Does quantum entanglement allow information to travel faster than light?

[byron178]

Does quantum entanglement allow information to travel faster than light? http://en.wikipedia.org/wiki/Faster-than-light if you scroll down to quantum mechanics.

 

[DrChinese]

No. It "seems as if" random results (i.e. no useful information) are transmitted instantaneously, but this is not the only interpretation possible.

 

[byron178]

No. It "seems as if" random results (i.e. no useful information) are transmitted instantaneously, but this is not the only interpretation possible.

even though no information is transmitted faster than light,something must be transmitted,what is it?

 

[DrChinese]

even though no information is transmitted faster than light,something must be transmitted,what is it?

The nature of the observation and the result.

 

[byron178]

The nature of the observation and the result.

does that mean the observation and the result traveled backwards in time,because anything that travels faster than light has to deal with time travel backwards.

 

[DrChinese]

does that mean the observation and the result traveled backwards in time,because anything that travels faster than light has to deal with time travel backwards.

If you say so.

Actually the result can appear to travel backward in time. Still doesn't allow you to communicate any faster.

 

[Drakkith]

does that mean the observation and the result traveled backwards in time,because anything that travels faster than light has to deal with time travel backwards.

That depends on your interpretation of quantum mechanics.

 

[byron178]

If you say so.

Actually the result can appear to travel backward in time. Still doesn't allow you to communicate any faster.

so the result violates causality?from what i understand if something were to travel backwards in time it would violate causality,but i might be wrong and I am all ears.

 

[byron178]

That depends on your interpretation of quantum mechanics.

are you talking about the copenhagen and many worlds interpretation?

 

[Drakkith]

are you talking about the copenhagen and many worlds interpretation?

I'm not sure honestly.

 

[byron178]

I'm not sure honestly.

so does quantum entanglement travel faster than light or not?

 

[Goldstone1]

Nothing travels from A to B simultaneously over very large distances. The objects where already connected, even before anyone observation on its wave function. Determinism solves this EPR problem beautifully.

 

[byron178]

Nothing travels from A to B simultaneously over very large distances. The objects where already connected, even before anyone observation on its wave function. Determinism solves this EPR problem beautifully.

at what point does the entanglement allow to travel backwards in time?

 

[v4theory]

Here's my take on the thing.

A particle pair is created. The particles, according to a quantum description, have "opposite spin". According to "conceptions" of the particle description if you apply a magnetic field to one of the particles it will reverse it's spin. As particle pairs always have opposite spin we assume that the other particle will have opposite spin. No matter how many times we apply a field and "reverse" its spin the other particle will have opposite spin.

No matter how far the two particles are from each other or how many times we hit one of them with a magnetic field they have opposite spin when we "observe" them. When we "make" a "particle pair" and "flip one of their spin" we actally do "observe" them both to have opposite spin"

The reason I use quotation marks above is that those terms refer to analogies we use to describe activities of particles according to conceptions we have of them. They also refer to extentions of analogies to predict certain actions and the actions that are observed under the terms of the conceptions. This "particle pair spin" relationship results in extensions that imply somthing is happening that, according to some conceptions, is faster than light but according to others is not. But it's such a poorly understood field that we can't say or describe in conclusive or even consistant terms what is happening. Though not conclusive or consistant some are convincing. Convincing enough that the most advanced studies institutions fund hundreds of billions of dollars studies of them.

To whit.

Lets say that we make a pair and send one of the pair to Alpha Centari. At a time agreed upon by a person here and an observer there we apply a magnetic force to our particle of the pair and then check the spin. The observers can know the information of what the spin of the particle on Earth is faster than light could send it. But it is not meaningful information because they didn't know what the spin was was before they observed it.

Lets say they knew the spin before the test time. If the spin was left and it is still left after the test that would mean stay if it was right that would mean come back. The sender of the command would simply either apply a field to flip the spin or not depending on the information, the command, he wanted to send. That would be meaningful information. You could send billions of such particles and use it as a digital or even morse code transmitter. Can't do that unless you know what the spin was before the test.

But something happened that sent "information", of a sort, that we can't access usefully. What could it be?

Consider the conception that the particle pair is somehow connected. Say by a wire connected to both north poles. If you point both north poles up the particles are spinning in opposite directions. If you point the north poles towards each other they are spinning in the same direction. The wire between them is also spinning in the same direction. So the two particles and connecting wire can be taken as a single rotating unit. Like a pair of wheels with an axle between. If you rotate one wheel in one direction the other wheel rotates in the same direction. If you change the direction of rotation of one whele the rotation of the other changes too.

But what is the nature of this "axle"? It can't be a connection in normal space abiding by rules we think are very iron clad. It wouldn't be able to transmit the rotation information faster than light. A normal axle couldn't do it with a normal set of wheels.

Then we concieve of this "axle" or "wire" weaving "around" "space" somehow. It solves the problem. But then what is the nature of this "other space"? It is a conception to cover "observations" interpreted in the light of other "conceptions".

That's not all that can be said about it. Some people are comming up with some interesting "conceptions" that treat for this and many other things. M theory for instance, multiverses, parallel universes and time travel of several flavors are some of the unconfirmed "implications" of some "conceptions".

 

[Drakkith]

at what point does the entanglement allow to travel backwards in time?

Entanglement only causes FTL if you take the view that the two particles communicate with each other instantly when they interact. In this view the entangled particles are not in a set state. When one is measured the other one instantly knows about it. Not only that, but it seems that even when one particle is measured AFTER another particle, it can still affect the other particle even though it was measured first. It seems that the particles communicate through time. However I must point out that all this is highly dependent on a specific interpretation of Quantum Physics.

One of the other views is that the entangled particles are pre-set to their states upon being generated or initially interacting. In this case there is no communication between particles and no FTL. However, I believe that current evidence does not support this view very well.

 

[Drakkith]

No matter how far the two particles are from each other or how many times we hit one of them with a magnetic field they have opposite spin when we "observe" them. When we "make" a "particle pair" and "flip one of their spin" we actally do "observe" them both to have opposite spin

Are you sure about this? I thought that once you altered the state of one particle the two were no longer entangled. For example, if two electrons are generated and each must have opposite spins, then if you measure them you will find that they always do. But if you do something so that one of the particles gets their spin flipped, then the entanglement is broken. After the interaction both electrons could be spin up or spin down depending on what you did.

 

[DrChinese]

so does quantum entanglement travel faster than light or not?

Entangled particles remain so despite spacetime separation. When the entanglement collapses (whatever that is), it does so instantaneously and therefore defies normal spacetime constraints (i.e. c). So quantum collapse is FTL.

It is not clear when collapse occurs. There is no observation possible to discern such state. Partial collapse is possible too.

 

[DrChinese]

so the result violates causality?from what i understand if something were to travel backwards in time it would violate causality,but i might be wrong and I am all ears.

It is not possible to unambiguously interpret the situation as being "the future causes the past" but it is a possibility. I think a better description is: The results are randomly based on the context, and the context consists of both past and future components. It you can find causality in that statement, great, but I don't see it.

 

[San K]

Partial collapse is possible too.

Interesting... can you please give an example (or link to a paper) of a partial entanglement collapse?

I went through a previous discussion, on this forum, and papers cited however there was not much.

 

[pawprint]

In this view the entangled particles are not in a set state. When one is measured the other one instantly knows about it.

Has this been experimentally verified? If so can you post a reference please.

 

[Drakkith]

Has this been experimentally verified? If so can you post a reference please.

I cannot as I don't really understand it all very well.

 

[byron178]

Entangled particles remain so despite spacetime separation. When the entanglement collapses (whatever that is), it does so instantaneously and therefore defies normal spacetime constraints (i.e. c). So quantum collapse is FTL.

It is not clear when collapse occurs. There is no observation possible to discern such state. Partial collapse is possible too.

is there an interpretation in whcih entanglement does not happen faster than light?

 

[Drakkith]

is there an interpretation in whcih entanglement does not happen faster than light?

Just so you don't get confused, Entanglement is a state of the particles. The "exchange of information" is what might be happening FTL. IE photon A telling photon B that it just interacted and had to assume an X polarization.

 

[byron178]

Just so you don't get confused, Entanglement is a state of the particles. The "exchange of information" is what might be happening FTL. IE photon A telling photon B that it just interacted and had to assume an X polarization.

So what is traveling backwards in time?

 

[entropy1]

That depends on your interpretation of quantum mechanics.

I'm I correct if I state that the observing of randomness vs. correlation of twin-particles properties depends on the information you consider about the observation? (The kind of observation (measurement) you make for instance)

Would it thereby make the problem an informational one?

 

[Drakkith]

So what is traveling backwards in time?

The information. Photon A tells photon B that it has been detected and is going to X polorization and B photon should go to Y polarization. However, photon B has already been detected, so how could it know what state to be in before photon A ever tells it? Hence the information is said to travel backwards in time. (Note that this is highly dependent on your view of QM and is not "proven" yet)

I'm I correct if I state that the observing of randomness vs. correlation of twin-particles properties depends on the information you consider about the observation? (The kind of observation (measurement) you make for instance)

Would it thereby make the problem an informational one?

What do you mean?

 

[entropy1]

What do you mean?

I'm not sure. I think I mean that one can have any view on entanglement, and only has to bring up the right arguments for it.

I know very little of the matter...

 

[byron178]

The information. Photon A tells photon B that it has been detected and is going to X polorization and B photon should go to Y polarization. However, photon B has already been detected, so how could it know what state to be in before photon A ever tells it? Hence the information is said to travel backwards in time. (Note that this is highly dependent on your view of QM and is not "proven" yet) so causality is violated?

 

[v4theory]

I thought that once you altered the state of one particle the two were no longer entangled. For example, if two electrons are generated and each must have opposite spins, then if you measure them you will find that they always do. But if you do something so that one of the particles gets their spin flipped, then the entanglement is broken. After the interaction both electrons could be spin up or spin down depending on what you did.

When you measure the spin of a particle its spin changes to a random spin again. You can't know which way it will be spinning the next time you measure it. The magnetic force you apply changes the spin. The change of spin releases the energy of the force you applied and that's how we know what its spin was before we measured it. But then we don't know what it is after we measure it. When we measure the spin of the other particle of the pair we also know what its spin was before we measured it. But then its spin changes after.

But now you should notice a semi paradox. When we measure the spin of the first particle and change its spin to a random state the other particle should also assume a random state not the opposite of what the first particle's spin was before we measured it.

When we apply a magnetic force to one of the pair but don't measure the spin we concieve that the particle and its mate have both changed their spin. But when we apply a magnetic force and measure the spin the other particle doesn't change its spin until we apply a magnetic force to it and measure its spin. We find that its spin has remained opposite of the what the first particle's spin was before we measured it. Also, if we change the spin of the first particle and measure it we think we know what the spin of the other particle is. But if we apply a magnetic force on the other particle without measuring the spin of it and then measure the spin of the first particle and find its spin we can then say that the other particle is opposite and then when we measure the second particle we find that it is. Further, when we measure the spin of the first particle and find it to have been left spin and we don't measure the spin of the second. Then we apply a random number of magnetic forces on the first particle so its spin should be changing a lot randomly. Then we measure the spin of the second particle we find that its spin is opposite of what the first particle's spin was before the first time we measured it.

Wiered huh?

Particle pairs are not "two electrons" they are a particle and an anti particle.


But you should know that to make the reading of treatments like this readable I and most people who write about them have left out a lot of qualifying terms like we think, we imagine, we concieve, it appears, under the conventions of... etc.

So remember that almost everywhere we write "it is..." you remember that there is an unwritten qualifyer of some sort. In higher studies of the field you learn what and where the qualifiers are. But to simplify teaching and describing a field the qualifyers are left out. And that doesn't even mention all the people who don't even know what they are writing about. Or are writing something completely untrue.

When you learn a subject in school you rely on the impimateuer of the teaching institution to have vetted what and how a subject is being taught. So you really shouldn't rely on any Internet source for descriptions. If you gain an understanding from an Internet source that allows you to understand institutionaly vetted material then you are doing well.

If you think you understand some Internet stuff and it doesn't match institutionaly vetted stuff choose the institutional vetted stuff. Unless you have a deep enough understanding of the subject yourself to vett the Internet or even the institutional stuff yourself.

The vetting and even dismissal of institutional stuff happens all the time. Then a reputable institution after doing their own vetting changes what is taught to reflect the new conception. Usualy the changes are by students who mostly show that institutional teaching in some subject is incomplete. Sometimes they show it was in error. I've done it myself to some small degree. In fact most student papers especially doctoral thesis are additions (changes) to a teaching institution's, and sometimes many institution's teaching.

 

[SpectraCat]

When you measure the spin of a particle its spin changes to a random spin again. You can't know which way it will be spinning the next time you measure it. The magnetic force you apply changes the spin. The change of spin releases the energy of the force you applied and that's how we know what its spin was before we measured it. But then we don't know what it is after we measure it. When we measure the spin of the other particle of the pair we also know what its spin was before we measured it. But then its spin changes after.

That is not correct. If you measure the spin of a particle in some basis, then you project it into one of the eigenstates of the basis. Since eigenstates are time-independent, it remains in that eigenstate, so if you measure it again in the same basis, you get precisely the same value. You only get an indeterminate value if you rotate the angle of the measurement basis. The you cannot be sure which eigenstate of the new basis will be measured, although you can predict the relative probabilities of the two possible measurements in the new basis, based on the rotation angle between the original basis and the new one (i.e. by Malus' law).

But now you should notice a semi paradox. When we measure the spin of the first particle and change its spin to a random state the other particle should also assume a random state not the opposite of what the first particle's spin was before we measured it.

When we apply a magnetic force to one of the pair but don't measure the spin we concieve that the particle and its mate have both changed their spin. But when we apply a magnetic force and measure the spin the other particle doesn't change its spin until we apply a magnetic force to it and measure its spin. We find that its spin has remained opposite of the what the first particle's spin was before we measured it. Also, if we change the spin of the first particle and measure it we think we know what the spin of the other particle is. But if we apply a magnetic force on the other particle without measuring the spin of it and then measure the spin of the first particle and find its spin we can then say that the other particle is opposite and then when we measure the second particle we find that it is. Further, when we measure the spin of the first particle and find it to have been left spin and we don't measure the spin of the second. Then we apply a random number of magnetic forces on the first particle so its spin should be changing a lot randomly. Then we measure the spin of the second particle we find that its spin is opposite of what the first particle's spin was before the first time we measured it.

That description is almost impossible to follow .. the principles in play can be described much more clearly as follows. The key for entangled states is that they behave as a single state. A spin measurement on either particle establishes the measurement basis for *both* particles. So assuming they have been entangled such that their spins are guaranteed to be opposite, then if you measure one particle (A) in some basis and find it to be in one of the basis states (|0>), then a measurement of the other particle (B) in the same basis will *always* find it to be in the other basis state (|1>).

If you instead measure particle B in another basis that is rotated from the original basis by an angle $\theta$, then you can no longer know with certainty which state of the new basis (|0'> or |1'>) will be the result, however, you can predict the probability of observing either result .. the amazing thing is that the probability relationship is still given by Malus' law(!). In other words, if the expected result in the original basis would have been |0>, then you will have the following probabilities in the new basis:

$|0'> = cos^2\theta$
$|1'> = 1 - cos^2\theta = sin^2\theta$

If the expected result in the original basis would have been |1>, then just switch the expressions on the right-hand sides above.

One way that the principles above can be stated concisely is that there is no preferred measurement basis for an entangled pair, but instead, the measurement basis is determined by a measurement on either member of the pair.

Wiered huh?

Particle pairs are not "two electrons" they are a particle and an anti particle.

That depends completely on context .. two electrons in a singlet state are also called a pair.

 

[Goldstone1]

at what point does the entanglement allow to travel backwards in time?

That's one interpretation. Doesn't make a lot of sense to talk about superluminal waves of information - as I said, think more deterministic. Think also there is no separation between the particles to begin with. These particles can quite easily be said to be the same in every way, and whatever happens on one of them, will effect the other because the information is written into spacetime itself. Introducing waves of information that are oscillating through the imaginary time dimension is just inconvenient or even superfluous, as we are never seen such superluminal stystems in nature. Well... we've observed Cherenkov Radiation, but I am unsure too much about those experiments to make much sense of talking about right now.

 

[San K]

You only get an indeterminate value if you rotate the angle of the measurement basis.

interesting new information. thanks Spectra.

You mean: we can change a photon from determinate to ("partial/probabilistic) indeterminate by changing the angle of the polarizer from zero to some degrees?

I have a feeling that this property has application in (understanding) DCQE...(in addition to/over and above the sub-sampling)

 

[byron178]

That's one interpretation. Doesn't make a lot of sense to talk about superluminal waves of information - as I said, think more deterministic. Think also there is no separation between the particles to begin with. These particles can quite easily be said to be the same in every way, and whatever happens on one of them, will effect the other because the information is written into spacetime itself. Introducing waves of information that are oscillating through the imaginary time dimension is just inconvenient or even superfluous, as we are never seen such superluminal stystems in nature. Well... we've observed Cherenkov Radiation, but I am unsure too much about those experiments to make much sense of talking about right now.

what is the interpretation in which entanglement does not travel backwards in time?

 

[byron178]

anyone...?

 

[Drakkith]

Have you tried looking up more info elsewhere? I'm sure a simple google or wikipedia search would yield plenty of info.