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Author Topic: Causality is it violated by quantum entanglement?  (Read 14684 times)

Offline Alan McDougall

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Can Causality be violated by say instantaneous quantum entanglement?

Spooky action as Einstein called it or quantum non-locality and entanglement have shown fundamental particles can interact instantaneously regardless of the distance between them. Alter the spin of one particle alters the spin of its twin in the other direction instantaneously.

Causality is fundamental to how the universe works, entropy for instant is intertwined with causality etc.

What are your thoughts on the matter?

Alan
« Last Edit: 19/06/2013 18:43:29 by Alan McDougall »


 

Offline imatfaal

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Re: Causality is it violated by quantum entanglement?
« Reply #1 on: 20/06/2013 12:19:52 »
Alan - it is an old and untrue chestnut that you can alter the spin of an entangled particle over a great distance.  An entangles pair of particles will be in an indefinite state - in a quantum superposition; the two particles are in a non-classical state where they can seem to be in a mish-mash /combination of states.   if you measure one particle and determine its state the other is (and seeminly always has been) in the opposite state.  But what you cannot say is that the partner changes state (you cannot possibly have measured/have known the state of the distant partner as that would have collapsed the system into two determined states already) - what happens is that the state becomes defined
 

Offline Alan McDougall

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Re: Causality is it violated by quantum entanglement?
« Reply #2 on: 20/06/2013 16:17:54 »
Alan - it is an old and untrue chestnut that you can alter the spin of an entangled particle over a great distance.  An entangles pair of particles will be in an indefinite state - in a quantum superposition; the two particles are in a non-classical state where they can seem to be in a mish-mash /combination of states.   if you measure one particle and determine its state the other is (and seeminly always has been) in the opposite state.  But what you cannot say is that the partner changes state (you cannot possibly have measured/have known the state of the distant partner as that would have collapsed the system into two determined states already) - what happens is that the state becomes defined

I think I know what you mean , that the two particle measures are really like two hands gloves, when you observe the one, the other is always opposite.

However, I am sure that this argument, put forward by no less than Albert Einstein has been disproved.

Alan
 

Offline imatfaal

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Re: Causality is it violated by quantum entanglement?
« Reply #3 on: 21/06/2013 11:29:58 »
Alan - it is an old and untrue chestnut that you can alter the spin of an entangled particle over a great distance.  An entangles pair of particles will be in an indefinite state - in a quantum superposition; the two particles are in a non-classical state where they can seem to be in a mish-mash /combination of states.   if you measure one particle and determine its state the other is (and seeminly always has been) in the opposite state.  But what you cannot say is that the partner changes state (you cannot possibly have measured/have known the state of the distant partner as that would have collapsed the system into two determined states already) - what happens is that the state becomes defined

I think I know what you mean , that the two particle measures are really like two hands gloves, when you observe the one, the other is always opposite.

However, I am sure that this argument, put forward by no less than Albert Einstein has been disproved.

Alan

I have given the simplest argument shorn of any details - but it is roughly correct.  I can promise you the notion that you can take an entangled pair, then set spin of particle A, and immediately have spin of particle B taking opposite value IS FALSE. 
 

Offline Alan McDougall

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Re: Causality is it violated by quantum entanglement?
« Reply #4 on: 21/06/2013 11:36:56 »
Alan - it is an old and untrue chestnut that you can alter the spin of an entangled particle over a great distance.  An entangles pair of particles will be in an indefinite state - in a quantum superposition; the two particles are in a non-classical state where they can seem to be in a mish-mash /combination of states.   if you measure one particle and determine its state the other is (and seeminly always has been) in the opposite state.  But what you cannot say is that the partner changes state (you cannot possibly have measured/have known the state of the distant partner as that would have collapsed the system into two determined states already) - what happens is that the state becomes defined

I think I know what you mean , that the two particle measures are really like two hands gloves, when you observe the one, the other is always opposite.

However, I am sure that this argument, put forward by no less than Albert Einstein has been disproved.

Alan

I have given the simplest argument shorn of any details - but it is roughly correct.  I can promise you the notion that you can take an entangled pair, then set spin of particle A, and immediately have spin of particle B taking opposite value IS FALSE. 


Please give source which scientifically proved that " quantum entanglement and non-locality are false?

Alan
 

Offline imatfaal

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Re: Causality is it violated by quantum entanglement?
« Reply #5 on: 21/06/2013 12:35:43 »
Alan - this is exactly what I was getting at in the other thread.  No where have I said that quantum entanglement is false.   You need to do a lot of basic reading - what you are describing is not entanglement, it is the common and erroneous conception of what entanglement is.   You cannot change the spin (etc) one of a pair of entangled by acting on the other - what happens is that a nondeterminate quantum mechanical state of superposition is determined into a more classical definite state. 

Quote from: Alan
Alter the spin of one particle alters the spin of its twin in the other direction instantaneously.

You are incorrect.

https://en.wikipedia.org/wiki/Quantum_entanglement
 

Offline yor_on

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Re: Causality is it violated by quantum entanglement?
« Reply #6 on: 21/06/2013 16:47:23 »
It's not two gloves Alan, it is only one glove :) You 'touch' any part of it and its wave function collapse, giving us two particles with opposite spin.
« Last Edit: 21/06/2013 16:53:20 by yor_on »
 

Offline yor_on

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Re: Causality is it violated by quantum entanglement?
« Reply #7 on: 21/06/2013 17:08:57 »
Don't know what to make of probability though. Take a look at http://xxx.lanl.gov/abs/1111.3328 .What it state seem to be that probability isn't enough in itself. There has to be a underlaying 'reality' for a wave function to exist. In a entanglement it must exist, measuring it you can't state what spin you first will measure, up or down, only that the 'opposite end' of that entanglement either way must have the opposite spin of what you measure.

Using that you can define a entanglement as one wave function, with a equal 'probability' of giving you up, or down. But if a wave function has a hidden demand of being 'real', as that pdf suggest, instead of a mathematical, statistically proven, artifact, then what should a probability mean?
 

Offline Alan McDougall

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Re: Causality is it violated by quantum entanglement?
« Reply #8 on: 22/06/2013 09:16:19 »
It's not two gloves Alan, it is only one glove :) You 'touch' any part of it and its wave function collapse, giving us two particles with opposite spin.

I know that , but it is imatfaan that thinks that this is the case, I agree with you?
 

Offline Alan McDougall

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Re: Causality is it violated by quantum entanglement?
« Reply #9 on: 22/06/2013 09:58:29 »
Quote
Quote from: Alan
    Alter the spin of one particle alters the spin of its twin in the other direction instantaneously.

Quote
quote from:imatfaan
You are incorrect.


https://en.wikipedia.org/wiki/Quantum_entanglement

I see how I am incorrect, sloppy wording by me!

When I stated "Alter the spin", I should have said "Measure the Spin" and the other entangled particle always has the reverse spin, semantics really you knew what I meant?

I will use the same above wikipedia link as you did, below

Quantum entanglement occurs when particles such as photons, electrons, molecules as large as buckyballs,and even small diamonds interact physically and then become separated; the type of interaction is such that each resulting member of a pair is properly described by the same quantum mechanical description (state), which is indefinite in terms of important factors such as position,momentum, spin, polarization, etc. "(I agree until measured the state of the particle is unknown, my comment Alan)"

Quantum entanglement is a form of quantum superposition. When a measurement is made and it causes one member of such a pair to take on a definite value (e.g., clockwise spin), the other member of this entangled pair will at any subsequent time be found to have taken the appropriately correlated value (e.g., counterclockwise spin).

Thus, there is a correlation between the results of measurements performed on entangled pairs, and this correlation is observed even though the entangled pair may have been separated by arbitrarily large distances. In quantum entanglement, part of the transfer happens instantaneously.

Repeated experiments have verified that this works even when the measurements are performed more quickly than light could travel between the sites of measurement: there is no slower-than-light influence that can pass between the entangled particles.

Recent experiments?? have shown that this transfer occurs at least 10,000 times faster than the speed of light which does not remove the possibility of it being an instantaneous phenomenon, but only sets a lower limit.

Alan


« Last Edit: 22/06/2013 10:01:36 by Alan McDougall »
 

Offline yor_on

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Re: Causality is it violated by quantum entanglement?
« Reply #10 on: 22/06/2013 12:09:49 »
If we ignore those tries for defining a 'speed' to a entanglement, instead defines it as instant, then one still have to answer what probability now will mean, if that link is correct? Statistically probability means a probability for every action and reaction. It doesn't separate what is possible from what is 'impossible'. more than by the probability given something to happen. But if a wave function only can be real when we find action and reaction realized, then all descriptions of a zero probability, as for example a probability of everything in the universe being entangled, impossible to verify, or why not the wave function of the universe, now should describe something without a wave function. Suddenly the wave function becomes something more than statistics it seems to me?

There is also the problem with me choosing a alternative measurement of a experiment. Depending on that the outcome changes. Either we then have several possible wave functions, all real, of which the one I 'specify' by my measurement becomes a outcome, or? But it makes sense to me to think of a wave function as something 'real', although the way we will define that 'reality' still must become statistics to me.
 

Offline dlorde

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Re: Causality is it violated by quantum entanglement?
« Reply #11 on: 22/06/2013 12:29:01 »
I think I know what you mean , that the two particle measures are really like two hands gloves, when you observe the one, the other is always opposite.

However, I am sure that this argument, put forward by no less than Albert Einstein has been disproved.
That would be the 'hidden variable' explanation, the idea that the spin of each particle is determined at entanglement, but unknown until one is measured. You're right that this has been falsified.

An alternative way of thinking of it was mentioned elsewhere on these forums - it's as if there are two pairs of 'potential' particles with opposite spins, and when you make a measurement, you're randomly selecting one pair to be 'real'...
 

Offline AndroidNeox

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Re: Causality is it violated by quantum entanglement?
« Reply #12 on: 24/06/2013 21:23:01 »
Entanglement is required by causality. Action at a distance violates relativity because it depends on the existence of a universe time standard (simultaneity).
 

Offline Alan McDougall

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Re: Causality is it violated by quantum entanglement?
« Reply #13 on: 25/06/2013 09:40:47 »
Entanglement is required by causality. Action at a distance violates relativity because it depends on the existence of a universe time standard (simultaneity).

As far as I know there is no such thing as  ' universal time standard" .This was Isaac Newtons idea of how time worked. Einstein "General relativity" proved this wrong Maybe I have misunderstood what you have stated?

If a reaction is instantaneous, what caused it to happen at the exact some moment in time?

Alan
 

Offline yor_on

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Re: Causality is it violated by quantum entanglement?
« Reply #14 on: 26/06/2013 00:09:26 »
I think you two agree, reading you?

Simultaneity may have existed just after a Big Bang, if we assume that 'place' to be perfectly isotropic, uniform and homogeneous. If it was it seems to me that you can define it as being at rest with itself. If that is true we can define that state as one single frame of reference. Then all clocks was perfectly synchronized at that 'time'. but as soon that you introduce two frames of reference, comparing, you must find time dilations, Lorentz contractions. If you don't accept this definition you can still define both as belonging to a same 'frame of reference', no matter what distance you find between them.

As always we forget the third part though, you measuring, using that local clock and ruler.
« Last Edit: 26/06/2013 00:12:57 by yor_on »
 

Offline Alan McDougall

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Re: Causality is it violated by quantum entanglement?
« Reply #15 on: 26/06/2013 09:07:51 »
I think you two agree, reading you?

Simultaneity may have existed just after a Big Bang, if we assume that 'place' to be perfectly isotropic, uniform and homogeneous. If it was it seems to me that you can define it as being at rest with itself. If that is true we can define that state as one single frame of reference. Then all clocks was perfectly synchronized at that 'time'. but as soon that you introduce two frames of reference, comparing, you must find time dilations, Lorentz contractions. If you don't accept this definition you can still define both as belonging to a same 'frame of reference', no matter what distance you find between them.

As always we forget the third part though, you measuring, using that local clock and ruler.

Before our universe emerged out of the primordial singularity, time did not exist, so I think that in reality only in this state, the only true, "actual single discrete moment" that ever existed, was then. After all if time did not flow, then, the primordial singularity, was stuck in a "moment" (Sloppy wording sorry for that.). Until something caused it to emerge and create our universe, (Big Bang/Emerge/ you choose?) No third party was there as far as I know?

Just a note of mine! There was never such an events a "big bang", this is as best,  loose terminology, in my opinion.

Alan
 

Offline yor_on

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Re: Causality is it violated by quantum entanglement?
« Reply #16 on: 03/07/2013 11:16:52 »
I think so too Alan :) To get something, as this universe, you must have a arrow existing to express outcomes in. So that original 'moment in time' must start when we get a first outcome. What was before that I don't know, quantum logic? But it should have nothing to do with our definitions of a arrow.

Statistics is a little like a detective to me, studying the past to define a future. Then, using this definition we must have a arrow to get to QM. So, one could also presume that the logic defined through such a arrow might be something preexisting, although not defined in specific outcomes, even before a Big Bang?
« Last Edit: 03/07/2013 11:19:47 by yor_on »
 

Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #17 on: 03/07/2013 20:26:31 »
Can Causality be violated by say instantaneous quantum entanglement?

Spooky action as Einstein called it or quantum non-locality and entanglement have shown fundamental particles can interact instantaneously regardless of the distance between them. Alter the spin of one particle alters the spin of its twin in the other direction instantaneously.

Causality is fundamental to how the universe works, entropy for instant is intertwined with causality etc.

What are your thoughts on the matter?

Alan
It can't be said that the measurement of the spin of one particle causes something to happen with the other one simultaneously. Recall that simultaneous is observer dependant so what is simultaneous in one frame is not simultaneous in another frame
(depending on the frame of course). Griffith discusses this in his QM text.
 

Offline yor_on

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Re: Causality is it violated by quantum entanglement?
« Reply #18 on: 03/07/2013 22:58:15 »
Pete , would you agree to that causality, and a arrow of time, must exist for both observers, to get to a logic?

Meaning that you can exchange definitions (coordinate systems), and relate them through Lorentz transformations? If that is true, then we have a arrow as I see it, and pointing in one direction (locally defined), as well as 'globally'. I have still to see someone (not you, just someone:) define a arrow going 'backwards' experimentally. Also, to me 'simultaneity' is not the same as 'the arrow of time'. I think of a arrow as something defining a logic. We can play it backwards and it 'must' make sense then too, if it didn't it would fail as a logic.
 

Offline yor_on

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Re: Causality is it violated by quantum entanglement?
« Reply #19 on: 03/07/2013 23:07:46 »
Although, if you take such a reasoning under Planck scale, it becomes meaning less, as I think. We get this arrow from frames of reference, assuming one single frame then to be related to Planck scale we lose that arrow under, and at, it.
 

Offline AndroidNeox

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Re: Causality is it violated by quantum entanglement?
« Reply #20 on: 22/09/2013 23:58:06 »
Entanglement is a direct consequence of causality. In a quantum sense, every quantum of information acquired about something is an observation. Prior to observation, while the observer possesses no information about the state of a system, the system exists (for the observer) in a multiplicity of all allowed states. Bell's inequality, proven by experiment, shows that this multiplicity of states is real. When the observer makes the observation, causality requires that all future observations will be consistent. Based on the old concept of "universe", this would require that the act of observation alters the state of physically distant systems instantly. There is no way to reconcile this interpretation with Relativity because it violates non-simultaneity and the speed of light.

Fortunately, there are alternative interpretations that are consistent with Relativity and the observations of Quantum Mechanics. One can presume that all physics is local, as required by Relativity, and that observation doesn't alter the universe, but that observation alters the observer.

However, these require that we exist in a multiverse which many (most?) people aren't comfortable thinking about.
 

Offline Skyli

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Re: Causality is it violated by quantum entanglement?
« Reply #21 on: 23/09/2013 17:39:25 »
Great discussion! Thank you to Alan and correspondents.

I cannot say by any means that I understand everything, but much has become clearer. You might describe me as an "interested layman" who has taken some (not enough) time to research QM; I am still far from being able to say "understand QM". In particular the reference to the Wikipedia article on Entanglement supplied by imatfaan was excellent and I wish I had the wherewithal to understand the mathematics of the second half of the article. There are, indeed, references to other Wiki articles that will, no doubt, help to furnish me with such but I would be very grateful to the forum if you could recommend a book or set of articles for the "interested layman" that could take me further.

I'm an old EDP guy - we didn't call it IT back in the 70's - with plenty of experience with structured techniques and concepts that, at first, appear counter-intuitive if that helps you with a recommendation.
 

Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #22 on: 24/09/2013 16:17:42 »
Quote from: AndroidNeox
Entanglement is a direct consequence of causality.
In what sense? What is the cause and effect that you speak of here? Entanglement is a direct consequence of other things such as conservation of angular momentum. What did you think it was?

Quote from: AndroidNeox
In a quantum sense, every quantum of information acquired about something is an observation.
Thatís incorrect. An observation in this sense has a radically different meaning than it does throughout the quantum mechanics literature. Please give a concrete example of what you mean by this and in your example please show how the wave function collapses from such an observation because that is what must happen during any observation in the quantum mechanical sense.

Quote from: AndroidNeox
Prior to observation, while the observer possesses no information about the state of a system, the system exists (for the observer) in a multiplicity of all allowed states.
I donít understand why youíre not using standard terminology here but your own terminology. What you said is more simply said as the system exists in a superposition of states. However youíve over generalized. Thereís no reason to assume that the system exists in a ďmultiplicity of all allowed states.Ē  A quantum state can be a linear combination of a finite subset of the allowed states.

Quote from: AndroidNeox
Bell's inequality, proven by experiment, shows that this multiplicity of states is real.
We didnít need that equality to know that the principle of superposition was real.

Quote from: AndroidNeox
When the observer makes the observation, causality requires that all future observations will be consistent.
Youíre being extremely unclear. Itís almost as if youíre just tossing words together to make a word salad. First you say above ďevery quantum of information acquired about something is an observation.ď and here you say ďthe observer makes the observationĒ and never do you correlate the two. And youíre talking about causality only in the most vaguest of ways. I canít see what it means in this context.

Quote from: AndroidNeox
Based on the old concept of "universe", this would require that the act of observation alters the state of physically distant systems instantly. There is no way to reconcile this interpretation with Relativity because it violates non-simultaneity and the speed of light.
What is this ďold concept of universeĒ that you speak of? And all light alters matter. Big deal. But nothing is instantaneous. Suppose I create pairs of photons that have opposite spin and fire them off in opposite directions, each pair having opposite spins but the direction of the pair is arbitrary. This results in the same effects on the universe as two photons in an entangled state. However in both cases nothing is moving faster than the speed of light. Nothing is instantaneous. I told you earlier to look this up in a text such as that of Griffith. Did you consider doing that? You can find it online. I can help you if you really want to learn about this.

Quote
However, these require that we exist in a multiverse which many (most?) people aren't comfortable thinking about.
Wrong. Youíve only come to this conclusion because you have some serious misunderstandings of quantum theory. The source of your mistake is confusing information traveling instantaneously with entangled states. It isnít and therefore there is no causality traveling instantaneously either. Any book about this topic makes this abundantly clear so I canít imagine where youíve picked this up from. Some of the things youíre saying may be meaningful to you but not to the quantum mechanics community. Hence my ďword saladĒ comment. Nothing personal. :)
« Last Edit: 24/09/2013 16:31:40 by Pmb »
 

Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #23 on: 24/09/2013 17:10:49 »
Quote from: Alan McDougall
Can Causality be violated by say instantaneous quantum entanglement?
No.

Quote from: Alan McDougall
Spooky action as Einstein called it or quantum non-locality and entanglement have shown fundamental particles can interact instantaneously regardless of the distance between them. Alter the spin of one particle alters the spin of its twin in the other direction instantaneously.
That is a misinterpretation. They do not interact instantaneously regardless of the distance between them. Thatís not what happens in quantum entanglement.

Quote from: Alan McDougall
Causality is fundamental to how the universe works, entropy for instant is intertwined with causality etc.
How so? When you make assertions like this you really need to state exactly what you mean. Just throwing two concepts together and saying theyíre intertwined with causality helps nobody. Iím not even sure that itís meaningful

Quote from: Alan McDougall
Can Causality be violated by say instantaneous quantum entanglement?
Thatís a confusing way to state that. Those two concepts donít belong side by side like that in a sentence. What you meant to ask was whether quantum entanglement can cause two events to occur instantaneously even when a finite distance separates them. If so then it will result in a violation of causality.

Quote from: Alan McDougall
Alter the spin of one particle alters the spin of its twin in the other direction instantaneously.
This is where you keep getting yourself into trouble. You seem to think that when the spin of a particle is measured then its altered by that measurement and as a result cause the spin of the other particle to take on a particular spin. This too is incorrect.

Letís get this straight once and for all. In what follows, if you attempt to rephrase this in any other way, trying to force your beliefs on how causality works, then you will be making a serious error. Quantum mechanics is hard and itís hard because of things exactly like this.
----------------------------------------------------------------------------------------------------
Quantum entanglement is a physical phenomenon that occurs when pairs (or groups) of particles are generated or interact in ways such that the quantum state of each member must subsequently be described relative to each other.

When a measurement is made on one member of an entangled pair and the outcome is thus known (e.g., clockwise spin), the other member of the pair is at any subsequent time always found (when measured) to have taken the appropriately correlated value (e.g., counterclockwise spin). Thus, there is a correlation between the results of measurements performed on entangled pairs, and this correlation is observed even though the entangled pair may be separated by arbitrarily large distances.
----------------------------------------------------------------------------------------------------

When you alter or rephrase anything above you will be making a mistake. Do not read more into what is going on in the funky world of quantum mechanics than is really there.

You keep mistaking this for action at a distance and itís not. You also keep taking this to mean that the spin of the first particle alters the spin of the other particle. This is very wrong too.
 

Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #24 on: 24/09/2013 17:16:15 »
Quote from: Skyli
I am still far from being able to say "understand QM".
Don't worry about that. Richard Feynman is famous for saying that he didn't understand quantum mechanics and that nobody does. What he meant was that it shreds your basic understanding of the world around you to peices. What there is to learn is what we can and what we can't know. If it doesn't seem very odd to you then you've missed something. :)
 

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Re: Causality is it violated by quantum entanglement?
« Reply #24 on: 24/09/2013 17:16:15 »

 

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