Why does quantum entanglement not allow ftl communication

[Ken G]

I'd rather simply look at the history of physics. I presume that's what Kuhn claims to have done, but I submit he was mostly seeing the inside of his glasses.

Of course I won't make that accusation without an effort to back it up. I'll just look at the introduction to Kuhn's views found at the website http://www.des.emory.edu/mfp/kuhnsyn.html,
annotated by my personal impressions of the value of the content:

A scientific community cannot practice its trade without some set of received beliefs.

Painfully obvious, but I'll grant the latitude to start with a meaningless "motherhood remark" to set the stage.

These beliefs form the foundation of the "educational initiation that prepares and licenses the student for professional practice".

Immediately we find a significant error in Kuhn's impression of what science education is about. Kuhn appears to think that science education is solely about propagating a body of scientific knowledge. That is indeed a big part of it, but by no means all. An extremely important aspect of any good science education, which Kuhn seems to miss, is the teaching of the scientific method and how to do science, i.e., how to add to or change that "educational initiation". Rather major oversight there.

The nature of the "rigorous and rigid" preparation helps ensure that the received beliefs are firmly fixed in the student's mind.

Same comment-- Kuhn just doesn't get it. Indeed, one of the most important advantages that science has over, say, religion, which I convey to my students and I know I'm not alone, is that science is allowed to be wrong-- because it is self-correcting and it evolves. In short, it is not "rigid" at all. How could Kuhn miss one of the most important of all elements of science, and still count himself an authority on it? Even in my own short career in astronomy I have witnessed countless examples of the flexibility of science. Sorry Kuhn, that's a miss.

Scientists take great pains to defend the assumption that scientists know what the world is like...To this end, "normal science" will often suppress novelties which undermine its foundations.

Now we find some significant errors in logic. Yes, scientists do attempt to convey a sense what they have learned is of value, but partly that stems from demonstrated results (men on the Moon, etc.) and partly that is common to all propagated human pursuits. It's a lousy pedagogical stance to start out with "don't take anything I say seriously, it's all basically baloney. Now, here's the syllabus...". The error in the logic is the implication that scientists effort to convince students there is value in a body of scientific knowledge somehow provides the reason that "novelties" are suppressed. That is flat false. Any real scientist is quite well aware of why novelties are suppressed-- they are vastly likely to be of no value at all, and most educators have enough trouble getting across what has been proven to be valuable. Why on Earth would any intelligent person look for any reason other than that? Too obvious?

Research is therefore not about discovering the unknown, but rather "a strenuous and devoted attempt to force nature into the conceptual boxes supplied by professional education".

Now the logic takes another step into fantasy land. I thought that people like Kuhn were supposed to understand logic, even if they don't know much physics. This is obviously the fallacy of the neglected middle, where Kuhn says essentially that since scientists don't give equal time to crackpot theories that would completely derail the progress of science, the only other possibility is that they set out entirely to maintain the status quo in scientific thought. To me that sounds like he knows little of either science or logic. How did he get to be so famous? Tell me this summary is way off base, because I'm not impressed.

In my experience, all scientists revere to the point of deification the people who have broken out of the boxes. We recognize that not only are our models limited by our intelligence, but also our intelligence is limited by our models, so we need geniuses to break through those limitations and we strongly encourage such geniuses to step forward and do just that. Unfortunately, there tends to be a concept that anyone who says something that disagrees with the mainstream must be such a genius, even if what they are saying makes no sense at all and doesn't even agree with existing observations. So what value does Kuhn's point really have?

A shift in professional commitments to shared assumptions takes place when an anomaly undermines the basic tenets of the current scientific practice. These shifts are what Kuhn describes as scientific revolutions - "the tradition-shattering complements to the tradition-bound activity of normal science".

This is probably the idea that made Kuhn famous, and here he is actually on to something. Yes, scientific advancement is not always the gradual and steady progress that it is sometimes portrayed by people who know little about it (again, not by any science educators I know). So that point is worth making, and if Kuhn made it first, good for him. Nowadays it is perfectly standard in any scientific education process, even for nonscientists (just look up "Galileo" or "Darwin" in any general education syllabus).

New assumptions –"paradigms" - require the reconstruction of prior assumptions and the re-evaluation of prior facts. This is difficult and time consuming. It is also strongly resisted by the established community.

Again we have an improper insinuation here. This is like saying "tearing down your house and building a new one would be costly and time-consuming, so is strongly resisted by homeowners". The appropriate response to that observation is "duh".

But I guess I'm getting off topic-- perhaps we need a new thread on Kuhn (if there isn't one).

 

[Hurkyl]

4. The Grandfather Paradox (and its twin sister argument against FTL, the Shakespeare Indeterminacy) are examples of self-reference. Mathematicians and logicians do not have a good track record in dealing with self-reference.

nonlinear logics. ... self-reference might be fundamental to quantum mechanics

Classical logic capable of treating other logics -- one never has to adopt a different logic as anything but a syntactic description of a traditional mathematical object.

Furthermore, every major 'interesting' logic of which I'm aware is completely subsumed by an ordinary, classical subject. e.g.

Intuitionistic logic is subsumed by topos theory
Constructivism is subsumed by computability theory (at least, some forms are)
Quantum logic is subsumed by C*-algebra

 

[Ken G]

Forget my remarks on Kuhn, I was probably a bit unnecessarily harsh and it makes no real difference in this thread because I'm going to argue that we are simply not seeing any paradigm-shift-driving issues here. The issue is what should count as an "anomaly" in a theory, versus the other possible classifications of something left unspecified by a theory, to wit: a limitation of a theory that is of no value to be concerned with until some specific observation points to a problem (as happened to Newton's laws), or a fundamental limitation of science, more so than the theory (as is likely the case with quantum mechanics seen in the Copehagen interpretation). So we have (at least) three classifications for sticky philosophically unappealing elements of any theory and the resolutions they suggest:
1) anomaly-- get busy fixing it by considering existing observations
2) unconstrained limitation-- it will probably be fixed in the future, but current observations offer no guide, so there is simply no current "action item"
3) fundamental limitation-- don't bother trying to "fix" this, there's nothing to fix.

As an example of each, (1) is like a car with a nasty noise from its engine, (2) is like a car that you wish got 100 miles per gallon, and (3) is like a car that can't fly to the Moon.

So in light of those possibilities, let's look at the interesting issues you raise, issues that indeed come up often in this context:

1. The Measurement Problem. The concept of a measurement is central to the mathematical and conceptual structure of CQM. It is the process by which the state of quantum systems, in general in a superposition of possibilities, is reduced to a single classical value. The only problem is that we have no frigg'n clue what causes a measurement.

I hear this a lot but to me this exposes a common misconception about measurement in quantum mechanics. In my view, there is very little question about what causes a measurement-- it is the decohering of the projections of a wave function onto a particular set of eigenstates. I know that has a lot of jargon in it, but it's really pretty straightforward-- you can always project a wavefunction onto a complete set of basis states, but the amplitudes that describe that projection retain coherences, which means you cannot simply pretend that one of the basis functions is "correct" while the others simply express your lack of knowing that. However, the first step in a measurement is the intentional destruction of those coherences, done expressly so that we can imagine that one of the basis functions is "correct" even if we don't yet know which one (or never look).

You might then ask, but how does the measurement "know" which set of basis states to perform this decoherence with respect to? The answer to that is, the question is being asked backward-- all we know about the measurement is what basis states it decoheres, indeed we chose that measurement expressly because of that property. How it accomplishes the decoherence is what we don't know, but that's not at all unusual in science-- at least we do know why we don't know: we don't know because we have chosen not to track that information (usually it would involve the coupling to macroscopic noise modes that are quite untrackable anyway, but the principle applies any time we simply choose not to track the information, as can occur for one part of an entangled system). So I really don't see any "measurement problem" at all-- it is category (3) above.

In an effort to solve this, (I believe it was Von Neuman) showed that one could draw the line of measurement anywhere. If beta decay is to be measured, is it the tracks in the bubble chamber that form the measurement? Or the photo of the bubbles? Or when the tech develops the film? Or when the grad student looks at the film? Or when the professor reviews the grad student's work? The infinite regress is hard to avoid. Von Neuman argued that this process could be continued until encountering a conscious observer, and then we didn't know enough to take the process further. This has lead some to conclude that measurements require a conscious observer, a dubious conclusion.

This is another very common story, but to me what it does is confuse the first step of measurement, described above (and which is a real connection with physical noise modes of an actual apparatus), with the second step, which is the recording of the result in a conscious mind. The second step is indeed a formal step in "measurement" as the term is used in science, but is in no way central to the quantum mechanics of the problem. The quantum mechanics was over in step 1, the destruction of the coherences. Step 2 is no different at all from classical situations like a person playing a shell game and revealing which shell the pea is under. It's under one of them already, by virtue of the decohering of the amplitudes or the lack of need for amplitudes in the first place, but the player just doesn't know which. Why people think quantum mechanics, once the coherences are destroyed by the classical apparatus doing the measurement, is any different from classical physics, is beyond me-- I don't see any problem there other than we have no idea what a conscious mind is doing.

Thus my answer to von Neumann's chain (if it was indeed him) is that the measurement in the quantum mechanical sense (step 1) occurs as soon as the coherences are destroyed, i.e., the first stage of that chain, but the classical meaning of measurement (step 2) is not resolved until some later and less well determined stage-- but that much was already true for the shell game, and quantum mechanics adds nothing to it. I would call this category (2) from above-- when we have a working model of what consciousness is, we can better address this issue, but until we have a greater body of experimental data on that topic, we are shooting blanks and really shouldn't bother ourselves with it at this juncture.

In contrast, in the abstract quantum systems we have studied, such as quantum tic-tac-toe, there is an objective measurement process. An entanglement that becomes cyclic is typically the trigger for a measurement, no outside macro system, much less a conscious observer, needs to be invoked. While such systems are abstractions and do not represent real physical systems, they do show that it is plausible that an objective measurement system is the real case in quantum physics. It becomes reasonable therefore to seek one, and this provides a fresh attack on the measurement problem.

I agree that quantum tic tac toe is an interesting game (congratulations), with some parallels with quantum mechanics that needn't be taken too literally. But given my answer above, I think you are trying to solve a "problem" of category (3). It is already clear to me that measurement in quantum mechanics (step 1 above) is an objective process, very akin to your quantum tic tac toe, and the Copenhagen interpretation already includes that just fine. I really don't know what all the buzz is about (and I know about non-unitariness and so forth, note that I already addressed that when I mentioned all the information that we have chosen not to track when a step-1 measurement occurs). The coupling to a device we can trust to behave classically, and therefore we know we are not going to track the full information of the reality, is an integral part of objective science, there's no other way to do science and therefore there is nothing to fix. I believe that is true to Bohr's way of looking at things.

 

[ThomasT]

.
2. ... common timelike cause is eliminated by Bell's theorem.

This is not eliminated by Bell's theorem.

Common timelike cause and common spacelike cause are how quantum entanglements are experimentally produced in the first place. There just isn't a generally accepted expression with a visualizable (classical) analog to explain the correlations. What Bell showed is that orthodox quantum mechanics is incompatible with such an explanation.

.
... this opens the door to considering spacelike causality despite the conceptual hurdles.

Common spacelike causality is already an experimental fact. This has been done to entangle even somewhat large groups of atoms if I'm not mistaken.

The other sort of spacelike causality -- ie. instantaneous action at a distance -- is physically meaningless.

Of course, something is happening instantaneously in EPR-Bell experiments. When the setting at one end or the other is changed, then the global setting (and the probability of joint detection) instantaneously changes. Of course, this angular difference isn't a local object. It's simply an observational perspective.

There isn't any evidence to suggest that ftl or instantaneous actions or connections have anything to do with quantum entanglement. Thus, the appropriate path to take in considering all the stuff related to EPR, Bell, quantum entanglement, etc. is to assume that nature is local -- at least until something a bit more compellingly suggestive of ftl or instantaneous actions or connections is discovered or invented.

 

[Ken G]

Thus, the appropriate path to take in considering all the stuff related to EPR, Bell, quantum entanglement, etc. is to assume that nature is local -- at least until something a bit more compellingly suggestive of ftl or instantaneous actions or connections is discovered or invented.

I agree, and that's why I object whenever I hear someone claim that Bell-type experiments exhibit a nonlocal influence when a measurement is made. I see it as entirely local influences, being used to intentionally "unpack" nonlocal information. You only run into trouble when you ask "where is the information stored", and combine local thinking with realism. But these are problems for philosophy, not physics, and really just say that we need to tailor successful philosophies more carefully for them to be informed by physics. Philosophies should not, on the other hand, be used to inform physics-- the history of trying that is pretty clear on that point. (Even the principle of relativity, which is often pointed to as a kind of philosophy-informing-physics, is actually just philosophy-informing-form, i.e., informing pedagogy, not physics itself. In my view, anyway-- there's a relativity thread on this which draws much fire for that position and I'd have to say it's still unresolved).

 

[Degeneration]

I don't understand. Isnt it that there is no SIGNIFICANT information sent? Suppose I wish to receive a signal to turn on a lamp and I have one of two entangled particles. When the particle has an up spin, I am to turn on the lamp. My partner, a couple lightyears away decides to do something to his particle to change its spin to down. My particle instantly reacts with an up spin meaning that I am to turn on my lamp. Isnt information sent here, as primitive of a method it might be?

 

[Ken G]

When the particle has an up spin, I am to turn on the lamp. My partner, a couple lightyears away decides to do something to his particle to change its spin to down. My particle instantly reacts with an up spin meaning that I am to turn on my lamp. Isnt information sent here, as primitive of a method it might be?

No, because your partner cannot "decide" to make his particle be down, and expect that will make your particle be up. If the partner makes a decision and gets a certain spin by design, that would break the entanglement. The entanglement is only unbroken if the partner makes no such decision and simply measures the spin-- but then he has no way to influence whether or not you turn on the lamp. Nothing is transmitted, nonlocal information is simply being "unpacked" by the experiment.

It only seems like a nonlocal "influence" if you imagine that the information being unpacked is somehow stored in the two particles, such that changing that information represents a physical change in both particles, but I would argue that such is a purely philosophical picture that is clearly problematic and retains no value in quantum mechanics, any more than imagining that any wave function is "stored" in the same region of space as it takes on its values. I would say that the place a wave function "resides" is in the mind of the physicist using it, not in the region of space where it takes on its values, and many people may not even realize they are implicitly assuming the latter instead of the former when they agonize over entanglement and delayed choice.

 

[Dar Kthulu]

hello everyone, I am very new to this discussion and i have just a few questions regarding this topic.

1.) how are these particles affected by speed. do they gain mass? can that be measured?
2.) Is the communication of these paricles affected by gravity such as the gravity well around massive objects.
3.) what do you suppose of this experiment on an entangled pair? One is left here on Earth and the other is placed aboard the International Space Station. both are observed.

Just some random thoughts and questions from a non student. Thanks for your time and information. :)

 

[Ken G]

1.) how are these particles affected by speed. do they gain mass? can that be measured?

They don't change rest mass, and if you consider the change in what is known as "relativistic mass", that is just a frame-of-reference issue, not a physical difference that should affect entanglement.

2.) Is the communication of these paricles affected by gravity such as the gravity well around massive objects.

The GR effects should just affect the background spacetime through which the system moves, but I don't see a direct impact on entanglement except perhaps in strong gravity environments where we would need a combined theory of quantum mechanics and gravity.

3.) what do you suppose of this experiment on an entangled pair? One is left here on Earth and the other is placed aboard the International Space Station. both are observed.

I think the normal quantum mechanical expectations, referenced to the system proper times, should work fine there.

 

[DrChinese]

The GR effects should just affect the background spacetime through which the system moves, but I don't see a direct impact on entanglement except perhaps in strong gravity environments where we would need a combined theory of quantum mechanics and gravity.

This is one of those areas where there are some interesting opportunities to consider QM and GR as a pair. If GR is correct, and there is no graviton, then you would certainly expect that entanglement is not affected by gravitational field. That might not be true, on the other hand, if the graviton exists. There have been a few papers that have speculated on this point. Of course without a specific QG candidate to work with, it is hard to say too much. But there might be some limits which could be derived to steer a potential candidate theory.

http://arxiv.org/abs/0910.2322

"We propose a thought experiment to detect low-energy Quantum Gravity phenomena using Quantum Optical Information Technologies. Gravitational field perturbations, such as gravitational waves and quantum gravity fluctuations, decohere the entangled photon pairs, revealing the presence of gravitational field fluctuations including those more speculative sources such as compact extra dimensions and the sub-millimetric hypothetical low-energy quantum gravity phenomena and then set a limit for the decoherence of photon bunches and entangled pairs in space detectable with the current astronomical space technology. "

 

[Ken G]

That's interesting, it would be somewhat ironic if gravity waves are first detected via their interaction with sublimely constructed entangled quantum states, rather than the more brutely classical application of watching them make masses jiggle!

 

[foxy1968]

By using a minimum of 2 sets of qubits in isolation and by freezing the spin of the entangled particles and specifying that set 1 is used to indicate the start of a message and set 2 is used to send the message. By influencing the spin of the particles at one site and monitoring the spin changes at the other site why is this not possible. In this manner would it not be possible to send data over an infinate distance with no delay and therefore ftl.

 

[K^2]

Because you can't check whether the spin was "influenced" by the sender or by your own attempt to check whether it was influenced. Both give you exactly the same result, and so no information is carried.

 

[Demystifier]

Sec. 3 of
http://xxx.lanl.gov/abs/1006.0338
gives a simple explanation why entanglement cannot be used for ftl signalization.
It also proposes how this inability (to use it for ftl signalization) could, in principle, be overcame.

 

[Brokinarrow]

So basically the reason FTL communication is not possible using quantum entanglement: Currently we cannot control the state of the entangled particles, we can only observe the changes that nature is making to the state of the particles. If we could figure out a way to control the state of these particles, FTL communications would be possible.

 

[Albert V]

I've read some papers that were aiming to use linearly and circularly polarized light as a protocol for communication - however, it seems difficult/impossible to distinguish these two when you have to rely on incident photons (eg. Physics Letters A
Volume 251, Issue 5, 1 February 1999, Pages 294-296). Anyone with an idea?

I recently saw another ideá from Arxiv.org. I am not able to discover the flaw in his argument, but I suspect that there will be no interference?

http://arxiv.org/abs/1106.2257

 

[Albert V]

This is a discussion of the Cornwall paper on superluminal communication from

http://arxiv.org/abs/1106.2257

quantum theory says that whatever you do on one side does not change what you observe on the other:

Total state |Phi> = (|H>|V> + |V>|H>)/sqrt2.

Not using the polarizing filter (no modulation)

rho = |Phi><Phi|
= (1/2) ( |H>|V><H|<V| + |H>|V><V|<H| + |V>|H><H|<V| + |V>|H><V|<H| ).

In order to see what we observe on the left side we have to "trace out" the right side

rho_right = Tr_left(rho) = (1/2) (|H><H|+|V><V|),

which is eihter a photon in the mode H or a photon in the mode V, which will give no interference.

Am I mistaken?

 

[N468989]

If I understand correctly, then quantum entanglement is explained by the simple fact that two particles behave the same way after being separated.

Take Machine A and B, each compute numbers from 1 to 10 and are synchonized. Separate the machines and get the output at a given moment in time. We know what the other machine reads, is this correct?

Another thing is to assume that something is propagating through space... ()

 

[DrChinese]

If I understand correctly, then quantum entanglement is explained by the simple fact that two particles behave the same way after being separated.

Take Machine A and B, each compute numbers from 1 to 10 and are synchonized. Separate the machines and get the output at a given moment in time. We know what the other machine reads, is this correct?

This is true in a sense. And the description you give works fine for identical measurements on the individual particles. But it does not yield a suitable explanation for Bell tests. I.e. it predicts the wrong results. This fact was not noticed for many years after the EPR paper appeared, until Bell discovered it around 1964.

Best way to think of it is to imagine polarization of a pair of Type II entangled photons Alice and Bob at angles 0, 120 and 240 degrees. I.e. 1/3 of the way around a circle. After a while, you will realize that using your example, there is an average of at least a 1/3 chance that 2 adjoining measurements (one on Alice, the other on Bob) yielding the same value. However, experiments yield a value of 25% which is in agreement with the quantum expectation value.

 

[unified]

This is true in a sense. And the description you give works fine for identical measurements on the individual particles. But it does not yield a suitable explanation for Bell tests. I.e. it predicts the wrong results. This fact was not noticed for many years after the EPR paper appeared, until Bell discovered it around 1964.

Best way to think of it is to imagine polarization of a pair of Type II entangled photons Alice and Bob at angles 0, 120 and 240 degrees. I.e. 1/3 of the way around a circle. After a while, you will realize that using your example, there is an average of at least a 1/3 chance that 2 adjoining measurements (one on Alice, the other on Bob) yielding the same value. However, experiments yield a value of 25% which is in agreement with the quantum expectation value.

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.

 

[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.