Does quantum entanglement allow information to travel faster than light?

[DevilsAvocado]

It looks like you and I are entangled, because all that comes out is random noise...

Where did I say that "faster than light happens"...??

NO, KEIN, AUCUNE, NINGUNO, НИКАКОЙ, NULLUM, NÃO faster than light communication is ever never possible!

The thing you’re fishing for "travel backwards in time", is more than a dead parrot (if you ask me), because then you will have to violate http://en.wikipedia.org/wiki/Causality_(physics)" , i.e. you travel back in time and kill your grandfather before he meets the your grandmother, and then you will never exist, thus you couldn’t do the time travel in the first place, so on and so forth.

The ONLY thing traveling in quantum entanglement is the photons at the speed of light. They are 'interconnected', in sharing the same http://en.wikipedia.org/wiki/Wave_function" . No one has ever seen the wavefunction. In current science – it’s just a 'virtual' mathematical tool.

But let’s pretend that the wavefunction does exist, like a 'rubber band' that gets stretched between two 'balls' (photons). Now, if you cut a rubber band in half – would you say it has "traveled" in any direction??

 

[Duplex]

so your saying when faster than light happens it will travel backwards in time and this happens with entanglement? i ask because alice receives the message -1.but doesn't something have to travel backwards in time since something is happening faster than light?

If you still hold out for traveling backwards in time after all the qualified answers in this thread, I am afraid you at least have to wait for a Kaluza-Klein type of a curled extra time dimension to be discovered in the future and brought into mainstream science.

No, I'm not saying that time travel backwards is possible in the future.
The only thing we know about the future physics is the possibility to discuss it in PF - in the future.

 

[Drakkith]

so your saying when faster than light happens it will travel backwards in time and this happens with entanglement? i ask because alice receives the message -1.but doesn't something have to travel backwards in time since something is happening faster than light?

Ok, let me try to explain this. IF it turns out that entangled particles communicate instantly and are able to tell each other what to do even after one has alrady been detected, then yes, it would be "time travel" in the sense that particle A gets detected BEFORE particle B, yet the path that B takes determines what A can do after it is already detected.

However it is NOT proven beyond reasonable doubt that this is what's happening. And even if it is, we have no way of sending signals between two people at a greater speed than c. Please, there is NO way to say either way at this point, so there is no reason to continually ask whether or not time travel is happening. Your better off forgetting about the whole matter in my opinion.

 

[Breakout Hit]

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.

Pretty sure they both change, its what Einstein called "spooky action at a distance." Believe it peeved him because it implied travel of something at faster than the speed of light. I could be wrong but that's how I remember it...

 

[Drakkith]

Pretty sure they both change, its what Einstein called "spooky action at a distance." Believe it peeved him because it implied travel of something at faster than the speed of light. I could be wrong but that's how I remember it...

If so, I haven't seen anything that implies that yet. The only thing that comes close to my limited knowledge is some experiments where they measured the averages of different properties of entangled particles, where the probabilities of each should have been equal. It turned out that measuring two particular properties were different than two other properties even though they should have been about the same. I can't remember exactly which is why I say I haven't seen anything yet.

 

[byron178]

Ok, let me try to explain this. IF it turns out that entangled particles communicate instantly and are able to tell each other what to do even after one has alrady been detected, then yes, it would be "time travel" in the sense that particle A gets detected BEFORE particle B, yet the path that B takes determines what A can do after it is already detected.

However it is NOT proven beyond reasonable doubt that this is what's happening. And even if it is, we have no way of sending signals between two people at a greater speed than c. Please, there is NO way to say either way at this point, so there is no reason to continually ask whether or not time travel is happening. Your better off forgetting about the whole matter in my opinion.

is it time travel backwards?

 

[Drakkith]

is it time travel backwards?

What do you think?

 

[DevilsAvocado]

* sigh *

backward contemplating

 

[byron178]

What do you think?

no i do not.

 

[Drakkith]

no i do not.

Could you elaborate a bit? What exactly are you saying?

 

[byron178]

Could you elaborate a bit? What exactly are you saying?

i thought entangled particles were proven to communicate instantly?

 

[Drakkith]

i thought entangled particles were proven to communicate instantly?

Have you actually read anything that has been posted? There isn't any proof beyond reasonable doubt that proves anything yet.

 

[bobc2]

It's not about entangled particles communicating with each other. There is a system wave function for the two particles. In QM you only consider particles after the wave function collapses. The Schroedinger wave evolves with time over extended space. So, don't think about one point in the wave causing anything to happen at another point (and certainly not one particle causing something to happen with another particle--it's all about a traveling wave).

But, when a measurement is performed (Bohr Copenhagen interpretation) the wave function collapses. Now, here is the problem. QM has no physical description of what exactly happens in transforming from a probability amplitude wave to a particle showing up in some state at a particular point. There's no communication between particles. The resulting states of two particles showing up at distant locations is strictly a result of the Schroedinger probability amplitude wave and its collapse.

Of course different physicists have had different interpretations of the mysterious wave collapse. Roger Penrose seems to think the wave function should be regarded as the objective reality. Hawking is probably more of a Copenhagen guy. Then there is Hugh Everett who thought there had to be a physical explanation for the wave collapse and came up with the many worlds concept.

In any case there is no faster-than-light information transfer from one point to another.

 

[edpell]

I have read this whole thread and am lost. Let me give an example. We have a process that emits two photon in opposite directions with opposite spins. One travels to the left and on to the right.

1) The observers on the left measure the spin in the up/down direction and finds half the time it is spin up and half the time it is spin down. Like for spin in the direction 90 degree from up/down. OK this poses no surprise no paradox.
2) Much later the observer on the right makes the same measurements and get the same results. No surprise no paradox.
3) Now we have both observers make up/down spins measures at the same time (or at times separated by less than distance between them divided by the speed of light). Each measures spin up 50% of the time no surprise no paradox. When we bring the list of results to one central location and compare them we see that they are always opposite. Again no surprise no paradox.

The thing that upsets people is that the observer on the left know the result that the observer on the right is getting before light can travel between the two observers. Why is this upsetting?

Lets image a different experiment a central person has a supply of tiles labeled with A and a supply labeled with B and a supply of boxes. They place at random a tile in a box that will be sent to the left and the other type tile in the box that will be sent to the right. When both boxes arrive both observers open their box at the same time. The observer on the left knows the result that the observer on the right is getting even before light can travel between the two. This is no surprise and no paradox. So why is the photon experiment upsetting?

 

[SpectraCat]

I have read this whole thread and am lost. Let me give an example. We have a process that emits two photon in opposite directions with opposite spins. One travels to the left and on to the right.

1) The observers on the left measure the spin in the up/down direction and finds half the time it is spin up and half the time it is spin down. Like for spin in the direction 90 degree from up/down. OK this poses no surprise no paradox.
2) Much later the observer on the right makes the same measurements and get the same results. No surprise no paradox.
3) Now we have both observers make up/down spins measures at the same time (or at times separated by less than distance between them divided by the speed of light). Each measures spin up 50% of the time no surprise no paradox. When we bring the list of results to one central location and compare them we see that they are always opposite. Again no surprise no paradox.

The thing that upsets people is that the observer on the left know the result that the observer on the right is getting before light can travel between the two observers. Why is this upsetting?

Lets image a different experiment a central person has a supply of tiles labeled with A and a supply labeled with B and a supply of boxes. They place at random a tile in a box that will be sent to the left and the other type tile in the box that will be sent to the right. When both boxes arrive both observers open their box at the same time. The observer on the left knows the result that the observer on the right is getting even before light can travel between the two. This is no surprise and no paradox. So why is the photon experiment upsetting?

You are correctly expressing the relationships between the information gained by the humans making the measurements. The question that vexes people who ask this sort of question (I know because I was once one of them) is not so much about the information the humans are getting, but whether or not the collapse of the entangled state itself somehow involves FTL information transfer. Before either person has made a measurement, the entangled wavefunction extends over a huge distance. At the instant one person makes a measurement, the wavefunction collapses, and *somehow*, the two results end up being properly correlated (or anti-correlated) 100% of the time (according to predictions of QM, and the idealized versions of the experiments that have been done to test this). What people are discussing is how that can possibly happen without some FTL information transfer between the particles.

 

[Drakkith]

I THINK it is because in an experiment which I can't remember the name of, they measured the value of a particular property or direction, and found that when they measure that one AND another one together, the chance that it was in a particular value or state was NOT what it was supposed to be for pure chance.

 

[bobc2]

My previous post seems to have not been communicated clearly. I think you guys are missing the point--it's about the wave function. Don't look to some magical communication from one point to another for the answer as to why the two particles always have a particular combination of states after the wave function collapses, i.e, maintains an Up and a Down for example. Again, there is no communication between the individual particles.

It's the wave function, and you must understand the wave function for a system of two particles in this case. The wave function represents the entangled combination of two particles. It's the combination of particles making up a global system that produces a system wave function. Thus, when the wave function collapses, it produces a specific allowed combination of particles, which again satisfy a global system state. No communication from point to point. Just a system wave function collapsing into an allowed system state, such as an Up at one location and a Down at the other location.

Again, the physics of Quantum Mechanics has absolutely no description of the mechanism of the collapse itself. Before collapse you have a wave function--after collapse you have a system of particles.

 

[Drakkith]

I understand you bob. That makes sense.

 

[SpectraCat]

My previous post seems to have not been communicated clearly. I think you guys are missing the point--it's about the wave function. Don't look to some magical communication from one point to another for the answer as to why the two particles always have a particular combination of states after the wave function collapses, i.e, maintains an Up and a Down for example. Again, there is no communication between the individual particles.

It's the wave function, and you must understand the wave function for a system of two particles in this case. The wave function represents the entangled combination of two particles. It's the combination of particles making up a global system that produces a system wave function. Thus, when the wave function collapses, it produces a specific allowed combination of particles, which again satisfy a global system state. No communication from point to point. Just a system wave function collapsing into an allowed system state, such as an Up at one location and a Down at the other location.

Again, the physics of Quantum Mechanics has absolutely no description of the mechanism of the collapse itself. Before collapse you have a wave function--after collapse you have a system of particles.

Sorry, but that's not an answer to the problem ... at least not any more than, "it just happens that way" or "it's MAGIC" is an answer. The fact is that we simply don't know the details right now .. all we can do is describe the predictions of QM, and the experimental results, which seem to agree based on the experiments that have been done in this area by Aspect, Zeilinger and others.

You are correct that QM has no description of how the collapse occurs, but that's just avoiding the question. The question of how the collapse happens is a legitimate one ... because it certainly seems right now that it might have to happen in a way that violates relativity. The other answer that is commonly given is, "QM is non-local", but again, that is not really an answer of how, or even whether or not, the breaking of entanglement avoids requiring FTL transfer of information.

 

[Drakkith]

Spectra, do you know the experiment(s) where they showed the effect I mentioned up a few posts ago? Something to do with Bells theorem or something?

 

[DevilsAvocado]

The thing that upsets people is that the observer on the left know the result that the observer on the right is getting before light can travel between the two observers. Why is this upsetting?

Lets image a different experiment a central person has a supply of tiles labeled with A and a supply labeled with B and a supply of boxes. They place at random a tile in a box that will be sent to the left and the other type tile in the box that will be sent to the right. When both boxes arrive both observers open their box at the same time. The observer on the left knows the result that the observer on the right is getting even before light can travel between the two. This is no surprise and no paradox. So why is the photon experiment upsetting?

That’s a good question. The 'setup' you describe is the one that was discussed by Niels Bohr and Albert Einstein for many years, starting with the 1935 EPR paper.

In 1964 John Bell formulated Bell's inequality, which shows that there are more 'subtle' values to gain from the EPR experiment, i.e. not only so called perfect correlations, i.e. 100% up/down (or A/B). There are several cases where the 'correlation rate' is spread over the full 'probability spectrum', i.e. 0-100%.

Please have a look at https://www.physicsforums.com/showpost.php?p=2833234&postcount=1241" for a fairly easy explanation, the example by Nick Herbert starts halfway down the post.

 

[Drakkith]

Devils, do you have a good link to experiments that show this by chance?

 

[DevilsAvocado]

ehh, do you mean my specific example or EPR-Bell test experiments in general (the most 'famous')?

 

[Drakkith]

ehh, do you mean my specific example or EPR-Bell test experiments in general (the most 'famous')?

One that shows the discordance discussed in the post you linked.

 

[DevilsAvocado]

One that shows the discordance discussed in the post you linked.

Aha! That’s what I suspected... This is of course a thought experiment, and I’m sorry to say I can’t give you a link to an experimental setup exactly like this... The original text by Nick Herbert is here:

A SIMPLE PROOF OF BELL'S THEOREM
http://quantumtantra.com/bell2.html

The closest I can think of when it comes to experiments, is Alain Aspect’s famous 1982 experiment (link to DrC):

A. Aspect, Dalibard, G. Roger: "Experimental test of Bell's inequalities using time-varying analyzers" Physical Review Letters 49 #25, 1804 (20 Dec 1982)
http://www.drchinese.com/David/Aspect.pdf

DrChinese has an excellent site with a lot of info:
http://www.drchinese.com/David/EPR_Bell_Aspect.htm

If I should add something, maybe this:

Entangled photons, nonlocality and Bell inequalities in the undergraduate laboratory
http://arxiv.org/abs/quant-ph/0205171

QuantumLab
http://www.didaktik.physik.uni-erlangen.de/quantumlab/english/

Experimental demonstration of quantum correlations over more than 10 km
http://arxiv.org/abs/quant-ph/9707042

Testing spooky action at a distance
http://arxiv.org/abs/0808.3316

Bell test experiments
http://en.wikipedia.org/wiki/Bell_test_experiments

Quantum Entanglement Experiment

https://www.youtube.com/watch?v=c8J0SNAOXBg

 

[Drakkith]

Whew, I'll have to take a bit and look at all this. Thanks Devils!

Edit: Ugh, can't look at half of that from work here. I'll have to look at home I guess.

 

[DevilsAvocado]

Welcome!

 

[bobc2]

Sorry, but that's not an answer to the problem ... at least not any more than, "it just happens that way" or "it's MAGIC" is an answer. The fact is that we simply don't know the details right now .. all we can do is describe the predictions of QM, and the experimental results, which seem to agree based on the experiments that have been done in this area by Aspect, Zeilinger and others.

You seem to keep missing the point. After you made the comment about the wave function spreading out over space in an earlier post, I thought you would understand that the wave function provides the state information for the particles at the instant of collapse, which answers the problem of Faster-Than-Light communication from particle to particle. Just because QM does not provide a detailed description of the collapse mechanism does not take away from the physics of the global wavefunction.

Our problem is still fundamentally the mystery of the two slit experiment. The entanglement issues all spring from that fundamental phenomena. After all of these decades (going all the way back to Planck and Einstein's papers around the turn of the 20th century) physics still does not answer the fundamental questions about the dual particle and wave properties of photons, electrons, muons, taus, Up quarks, Down quarks, Strange quarks, Charmed quarks, Top quarks and Bottom quarks--much less the entangled coherent combinations of these elementary particles forming complex systems.

I am certainly not the one who will unravel this fundamental mystery and was not trying to in my post, and I don't expect to see it unraveled on this forum--but I'll be cheering on any honest efforts.

But I still maintain that you are missing the point of the global character of the wave function that produces a system of coherent particles at the instant of collapse (in other words, don't look for Faster-Than-Light communication between the particles--the wave function already had that taken care of that--even if we don't understand the mechanism).

 

[DevilsAvocado]

... because it certainly seems right now that it might have to happen in a way that violates relativity.

Spectra, you do mean Relativity of Simultaneity (RoS), right?


EDIT:

... What people are discussing is how that can possibly happen without some FTL information transfer between the particles.

... but again, that is not really an answer of how, or even whether or not, the breaking of entanglement avoids requiring FTL transfer of information.

IMHO, it’s maybe a little bit 'risky' to use the words "FTL" and "information"... some reader might get the wrong impression...

It’s completely impossible to send any information from Alice to Bob, or vice versa, utilizing QM Entanglement. All we’ll ever get is random noise, in both 'ends'. There is not even a way to know if a measurement has been performed in the other 'end', or not. Everything that is 'weird' about entanglement is established after the measurements, at or below the speed of light.

Hence, FTL is completely out of the question.

I agree though, that the shared (global) wavefunction (between Alice and Bob) seems to collapse instantaneously, and it has been proven that the speed of this "spooky influence" would have to exceed that of light by at least 4 orders of magnitude. Still, this is not the 'usual' FTL we are talking about...

 

[SpectraCat]

Spectra, you do mean Relativity of Simultaneity (RoS), right?


EDIT:




IMHO, it’s maybe a little bit 'risky' to use the words "FTL" and "information"... some reader might get the wrong impression...

It’s completely impossible to send any information from Alice to Bob, or vice versa, utilizing QM Entanglement. All we’ll ever get is random noise, in both 'ends'. There is not even a way to know if a measurement has been performed in the other 'end', or not. Everything that is 'weird' about entanglement is established after the measurements, at or below the speed of light.

Hence, FTL is completely out of the question.

I agree though, that the shared (global) wavefunction (between Alice and Bob) seems to collapse instantaneously, and it has been proven that the speed of this "spooky influence" would have to exceed that of light by at least 4 orders of magnitude. Still, this is not the 'usual' FTL we are talking about...

Yes .. I should not have used "information" at all, even though I was careful to qualify that I was talking about "information" between the quantum particles, not anything that is accessible to Alice or Bob. It's better scientifically to just say that the nature of the collapse is not understood and leave it at that ... but the problem is that the real significance of that kind of phrasing is rather subtle, and you need to have more than a lay-persons familiarity with quantum mechanics to understand what is being said.