Are The Odds Regarding Particles Definitely Independent Events?

[Metric]

Thanks for the refs! I'd certainly be interested in a distilled summary if you get the chance -- those papers seem to be cited a lot in the context of "retrocausation." This makes me a bit nervous, but I don't know -- there could be something really profound here...

[Metric]

Yes, what you're describing is the difference between the standard quantum eraser and the delayed choice quantum eraser (if I read you correctly). And as you seem to be anticipating, there is no change in the outcome of the experiment determined by whether the erasure happened before or after observation of the interfering photons.

This is a very non-trivial result. It's not so easy to see how this is possible in the standard "projective collapse" formalism -- it is somewhat easier to see using a formalism without collapse. This makes me wonder how Scully et al. predicted the outcome in advance, unless they simply appealed to "no superluminal signaling" type arguments.

[PairTheBoard]

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Yes, what you're describing is the difference between the standard quantum eraser and the delayed choice quantum eraser (if I read you correctly). And as you seem to be anticipating, there is no change in the outcome of the experiment determined by whether the erasure happened before or after observation of the interfering photons.

This is a very non-trivial result. It's not so easy to see how this is possible in the standard "projective collapse" formalism -- it is somewhat easier to see using a formalism without collapse. This makes me wonder how Scully et al. predicted the outcome in advance, unless they simply appealed to "no superluminal signaling" type arguments.

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I think I understand that. What I don't understand is why you can't bring back the interference pattern for All the photons by applying the Eraser to All the idler photons?

PairTheBoard

[Metric]

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I think I understand that. What I don't understand is why you can't bring back the interference pattern for All the photons by applying the Eraser to All the idler photons?

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I think you actually can bring back the interference pattern for all photons with a slightly different experimental setup (those which don't involve sorting out coincidence data). However, I haven't studied this particular experiment it in that much detail, so it's possible that I'm just wrong here.

[PairTheBoard]

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I think I understand that. What I don't understand is why you can't bring back the interference pattern for All the photons by applying the Eraser to All the idler photons?

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I think you actually can bring back the interference pattern for all photons with a slightly different experimental setup (those which don't involve sorting out coincidence data). However, I haven't studied this particular experiment it in that much detail, so it's possible that I'm just wrong here.

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The thing is, if you could bring back the interference pattern for all the photons by applying the Eraser to all the idler photons then you could signal someone sitting at the Screen. You apply the Eraser on the Left and someone sitting on the Right sees the Interference for All the Photons. You Disconnect the Eraser and the person on the Right sees the interference go away. You are in instantaneous communication with him.

PairTheBoard

[Metric]

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I think I understand that. What I don't understand is why you can't bring back the interference pattern for All the photons by applying the Eraser to All the idler photons?

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I think you actually can bring back the interference pattern for all photons with a slightly different experimental setup (those which don't involve sorting out coincidence data). However, I haven't studied this particular experiment it in that much detail, so it's possible that I'm just wrong here.

[/ QUOTE ]

The thing is, if you could bring back the interference pattern for all the photons by applying the Eraser to all the idler photons then you could signal someone sitting at the Screen. You apply the Eraser on the Left and someone sitting on the Right sees the Interference for All the Photons. You Disconnect the Eraser and the person on the Right sees the interference go away. You are in instantaneous communication with him.

PairTheBoard

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I see what you're saying -- let me work this out in some detail and get back in a bit. I'm used to thinking about the quantum eraser experiment on a single photon, where the polarization wave function is entangled with the position wave function (hence no FTL possibilities). In this particular setup we're entangling the polarization and position wave functions of two different photons, which throws another element into the mix and at least allows you to talk about communication. However, there is always some way out of these things -- no signaling is guaranteed the moment you invoke quantum field theory (which describes quantum photons).

[Piers]

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but I have often wondered whether the randomness associated with subatomic particles, 50% chance they will decay in 13 microseconds, 50% chance they spin up rather than down, etc. etc. is independent.

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It think its clear that know one knows.

However I think the universe is much more holistic than is normally assumed. We tend to put boundaries around things to make them easy for us to model. However in the real world I don’t think such boundaries exist. I would be amazed if such randomness was independent of the rest of the universe. I fully expect there are more accurate models of the universe, currently beyond us where the random factor completly drops out.

[Metric]

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I think I understand that. What I don't understand is why you can't bring back the interference pattern for All the photons by applying the Eraser to All the idler photons?

[/ QUOTE ]
I think you actually can bring back the interference pattern for all photons with a slightly different experimental setup (those which don't involve sorting out coincidence data). However, I haven't studied this particular experiment it in that much detail, so it's possible that I'm just wrong here.

[/ QUOTE ]

The thing is, if you could bring back the interference pattern for all the photons by applying the Eraser to all the idler photons then you could signal someone sitting at the Screen. You apply the Eraser on the Left and someone sitting on the Right sees the Interference for All the Photons. You Disconnect the Eraser and the person on the Right sees the interference go away. You are in instantaneous communication with him.

PairTheBoard

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I checked up on this... You can indeed restore the interference pattern for all photons. However, the interference pattern associated with detection of idler photon at "D1" is different than the interference pattern associated with detection of idler photon at "D2." The troughs of one pattern correspond to the peaks in the other, and the total pattern still shows no interference -- you still need coincidence information to see the interference pattern, even if every photon is interfering. So since coincidence info only travels at c, there are no ftl communication possibilities.

[PairTheBoard]

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I think I understand that. What I don't understand is why you can't bring back the interference pattern for All the photons by applying the Eraser to All the idler photons?

[/ QUOTE ]
I think you actually can bring back the interference pattern for all photons with a slightly different experimental setup (those which don't involve sorting out coincidence data). However, I haven't studied this particular experiment it in that much detail, so it's possible that I'm just wrong here.

[/ QUOTE ]

The thing is, if you could bring back the interference pattern for all the photons by applying the Eraser to all the idler photons then you could signal someone sitting at the Screen. You apply the Eraser on the Left and someone sitting on the Right sees the Interference for All the Photons. You Disconnect the Eraser and the person on the Right sees the interference go away. You are in instantaneous communication with him.

PairTheBoard

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I checked up on this... You can indeed restore the interference pattern for all photons. However, the interference pattern associated with detection of idler photon at "D1" is different than the interference pattern associated with detection of idler photon at "D2." The troughs of one pattern correspond to the peaks in the other, and the total pattern still shows no interference -- you still need coincidence information to see the interference pattern, even if every photon is interfering. So since coincidence info only travels at c, there are no ftl communication possibilities.

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Aha. That makes sense. Although, saying you've restored the interference pattern for "All" the photons is a little ambiguious. There is no interference seen for "All" the photons by the observer at the screen. What's seen at the screen on the Right by an observer looking at All the photons is the same as what he would see if no Erasure were taking place on the Left. The interference is only seen for subgroups of All photons identified by their corresponding idler photons reaching D1 and D2. The Erasure mechanism on the Left has no effect on what the observer sitting on the Right sees. At least not until he is told which subgroup of photons to look at by the observer on the left. So no FTL communication.

It looks like "Erasing" the Which-Slit information requires a splitting into subgroups with interference restored only for individual subgroups. It's tempting to try to pass the D1,D2 idler photons on to a Final F detector in such a way as to make it impossible to tell which D1,D2 pass-through they came from. But to do that you would have to "Erase" the D1,D2 Which-Way information which would require more splitting into subgroups. You can't bring All the idler photons together into one Final F detector in such a way that all Which-Way information has been Erased.

It's a fascinating experiment. Another one of those where you get the feeling that you aren't really grasping all the implications.

PairTheBoard

[m_the0ry]

Yeah this is the locality debate and believe me a lot of words can be said about it.

From what I've been reading there is increasing evidence showing that locality is in fact false and that action at a distance is possible. There have been a few experiments devised to test this hypothesis. You'll never guess what they're waiting on - the LHC. (/joke)