Why would non-locality solve the time paradox in dcqe?

[Emmerich]

I've been trying to work out exactly what part of the experiment I'm fundamentally not getting.

The experiment basically says that no information is being sent back in time because the coincidence counters are needed to isolate the signal photons and expose the interference pattern.

But the fact remains that if you expose the interference pattern then that right there is evidence that the photons interfered before they knew they were going to get recorded.

in other words, if I throw a dice and get 3 and then discover a note in my pocket that says you've thrown 3, then that means something already knew that was going to happen. There is no information being sent because i already knew i had thrown 3 when i read the note but still, the note needs to be explained. I don't see why the concept of nonlocality would explain this.

I know the analogy is very bad but I use it to point out that i understand the impossiblity of sending information back in time with the dcqe experiment but there is still this "note" that is evidence of something strange happening in time.

 

[Nugatory]

I've been trying to work out exactly what part of the experiment I'm fundamentally not getting.

Which experiment?

 

[Emmerich]

Which experiment?

The dcqe (delayed choice quantum eraser) experiment by kim et al

 

[PeroK]

But the fact remains that if you expose the interference pattern then that right there is evidence that the photons interfered before they knew they were going to get recorded.

Some of your confusion may stem from trying to attribute classical wave-particle concepts to quantum phenomena. Where are you reading about the experiment?

 

[Emmerich]

Some of your confusion may stem from trying to attribute classical wave-particle concepts to quantum phenomena. Where are you reading about the experiment?

Multiple sources, mainly wikipedia, the video on it by pbs space time and earlier threads on this forum.

I did delve into it quite deeply (although not quite so deep in the actual mathematics behind it). The main conclusion I read on multiple occasions is that 1. there is no real paradox and the results of the experiment are well understood 2. there is no retro causality and 3. the main problem is our notion of locality and simultaneity.

The counterargument for retrocausality is something like: well you can't actually send back information so there's no problem. But I feel like it's not adressing the point that there is still evidence of some retrocausal link between two events. The fact that it cannot be exploited somehow to send information is another point altogether.

 

[zonde]

The counterargument for retrocausality is something like: well you can't actually send back information so there's no problem. But I feel like it's not adressing the point that there is still evidence of some retrocausal link between two events. The fact that it cannot be exploited somehow to send information is another point altogether.

Well, retrocausality can not really be falsified. But the argument is that retrocausality is not required to explain DCQE experiment.
So if you want to test this argument you have to try to see if DCQE makes sense even without retrocausality and not the other way around.

 

[DrChinese]

You may find this experiment a little easier to envision the time issue in this experiment:

https://arxiv.org/abs/quant-ph/0201134

"Such a delayed-choice experiment was performed by including two 10 m optical fiber delays for both outputs of the BSA. In this case photons 1 and 2 hit the detectors delayed by about 50 ns. As shown in Fig. 3, the observed fidelity of the entanglement of photon 0 and photon 3 matches the fidelity in the non-delayed case within experimental errors. Therefore, this result indicate that the time ordering of the detection events has no influence on the results and strengthens the argument of A. Peres [4]: this paradox does not arise if the correctness of quantum mechanics is firmly believed."

In all scenarios such as these, the ordering of detections does not affect the outcome. In an entanglement swapping operation, you can entangle particles before or after they are already detected - which seems paradoxical. But: Outcomes are random at each spot, and you need classical communication to see the non-local correlation. If all you see is random outcomes, not much information can be transferred.