on "states" of the quantum system, and the states can be thought of as wavelike, while the operators can reduce the wave to an "eigenstate" - a sharp localized value. Since strings are quantized in string theory, they share this apercu.

However it has to be stated that after all is said and done, string theory is relativistically covariant, and does not support dreams of a nonlocality at the root of being.
 
  • #5
Canute
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Thanks. I'm out of my depths here so please bear with me, but this seems self-contradictory. You seem to be saying that non-locality is not a property of fundamental quanta after all, because string theory is relativistically covariant. I thought non-locality was an established fact, and that therefore strings must have this property. How can electrons, protons, atoms etc. have a non-local aspect but strings not have one?

Also, what does "nonlocality at the root of being" mean? Do you mean that string theory does not support the dream that non-locality is a property of the fundamental constituents of matter? If you have the time and patience could you also unpack "relativistically covariant" a little for me, I have the glimmer of an idea of what it means, but that's all.

Thanks
Canute
 
  • #6
selfAdjoint
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Canute said:
I thought non-locality was an established fact, and that therefore strings must have this property.

I think you misunderstand entanglement. No cause can pass between spacelike separated entangled particles, according to quantum theory. After the fact, in the intersection of the future light cones of the particles, you can establish a correlation in their behaviors, but one does not affect the other in real time. This is quantum weirdness if you like but it is not what I think you mean by nonlocality.

Relativistic covariance means that an equation that is true in one frame remains true in any boosted frame. The two sides of the equation may vary due to Lorentz transformations, but they remain equal. The equations of the Dirac electron, QED, the Standard Model, and string theory all meet this criterion. It is a consequence that they do not support nonlocality in the sense of causes acting over spacelike intervals, or to put it in other words, causes traveling faster than light.
 
  • #7
Canute
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I'm not suggesting that something travels between entagled particles faster than light, and I don't believe anything does, and certainly not causes. I didn't think anybody thought this (although the absorber theory of time seems to me to allow faster than light communication in a sense). I'm just wondering how string theory deals with the issue of non-locality. After all, if particles are made out of strings then presumably the behaviour or particles can be, indeed must be, theoretically explained in terms of the behaviour of strings. I'm just wondering how theorists go about doing this, or whether it's a problem that's being left to one side for now. The books I've read on string theory, QLG etc. (Kaku, Greene, Smolin etc) mention non-locality but do not relate it string theory. I'm just wondering why not.

As far as I know I do not misunderstand the concept of entanglement. I'm asking how string theory deals with the dual nature of particle/waves, and in particular the issue of non-locality, not specifically about entanglement.

It's really a very naive question. If protons are made of strings and protons behave non-locally, to put it clumsily, then presumably strings also behave in this way. I just wondered why this has not been discussed in what I've read.
 
  • #8
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Canute said:
If protons are made of strings and protons behave non-locally, to put it clumsily, then presumably strings also behave in this way. I just wondered why this has not been discussed in what I've read.

Could you enlarge on what you mean by non-local in your premise: "... and protons behave non-locally"? I am not aware of any behavior of protons that I would myself characterize as non-local.
 
  • #9
Canute
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By non-locality I mean what Einstein called "spooky action-at-a-distance", or more generally the idea that all particles that have ever interacted are part of a single wave function. Particular effects would be entanglement, the interaction of spatially separated particles as if they were in the same place, and the spatial/temporal distribution of probable postions for unobserved particles, which seem to have a finite probability of being anywhere in the universe at any time.
 
  • #10
Spin_Network
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Canute said:
By non-locality I mean what Einstein called "spooky action-at-a-distance", or more generally the idea that all particles that have ever interacted are part of a single wave function. Particular effects would be entanglement, the interaction of spatially separated particles as if they were in the same place, and the spatial/temporal distribution of probable postions for unobserved particles, which seem to have a finite probability of being anywhere in the universe at any time.

And here are five 'die' cast recently:http://physicsweb.org/articles/news/8/6/18

Abstract Quote:By taking advantage of quantum phenomena such as entanglement, teleportation and superposition, a quantum computer could, in principle, outperform a classical computer in certain computational tasks. Entanglement allows particles to have a much closer relationship than is possible in classical physics. For example, two photons can be entangled such that if one is horizontally polarized, the other is always vertically polarized, and vice versa, no matter how far apart they are.

This is going to get tougher as the cross-sections of the combined photons are extended, the first encounter with anything that is 'NOT' part of the entanglement, will according to QMI, collapse the wavefunction generated.

The reason TWO-STATE entangled photons cannot be at either end of the Universe, is there has to be no intervening matter to 'intefere', regardless of what quantum state is produced or invisaged.

If TWO-PHOTON's are deeemed to be entangled at either end of the Universe, then acccording to the photons, its a pretty SMALL Universe!
 
  • #11
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And in addition to what Spin_Network said, all that "spooky action at a distance" is precisely the action of causes over spacelike intervals, AKA FTL, that quantum mechanics DOES NOT assert. The Einstein-Podolski-Rosen (EPR) conjecture that you could measure both of two complementary observables momentum and position precisely for the same particle at the same time, by exploiting entanglement, was DISPROVED by the experimental confirmation of the Bell inequalities.
 
  • #12
Canute
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OK I'll try another way of asking the question, since my mention of non-locality seems to have confused the issues. If particles have a wave aspect then what they are made out of must also have a wave aspect, it seems to me, with my simpleminded appreciation of the issues. Is this true or false? If it is false then as yet I don't understand why it is false; if it is true then how, roughly-speaking, does string theory incorporate this feature? Thanks for your patience.
 
  • #13
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Canute said:
OK I'll try another way of asking the question, since my mention of non-locality seems to have confused the issues. If particles have a wave aspect then what they are made out of must also have a wave aspect, it seems to me, with my simpleminded appreciation of the issues. Is this true or false? If it is false then as yet I don't understand why it is false; if it is true then how, roughly-speaking, does string theory incorporate this feature? Thanks for your patience.

The states of a quantum system are vectors (actually rays) in a complex vector space. The operators that act on them are unitary. These two facts mean the states can be given a wavelike interpretation. But these "waves" are in Hilbert or Fock space; that is they are a part of the mathematical formulism, not events in spacetime. Quantum mechanics does say that the waves are projected down into probabilities of actual phenomena by "observation", but the waves themselves are not part of spacetime reality. This is a subtle point because it is the probabilities that support wavelike phenomena in spacetime such as two slit interference. But note that "quantum eraser" and "delayed choice" experiments show that these probabilities are more complicated than simple probabilities of stochastic systems in spacetime. You can't get away from the linear algebra of the complex vector space.

Entanglement is the sharing of a single compound state in Hilbert or Fock space between two or more localized quantum objects. An observation that projects the entangled state into probabilities destroys the entanglement. An observation of one of the localized particles produces probabilities for both of them, and the probabilities are algebraically related.

When one probability is pinned down, so is the other, but this is not the action of one particle on the other. In one relativistic frame the two reductions are simultaneous, but you can easily find two other legitimate inertial frames in which one of the particles came first and the other followed (i.e. there a frame in which A seems to have caused B and another equally good frame in which B seems to have caused A, together with the one frame in which A and B were simultaneous).

You have to juggle the quantum assertions and the relativity assertions at the same time, but it can be done and it does give the answer for standard relativistic quantum mechanics.
 
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  • #14
Canute
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Thanks. But what about my question? I'll try another version.

In the formalism of the different string theories do strings have the same complementary/contradictory properties that particle/waves have in quantum theory, or do these properties emerge only at the level of electrons, protons etc.?
 
  • #15
mcgucken
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Canute--you are right. String Theory is a complete waste of time, as it allows for no explanation of non-locality, a demonstrated FACT, as show below.

[deleted - reference to non-mainstream and unverified work]

http://en.wikipedia.org/wiki/B ell's_inequality

[deleted - you have already made a reference to the Wikipedia site. There is no need to copy it to here]
 
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  • #16
mcgucken
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String Theory is non-verified and non-mainstream work!

String theory is non-verified and non-mainstream work!

Only 1,000 physicists use it: a tiny, tiny percentage of the human population. They use it to raise government grants, enslave students to meaningless careers, and pick the pock of the tax-payer.

Billions use QM and SR every day, to communicate on phones and over the internet.

I propose that all posts pertaining to string theory be deleted.

That way all the hundreds of millions of dollars they consume can go to support real physics, based in logic, reason, and reality.

[deleted]
 
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  • #17
Canute
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mcgucken said:
Canute--you are right. String Theory is a complete waste of time, as it allows for no explanation of non-locality, a demonstrated FACT, as show below.
I wasn't arguing for or against string theory, just asking a question. But thanks. I didn't think it allowed such an explanation but wasn't sure. I'll just hang on to see if anyone disagrees with you.
 
  • #18
an observation: there is in general an inverse relationship between the depth of a person's emotional attachment to a problem and the likelihood of that person making any contributions toward a solution.

nc
 
  • #19
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Canute said:
I wasn't arguing for or against string theory, just asking a question. But thanks. I didn't think it allowed such an explanation but wasn't sure. I'll just hang on to see if anyone disagrees with you.


There's another current thread on the general value of string theory. Let's keep this one for the issue of non-locality, or if we have exhausted what we have to say on that subject, let's close it.
 
  • #20
Canute
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I don't want to discuss the general value of string theory either. All I want is an answer to my question. But it seems I'm not going to get one here so I suppose I'll have to ask elsewhere.
 
  • #21
mcgucken
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Hello Canute,

String Theory does not account for the non-locality observed in QM.

It does not provide a deeper, more fundamental model to explain the EPR paradox and the experimental verifications of Bell's Inequalities.

String Theorists are very discrete in choosing their battles. They only tie certain knots that they know they can untie, and even then, all those knots are yet tied.

But to answer you question, no--String Theory does not account for QM's non-locality. It doesn't even try.
 
  • #22
Canute
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Yeah, that's all I was asking. It seemed that way to me but I thought I might have missed something and wanted to be sure. Thanks.
 
  • #23
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Canute said:
Yeah, that's all I was asking. It seemed that way to me but I thought I might have missed something and wanted to be sure. Thanks.

Don't go away without at least considering a revision of your "particle at the end of the universe" view of quantum nonlocality. I don't know where you picked that up (Capra maybe?) but it's just not what QM says. Further discussion if any should be on the Quantum Physics board.
 
  • #24
Canute
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I see no need to revise my view. It's in accord with all the physicists I've read to date, even if perhaps I put it badly. My view of nonlocality is irrelevant here anyway, since my question did not depend on any particular interpretation. I think you may have misunderstood what I was asking, but thanks for your help.
 
  • #25
mccrone
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Canute said:
I see no need to revise my view. It's in accord with all the physicists I've read to date, even if perhaps I put it badly. My view of nonlocality is irrelevant here anyway, since my question did not depend on any particular interpretation. I think you may have misunderstood what I was asking, but thanks for your help.

Hey Canute - seems I've just asked the same basic question again in the thread “Why are strings not invoked as a solution to QM nonlocality?", which has been moved here after I originally posted to the QM group.

It seems you didn't get a good answer either. Any luck elsewhere?

Your take on nonlocality seemed correct to me.

Selfadjoint said "Don't go away without at least considering a revision of your "particle at the end of the universe" view of quantum nonlocality."

But you correctly state that it is not about communication between locations across spacetime. It is about a correlation between two far flung particles (or the entanglement of a photon with the history of a two slit experiment). Locally, the event looks random. Globally, the event turns out to be determined. The puzzles (and likely solutions) lie in the dichotomistic local~global nature of the situation. There are quite literally two view of what happens.

As to your original question on strings and particle~wave complementary descriptions, I have not seen a good statement on this. But it would be my feeling that imagining a string as an actual loop of something is synonmous with a discrete particle and imagining it as a vibration, a harmonic resonance orbiting a compact set of dimensions, would be its wave description.

Remember that a string would not spread out into 3D space as a wave-like smear would it? It would exist only as a waviness within its own 6D space. In the 3D realm, you now switch to a point-like particle that gets smeared out like a wave in 3D space.

This is one of the points I tried to raise in my own thread. In the 6D string realm, you get a compactified waveform as any vibration would have the chance to complete its orbit around its world in a Planck timescale (presuming that the speed of light rules there as well). And so it could self-organise into a standing wave of some sort. But the aspect of a particle~wave that lives in the 3D realm could not complete even a single round trip around an expanding universe.

In effect, this stringverse story would give every location in 3D space a memory. The memory for what a particle stands for (mass, charge, speed, etc) would be a resonant echo in the string dimensions while in 3D space the particle would be living out an unfinished, still open, history.

This all seems quite a natural reading of string theory. But it is not what I've seen people say. So I am curious why?

Cheers - John McCrone.
 
  • #26
Canute
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Hi John

Welcome to the forum. I haven't read your thread on this question yet but assume from what you say you didn't have much luck either. The answers to such questions seem hard to come by, and they are often answered as if they were intended as criticisms rather than questions for some reason. And no, I've had no luck elsewhere.

I've no idea if your answer (strings/particles - vibrations/waves) makes sense, but it's a stab at a solution at least, and the only stab I've ever seen. Coincidently I've wondered if the same sort of thing might apply to particles/waves - postion/momentum, ie. that particles have position and waves have momentum. However, despite the naivety of this idea I haven't found anyone who finds it plausible yet. Duality and complementarity have to be disconnected phenomena for reasons I haven't understood. On the question here I'm rather baffled as to how string theory can have been developed to this point without addressing duality and non-locality, but then there's much about the theory that I don't understand. It seems that many people think it's untestable nonsense anyway so it's difficult for an outsider to know how seriously to take it. Anyway, welcome to the discussions.

Canute
 
  • #27
mccrone
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Canute said:
Coincidently I've wondered if the same sort of thing might apply to particles/waves - postion/momentum, ie. that particles have position and waves have momentum.

Wave~particle would be to do with the kind of behaviour seen - as in twin slit where photon or electron does/doesn't show interference. So it is how things seem from a system viewpoint. Then position~momentum would be what you might measure of an individual wave~particle.

Canute said:
On the question here I'm rather baffled as to how string theory can have been developed to this point without addressing duality and non-locality, but then there's much about the theory that I don't understand. It seems that many people think it's untestable nonsense anyway so it's difficult for an outsider to know how seriously to take it.

String theory certainly makes a lot of people angry because it is a bandwagon that takes more than its fair share of people and resources. The testability issue is also corrosive. It leads to silly things like the promotion of quite unlikely ideas (clashing brane world cosmology) simply because these ideas seem within grasp of experiment. It is rather like the Higgs. After WW2, the big physics labs got a blank cheque for delivering the bomb. That created a social institution that has come to depend on some grand new idea which is always just within reach if only the government will fund the next generation of lab hardware and keep paying the salaries of several thousand personel.

Should strings be taken seriously? Well I think there are aspects that are obviously the right way to be going. The exploration of symmetries - because this gives us an idea of the kinds of arrangements that worlds more or less must fall into to have any kind of persisting existence. Likewise the modelling of everything in terms of dimensionality - if anything is going to be basic, it will be (dynamic) geometry.

I suppose what I would like to see is a physically realistic interpretation of what the current maths formalisms represent. For example, the idea of actual little strings wriggling about is as unrealistic an image as the idea of billiard ball particles. I can only think in terms of a resonance - some kind of standing wave - in a closed string space. But then this leads to many further questions, like won't it get a little crowded in there if all the Universe's particles have to share the same Planck scale realm as the "memory" for their various states.

That is what makes the question of how string theory views nonlocality so interesting to me. If there is an obvious reason why the two things have nothing to do with each other, then fine. But it would be worrying if it was part of the politics of strings that these sorts of broader connections to physical theory don't even get discussed.

Cheers - John McCrone.
 
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  • #28
Canute
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mccrone said:
Wave~particle would be to do with the kind of behaviour seen - as in twin slit where photon or electron does/doesn't show interference. So it is how things seem from a system viewpoint. Then position~momentum would be what you might measure of an individual wave~particle.
Yes. But why not say that position~momentum would be to do with the kind of behaviour seen, and wave~particle would be what you might measure? It seems a mess of words to me. What's the difference between measuring, seeing, observing, detecting and so on? It seems to me that if the wave~particle duality is not directly linked to the momentum~position complementarity then the fact that we find both of these paradoxical dual properties attaching to quanta would be a completely implausible coincidence.

After WW2, the big physics labs got a blank cheque for delivering the bomb. That created a social institution that has come to depend on some grand new idea which is always just within reach if only the government will fund the next generation of lab hardware and keep paying the salaries of several thousand personel.
Hmm. Now you mention it...

I suppose what I would like to see is a physically realistic interpretation of what the current maths formalisms represent.
Me too. Perhaps the people who can do the maths can't see the model, and the people who see the model can't do the maths.

I'd like to pursue this but I'm away for a bit soon so trying to extricate myself from discussions at the moment. Another time.

Canute
 
  • #29
vanesch
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Canute said:
Thanks. But what about my question? I'll try another version.

In the formalism of the different string theories do strings have the same complementary/contradictory properties that particle/waves have in quantum theory, or do these properties emerge only at the level of electrons, protons etc.?

Maybe another view can help. There is on one hand, abstract quantum theory, which says that the "system" is described by a vector in Hilbert space, that there are hermitean operators acting on that space which correspond in a yet-to-be-specified way with whatever is postulated to be observable of the system, and that if t is the time coordinate of your observer, he'll observe these states (or observables, pick your choice: Schroedinger/Heisenberg) evolve with a unitary operator whose derivative is a hermitean operator we call the Hamiltonian.

On the other hand, there are specific models of systems to which this abstract quantum theory can be applied:
*) classical phase spaces with a finite number of dimensions and classical Hamiltonian dynamics -> this gives us what is usually called non-relativistic quantum mechanics, through the canonical quantization rules (Poisson brackets become commutators)

*) discrete states -> this becomes things like spin networks or qbits

*) classical fields over Minkowski space -> this gives us quantum field theory

*) classical relativistic strings in N dimensions -> this gives us string theory

etc...

The idea of entanglement, however, is incorporated in the general, abstract quantum theory AND HAS NOTHING TO DO WITH THE UNDERLYING SPECIFIC MODEL. So this "collapse at a distance" happens in all models where "distance" makes sense (it is difficult to talk about collapse at a distance of qbits for instance). It is not the underlying model that will "explain" it.
It gets spectacular when the underlying model has an explicit rule that forbids dynamical causal influences between certain parts of the system (such as space-like separated field values) because then we say: hey this can't be causal ?! But it is just because then we're pushed with our nose onto the thing that we were happily not understanding already elsewhere (for instance, the exchange terms in molecules). "collapse of another part of the system wavefunction which has nothing to do with what I'm measuring" is simply part of the general quantum machinery, and has nothing to do with a specific underlying model.
 
  • #30
mccrone
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vanesch said:
So this "collapse at a distance" happens in all models where "distance" makes sense (it is difficult to talk about collapse at a distance of qbits for instance). It is not the underlying model that will "explain" it. It gets spectacular when the underlying model has an explicit rule that forbids dynamical causal influences between certain parts of the system (such as space-like separated field values) because then we say: hey this can't be causal ?! But it is just because then we're pushed with our nose onto the thing that we were happily not understanding already elsewhere (for instance, the exchange terms in molecules).

So is your point here that all systems would have an entangled aspect - a complementary local~nonlocal causality at work - but it is only in contrived situations that this general duality becomes too apparent to be ignored? I would agree with that.
 
  • #31
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Two strings can be nonlocally entangled in the same way as two particles can be nonlocally entangled. However, as a single string is nonlocal by itself, there is an additional form of nonlocality in string theory - an entanglement between different parts of the string.

The hidden-variable formulations of quantum mechanics make this entanglement nonlocality manifest. The most successfull hidden-variable theory is the Bohmian interpretation. For the case of strings see
http://arxiv.org/abs/hep-th/0605250
But can string theory bring a new explanation of this nonlocality? In
http://arxiv.org/abs/hep-th/0512186
it is suggested that the Bohmian interpretation can be DERIVED from string theory, so in this sense the answer could be - yes!
 

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