Why does quantum entanglement not allow ftl communication

[DrChinese]

Agreed. But this leaves the question of how the entangled particles "know" what to do. If the correlation can't be explained in terms of a past interaction, I don't see how you can ever escape from "what I do over hear influences what happens over there". I think that's the whole point of Bell's theorem. It's not that hidden variables must be non-local, but any theory explaining this must be non-local.

Welcome to PhysicsForums, unified!

You've probably seen some of the different interpretations that are currently in play. Of course the Bohmian view should be right up your alley. There are several others, including the time symmetric group. In those, the mantra is: "what I do now affects the past" and locality is preserved in the sense that influences do not propagate faster than c.

 

[questionpost]

quite simply the above question.
Why does quantum entanglement not allow for faster than light communication?
Thanks

They are the same particle, there's nothing to send information between. It would be like bouncing a ball and asking "why aren't other balls magically bouncing now?"

 

[unified]

Welcome to PhysicsForums, unified!

You've probably seen some of the different interpretations that are currently in play. Of course the Bohmian view should be right up your alley. There are several others, including the time symmetric group. In those, the mantra is: "what I do now affects the past" and locality is preserved in the sense that influences do not propagate faster than c.

Thanks for the welcome!

I've actually been reading your posts for quite some time now. I thought we could have some good talks. I'm not so interested in alternative theories to quantum mechanics, with the single exception of Bohmian Mechanics. I sometimes wonder why there are so few Bohmians. Bell thought it was almost scandalous. More interesting than Bohmian mechanics to me is the question of non-locality in quantum mechanics. Is it local? The most interesting thing I've come across lately is William Unruh, who is no fringe scientist. He makes the argument that quantum mechanics is completely local, and that there can be a simple answer to my question, "how do the electrons" know what to do. He explains everything in terms of past interaction, which confuses me because I thought the point of Bell's theorem is that this explanation is wrong. Unruh, though, certainly understands this theorem better than I do. Link included below.

Also, I would like to mention that I have never, ever come across someone who said quantum mechanics was non-local who was NOT also pursuing realistic theories, eg. Bohmian mechanics, GRW, etc. I suppose it's possible that this biases their opinions on quantum mechanics. Bell, surely could fall into this category.

 

[J Edwin Gray]

I find this subject interesting, If two particles were really entangled and mirrored each others patterns, in order to prove they are not just reacting on a past interaction. you would have to separate them by elevation for instance for several weeks for enough time has gone by that time dilation can be observed. After this time if the two particles are brought together and they are still in-sync they have been in active communication and not repeating a pattern. Is this an adequate experiment?

 

[San K]

I am pointing out the distinct difference between "random information" and
"no information" according to Shannon's information theory.

Hans, if something is truly random then how can it have/carry information?

Can you send any references/link/papers that distinguish between the two categories mention above?

 

[audioloop]

I find this subject interesting, If two particles were really entangled and mirrored each others patterns, in order to prove they are not just reacting on a past interaction. you would have to separate them by elevation for instance for several weeks for enough time has gone by that time dilation can be observed. After this time if the two particles are brought together and they are still in-sync they have been in active and not repeating a pattern. Is this an adequate experiment?

can delve it more ?

 

[J Edwin Gray]

I am relatively new to the forum but as a researcher and amateur scientist please forgive me for not quoting information for this is my first attempt in joining a conversation with what would seem more educated individuals than myself.

(By pattern I mean anything observable that would indicate the particles or structures are in sync.)


From some of the earlier post in this string of discussion it would seem as though there is a question of if the entangled particles actually are in constant communication mirroring each other in a form observable or if it is a pattern like that of two in-sync machines behaving off of a past interaction or setting.

I do not know if Shannon's theory of information can be used for this sort of information structure but in the before mentioned experiment (current abilities of science may not suffice) if the two particles or atomic structures were in communication be it random or ordered information it will be in-sync proving information transference , even random information is transferred. If it is not in sync and the patterns are identical it is not random information at all but a complex pattern we can not understand because if it is truly random the information would be different from both particles.

Both outcomes would advance a study but I would much rather see them in sync for the probability of structured information transmission in an instantaneous manner.

With time dilation in mind the pattern would occur faster for the particle in a reference frame with more time dilation, the observer would see it happen faster than the observer that is in a more rested frame (lower elevation) or it could be opposite. The possibility of a parent particle influencing another may be true. One particle may follow a specific one of the pair or would they produce a mean frequency of the both?

This is theoretical and I do not know if any such experiment has been performed as of yet but it would shed some light on the subject.

As to the idea that the constant velocity of light is broken it is not broken unless it travels in a quanta of space faster than the speed of c when this signal or transference of information is instantaneous. Take Plank's constant for instance of the smallest measurable distance, is is similar to a node in space time, distance is a number but nothing says one node cannot communicate with anther node some distance away. This is another theoretical view but if it skips a quanta of space time then it did not travel it appeared to travel instead. This keeps the constant max velocity of c without breaking any accepted laws. I could say more on this idea of node like theory of the space time fabric or structure but maybe for another discussion and not this thread.

 

[DrChinese]

I am relatively new to the forum but as a researcher and amateur scientist please forgive me for not quoting information for this is my first attempt in joining a conversation with what would seem more educated individuals than myself.

(By pattern I mean anything observable that would indicate the particles or structures are in sync.)


From some of the earlier post in this string of discussion it would seem as though there is a question of if the entangled particles actually are in constant communication mirroring each other in a form observable or if it is a pattern like that of two in-sync machines behaving off of a past interaction or setting.

I do not know if Shannon's theory of information can be used for this sort of information structure but in the before mentioned experiment (current abilities of science may not suffice) if the two particles or atomic structures were in communication be it random or ordered information it will be in-sync proving information transference , even random information is transferred. If it is not in sync and the patterns are identical it is not random information at all but a complex pattern we can not understand because if it is truly random the information would be different from both particles.

Both outcomes would advance a study but I would much rather see them in sync for the probability of structured information transmission in an instantaneous manner.

With time dilation in mind the pattern would occur faster for the particle in a reference frame with more time dilation, the observer would see it happen faster than the observer that is in a more rested frame (lower elevation) or it could be opposite. The possibility of a parent particle influencing another may be true. One particle may follow a specific one of the pair or would they produce a mean frequency of the both?

This is theoretical and I do not know if any such experiment has been performed as of yet but it would shed some light on the subject.

As to the idea that the constant velocity of light is broken it is not broken unless it travels in a quanta of space faster than the speed of c when this signal or transference of information is instantaneous. Take Plank's constant for instance of the smallest measurable distance, is is similar to a node in space time, distance is a number but nothing says one node cannot communicate with anther node some distance away. This is another theoretical view but if it skips a quanta of space time then it did not travel it appeared to travel instead. This keeps the constant max velocity of c without breaking any accepted laws. I could say more on this idea of node like theory of the space time fabric or structure but maybe for another discussion and not this thread.

I am not sure there is a specific question in here, but I can comment.

Experiments have been performed to attempt to determine the time sequencing of entanglement. The current lower bound on the speed of entanglement is 10^4 c (10,000 times the speed of light). Quantum theory does not give time or distance parameters as part of an entangled state description. So the "communication" is presumed to be instantaneous. Actually, that is not even a good term when you get down to it. The "communication" can depend on future events and in fact does not even need to be between particles that existed at the same time. So normal concepts of temporal sequence do not apply.

http://arxiv.org/abs/0808.3316
Lower limit of spooky action at a distance

http://arxiv.org/abs/quant-ph/0201134
Particles can be entangled after they are detected

 

[audioloop]

(By pattern I anything observable that would indicate the particles or structures are in sync.) From some of the earlier post in this string of discussion it would seem as though there is a of if the entangled particles actually are in mirroring each other in a form observable or if it is a pattern like that of two in-sync behaving off of a past interaction or setting.

mirrored because of collapse ?
after the collapse the englament is broken.

With time dilation in mind the pattern would occur faster for the particle in a reference frame with dilation, the observer would see it happen faster than the observer that is in a more rested frame (lower elevation) or it could be opposite.
This is theoretical and I do not know if any such experiment has been performed as of yet but it would shed some on the subject.

in a relativistic scheme.
done.

Experimental test of nonlocal quantum correlation in relativistic configurations
in/and
http://arxiv.org/abs/quant-ph/0007009-----
and if you ask for the speed of collapse itself (per se, not entanglement time), that is another question.

 

[audioloop]

I do not know if 's theory of information can be used for this sort of information structure but in the before mentioned experiment (current abilities of science may not suffice) if the two particles or atomic structures were in communication be it random or ordered information it will be in-sync proving information transference , even random information is transferred. If it is not in sync and the patterns are identical it is not random information at all but a complex pattern we can not understand because if it is truly random the information would be different from both particles.

Both outcomes would advance a study but I would much rather see them in sync for the of structured information transmission in an instantaneous manner.

you wish to explain or justify the correlations ?

 

[GwtBc]

I'm not a professional physicist, neither am I very familiar with quantum physics, so the following question might seem silly to you. Suppose there were two side, a and b, that wanted to relay information using quantum entanglement. They have two pairs of entangled particles, one to send information from a to b and one to send data from b to a. They agree that if they wanted to communicate information they would increase or decrease the spin rate of their transmission particle, the other side would constantly monitor their receiver particle for changes in it's spin rate. Could information, in binary form, be communicated using this method?

 

[Vanadium 50]

Did you read this thread? This very thing (it's spin direction, not rate, BTW) is discussed. If there is something you didn't understand, please point it out.

 

[GwtBc]

Did you read this thread? This very thing (it's spin direction, not rate, BTW) is discussed. If there is something you didn't understand, please point it out.

Sorry the spin rate issue was caused by a blunder.

 

[DrZoidberg]

Here is an interesting talk that explains in detail what would happen if you tried to use entangled particles to send information.

 

[Hamzaa]

What if there was a measurable speed for the transfer of information about the state of an entangled particle that we simply haven't calculated yet?

 

[DrChinese]

What if there was a measurable speed for the transfer of information about the state of an entangled particle that we simply haven't calculated yet?

Welcome to PhysicsForums, Hamzaa!

Assuming you are referring to the speed of collapse of entanglement, otherwise believed to be instantaneous: this has been measured to occur no less than 10,000 c.

http://arxiv.org/abs/0808.3316

 

[StrangeCoin]

Correlations can still be preserved even by measurements like that.

Correlations. How is some probability percentage between two binary streams of data supposed to contain such information to lead us into all these metaphysical conclusions we somehow indirectly infer from it? Shouldn't we label it as "inconclusive", rather than jump to such extreme conclusions standing in contradiction with the rest of the physics?

 

[DrChinese]

Correlations. How is some probability percentage between two binary streams of data supposed to contain such information to lead us into all these metaphysical conclusions we somehow indirectly infer from it? Shouldn't we label it as "inconclusive", rather than jump to such extreme conclusions standing in contradiction with the rest of the physics?

What is inconclusive? Metaphysics is only involved when trying to interpret the known (and predicted) results.

 

[StrangeCoin]

What is inconclusive?

Correlations, the experiments. Two polarizers are set to 30 degrees relative angle and we measure some probability percentage of 25%. Then we set them to 60 degrees apart and we measure 75%. Then we go like, wow 75%, that number means photons are communicating faster than light! To me that sounds like a pretty big leap to unnecessary conclusion. Based on what logic we ever expected to get any other number but 75% in the first place?

 

[DrChinese]

Correlations, the experiments. Two polarizers are set to 30 degrees relative angle and we measure some probability percentage of 25%. Then we set them to 60 degrees apart and we measure 75%. Then we go like, wow 75%, that number means photons are communicating faster than light! To me that sounds like a pretty big leap to unnecessary conclusion. Based on what logic we ever expected to get any other number but 75% in the first place?

And that correlation alone does not prove FTL influences.

But add Bell's Theorem, and you now know that either there are FTL (nonlocal) influences OR that particles do not have well determined properties outside of the context of a measurement (contextuality or nonrealistic). Could be either (or both). So it depends on which interpretation of QM you choose to adhere to. Many Worlds or Bohmian Mechanics are examples interpreting differently. Both follow Bell. You merely have to decide *which* classically intuitive idea you wish to abandon. There is nothing inconclusive about needing to drop one or the other.

 

[StrangeCoin]

But add Bell's Theorem, and you now know that either there are FTL (nonlocal) influences OR that particles do not have well determined properties outside of the context of a measurement (contextuality or nonrealistic).

Is that the same thing as non-deterministic vs. deterministic, or quantum vs. classical physics?

Could be either (or both). So it depends on which interpretation of QM you choose to adhere to. Many Worlds or Bohmian Mechanics are examples interpreting differently. Both follow Bell. You merely have to decide *which* classically intuitive idea you wish to abandon. There is nothing inconclusive about needing to drop one or the other.

I didn't know Bohmian Mechanics was considered as equally valid theory. I know of Bohmian Mechanics interpretation of double-slit experiment, but I've never seen anything like that for these types of experiments about quantum entanglement. Is Bohmian Mechanics deterministic, or maybe probabilistic, theory, and is there actually any difference between these two types of "determinism"?

 

[DanCarpenter]

Nor am I a professional physicist, but if you will look at my recent post, I'm sure you will be interested. It deals with the practical application of quantum entanglement in communication

 

[PhysicalArch]

What is the main reason to think that there has to be state transfer? In other words What is the main reason to think that relationship of entangled particles is not simply hidden until the measurement?

 

[bhobba]

In other words What is the main reason to think that relationship of entangled particles is not simply hidden until the measurement?

That's a valid view.

You will find a lot of hidden assumptions of that sort in discussions of EPR type stuff.

That's why it was important Bell came up with his theorem, because it puts it on a sound basis devoid of semantics.

Thanks
Bill

 

[PhysicalArch]

I got huge problem with QM because i know little math.
Bit more complicated algebraic equation and I don't even try to read it.

QM seems to go deep in laws that differ from ones that our minds evolved for.
Example - if we learn Newtonian physics, we learn maybe one new concept at a time. Few individual concepts don't make good insight but because it explains phenomena of everyday movement we can map it on previous knowledge, fill gaps with intuition. That is nice and natural way to learn.

Then history takes a turn and we have to learn laws that need lot more work to fit in our intuitive world view.

R.Feynman explained this very nicely in one of his interviews.
Maybe only reason QM is hard is that it is too new and too different mind model from anything before.

How did pioneers got so far so quick, when huge masses of people do way worse on already obtained and explained laws of quantum physics? Even Einstein had much more problem with it than bit more involved researchers.

That is good question to answer not only for benefit of QM research but for understanding of ourselves. What does it mean to learn something most unrelated to your basic knowledge.

For me answer to that comes almost easy. Critical thinking has been slowly developed for millennia, marginalized as useless overthinking or simply philosophy.
To truly know something at its full depth you have to be able to investigate in steps like these:

• What what is it that makes something different from similar things.
• Is that sufficient to make it essentially different or does it only change the name
• How is it, in a way, essentially the same as other different things with different names and functions

It can be hard time consuming work to understand everything like that. We probably do that only with most important things in our lives (hopefully). We can get thru everyday life with recognition of general situations we are in and what premade optimized thought should be used. Deeper investigation of things naturally is left for very stressful or curiously playful situations.

For QM pioneers there were two factors that made it exceptionally easy to learn:

1. Deeper knowledge. As it was top cutting edge science, They had to find and check everything new by themselves. It was impossible for them to do easy thing and use pre-made concepts.
2. As it was their life work with real possibility of gaining global recognition, they were strongly motivated to the strongest research possible.

After few loudest discoveries everyone's motivation diminished. Not only because there was less to discover but because fame got harder to attain. Disagreement between interpretations indicates that depth of understanding differs widely even up to this day.

It's interesting because when it becomes clear that even entitled persons cannot understand each others interpretations, maybe it can turn out to be transformative to culture of teaching and learning, you know, the one that is in a very sad state. Maybe education can move away from role of social conditioning and take a good hard look of what learning really is about. Or maybe we need more important and harder discoveries for that to happen.

What a long rant :D tnx if you read it

As for my previous question, what makes one believe that there is state transfer instead of hidden variable, I was able to imagine right after I defined it as a clear question. Just after I clicked submit button. And I must say ability to imagine in somewhat familiar form makes it so much easier to understand.

I imagine that 2 entangled particles are like 2 solid spheres. They are opaque and look the same. Whenever you cut one in half you see the cutting angle against inner structure and imprint of the cutting tool let's say knife. At the same time knife gets imprinted from inner structure of this first sphere
You can read information about spheres insides but somewhat masked with information about knife. Same with knife, you can read information that you didn't know but it is limited by the process. You can never get much better deal of information because all knifes and spheres come in similar sizes.. and too big knife just doesn't cut it

You still have other solid whole mystery sphere left and whenever and wherever and with whatever you cut it. It will cut in same angle and it will give that same information only this time what's missing is the part that you already have from first ball. You may use different knife but even that by its specific imprint won't take missing information away.
From two pieces of matter you get information that describes whole.

Imagine like this and you can draw intuitive conclusions.
Example:

​

Things on quantum scale has unseen properties. Does it mean Q scale is somewhat different? Looks like physical law acts increasingly different on another scale. That is simple statement that goes against intuition. Why does it go against intuition? Probably because evolution perfected our mind like that. There is even stronger intuition that laws should be consistent against distances. We evolved like that because on our scale things happen consistently. Do we know this intuition is right about scaled or far away physics? I don't think so. Evidence is against. Warped space, stretched time. Universal speed limit, density limit. Ofc there is reason why our scale is consistent its not only illusion of mind we are biased by it because its there. If laws are scale relevant there might be change in laws on larger scales, that goes well with fact that we have limits that prevent us from moving out in structures of large scale or moving down in structures beyond small. The fact that we are fundamentally limited could be mistaken for notion that there is nothing there beyond our reach. Not evidence based. Intuition based. Imagine that evolution would have made us with strong intuition that not every place is acting the same, not every size acts as in the same place. If it was so, how would it change our way of doing research, looking for evidence, discarding data that feels useless. We would have totally different evidence based models. We would imagine unreachable beyond in different way.

These may be superficial and irrelevant conclusions for current research, yet still, for personal understanding that is so much better than learning from abstract descriptions about things that you don't know in detail. Without intuition to fill missing spaces, i cannot think of a way to build whole coherent mental framework.

That leads to questions about intuition.

• How does intuition work
• What does it work with
• Why does it work like that
• What is it similar to and what are critical points that make it work better
• How did it came to be
• Can we engineer it? Maybe quicker, better and more optimal for our needs, keep it up to date
• What would it take
• If we can do it what could be the consequences
• How is it going to be used
• is it worth the risk

There can be more or better questions of course :)

 

[bhobba]

How did pioneers got so far so quick, when huge masses of people do way worse on already obtained and explained laws of quantum physics? Even Einstein had much more problem with it than bit more involved researchers.

Generally speaking the math is smarter than we are.

Once Dirac came up with his transformation theory in 1927 QM was basically complete.

Figuring out what it meant took a lot longer and is still going on.

Thanks
Bill

 

[stevendaryl]

Generally speaking the math is smarter than we are.

Once Dirac came up with his transformation theory in 1927 QM was basically complete.

Figuring out what it meant took a lot longer and is still going on.

Thanks
Bill

The Dirac Equation seems really an example of the math being smarter than we are. He only had one goal: to make a first-order differential equation that was the relativistic generalization of Schrodinger's equation. But the math forced him to a theory that had particle spin, antiparticles, particle creation, etc.

 

[bhobba]

The Dirac Equation seems really an example of the math being smarter than we are. He only had one goal: to make a first-order differential equation that was the relativistic generalization of Schrodinger's equation. But the math forced him to a theory that had particle spin, antiparticles, particle creation, etc.

It is.

And its notable other physicists thought Dirac too smart by half. But all he thought he was doing was mucking around with equations.

Some people attracted to physics say its just math, it can't be reality, yada, yada yada, regular posters here know the drill. Physicists did not go down that route without reason - and Dirac's success certainly played a part in it.

Thanks
Bill

 

[realbart]

Let's do a thought experiment.

A long time ago in a galaxy far far away, somebody used his entangled particle generator to create a gazillion pairs of entangled particles.
The first of each pair was shipped to Alice Alien, who lives several thousand light years away from us. My neighbour Bob just received the other ones.

Alice measures the particle spin of each partice. All in the same direction.
Bob measures the spin of each particle in a random direction and plots the results.

q: what will the graph look like?

[PLAIN]https://upload.wikimedia.org/wikipedia/commons/7/77/StraightLines.svg[URL='https://upload.wikimedia.org/wikipedia/commons/7/77/StraightLines.svg'][/URL]

https://upload.wikimedia.org/wikipedia/commons/7/77/StraightLines.svg

I think it'll look like the dotted curve in the graph above.
q: Does Bob learn the direction Alice is measuring at?
q: Does this violate the no-cummunication theorem?

 

[Heinera]

Let's do a thought experiment.

A long time ago in a galaxy far far away, somebody used his entangled particle generator to create a gazillion pairs of entangled particles.
The first of each pair was shipped to Alice Alien, who lives several thousand light years away from us. My neighbour Bob just received the other ones.

Alice measures the particle spin of each partice. All in the same direction.
Bob measures the spin of each particle in a random direction and plots the results.

q: what will the graph look like?

The graph you have enclosed is a plot of the correlations between Alice's and Bob's measurement results. Bob (without knowing Alice's results) can not make this plot by himself.

 

[Ken G]

Which makes the answer to the first question "only if Alice tells him her outcomes", and that makes the answer to the second "no."

 

[DrChinese]

Let's do a thought experiment.

...

q: Does Bob learn the direction Alice is measuring at?
q: Does this violate the no-cummunication theorem?

Welcome to PhysicsForums, realbart!

Bob does NOT learn anything from Alice. The "no-signaling" theorem remains intact.

As Heinera says, Alice must first send her results by traditional means (signals propagating at c) to Bob in order for Bob to prepare your graph.

What Bob sees is the same 50-50 statistical result at any angle setting he chooses. Ie no different than flipping coins.

 

[realbart]

The graph you have enclosed is a plot of the correlations between Alice's and Bob's measurement results. Bob (without knowing Alice's results) can not make this plot by himself.

You're absolutely right, Heinera. I expected to see the graph as function of the angle between the measurement and the Z-axis.

So let's say Alice will measure every particle spin along the Z-axis.
What will Bobs measurements be along the horizontal plane? (perpendicular to the Z-axis)

 

[Heinera]

You're absolutely right, Heinera. I expected to see the graph as function of the angle between the measurement and the Z-axis.

So let's say Alice will measure every particle spin along the Z-axis.
What will Bobs measurements be along the horizontal plane? (perpendicular to the Z-axis)

Bob's measurements will be completely random to him, no matter what axis he chooses. They will be "up" or "down" with 50/50 % probability.