Causality is it violated by quantum entanglement?

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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 »
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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
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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
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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. 
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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
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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
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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 »
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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?
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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?
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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 »
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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.
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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'...

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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).

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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
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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 »
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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
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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 »
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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.

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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.
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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.
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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.

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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.
This above all else, to Thine own Self be true.

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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 »

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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.

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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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Offline dlorde

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Re: Causality is it violated by quantum entanglement?
« Reply #25 on: 24/09/2013 17:56:09 »
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. :)
I'm glad it's not just me who thought it sounded a bit hokey...

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #26 on: 24/09/2013 19:58:44 »
What the latest experiments seem to demonstrate is that there is a correlation which is faster than light but the only way we have, at least for now, is to verify it with a light signal. So in the end, we can't really observe the correlation faster than the speed of light.

It doesn't mean there is no causality faster than the speed of light, what it means is we have not find it yet and maybe it is just a trick of nature. I must say that it is not true that QM explains the mechanism of entanglement, it just tries to describe the possible outcomes. A spin has not really only two possible outcomes, up or down, it has a 360o in 3D... QM does not say much about entanglement, so the doors are still wide opened in both ways, Einstein's way and his opponents' way... Though great experiments have been done, there is still much to do to clear the confusion. On the other hand, we still don't know what mediates gravity: nothing can stop gravity... How and why?

If causality would be violated, this would be the end of the road for science. I am sure there is still a long road forward...
« Last Edit: 24/09/2013 20:08:42 by CPT ArkAngel »

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Offline distimpson

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Re: Causality is it violated by quantum entanglement?
« Reply #27 on: 24/09/2013 21:19:07 »
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.
I've seen this misinterpretation more than once. Just my opinion here, some of the technical papers use jargon that is defined in that context but can be misunderstood or misused in the magazines and TV of pop culture science where sales are top priority, teleportation and ftl always generate interest. But on the bright side, at least it gets people talking about science.

For what it's worth, the examples at this site helped make things much less spooky for me: http://www.askamathematician.com/2013/01/q-what-is-quantum-teleportation-why-cant-we-use-it-to-communicate-faster-than-light/comment-page-1/#comment-269796. I'm still wading through the math for Bell's <= for these cases.

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #28 on: 24/09/2013 21:51:00 »
Regarding the article, it is wrong to say it is teleportation because it is not proved that it has exactly the same alignment of the spin. They just know it has a spin up or down, not the precise direction of the spin. I would never go in their teleportation machine... :o)

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Offline Skyli

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Re: Causality is it violated by quantum entanglement?
« Reply #29 on: 24/09/2013 22:24:15 »
Great answer! I must admit, what I have read and tried to understand probably hasn't done my sanity much good to date, and I have no illusions about ever being anything other than an interested spectator, but it's hard to describe the field as anything but fascinating; the mother of all Mindbogglings. As luck would have it, I was extolling the site to my nephew last night and he had a couple of "Teach Yourself QM" type books. Between that and NSF I should be drooling by Christmas. Thanks.
This above all else, to Thine own Self be true.

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Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #30 on: 24/09/2013 22:36:33 »
Quote from: CPT ArkAngel
What the latest experiments ..
What "latest experiments"?

Quote from: CPT ArkAngel
..seem to demonstrate is that there is a correlation which is faster than light but the only way we have, at least for now, is to verify it with a light signal.
That's incorrect. Correlation has been demonstrated when entanglement was demonstrated. And one doesn't need faster than light signals to verfify it. One need only record the time, location and state of measurements of particles and then later correlate the data.

Quote from: CPT ArkAngel
So in the end, we can't really observe the correlation faster than the speed of light.
That's incorrect for the same reason. Where are you getting these hokey ideas from?

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #31 on: 24/09/2013 22:47:49 »
Prof Zeilinger 's team, Chinese physicists and now others have demonstrate entanglement at long distances, switching the states of detectors during the flight path of photons. They showed clearly that correlations appeared faster than the speed of light. The limitation is in the validation between the two locations where they have no way to do it faster than light. But there is still possible loopholes...

I am entirely correct!

Are you giving up causality or faster than light correlations or the possibility Einstein was right and there is still loopholes?
« Last Edit: 24/09/2013 22:51:15 by CPT ArkAngel »

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Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #32 on: 24/09/2013 22:53:59 »
Prof Zeilinger 's team, Chinese physicists and now others have demonstrate entanglement at long distances, switching the states of detectors during the flight path of photons. They showed clearly that correlations appeared faster than the speed of light. The limitation is in the validation between the two locations where they have no way to do it faster than light. But there is still possible loopholes...

I am entirely correct!
Nope. You're mistaken. You've mistaken the interpretation of this and you continue to do so. And I have no intention to keep repeating myself if you're not going to make an attempt to demonstrate that your assertions are correct rather than merely state it.

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #33 on: 24/09/2013 22:55:09 »
Open your mind a bit... I gave you 3 choices...

I just give up non causality. That's it!

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Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #34 on: 24/09/2013 22:56:34 »
Open your mind a bit...
My mind is more open than you'll ever be able to understand.

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #35 on: 24/09/2013 23:02:55 »
You seem to adopt the usual "shut up and calculate" interpretation of QM that doesn't care about the causality of the possible faster than light correlations. You say no information travel faster than light, you say there is faster than light correlations. How to reconcile both point of view? QM has absolutely no answer to that!

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Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #36 on: 24/09/2013 23:46:26 »
You seem to adopt the usual "shut up and calculate" interpretation of QM that doesn't care about the causality of the possible faster than light correlations. You say no information travel faster than light, you say there is faster than light correlations. How to reconcile both point of view? QM has absolutely no answer to that!
Your mind reading skills have a lot to be desired. lol!

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #37 on: 24/09/2013 23:55:02 »
I have no pretention that is the way you think for all physics subjects and I know you have many things on your mind.



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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #39 on: 25/09/2013 01:03:58 »
They pretend to have closed all loopholes.

If it is the case, I see 3 possibilities:

1) information can travel faster than light.

2) information can travel no faster than light but can travel backward in time, from the future to the past, pilot wave, transactional interpretation or others...

3) many worlds interpretation (multiverse).

For me, the third one is clearly science-fiction and it is equivalent to giving up causality. And I don't see how it can explain the causal relationships of these experiments.

And I just wonder what Einstein would have preferred between the first and the second one...



« Last Edit: 25/09/2013 01:12:24 by CPT ArkAngel »

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Offline dlorde

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Re: Causality is it violated by quantum entanglement?
« Reply #40 on: 25/09/2013 09:35:59 »
You say no information travel faster than light, you say there is faster than light correlations. How to reconcile both point of view? QM has absolutely no answer to that!
No information travels at all; the spin of either particle is indeterminate until a measurement is made - the only certainty is that they are opposite. This was covered in more detail on another thread. The particle pair is a single quantum object in a superposition of states; when you make a measurement on this object, you resolve which particle of the pair you're looking at, and the spin of the other is, inevitably, opposite. You could visualise it as if there are two pairs of particles of opposite spins and by a measurement you select which pair you're dealing with, or as if there's a single particle pair synchronously flipping spins, and by a measurement you stop the flipping at some random point.

All of the 3 possibilities you listed have been used in science fiction; it's not a particularly good guide to the best-fit model for our observations. The multiverse model simply fits the observations better, without the unresolved problems that other models have. Presumably you have a better reason for your objection than it's "clearly science fiction"?   
« Last Edit: 25/09/2013 09:43:25 by dlorde »

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #41 on: 25/09/2013 10:52:08 »
Your explanations is flawed and it is inspired by the Copenhagen interpretation which is simply non causal. In fact, it just stop before any causal explanation. This is exactly why the many-worlds interpretation came to existence, to give a first causal interpretation of the collapse of the wave function. The superposition is impossible to prove and the only causal interpretation that supports it is the many-worlds. If the spin is indeterminate before measurement where is the causality if not in a multiverse?

The pilot-wave theory and the transactional interpretations are not as far-fetched as you might think. Just read about it and you will understand.

The problem is most people don't really bother to look for the real proofs and just believe in unproved things, either by a lack of self-confidence, laziness or simply a lack of time. Einstein was a genius but he knew his theory was not perfect. He searched for answers until his death. He said there is no black hole singularities, people convinced him of the contrary. He said there is no gravitational waves, people convinced him of the contrary. When we will find he was right about these two things, people will say he was wrong!

Stop believing and start searching for the truth. Watch Lee Smolin talks, it is a good start.
The truth is somewhere out there...

For me, the superpositions are in our universe, they are in all other elementary particles of our universe and we will get proofs of that because it explains more things than any other interpretations and it is simpler, much simpler... In fact, we have already a large amount of circumstantial proofs, more than all other interpretations combined. Look for Pauli exclusion principle...

« Last Edit: 25/09/2013 12:03:41 by CPT ArkAngel »

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #42 on: 25/09/2013 11:49:57 »
If you read the articles on non-causal quantum eraser, you will see that they disconnected the events, meaning there is faster than light correlations. It does not mean usable information, but it is still information.

They say it is non causal but they have no proof... If it is non causal how does it respect Bell's theorem?

But in the end, they somehow admit that there might be some loopholes left, caused by the set up of apparatus.
« Last Edit: 25/09/2013 12:03:24 by CPT ArkAngel »

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Offline JP

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Re: Causality is it violated by quantum entanglement?
« Reply #43 on: 25/09/2013 17:26:41 »
ArkAnglel, you're misunderstanding what the various interpretations of QM say.  Causality implies that no information can be sent FTL.  Wavefunction collapse is not a form of information being sent, i.e. you could imagine sending a bomb a light year away and setting it off via quantum entangled particles: one here on earth, and one on the bomb.  You cannot say "I will detonate the bomb when the wavefunction collapses."  There is no way for the bomb side to know when this happens.  The only way it could know if a measurement has been done on earth is if the earth sends a signal to it saying "I just took a measurement," which would be limited by the speed of light.

Admittedly, it is "spooky action at a distance," but every interpretation of quantum mechanics involves bizarre, counter-intuitive elements because the quantum world itself is bizarre and counter-intuitive.

Furthermore, the experiment you bring up is a demonstration that our equations of QM are correct.  It doesn't imply anything about interpretations.  All the interpretations agree with the equations and all involve weirdness.  It's a personal preference which weirdness you prefer.

Copenhagen says that wavefunctions can collapse over large areas instantaneously, but this can't sent usable information without standard (light-speed-limited communication) between distant observers.  Many-worlds gets rid of this collapse problem by saying there is no collapse: the universe branches into sub-universes corresponding to the results of each measurement, so that nothing has to happen instantly over large regions.  The cost of this is saying that every possible outcome of a quantum event happens in some universe, so that there are a huge (possibly infinite) number of universes out there.  These universes also have no way of communication with each other, so we can't verify if they exist or not.  So the choice between those two really depends on whether you think that the wavefunction is some funny "thing" that exists or whether you choose to believe in a plethora of universes that we can never find. 

At the end of the day, though, interpretations are just philosophy.  Physics involves predicting measurable results and testing those.  It turns out that the mathematical formulation and predictions made for all these interpretations are the same.  So at the end of the day, it doesn't matter which interpretation you favor.

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Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #44 on: 25/09/2013 18:07:17 »
Quote from: CPT ArkAngel
You seem to adopt the usual "shut up and calculate" interpretation of QM ...
You have the bad habit of misinterpreting a great deal of what you come across and then act sarcastic to me when I try to correct you. There is no excuse for such behaviour and I'd like to ask you to please stop it!

Quote from: CPT ArkAngel
...that doesn't care about the causality of the possible faster than light correlations.
The "shut up and calculate" idea is more of a joke than anything else. It means that you need to stop worrying how the answer can be that way or what it means since it's not the purpose of the Schrodinger equation to provide those answers. To arrive at the answers that the Schrodinger equation can give you, you need to stop worrying about the metaphysics and simply apply the equation to get your result.

There is no reason to care about what you're concerned with, i.e.
"causality of the possible faster than light correlations" because it doesn't exist in quantum mechanics. The only thing that happens FTL/instantaneously is the collapse of the wave function. That collapse does not transmit anhy information so it can't transmit it FTL. Your problem in this thread is that you've made the mistake of believing that it can. Then you try to pass that misbelief on to others as if it's fact. Just pick up a decent text on quantum mechanics to see this fact.

Quote from: CPT ArkAngel
You say no information travel faster than light, you say there is faster than light correlations. How to reconcile both point of view?
They already are reconciled. Youre stuck in a world of classical mechanics and are trying to use that kind of thinking in a quantum world and are coming up with erroneous assuptions like this one. There simply isn't any problem with instantaneous collapse and sublight information transmission. If you'd stop using bad terminology, i.e. "faster than light correlations" then you  might start to understand all of this.

Quote from: CPT ArkAngel
QM has absolutely no answer to that!
There's no legitimate question about it so there doesn't need to be an answer to anything.

Pick up a copy of Introduction to Quantum Mechanics - 2nd Ed. by David Griffiths and turn to page 428 and read the following(he's talking about a spin-singlet state composed of an electron and a positron which are moving apart after a pi0 particle decays into such a system)
Quote
Does the measurement of the electron influence the outcome of the positron measurement. Assuredly it does -- otherwise we cannot account for the correlation of the data. But does the measurement if the electron cause a particular outcome for the positron? Not in any ordinary sense of the word. There is no way that the person manning the detector could use his measurement to send a signal to the person at the positron detector, since he does not control the outcome of his own measurement (he cannot make a given electron come out spin up, any more than the person at X can affect the passing shadow of the bug)... Causal influences cannot propagate faster than light, ...
That expresses the facts that I've been trying to get across to you. Now please stop escalating this to the point where this gets heated, okay?

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #45 on: 25/09/2013 22:13:39 »
You imply that no information can travel FTL. Experiments show FTL correlations, so your only response is it is non causal.

I never said you have the wrong answer. The only thing I say is that you still don't really know if information can really travel FTL.

You are making a choice of not looking at a causal explanation. Don't impose it on everybody.

If I flip a coin on earth and you flip a coin on the moon and the results are clearly somehow related, there is a causal relation.

I understand why you say it is non causal, I am not dumb. What I say is that there must be a mechanism under the hood which can be describe.

You must admit that the theories are not complete and there might be big surprises ahead.

I just think we shouldn't give up the search for causality, even if it is in the act of measurement...
« Last Edit: 25/09/2013 22:18:16 by CPT ArkAngel »

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Offline CPT ArkAngel

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Re: Causality is it violated by quantum entanglement?
« Reply #46 on: 25/09/2013 22:41:51 »
The last thing I will say about this is, I really think that particles have always determinate states, not only when you measure them. But when you measure them, you change some of these states.

If you want to understand me, you must never forget this. I am not alone on this side...

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Offline JP

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Re: Causality is it violated by quantum entanglement?
« Reply #47 on: 25/09/2013 23:40:58 »
ArkAngel, you've defined a narrow version of causality and information that makes your explanation correct.  The rest of the scientific world doesn't use those terms the same way which is why you're getting so much resistance.  Sure, the wave-function collapse, if taken literally, happens over a large area instantly and would be non-causal if it could be used to trigger a distant event.  But it can't, and so there's no paradox.  This couldn't be otherwise since the many-worlds interpretation, which you're claiming gets around the non-existent problem here makes the exact same predictions as the Copenhagen interpretation, including the causal ordering of events.

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Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #48 on: 26/09/2013 01:22:00 »
Quote from: CPT ArkAngel
You imply that no information can travel FTL.
Iím not implying it. Iím stating it as a fact in the sense that itís a law of nature, i.e. an axiom

Quote from: CPT ArkAngel
Experiments show FTL correlations, so your only response is it is non causal.
Is there a reason you keep calling this FTL correlations? Why not call it what it is? I.e. quantum entanglement?  Otherwise itís a bit misleading. E.g. suppose we put two marbles in a box, one white and one black. Then we each get to pick one marble out of the box and put it into our pockets until weíre one light hour apart. When we reach that distance we agree to take the marble out and look at it. At that time I know what color your marble is. Do you really think that this information traveled faster than the speed of light?

Quote from: CPT ArkAngel
I never said you have the wrong answer. The only thing I say is that you still don't really know if information can really travel FTL.
That doesnít explain why you keep repeating yourself when youíre telling me something I know all too well? Why havenít you ever asked me why information cannot travel faster than the speed of light? If you did then youíd learn that itís an axiom. That axiom was formulated based on the premise that if information can travel faster than the speed of light then it can be used to send information back in time and that can cause a paradox. For that reason itís assumed that it canít be done. That assumption is called an axiom and is taken very seriously. Saying that you still donít really know if information can really travel FTL[/b] is an statement based on your lack of knowledge of me.

Quote from: CPT ArkAngel
You are making a choice of not looking at a causal explanation. Don't impose it on everybody.
Hardly. I know exactly what Iím doing. Do you really think you do and why?

Quote from: CPT ArkAngel
If I flip a coin on earth and you flip a coin on the moon and the results are clearly somehow related, there is a causal relation.
Donít compare classical mechanics and quantum mechanics or youíll run into trouble.

Quote from: CPT ArkAngel
What I say is that there must be a mechanism under the hood which can be describe.
Thatís called a local hidden variable theory which has been proved wrong by experiment.

Quote from: CPT ArkAngel
You must admit that the theories are not complete and there might be big surprises ahead.

I just think we shouldn't give up the search for causality, even if it is in the act of measurement...
Let me worry about what I think. You worry about what you think, okay?

Let me ask you a question or two Ė What is your background in quantum mechanics? Have you studied it up through the undergraduate level or into the graduate level? ARE you fully versed in quantum theory or do you lack the mathematical knowledge to have studied it completely?

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Offline Pmb

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Re: Causality is it violated by quantum entanglement?
« Reply #49 on: 26/09/2013 01:23:51 »
Quote from: CPT ArkAngel
I am not alone on this side...
JP and myself have a few things in common. One of them is that we both know all too well that because a position has supporters does not mean that those supporters know the theory.