Quantum entanglement IS EVIL

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Physicist say "Quantum Entanglement is when you place 2 electrons together.
They Vibrate in Unison.
When you take them across the galaxy if you "jiggle" one, The other also "jiggles"

Physicist say" however it does not transfer any meaningful information"


This is a EVIL way of speaking.

Why cant you Jiggle Once For YES
Twice for NO

10101010?

That is to say you take one electron , go to the far side of the galaxy, spend trillions of years flying there
you have a question that both sides already agreed upon for when you reach your destination
say "is it raining?"
Once you arrive they "jiggle" yes

How is this not New and Meaningful FTL information

FTL you now know that on the other side of the galaxy it is raining.
 
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If you "jiggle" the entanglement is broken. The next "jiggle" will not do anything.


EVIL...?
 
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They say that if you alter the state of one, the state of the other is also altered and can be observed.
but also claims that this is not meaningful information.

But that's a false statement, as long as you can alter and observe the alteration, that is meaningful information.

unless your saying that you cannot observe the alteration in any way.

even if the entanglement breaks after 1 alteration, 1 bit of data is still meaningful information.
 
Drakkith
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Quantum entanglement does not work the way you are imagining it. You CANNOT tell whether the value you get upon measuring a particle is due to pure chance, or because someone altered the state. Shaking one electron does NOT cause the other one to move. What is meant is that when you measure the state of one particle the other particle must be in a different state. However neither one knows which state it is in until one of the particles is measured. At that point in time BOTH particles know which state to be in, no matter how far the distance is between them. No information can be transmitted using entanglement.
 
DrChinese
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They say that if you alter the state of one, the state of the other is also altered and can be observed.
but also claims that this is not meaningful information.

But that's a false statement, as long as you can alter and observe the alteration, that is meaningful information.

unless your saying that you cannot observe the alteration in any way.

even if the entanglement breaks after 1 alteration, 1 bit of data is still meaningful information.
Welcome to PhysicsForums, Causetic!

When you interact with one member of the pair, let's say Alice, you cannot impart any specific action to it which will be transmitted to the other (who we will call Bob).

The rule is: an observation about Alice tells you something about Bob. But that does NOT tell Bob anything specific. The reason is that the observation of Alice always produces a random result (otherwise Alice and Bob are not entangled). It is true that Bob will see that random result, but so what? All Bob sees is the equivalent of a random series of 0's and 1's. I.e. no useful information.

Further, there is no experimental technique to even assure ourselves that it is Alice causing the collapse into a known state - it could be Bob. *Regardless of sequence*, there is no preference given to one's actions over the other. So who is to say that Alice collapses things; when Bob might see it the other way around.
 
Sounds like another case of quantum misinformation!

The easiest way to picture it in most cases is to imagine the entanglment as this;

Take two socks, a red and a blue one.
You take the socks and put them in boxes, you then randomize the boxes so you don't know what sock is in what box.
We could describe the state of each box as 'red + blue' there's an equal probability that we have a red sock or a blue sock in our box.
We then seperate the boxes by whatever distance you want. We then measure the box, just say we find red in our box, then the state of our box can then be described by just 'red' but in doing this we have changed the description of the state of the other box, it's state has gone from 'red + blue' to just 'blue'
Can we convey information in this manner?

No, we cannot.
 
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Thank you so much for your answers, I've been so frustrated with this issue ever since i was told my original statement.

digging into my brain.

i just wanted someone to dispute the bad description given to me but can't find anything on wiki /previous post specifically disputing it. (one that i can understand at least)

thanks all

:D
 
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Ken G
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The easiest way to picture it in most cases is to imagine the entanglment as this;

Take two socks, a red and a blue one.
You take the socks and put them in boxes, you then randomize the boxes so you don't know what sock is in what box.
Your analogy serves to explain how two things can be entangled without sending signals, but be aware that this is the usual example used to distinguish classical entanglement (the socks) from quantum entanglement (which is quite a bit more subtle and doesn't happen with socks). Only the latter leads to Bell's theorem and "spooky action at a distance." To be clear, as it has been said, neither can be used to transmit information.
 
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Sounds like another case of quantum misinformation!

The easiest way to picture it in most cases is to imagine the entanglment as this;

Take two socks, a red and a blue one.
You take the socks and put them in boxes, you then randomize the boxes so you don't know what sock is in what box.
We could describe the state of each box as 'red + blue' there's an equal probability that we have a red sock or a blue sock in our box.
We then seperate the boxes by whatever distance you want. We then measure the box, just say we find red in our box, then the state of our box can then be described by just 'red' but in doing this we have changed the description of the state of the other box, it's state has gone from 'red + blue' to just 'blue'
Can we convey information in this manner?

No, we cannot.
Einstein, Podolsky, and Rosen thought that quantum entanglement is not any more mysterious than you socks example, but then Bell presented a powerful argument that a "socks" explanation does not suffice to understand the phenomenon. You can read about Bell's proof here.
 
Einstein, Podolsky, and Rosen thought that quantum entanglement is not any more mysterious than you socks example, but then Bell presented a powerful argument that a "socks" explanation does not suffice to understand the phenomenon. You can read about Bell's proof here.
Hmm... I would say that the link you provided misses half the point of Bell's Theorem. Without getting too deep into it, you can read for instance here that the proof you presented misses the possibility of violation of counterfactual definiteness, which happens to be a property of the Many-Worlds interpretation, because of the basic postulate of multiple parallel universes due to superpositions at the macroscopical scale.

The way I understand it, once the two photons are entangled, they are in a superposition of an infinity of polarisations, as good wavefunctions they are. And so, once you observe the photon, you become a part of the superposition, and all that.
Now, the probability of mismatch described by the example given seems to be quite like the Born Probabilities which describe the pseudo-probabilistic nature of the evolution of the wavefunction.
It seems, to me, that what happens is simply that the universe has entered a superposition of states, and so, according to the Born Probabilities, given that the two photons are entangled, and given that there is a 60º difference between the two SPOTs, it just so happens that in 75% of the universes the two bits will mismatch.
 
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Hmm... I would say that the link you provided misses half the point of Bell's Theorem. Without getting too deep into it, you can read for instance here that the proof you presented misses the possibility of violation of counterfactual definiteness
No, Herbert doesn't miss this. His purpose is to disprove the hypothesis that "reality is local" AKA local realism or locality + counterfactual definiteness.
 
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The EPR example gives a good illustration of the impossibility of transmitting information. If you have two entangled electrons A and B then a measurement of the spin of A on a particular axis will lead to a measurement of the spin of B which will have a probability of an opposite spin equal to the square of the cosine of the angle between the two axis. So if A is measured along the x axis and B is later measured on the same axis then B will always have an opposite spin. If A and B are light years apart then the fact that A was first measured on a particular axis will immediately effect the probabilities of the measurement of B's spin, however there is no way for B to know what the spin of A is, all B knows is whether the spin is up or down on the axis he measured, and while A knows that once he measures spin along a given axis, then the probabilities for B will be determined by that, he has no way to know what axis B will chose to measure and is of course limited to the speed of light in attempting to communicate to B which axis was chosen.
 
zonde
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Einstein, Podolsky, and Rosen thought that quantum entanglement is not any more mysterious than you socks example
Where did you get that idea?
 
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Where did you get that idea?
I mean, they thought the only reason quantum entanglement seemed "spooky" was that quantum mechanics was an incomplete theory. But they thought a future, more complete theory would explain away "spooky action at a distance". so that quantum entanglement would be no more mysterious than the socks example.
 
lol guys, the socks example is pretty much the best thing you can do without invoking maths, at least it's the best example I've seen so far that doesn't give people ideas of ftl stuff :shy:

imo any explaination that doesn't use the maths directly will be insufficient in some way
 
Ken G
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It's not strictly necessary to invoke difficult maths to get the spirit of what is "spooky" about quantum entanglement, only if one wishes to actually verify that spookiness for one's self. At issue in EPR was not what is true about socks, it was expressly what is true in quantum mechanics that is not true about socks. Einstein and company understood socks just fine, indeed they felt that all matter had to act like socks. The whole point of EPR is that quantum mechanics does not act like socks, and EPR used that to try and conclude that therefore quantum mechanics was incomplete. Bell found a way to verify experimentally that quantum mechanics was actually right-- the reality of the particles was not like the reality of the socks, and thus quantum mechanics could still be a complete description. Of course how we interpret that completeness is still left wide open, and Bell favored the most "sock-like" of the interpretations, which is Bohm's. But even Bohm's allows behaviors that socks can't do, so it is still the crux of the matter as to how quantum particles don't act like socks.
 
zonde
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I mean, they thought the only reason quantum entanglement seemed "spooky" was that quantum mechanics was an incomplete theory. But they thought a future, more complete theory would explain away "spooky action at a distance". so that quantum entanglement would be no more mysterious than the socks example.
Well, yes, when it will be explained away it won't be mysterious. But then (and now) it was not explained away. Your statement kind of implies that they believed there was nothing to explain away.

Actually Einstein said something like what you imply:
"The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems."
But considering that he does not say where he sees the difference between individual system and ensemble it can not be viewed as a way to explain entanglement away. IMHO
 
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Well, yes, when it will be explained away it won't be mysterious. But then (and now) it was not explained away. Your statement kind of implies that they believed there was nothing to explain away.
OK, all I was trying to say is that Einstein et al. believed that ultimately quantum entanglement would be understood with a "socks" explanation, not anything "spooky".
 
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The analogy with socks is misleading, because it presupposes ignorance from the side of the observer. In QM entanglement is not about ignorance over the states of the two particles like in statistical mechanics. It is intrinsically inherent in the particle system itself. If we want to force the analogy between socks randomization and particles in QM we could say that when the blue and red socks come together they will form a red+blue=green physical 'entity'. And that 'entity' will remain green as long as it spreads throughout the universe and someone doesn't look at it. Then, when the measurement occurs, the green colored entity will collapse instantly to the red and blue socks (possibly light years apart). But which sock will have which color is a process that happens by pure chance, you can't force it to your advantage for encoding messages. We might say that entanglement is about a 'state of being', and not as a set of possible microstates as in statistical mechanics.
 
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If you "jiggle" the entanglement is broken. The next "jiggle" will not do anything.
So the entanglement is quite unstable [or should I say not verry stable]? If this is so, then does it mean that in the sub-atomic levels entanglements appearing [being build] and disapperaing [being destroyed] all the time?
 
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If we want to force the analogy between socks randomization and particles in QM we could say that when the blue and red socks come together they will form a red+blue=green physical 'entity'. And that 'entity' will remain green as long as it spreads throughout the universe and someone doesn't look at it. Then, when the measurement occurs, the green colored entity will collapse instantly to the red and blue socks (possibly light years apart).
Hi Aidyan, I posted in another thread about this but you've kinda cleared somethings up for me with your post.

So keeping with the sock analogy, you're saying that together they could produce green and it will remain green no matter the distance, until a measurement is made. My next question is how do you determine they are both green? I thought measuring it would instantly determine if it is red or blue, so how can you measure to tell it's green?

I appologise if this is hard to explain with such a stuipd analogy, my understanding of these things at this point is pretty basic.
 
So the entanglement is quite unstable [or should I say not verry stable]? If this is so, then does it mean that in the sub-atomic levels entanglements appearing [being build] and disapperaing [being destroyed] all the time?
In a way, yes.

Hi Aidyan, I posted in another thread about this but you've kinda cleared somethings up for me with your post.

So keeping with the sock analogy, you're saying that together they could produce green and it will remain green no matter the distance, until a measurement is made. My next question is how do you determine they are both green? I thought measuring it would instantly determine if it is red or blue, so how can you measure to tell it's green?

I appologise if this is hard to explain with such a stuipd analogy, my understanding of these things at this point is pretty basic.
This thing of "measuring will instantly determine" is a little bit too mystical.

What happens is not that the socks are 'green'. Neither of them is 'green'. They're just in a joint state of red+blue, what we should call a superposition, and we conveniently named this superposition 'green'. That basically means that each sock is red and blue at the same time (more or less what happens with Schrödinger's Cat), and furthermore, what's really impressive about this is that while the 'green system' doesn't interact with anything else (i.e. no outside particles happen to meet the system), the socks can interact with themselves (that's what happens with the electrons in a double-slit experiment), because they are in what's called a 'coherent' system.

Now let's be clearer here. Measuring does not alter the system itself in any way. If we define measuring in this particular case as a person opening the box and seeing the one sock, this is what happens. What happens is that what once was a coherent superposition of red+blue socks is now another superposition of 'red sock and human who saw red sock+blue sock and human who saw blue sock'. That is, you are superposed with yourself.

But of course, you yourself don't realise that. There is one 'you' who will only see a red sock, and there is another 'you' who will only see a blue sock. And because of that measurement, each of the 'you's will know what colour the other sock is.

And the analogy breaks down here, because in the sock case, if one sock is red, the other is definitely blue, and vice-versa. That is not so with entangled systems. It also depends on the "way" they are measured. I will take the example given earlier at the explanation of Bell's theorem.

In the example, they have a source that sends pairs of entangled photons (let's call them socks) to Alice and Bob, in different places. Alice and Bob each have a copy of a certain measuring apparatus, the SPOT, and depending on how the spot is positioned they can or cannot see each photon. Let's call 'blue' the state where one of them can see the photon, and 'red' the state where they cannot.

In this experiment, there is a multitude of entangled socks, one after the other. What is observed is that if Alice and Bob have the SPOT positioned in the same way, their results will seem completely random (half the times they will see red, half the times they will see blue, with no apparent order), but once they meet, they will see that the exact order of their results will match to a T.
Now, suppose Bob rotates his spot 90º. From that moment on, while the results will still appear random, once Bob and Alice compare their results, they will see that they are all inverted, that is, whenever Bob saw Red, Alice saw Blue, and vice-versa.
Next step, suppose Bob and Alice's SPOTs are aligned again, but Bob rotates his 30º clockwise. From then on, they will see that 25% of their results disagree. That is, one out of four times Bob saw red, Alice saw Blue, but the other three times they both saw the same thing.
Suppose now Alice rotates her SPOT another 30º, except counterclockwise, so that there is an angle difference between both SPOTs of 60º. One should expect that then half their measurements would differ, right? Except this doesn't happen, and 75% of the time there is a difference in measurement.
This happens because the probability of a match is given by the cosine squared of the angle difference between both SPOTs, and that has to do with the Born Probabilities.

Let's explain what really happens. At first, before any measurement is made, we have an entangled, superposed state of two photons, each going in a different direction. Once they are detected, however, the superposition of states gets a little bit more complicated.
We have 'Alice sees red and Bob sees blue + Alice sees red and Bob sees red + Alice sees blue and Bob sees blue + Alice sees blue and Bob sees red'. These are the four possible different systems that happen. Once measurement was made, Alice and Bob became part of the superposed system. But that's not all. Because of the Born probabilities, not all four states are equally likely (although since all of them physically happen, likely isn't a good word here; let's just say that there's not an equal number of Alices and Bobs that fit in each state).

Actually, if we define chance as the probability that Alice and Bob will find themselves in a given state, then there is a 3/8 chance of 'Alice red, Bob blue', a 3/8 chance of 'Alice blue, Bob red', a 1/8 chance of 'Alice red, Bob red' and a 1/8 chance of 'Alice blue, Bob blue'.

And if you then ignore Bob's result (i.e. if you don't ask Bob about his detection), then you have exactly 1/2 chance of 'Alice red' and 1/2 chance of 'Alice blue'. Once you know Alice's result, if you ask Bob, you know that there is a 3/4 chance of 'Bob disagrees with Alice' and a 1/4 chance of 'Bob agrees with Alice'.

That's... about it, I guess. I'm not sure I made myself perfectly clear, Quantum Entanglement isn't exactly easy to explain or understand :P
 
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Ken G
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Actually, if we define chance as the probability that Alice and Bob will find themselves in a given state, then there is a 3/8 chance of 'Alice red, Bob blue', a 3/8 chance of 'Alice blue, Bob red', a 1/8 chance of 'Alice red, Bob red' and a 1/8 chance of 'Alice blue, Bob blue'.
Again you are using too classical a concept of probability here. There is zero chance of Alice blue, Bob blue, if we later ask Alice and Bob to compare results. What you are describing is more like a "many worlds" kind of interpretation, which is not a necessary interpretation to take, is a bit bizarre to many, and above all, requires renormalizing the probabilities all the time because you end up with copies of Alice and Bob-- so you can't just use standard classical probability arguments.
 
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So the entanglement is quite unstable [or should I say not verry stable]? If this is so, then does it mean that in the sub-atomic levels entanglements appearing [being build] and disapperaing [being destroyed] all the time?
-------------------------------------------------------
In a way, yes.
So in the case with the two little diamonds that were entangled by scientists - if one of the diamonds is droped on the floor or trown - this will break the entanglement ? [I must be getting this wrong, but.... ]
 
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My next question is how do you determine they are both green? I thought measuring it would instantly determine if it is red or blue, so how can you measure to tell it's green?
With the 'colored' sloppy terminology the 'green' state obviously meant a specific quantum state which is the superpositon of the two particles states. But it is not only that, because that state must also respect the principle of quantum indistinguishability (that's why the correct state vector is written |Psi_c>= (|blu>|red>+-|red>|blue>)/sqrt(2) and not just the wrong |Psi_w>=(|red>+|blue>)/sqrt(2)). At the bottom it all boils down to the principle of complementarity (of which Heisenberg's uncertainty is only an example). When two particles interact or scatter with each others in a tiny volume of space the uncertainty over their position and impulse (as spin and other non commuting observables) is such that the possibility to distinguish which path (spin state, etc.) the one or the other particle took is 'washed out', they become indistinguishable. Again, not because of our ignorance, they are not distinguishable even not in principle, there simply isn't anything like 'two particles' scattering but a 'single whole' (the 'green' thing) and that we describe with the wavefunction |Psi_c>. How do we know that? If you are tempted to calculate the scattering rate by describing the system with |Psi_w> (scattered particles distinguishable) you simply get the wrong answer. Experimental results will instead fit only if you describe the scattering process by |Psi_c> (scattered particles indistinguishable).

E.g. see: http://www.phy.cuhk.edu.hk/course/2011-2012/2/phys5520/download/1/Indistinguishability.pdf Fig.3 is our 'naive' view of the process. What really happenes is in Fig.2
 

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