Quantum entanglement -> retro/FTL communication?

[Ayatollah So]

If I did this experiment, but instead of observing (or not observing) the 2nd particle 50ms later, but instead I kept it bouncing around, or running through 50,000,000,000 km of fibre-optic cables, and in the mean time I looked at my detector, found wave-like behaviour, did a print out of it on paper, held the paper in my hand and looked at it, then a few hours later I decided, "wait, I'm going to detect the particle's path, thereby making particle 1, which I have already detected, behave like a bullet instead", what would happen?

I dunno. But, with what else I've seen from QM, I wouldn't be surprised if there's some law whereby as soon as you read out the detector's results, you destroy the information that would otherwise be available in the second photon. Just guessing.

 

[Mise]

I dunno. But, with what else I've seen from QM, I wouldn't be surprised if there's some law whereby as soon as you read out the detector's results, you destroy the information that would otherwise be available in the second photon. Just guessing.

I don't think the universe cares whether the result is observed by a detector, or by human eyes. At least it never has done in any previous experiments. In fact, in the diffraction of light, the "observer" is simply a slit...

 

[Mise]

Okay, this report seems to shed some light on all of this. You don't choose whether or not to detect the which-path information; rather, the beamsplitter does. So you can't control whether or not you know which path the photons went down, all you can do is detect it. Case closed, mystery solved, no contradictions here...

EDIT: Wait, that's wrong. I understand it better now though. You can in principle choose whether or not to detect it, but that wasn't what was reported in this experiment. In this experiment, they let the beamsplitter choose. For some reason, I'd have more faith in the universe if it let a beamsplitter choose, but not a human... Spooky shizzle....

 

[Ayatollah So]

Too bad Betazed and The Last Conformist won't give us the straight scoop. And I guess Perfection gave up after failing to see my link in the OP

But, reading that original report kills my idea for how the FTL communicator would work. These guys rely on a coincidence detector which compares the behind-the-slits detector to one of the other detectors. In other words, in my scenario, comparing the Earth results to the Mars results - and if you have to do that, you ain't getting any FTL communication. Rats!

 

[Mise]

Too bad Betazed and The Last Conformist won't give us the straight scoop. And I guess Perfection gave up after failing to see my link in the OP

But, reading that original report kills my idea for how the FTL communicator would work. These guys rely on a coincidence detector which compares the behind-the-slits detector to one of the other detectors. In other words, in my scenario, comparing the Earth results to the Mars results - and if you have to do that, you ain't getting any FTL communication. Rats!

Yeah, an FTL communicator wouldn't work, but it is quite incredible that the entanglement still works backwards in time. Does anyone know how the Copenhagen Interpretation deals with this? When does the first particle's wavefunction collapse?

 

[Sidhe]

Yawn, seen it all before, if your talking FTL transfer, link us to a peer reviewed paper this bunk is little more than crackpottery.

Now there have been some experiments that show certain events that seem to be odd, but sadly they all seem to obey the Copenhagen interpritation(CI) when looked at rigorously.

Mise try this already been done.

If your really interested the wikipedia article isn't very good try googling. Or read the paper linked.

http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser

Essentially all these experiments have proved is that the CI is in fact correct and nothing else.

This is interesting, but trust me on this, he's full of it.

No one has ever seen a particle go back in time, no one has ever proved retro causality.

Yes reality sucks Elrohir and Bill3000 is quite correct.

 

[Souron]

Too bad Betazed and The Last Conformist won't give us the straight scoop. And I guess Perfection gave up after failing to see my link in the OP

But, reading that original report kills my idea for how the FTL communicator would work. These guys rely on a coincidence detector which compares the behind-the-slits detector to one of the other detectors. In other words, in my scenario, comparing the Earth results to the Mars results - and if you have to do that, you ain't getting any FTL communication. Rats!

But you only need the coincidence detector if you have a beams splitter at BSA and BSB. If you have a person decide, the you don't need the coincidence detector.

 

[Sidhe]

Wednesday, November 15, 2006

Considering the date of the report, I think we can safely say the experiment didn't work don't you

 

[Mise]

Now there have been some experiments that show certain events that seem to be odd, but sadly they all seem to obey the Copenhagen interpritation(CI) when looked at rigorously.

How? How does the CI explain this? When does the first particle's wavefunction collapse?

 

[Sidhe]

How? How does the CI explain this? When does the first particle's wavefunction collapse?

This has been peformed and rigorously analysed by scientists and proven sadly and rather disappointingly to confirm or accord with CI or QM theory in all respects, it's uncanny but I was having this discussion not three days ago on a physics forum. Anyway I'll fish out some links.

Delayed quantum eraser experiment and analysis

Full PDF

There you go, enjoy.

Comment: To the physicist, the results "are all consistent with prediction." To the layperson, the results should be shocking. Let us review the course of the experiment as it unfolds, beginning when the incoming photon from the laser generates an entangled pair at the crystal.

Time 1. The entangled pair leaves either region A or region B of the crystal. The signal photon heads off to detector D0, and the idler photon heads off to the interferometer.

Time 2. The signal photon is registered and scanned at detector D0 according to its position. This information (the position of the signal photon upon "impact" at D0) is sent on its way to the Coincidence Circuit.

Time 3. The idler photon reaches the first pair of beamsplitters, BSA, BSB. There, QM makes a choice which direction the idler photon will go – either to detectors D3, D4; or to the quantum eraser BS and on to detectors D1, D2.

Time 4a. If the idler photon is shunted to detectors D3, D4, it is detected with which-path information intact. Then and only then do we know which-path information for its twin signal photon that already has been detected, scanned, registered and recorded at D0.

Time 4b. If the idler photon passes through to detectors D1, D2, it is detected with no which-path information (the which-path information having been "erased" at BS).

Time 5. The Coincidence Circuit correlates the arrival of a signal photon at detector D0 with the arrival of its twin at D1, D2, D3, or D4. If the correlation is with an idler arriving at D3 or D4, then we know (after-the-fact) the which-path information of the signal photon that arrived earlier at D0. If the correlation is with an idler arriving at D1 or D2, then we have no which-path information for the signal photon that arrived earlier at D0.

Time 6. Upon accessing the information gathered by the Coincidence Circuit, we the observer are shocked to learn that the pattern shown by the positions registered at D0 at Time 2 depends entirely on the information gathered later at Time 4 and available to us at the conclusion of the experiment.

The position of a photon at detector D0 has been registered and scanned. Yet the actual position of the photon arriving at D0 will be at one place if we later learn more information; and the actual position will be at another place if we do not.

Ho-hum. Another experimental proof of QM. This is the way it works, folks.

Canton, Ohio
September 4, 2002

 

[Mise]

Well I read the original PDF 3 days ago.

The other link you gave me didn't have anything about CI; it just repeated the experiment but with more words.

 

[Sidhe]

Well I read the original PDF before.

The other link you gave me didn't have anything about CI; it just repeated the experiment but with more words.

It says it confirms QM, do you think that might also mean that it agrees with the CI, since that's the most widely acknowledged interpritation in Physics at the moment, with MWI and Bohmian and QRM bringing up the rear.

The two slit experiment is why the CI exists. It was because of Feynman's two slit that the CI has been credited as the most experimentally consistent interpretation. Well that and SQUID experiments.

I can link Feynman's two slit if you'd like.

This experiment is just another version of the two slit with a delayed quantum eraser effect.

Ho-hum. Another experimental proof of QM. This is the way it works, folks.

As the guy who analysed the experiment said.

Put simply the CI says that if we have information or we decohere the photon then the wave function collapses if we don't then we obtain a wavelike distribution, all this does is confirm this in an easer experiment pretty much, and shows that yes folks QM and CI's integrity is intact.

It's shocking yes, but it doesn't show us anything we don't already know. Quantum mechanics is shocking

 

[Mise]

As the guy who analysed the experiment said.

Put simply the CI says that if we have information or we decohere the photon then the wave function collapses if we don't then we obtain a wavelike distribution, all this does is confirm this in an easer experiment pretty much, and shows that yes folks QM and CI's integrity is intact.

Yeah, so when does the first particle's wavefunction collapse!

 

[Sidhe]

Yeah, so when does the first particle's wavefunction collapse!

You obviously didn't understand either the experiment or its implications I think, CI states simply that by meauring the wave we decohere it, we have no measure then it remains as a wave function, that's it.

In a single photon two slit, the superposition of the photon interferres with itself producing a wave like pattern, if we put detectors at both slits it hits the screen as if it was a particle with 50/50 distribution. This tells us that the measurement in fact is what effects the photon in some way, so what we see is not what a photon actually is, in other words if we disturb the photon in anyway we are not observing the photon as it truly is. Which is commonly called the measurement problem.

The wave function colapses when we have information, when we erase that information then the wave function reappears, just as CI maintains. So the act of erasing the info or measurement is what influences decoherence, you take away the effect of that measurement by erasing the information you get a wavelike pattern again, ala CI, also postulated by the man who first thought up the delayed two slit thought experiment. And confirmed by experiment 30 years later.

You might also be interested to know that after decoherence when a photon has travelled far enough it actually becomes wavelike again, so if you do a double slit far enough apart you will have both decoherence patterns and wave patterns.

Yes it's very odd, yes it's merely the CI in practice. Move along nothing to see here folks

If your talking about the original article, the experiment no doubt failed. So it doesn't happen that way, retrocausality has no proof neither does a particle travelling back in time, I'm not saying they're impossible, just that no one has seen any proof, QM is as ever stubbornly robust, much to the annoyance of CI antagonists.

 

[Mise]

You obviously didn't understand either the experiment or its implications I think, CI states simply that by meauring the wave we decohere, it we have no measure then it remains as a wave function, that's it.

The wave function colapses when we have information, when we erase that information then the wave function reappears, just as CI maintains. So the act of erasing the info or measurement is what influences decoherence, you take away the effect of that measurement by erasing the information you get a wavelike pattern again, ala CI, also postulated by the man who first thought up the delayed thought experiment. And confirmed by experiment 30 years later.

In a typical two slit experiment, the particle's wavefunction collapses as soon as which-path information is observed. This can happen in many ways experimentally: you can block off one of the slits, in which case you know that the particle's gone down the other slit and therefore have observed which-path information; you can stick detectors directly in the line of sight of each slit; (if you have previously added a lens to observe far-field diffraction) you can remove the lens and use a series of mirrors (which I suppose is optically equivalent to sticking detectors in front of the slits). If the wavefunction collapses, you get a bullet-like pattern on your detector. If you don't collapse the wavefunction (e.g. if you use a lens to observe far-field diffraction on a screen, for example), you get an interference pattern.

In this experiment, we don't acquire which-path information at the time of detection, we acquire it some time after detection. But the wavefunction at least appears to have collapsed at the time of detection, because you get a bullet-like pattern on your detector (consistent with wavefunction collapse) as opposed to an interference pattern (consistent with wave-like throughout). So when does the wavefunction actually collapse?

 

[Sidhe]

In a typical two slit experiment, the particle's wavefunction collapses as soon as which-path information is observed. This can happen in many ways experimentally: you can block off one of the slits, in which case you know that the particle's gone down the other slit and therefore have observed which-path information; you can stick detectors directly in the line of sight of each slit; (if you have previously added a lens to observe far-field diffraction) you can remove the lens and use a series of mirrors (which I suppose is optically equivalent to sticking detectors in front of the slits). If the wavefunction collapses, you get a bullet-like pattern on your detector. If you don't collapse the wavefunction (e.g. if you use a lens to observe far-field diffraction on a screen, for example), you get an interference pattern.

In this experiment, we don't acquire which-path information at the time of detection, we acquire it some time after detection. But the wavefunction at least appears to have collapsed at the time of detection, because you get a bullet-like pattern on your detector (consistent with wavefunction collapse) as opposed to an interference pattern (consistent with wave-like throughout). So when does the wavefunction actually collapse?

See post number 41

 

[Souron]

I still haven't seen adequate responses to these two questions posted above.

I agree that there must be a simple solution that does not seem to profoundly defy FTL limitations, result in a paradox, or eliminate free will, but I do not as of yet see it.

Set up the delayed choice quantum eraser experiment on Mars with the second photon going to Earth. Repeat the experiment 1 million times/sec, or whatever you feel is sufficient to get a clearcut difference in 1 sec between "interference pattern" and "bullet-like behavior" on your behind-the-2-slits detector.

To send a "1" to Mars in any given second, "erase" the information contained in the second-photons. To send a "0", detect the information. Every second, Mars will check its detector for interference pattern vs bullet-like behavior.

Well? Am I missing something?

Can someone answer something for me please?

If I did this experiment, but instead of observing (or not observing) the 2nd particle 50ms later, but instead I kept it bouncing around, or running through 50,000,000,000 km of fibre-optic cables, and in the mean time I looked at my detector, found wave-like behaviour, did a print out of it on paper, held the paper in my hand and looked at it, then a few hours later I decided, "wait, I'm going to detect the particle's path, thereby making particle 1, which I have already detected, behave like a bullet instead", what would happen?

 

[Ayatollah So]

I still haven't seen adequate responses to these two questions posted above. [Ayatollah's question; Mise's question]

Well, I refuted my own speculation in post #24. And then you made an important point in response, in post #27. And I'm still trying to think about that. I guess I don't really understand the motivation for using the coincidence detector in the original DCQE (delayed choice quantum eraser - my fingers will tire if I have to type that too often) experiment. So, I can't figure out if it's dispensable or not.

 

[Sidhe]

Well, I refuted my own speculation in post #24. And then you made an important point in response, in post #27. And I'm still trying to think about that. I guess I don't really understand the motivation for using the coincidence detector in the original DCQE (delayed choice quantum eraser - my fingers will tire if I have to type that too often) experiment. So, I can't figure out if it's dispensable or not.

Ayatollah don't try, your just at the same point everyone is, bemused by QM. I've spoken to PhD's and professors who couldn't get to grips with it, Feynman couldn't, no one can at the moment; Worry not, we are missing the bigger picture, but don't feel you have to understand it, or you have to make sense of it in classical terms, because as science stands, no one can; it's all a matter of interpretation; and that's all a matter of not really knowing what is going on.

Sauron can't get an answer to his question because it's unanswerable. And he knows it he's messing with you.

 

[Souron]

Ayatollah don't try, your just at the same point everyone is, bemused by QM. I've spoken to PhD's and professors who couldn't get to grips with it, Feynman couldn't, no one can at the moment; Worry not, we are missing the bigger picture, but don't feel you have to understand it, or you have to make sense of it in classical terms, because as science stands, no one can; it's all a matter of interpretation; and that's all a matter of not really knowing what is going on.

Sauron can't get an answer to his question because it's unanswerable. And he knows it he's messing with you.

I've been assured by somebody who used to teach QM that there exists a proof that entanglement cannot be used to for FTL information. Yet Ayatollah's variation of the experiment seems to contradict that. There has to be an answer one way or another. Either you can transmit information FTL, or something will prevent such an experiment from working as I expect.

To Mise's question I am more apt to accept a no answer is known response.