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Author Topic: Causality is it violated by quantum entanglement?  (Read 14636 times)

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...
 

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 »
 

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.
 

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)
 

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.
 

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?
 

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 »
 

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.
 

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!
 

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.
 

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!
 

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!
 

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.

 


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 »
 

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 »
 

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 »
 

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 »
 

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.
 

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?
 

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 »
 

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...
 

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.
 

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?
 

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.
 

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Re: Causality is it violated by quantum entanglement?
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