Why can't we use quantum bit entanglement for FTL information?

[zeromodz]

I don't understand. Why can't we use quantum entanglement by the means of altering a state of an entangled electron so we can send an instantaneous bit of information to anywhere in the universe infinitely fast by the other electron changing its quantum state? We can can in theory transmit information faster than c.

Why exactly can't we do this?

 

[Academic]

Try this at home with a friend,

Consider a yes or no message to be sent. Then take a coin and flip it, hold what it lands on up to your eyes and the other side up to your friends. This is like an entangled state that collapses, if you see head your friend will see tails (or vise versa) and you each know what the other sees. Now using this coin alone see if you can transmit a yes or no message to your friend.

 

[zeromodz]

Try this at home with a friend,

Consider a yes or no message to be sent. Then take a coin and flip it, hold what it lands on up to your eyes and the other side up to your friends. This is like an entangled state that collapses, if you see head your friend will see tails (or vise versa) and you each know what the other sees. Now using this coin alone see if you can transmit a yes or no message to your friend.

Okay, I see the point. Is there anyway we could choose what state the electron goes into somehow so then we could transmit a bit?

 

[Academic]

Nope.

 

[zeromodz]

Nope.

Okay, what about sequencing when the electron has its wave function destroyed. It doesn't matter what the outcome is, it just depends on the timing of when the function is destroyed to transmit information indirectly. For example, collapsing 3 electron functions in 10 seconds means a specific bit say "yes" of information and collapsing 6 in ten seconds means "no". How can we not transmit information this way? Is this possible?

 

[Hurkyl]

How can we not transmit information this way?

By looking at my coin, how can I tell if you've looked at your coin yet to "destroy" the uncertainty?

 

[jambaugh]

I don't understand. Why can't we use quantum entanglement by the means of altering a state of an entangled electron so we can send an instantaneous bit of information to anywhere in the universe infinitely fast by the other electron changing its quantum state?
Why exactly can't we do this?

Because acting on one half of an entangled pair has no causal effect on the other half. There is no (reason to suppose a) FTL effect, not even one which is hidden.

The non-locality issues in Bell/EPR thought experiments are red herrings. The critical issue is that quantum systems do not have objective (classical) states of reality.

Entanglement is simply correlation. What is different in the quantum case is that the assertion of correlation (like any meaningful physical assertion) implies a measurement has been made (think of preparing the system as measuring a number of systems until one with the desired trait is found). This entangling measurement does not commute with the critical measurements of half the pair we take and thus prior to that second measurement each half does not have its own definite "state". Thus the correlation is meaningful in and of itself but can't be expressed in the classical way of:
"Either system A is in state x and so is system B, or"
"system A is in state y and so is system B, or "
"system A is in state z and so is system B,"

Each of these statements, when said along with "A and B are entangled so as to be perfectly correlated" is just as wrong as saying a particle has momentum p and has position x or has momentum p and position x'."

I think part of the problem is the use of the term "entanglement" which intuitively hints at a causal connection, i.e. some string connecting the two halves. Translate "entanglement" to "quantum correlation" and you'll be less likely to incorrectly introduce a classical bias.

Quantum systems are not just tiny classical systems.

 

[zeromodz]

Because acting on one half of an entangled pair has no causal effect on the other half. There is no (reason to suppose a) FTL effect, not even one which is hidden.

The non-locality issues in Bell/EPR thought experiments are red herrings. The critical issue is that quantum systems do not have objective (classical) states of reality.

Entanglement is simply correlation. What is different in the quantum case is that the assertion of correlation (like any meaningful physical assertion) implies a measurement has been made (think of preparing the system as measuring a number of systems until one with the desired trait is found). This entangling measurement does not commute with the critical measurements of half the pair we take and thus prior to that second measurement each half does not have its own definite "state". Thus the correlation is meaningful in and of itself but can't be expressed in the classical way of:
"Either system A is in state x and so is system B, or"
"system A is in state y and so is system B, or "
"system A is in state z and so is system B,"

Each of these statements, when said along with "A and B are entangled so as to be perfectly correlated" is just as wrong as saying a particle has momentum p and has position x or has momentum p and position x'."

I think part of the problem is the use of the term "entanglement" which intuitively hints at a causal connection, i.e. some string connecting the two halves. Translate "entanglement" to "quantum correlation" and you'll be less likely to incorrectly introduce a classical bias.

Quantum systems are not just tiny classical systems.

Okay, I understand what you mean by both particles still don't have definite states objectively, but wouldn't the particles show any objective sign whatsoever of the collapse of the function?

That's all we need, just some sign in change of measurement or momentum. Then we could use sequencing of particles to indirectly transmit information like I said above.

 

[zeromodz]

By looking at my coin, how can I tell if you've looked at your coin yet to "destroy" the uncertainty?

Wouldn't altering a quantum position change any sign of the position or momentum? One or the other more or less. We could use special measurement tools.

 

[Academic]

Im not sure what you mean. But like Hurkyl says, you cannot tell if the other person looked by looking yourself.

 

[zeromodz]

Im not sure what you mean. But like Hurkyl says, you cannot tell if the other person looked by looking yourself.

You don't need to check. I just want to know if you entangle 2 electrons and separate them across the universe, could you break one and the other will act instantly by the means of any measurement. It doesn't matter what it does, just as long as it does something. Once this happens you can take more electrons and use a pattern of when the electrons behave in a certain way to transmit information indirectly.

 

[Vanadium 50]

Zeromodz, what would it take to convince you that the answer is "no"?

 

[unusualname]

jambaugh just complicated the issue by spamming the thread with an unnecessary personal interpretation of QM.

The original answer by Academic is sufficient: ie there is no known way of deterministically selecting a quantum state so there is no known way of transmitting information via entanglement.

And you can't tell whether a measurement was made on an entangled partner by the result of measuring the other one, so zeromodz's other suggestion of 'just as long as it does something' won't work either.

 

[JDługosz]

It doesn't matter what it does, just as long as it does something. Once this happens you can take more electrons and use a pattern of when the electrons behave in a certain way to transmit information indirectly.

It doesn't play an alarm or raise a flag or anything. It just carries on being an electron. Nothing comes of it until you make a measurement. When you do, you get a random result. Can you tell if I also obtained a result on my half?

Worse, it doesn't matter when each side makes a measurement. There is no "first". They just agree. If they are far apart and the measurements made near the same time, there is no universal agreement over the ordering! It depends on the observer, and there is no time ordering between them.

If you still can't understand, it might do to work through a more concrete example. E.g. you are on a star ship, in deep space. There is an electron sitting in a trap in the safe. Has it "done something"? No, and it won't. At some point you decide to pass it through a polarizer and measure the result. What can you tell from that?

 

[Born2bwire]

It doesn't play an alarm or raise a flag or anything. It just carries on being an electron. Nothing comes of it until you make a measurement. When you do, you get a random result. Can you tell if I also obtained a result on my half?

Worse, it doesn't matter when each side makes a measurement. There is no "first". They just agree. If they are far apart and the measurements made near the same time, there is no universal agreement over the ordering! It depends on the observer, and there is no time ordering between them.

If you still can't understand, it might do to work through a more concrete example. E.g. you are on a star ship, in deep space. There is an electron sitting in a trap in the safe. Has it "done something"? No, and it won't. At some point you decide to pass it through a polarizer and measure the result. What can you tell from that?

Special relativity challenges the classical ideas of simultaneity. Depending upon the conditions, we could easily have observers that could say that group A measured before group B and another set of observers that say group B was first. Even with these conflicting views, they would all have to be correct. So as JDługosz states, there is no "first."

Not only that, but you have to measure the system and the simple act of doing this collapses the state. You cannot monitor the system passively on your end and tell when the other group measured the system themselves.

 

[jambaugh]

jambaugh just complicated the issue by spamming the thread with an unnecessary personal interpretation of QM...

Firstly my "personal" interpretation is the orthodox one. It just doesn't get as much Hollywood airtime since it doesn't predict such ridiculous effects as FTL signals or infinite parallel dimensions that makes for good SciFi plot elements or fantastic article titles in the popular press.

Secondly the quickest way to prove a theory (with multiple interpretations) doesn't in anyway predict an effect is to demonstrate that a valid interpretation of that theory excludes that effect. (Similar to demonstrating that say the parallel postulate is not a result of the other postulates by demonstrating a valid model satisfying the other postulates but definitely invalidating the parallel postulate).

Thirdly and finally, I am not initiating the invocation of interpretations here. The whole FTL business comes from a ("mis")interpretation of the QM. I'm just piping in with classic CI for equal time.

To zeromodz,

Okay, I understand what you mean by both particles still don't have definite states objectively, but wouldn't the particles show any objective sign whatsoever of the collapse of the function?

To make it clear, "not having an objective state" implies no observation of an objective state. Without such observation there is no possibility of observing a change. "any objective sign" as I understand your meaning must mean an observable sign.

Also The wave-function is initially (in the sequence of definition) a representation of our knowledge about the system. It takes an act of (mis-)interpretation to also give it meaning as a representation of a state of reality. In the first case the collapse is just a representation of the change in our knowledge about the system. Only if you add the "reality" do you assert that this collapse is actually occurring "out there" in the same instantaneous way that it is occurring on paper (and thus get instantaneous (meta)physical effects instead of just instantaneous updates in predictions.)

Without that ("mis")interpretation one can only say that the wave-function collapse is expressing the same sort of discontinuity as we see in a classical probability distribution collapse once one invokes new information. One is making the transition to a conditional probability. "Give we observed X we no longer look at Pr(A) but Pr(A|X)." e.g. "Once we know the number 4 is drawn in the lotto, all the tickets without a 4 instantaneously become worthless."

Now you can choose an alternative to the minimal interpretation I describe provide it consistent as far as empirical predictions goes. But given it is consistent with QM and given it doesn't predict beyond the predictions of QM it cannot predict phenomena inconsistent with the orthodox Copenhagen interpretation. Since that interpretation is consistent with relativistic causal locality and with QM there is
a.) no way QM explicitly predicts an observable FTL causal event (of which a FTL signaling device would certainly be an example) and
b.) no way an FTL causal event is consistent with both QM and relativity.

This does not preclude an alternative theory: "QM plus a a relativity violating theory" which allows FTL signals. But my point is that adding QM in no way adds to our expectation of FTL effects. Speculating about "hyperwave radios" and "warp drives" are independent of the assertions of QM excepting that they should be consistent with QM if you believe in QM. But it is simply speculating both classically or quantum mechanically that relativity is wrong and not inferring anything at all from QM itself.

Ask if there is any way we might sent an FTL signal. Why invoke QM per se?

P.S. Actually, technically Relativity doesn't preclude FTL causality as such. It simply asserts that FTL causal signals as seen by one observer are backward in time signals as seen by another. You cannot invoke FTL without invoking Time Travel and remain consistent with relativity. It is sufficient to resolve the causal loop paradoxes one generates by asserting backward-in-time communication to retain both relativity and the hoped for FTL causation. But without some empirical examples such belief is an act of faith and such speculation is just "out there".

 

[unusualname]

Firstly my "personal" interpretation is the orthodox one. It just doesn't get as much Hollywood airtime since it doesn't predict such ridiculous effects as FTL signals or infinite parallel dimensions that makes for good SciFi plot elements or fantastic article titles in the popular press.

Secondly the quickest way to prove a theory (with multiple interpretations) doesn't in anyway predict an effect is to demonstrate that a valid interpretation of that theory excludes that effect. (Similar to demonstrating that say the parallel postulate is not a result of the other postulates by demonstrating a valid model satisfying the other postulates but definitely invalidating the parallel postulate).

Thirdly and finally, I am not initiating the invocation of interpretations here. The whole FTL business comes from a ("mis")interpretation of the QM. I'm just piping in with classic CI for equal time.

By "orthodox one" I think you mean "the oldest one" (it's hard to tell because you just posted vague stuff about correlations), I don't think there's anything "orthodox" about it, it was accepted mostly because the mainstream scientists actually producing results weren't really bothered by the interpretation problem since it doesn't add anything useful to the work they were developing.

This is still the case really, since the QM + unification project doesn't immediately require a resolution to the interpretation problem.

In fact the interpretation issue will probably fall out rather easily once the really difficult work of building a mathematical model of microscopic reality and cosmology is complete. Unfortunately this is taking humankind a long time and in the the interim we have to put up with unhelpful would-be philosophers espousing their underwhelming ideas on what it might be like (yawn).

You have no idea how FTL causality might be operating in QM, it may be just an apparent FTL effect due to holographic projection into the 3 dimensions we observe, or there may be a tachyon field generating a bohm type pilot wave, or there may be other dimensional spaces in which signalling can take place etc etc. The uncertainty principle may fall out of a simple resolution issue due to finite 'pixels' on a remote holographic screen, quantum randomness may occur at singularities in the microscopic dynamics or at dimensional boundaries where new degrees of freedom suddenly become available etc etc

Of course it may just be a case of matched correlations due to some unknown mechanism or model of reality, but you certainly don't know that.

You see there is little point answering a question about FTL signalling by appealing to "orthodox" interpretations or similar, the answer to the question is, that as far as we know there is no way of deterministically selecting a quantum state, so we can't transfer FTL information. This is a scientific observation which explains the state of our current knowledge.

 

[ACPower]

A personal thought experiment on classical entanglement:
Consider a sock draw with N pairs of different colored socks, with each pair clipped together. Alice closes her eyes, takes out a pair, unclips the socks, and puts one in each of two waiting brown lunch bags. She then hands one bag to Bob, who carries it across town on the bus. They are now poised for an EPR type experiment. Can useful information be transmitted instantaneously in this arrangement?
I think it should be obvious that the answer is no.

 

[jambaugh]

By "orthodox one" I think you mean "the oldest one" (it's hard to tell because you just posted vague stuff about correlations), I don't think there's anything "orthodox" about it, it was accepted mostly because the mainstream scientists actually producing results weren't really bothered by the interpretation problem since it doesn't add anything useful to the work they were developing.

I mean "orthodox" one because it is the most widely accepted one. This is the (orthodox) definition of "orthodox" whether anyone person thinks it should be or not. http://wordnetweb.princeton.edu/perl/webwn?s=orthodoxy"

This is still the case really, since the QM + unification project doesn't immediately require a resolution to the interpretation problem.

I see no problem...except for those demanding a particular metaphysical interpretation to satisfy their own need to retain an old classical mindset. The operational interpretation is already unambiguously given in the mapping from formal mathematics to physical operations in the laboratory. CI simply makes that explicit which is why it has become the orthodox interp.

In fact the interpretation issue will probably fall out rather easily once the really difficult work of building a mathematical model of microscopic reality and cosmology is complete. Unfortunately this is taking humankind a long time and in the the interim we have to put up with unhelpful would-be philosophers espousing their underwhelming ideas on what it might be like (yawn).

Don't hold your breath. Your supposed need for a "mathematical model of microscopic reality..." is itself interpretationially driven and represents a pre-QM bias towards classical worldviews. What we DO need is a synthesis of the operational, predictive principles of both QM and GR. Recent attempts (Field Theories and String/Brane theories and even Loop QG) have been motivated by this same classical bias. [I'll happily elaborate in another thread or private message if you like] Their lack of success (in incorporating GR) is thus not unexpected (in hindsight).

You have no idea how FTL causality might be operating in QM...

See below [Reparse my ...]

Of course it may just be a case of matched correlations due to some unknown mechanism or model of reality, but you certainly don't know that.

It IS due to matched correlations due to a known mechanism, the prior interactions of the two half-systems. There is no mystery until you try to reconcile the QM prediction with a realist's interpretation.

You see there is little point answering a question about FTL signalling by appealing to "orthodox" interpretations...

Re-parse my last post more carefully. I demonstrated that there IS an answer to the question. It just isn't the answer you want. Given a valid interpretation exists which denies FTL signaling then this demonstrates quite clearly that there is no prediction of FTL signaling within QM itself. As I said QM doesn't exclude the possibility but neither does it suggest it. The question itself doesn't come up unless you wish to --without any empirical or theoretical support-- posit that FTL signaling occurs in nature. Without such an assertion there is no problem to resolve and no need to reconcile FTL effects with QM, anymore than there is need to reconcile QM with unicorn levitation.

 

[unusualname]

I can't work out if you're differentiation between FTL signalling and FTL causality, the latter may exist without the former since you may have conservation laws requiring FTL causality (conservation of spin with entangled photons) but have no way of using that for signalling (since neither spin state can be deterministically selected)

 

[jambaugh]

I can't work out if you're differentiation between FTL signalling and FTL causality, the latter may exist without the former since you may have conservation laws requiring FTL causality (conservation of spin with entangled photons) but have no way of using that for signalling (since neither spin state can be deterministically selected)

If FTL causality is observable then it can be used to send a signal. If it isn't observable then it isn't operationally meaningful and may (like the aether) be excised from the theory.

Contrawise, of course an FTL signal is an example of FTL causality. In so far as what theories predict, the two are synonymous. But this distinction is a good one to red flag the fact that one is speaking about unobservable realities and thus going beyond physical predictions and into ontological speculations (again like the aether).

A local relativistic conservation law cannot require FTL causality it rather enforces relativistic locality since physical effects must propagate via some gauge charge flux be it energy, spin, or whatever.

Typically conservation laws dictate the correlations in the EPR experiments, they do not interpret them as real FTL signaling between the separated acts of observation. That's happening in the metaphysical speculator's mind.

 

[Caelus]

well if you had two entangled coins in there original state (when they where entangled) and one chainges to a random state, then you know that the other one is not in it's original state. (does what somthing isent count as information)

 

[unusualname]

If FTL causality is observable then it can be used to send a signal. If it isn't observable then it isn't operationally meaningful and may (like the aether) be excised from the theory.

Contrawise, of course an FTL signal is an example of FTL causality. In so far as what theories predict, the two are synonymous. But this distinction is a good one to red flag the fact that one is speaking about unobservable realities and thus going beyond physical predictions and into ontological speculations (again like the aether).

A local relativistic conservation law cannot require FTL causality it rather enforces relativistic locality since physical effects must propagate via some gauge charge flux be it energy, spin, or whatever.

Typically conservation laws dictate the correlations in the EPR experiments, they do not interpret them as real FTL signaling between the separated acts of observation. That's happening in the metaphysical speculator's mind.

Gee, and to think so much fuss was made of the experimental results of Aspect et al, pity you weren't around to set them straight and explain it all so simply, maybe you should write to the 2010 Wolf Prize panel and point out that all those experiments haven't really demonstrated anything worth knowing.

Actually you should go post in the ~100 page thread on EPR/Bell in the QM forum, you'd have a ball.

 

[jambaugh]

well if you had two entangled coins in there original state (when they where entangled) ...

That original "state" is a composite state of the pair namely that they were entangled. Presupposing individual states for each goes beyond the QM. You at best can ascribe to each a "statistical state" i.e. assign each a non-trivial density operator. And so...

and one chainges to a random state, then you know that the other one is not in it's original state. (does what somthing isent count as information)

I don't know what you mean by one or the other changing to a random state. The presupposed entanglement dictates that the measurement of one correlates with the measurement of the other. But that is the first measurement of each individual half of the pair so there's no sense in stating anything about the individual pieces changed...or didn't change. It is exactly the same issue as speaking about e.g. the momentum of a particle with a known position. The entangling action doesn't commute with the individual measurements.

 

[jambaugh]

Gee, and to think so much fuss was made of the experimental results of Aspect et al,...

Wonderful confirmations of the predictions of quantum mechanics, they were.

... pity you weren't around to set them straight ...maybe you should...Actually you should...

And this tirade evades the issue and doesn't deter me in the least. I've stated the clear point that QM w/ CI does not imply FTL effect so thus QM does not imply FTL effect.

The fact that some QM w/ Reified wave-function interpretation does require FTL causality isn't a supporting argument for FTL causality but rather a blow against the interpretation.

You can't separate these FTL questions from the issues of interpretation because that is the source.

My posts are directly on point with the OP so kindly address them and save your sarcastic jibes for PM.

 

[unusualname]

Wonderful confirmations of the predictions of quantum mechanics, they were.

And this tirade evades the issue and doesn't deter me in the least. I've stated the clear point that QM w/ CI does not imply FTL effect so thus QM does not imply FTL effect.

The fact that some QM w/ Reified wave-function interpretation does require FTL causality isn't a supporting argument for FTL causality but rather a blow against the interpretation.

You can't separate these FTL questions from the issues of interpretation because that is the source.

My posts are directly on point with the OP so kindly address them and save your sarcastic jibes for PM.

No, what you've done is use this thread as an oppurtunity to promote your preferred interpretation of QM, which, as I pointed out, has unnecessarily complicated the issue of FTL information.

There is no need for an interpretation here, this is a science forum so you should stick to scientific results where possible. In this case it is an experimentally demonstrated fact that we can not deterministically select a quantum state. We don't know the mechanism which underlies entanglement correlations but we don't need to speculate here. Whatever the mechanism, it doesn't allow us to transmit information.

That may or may not change in the future, but neither you nor I know that.

If want to think FTL influences are ruled out then that's up to you, I hope it makes you happy, you may even be right, but don't post misinformation suggesting it is a settled issue.

 

[JDługosz]

well if you had two entangled coins in there [their?] original state (when they where entangled) and one chainges [changes] to a random state, then you know that the other one is not in it's [its] original state. (does what somthing [something] isent [isn't ?] count as information)

Wow, the density of errors in your prose is amazing. "there" is a word which means something, and it's painful to figure out after reading on that you meant "they are" (or "their"). Likewise, "not in it is original state" is jarring to read. If you are not paying attention to what you're writing, one wonders if you are really taking in what we are posting, too.

Now PAY ATTENTION! When you choose to look at your particle, you get a random result. Suppose mine is still in the vault back home, and has not been disturbed, and won't be for some time. When you look at yours, you get a random result.

Now suppose instead that I took mine out of the vault and made my observation, early on, while you were brushing your teeth. Then, you go make your observation: when you look, you get a random answer.

How are those two cases different? Can you tell when your electron, sitting in its trap undisturbed, underwent a collapse of some kind? You don't know anything until you look at it. When you look at it, you note what you find. Summarize the cases:

A) I already examined mine. - your result is random.
B) I have not examined mine yet. - your result is random.
C) I'm not going to look at mine at all. - your result is random.
D) I gave you the wrong electron. - your result is random (to you anyway).

Based on your observation, which case is it? Tell me.

 

[jambaugh]

Pardon the delay but our semester starts early and I've been terribly busy.

No, what you've done is use this thread as an oppurtunity to promote your preferred interpretation of QM, which, as I pointed out, has unnecessarily complicated the issue of FTL information.

The issue of FTL information arises as a complication of issues of interpretation. Without an ontological interpretation one never raises the issue of FTL communication between entangled pairs.

There is no need for an interpretation here,

I agree but there is the need to point out the influence of interpretations. CI if you read it carefully is the absence of interpretation of QM beyond its necessary operational interpretation (what the symbols mean w.r.t. laboratory operations).

this is a science forum so you should stick to scientific results where possible. In this case it is an experimentally demonstrated fact that we can not deterministically select a quantum state.

Nope, it is not (experimentally demonstrated). It is a theoretical prediction of QM. (Specifically that sharp descriptions are maximal.) That you assert --experimental proof of the absence of a possibility-- should have made that glaringly obvious to you.

We don't know the mechanism which underlies entanglement correlations...

Of course we do. Two systems become entangled (correlated) by virtue of prior interactions. No mystery, no issues. ... and so... yes

... we don't need to speculate here.

If want to think FTL influences are ruled out then that's up to you, I hope it makes you happy, you may even be right, but don't post misinformation suggesting it is a settled issue.

Not so much a "settled issue" alternative theories may change ones expectation, but with respect to QM it is a non-issue, which is something else all together.

In particular, in parsing the assumptions of Bell's inequality derivation in order to identify the correct RAA hypothesis (since QM and experiment violate this ineq.) Those unable to drop the implicit hypothesis inherent in their ontological interpretation are left only with the local causality hypothesis. I've pointed out in other posts that this isn't really a necessary hypothesis for the derivation. Locality is a red herring w.r.t. Bell's derivation and Einstein's thought experiment. Reality and hence interpretation is the crux of the issue and you can't avoid that "reality".


Look at the OP. The original question shows the OP'er's belief that entanglement involved causal interaction at a distance between the pairs. (This in part stems from the unfortunate choice of term "entanglement" which would better have been simply called quantum correlation.) This assumption historically emerged from attempts to interpret QM phenomena in terms of some underlying ontological structure. You cannot divorce the question of interpretation from this subject since it is the starting point. To educate the OP as to the fallacy in his assumption it is best IMNSHO to point out the root cause of that fallacy.

You disagree? I don't care.

 

[unusualname]

Pardon the delay but our semester starts early and I've been terribly busy.

The issue of FTL information arises as a complication of issues of interpretation. Without an ontological interpretation one never raises the issue of FTL communication between entangled pairs.

I agree but there is the need to point out the influence of interpretations. CI if you read it carefully is the absence of interpretation of QM beyond its necessary operational interpretation (what the symbols mean w.r.t. laboratory operations).

By trying to argue FTL signalling is forbidden by claryfying the interpretation you get dubious circular arguments eg see http://www.jstor.org/pss/188551.

Which is why the question can't really be answered by appealing to a "correct" interpretation

Nope, it is not (experimentally demonstrated). It is a theoretical prediction of QM. (Specifically that sharp descriptions are maximal.) That you assert --experimental proof of the absence of a possibility-- should have made that glaringly obvious to you.

There's no such thing as an "experimental proof", my sloppy use of the term "experimentally demonstrated fact" may have confused you, but I have used the phrases "as far as we know" and "this may change" to emphasize that quantum randomness is experimentally observed and no counter-observations have been reported

Of course we do. Two systems become entangled (correlated) by virtue of prior interactions. No mystery, no issues. ... and so... yes

well you can argue that the entire universe is entangled by that argument so it doesn't really help much here.

Look at the OP. The original question shows the OP'er's belief that entanglement involved causal interaction at a distance between the pairs. (This in part stems from the unfortunate choice of term "entanglement" which would better have been simply called quantum correlation.) This assumption historically emerged from attempts to interpret QM phenomena in terms of some underlying ontological structure. You cannot divorce the question of interpretation from this subject since it is the starting point. To educate the OP as to the fallacy in his assumption it is best IMNSHO to point out the root cause of that fallacy.

You disagree? I don't care.

You're entitled to your opinion. I believe that no-signalling is ruled out by the (experimentally supported) fundamental randomness of QM, you believe it is ruled out by particular interpretation of correlations.

It seems likely that the topology of reality is quite complex and locality does not have a simple description in a holographic reconstruction of bulk space for example, so I wouldn't appeal to theoretical interpretations until we understand reality better.

Best to stick to what experiments demonstrate, and experiments can't differentiate between interpretations (yet) but they do show us that QM seems random.

 

[jambaugh]

By trying to argue FTL signalling is forbidden by claryfying the interpretation you get dubious circular arguments...

Read my posts more carefully. The only argument I've put forth that FTL signaling is forbidden has been the classic SR argument. My principle point, repeatedly, is that FTL signaling has never been a part of QM or necessary to explain QM except with regard to certain (in my opinion bad) interpretations.

This can be seen by looking at a "correct" interpretation.

well you can argue that the entire universe is entangled by that argument so it doesn't really help much here.

Yes, an excellent way to look at entropy is as the entanglement of a given system with "the rest of the universe".

You're entitled to your opinion. I believe that no-signalling is ruled out by the (experimentally supported) fundamental randomness of QM, you believe it is ruled out by particular interpretation of correlations.

It is rather like the understanding that such signaling is on par with the lumineferous aether...SR didn't "rule it out" but showed it an unnecessary component. There is no reason to believe there is a channel with which one might otherwise be able to signal should one be able to access beyond QM randomness.

If the OP had rather asked...
"Why can't we use quantum bit entanglement to ______________?"
where the blank was one of...
"talk to God"
"create a wormhole."
"pick up trashy women in bars"

Would you not then rather ask that person to re-examine their assumptions rather than point out that they can't control the assumed effect?

It seems likely that the topology of reality is quite complex and locality does not have a simple description in a holographic reconstruction of bulk space for example, so I wouldn't appeal to theoretical interpretations until we understand reality better.

There you go implicitly invoking an interpretation again. Why must you invoke a topological reality? or holographic reconstruction? Things happen. QM describes how, or what we can know about how they happen.

At the classical level we can then model the happenings in terms of an objective reality. That indeed is what defines and distinguishes the classical limit. That "reality" is an idealization. Speculate what forms you can give it, consistent with experiments, but don't speculate about how it "really is" since its is your and my invention.

 

[ThomasT]

jambaugh, thanks for your clarifications. It's clearly your primary antagonist, unusualname, that has more or less hijacked the thread for personal reasons (he's one of those would be metaphysicians who seems to like to think of reality in 'holographic' terms).

Anyway, the OP's question has been answered.

 

[huge10]

transmit information indirectly.

But basically you're not transmitting any information.
The effects of entanglement are not due to any transfer of information (which would violate Einstein's special relativity).

The information is already contained in the whole system since the beginning.

 

[least_action]

How does one state the original question mathematically? (As one might do before attempting to prove it)

You use the tensor product of dirackets to entangle states but how can you say the information cannot travel faster than light?

 

[unusualname]

How does one state the original question mathematically? (As one might do before attempting to prove it)

You use the tensor product of dirackets to entangle states but how can you say the information cannot travel faster than light?

You essentially argue that a measurement at either end doesn't alter the probability distribution of any observable at the other end, but as mentioned above the argument might be considered tautological.

I can't get tex to work but there should be a derivation on the wikipedia page (if it's not ruined by an edit war)
http://en.wikipedia.org/wiki/No-communication_theorem

For a deeper argument see Eberhard & Ross' 1989 paper Quantum field theory cannot provide faster-than-light communication

 

[mrspeedybob]

But basically you're not transmitting any information.
The effects of entanglement are not due to any transfer of information (which would violate Einstein's special relativity).

The information is already contained in the whole system since the beginning.

How can that be? Suppose two particles are entangled. If I precisely measure the position of one and the momentum of the other then I should know precisly the position and momentum of both. This is impossible.