Who is puzzled by the delayed choice?

Demystifier

Yes. Try first to understand at least one of the interpretations in post #1.

Dadface

Thank you,but for other things I understand,such as Schrodingers cat,I have my own interpretation.It doesn't fit in any of the categories listed in post one but is closest to "shut up and calculate".
I want to look at this for the fun of it but my main problem has been in finding an article which is at my level of understanding and which describes the experiment in enough detail.

Dadface

That's very kind of you to post the older version.It does go further but still leaves me with a load of questions.I do not wish to bother people here with my questions until and if I get a better understanding of the experiment.Thank you.

audioloop

What about this one, Demystifier ?

Can a Future Choice Affect a Past Measurement's Outcome?
http://arxiv.org/ftp/arxiv/papers/1206/1206.6224.pdf


not delayed choice of course

Demystifier

Let me quote from the paper:
"Consequently, nonlocal effects between the two particles have been commonly accepted as the only remaining explanation. It is possible, however, to explain the results without appeal to nonlocality, by allowing hidden variables to operate within the Two-State Vector Formalism (TSVF). The hidden variable would then be the future state-vector affecting weak measurements at present."

In other words, they propose an alternative interpretation of certain EPR-like correlations, as being caused not by nonlocality but by backward causation. They do not claim that their alternative interpretation is the only possible one, but only that it is a possible one. Indeed, this type of alternatives to quantum nonlocality already exists on my list:
http://www.physicsforums.com/blog.php?b=3622

Ken G

I was interested to see that you classify your solipsistic hidden variables approach as local but only describing the observers, because that's very much the intepretation I take-- that physics is the study of how physicists interact with, and learn about, nature. That's probably why we agree so much on the way to strip delayed choice of its mystical qualities. But I thought you were a Bohmian, who would therefore take a very realist perspective on nature outside of the physicist, so I'm surprised to hear you as applying local thinking to the observer only. Would you then say you are not really a Bohmian at all?

audioloop

ok.
listed under

.-backward causation - objective reality exists and is local, but there are signals backwards in time (transactional interpretation).


ok. then but not transactional, if not two state vector formalism.
by aharonov.

Demystifier

First, I am open to various possibilities, not only to Bohmian and/or solipsistic.

Second, my solipsistic model is technically very similar to Bohmian mechanics; both are based on deterministic particle trajectories guided by the state of the system.

Third, in the paper I discuss also some unappealing features of the solipsistic model. Bohmian mechanics does not share these unappealing features. In fact, Bohmian mechanics is still my favored interpretation. But it has some unappealing features as well, and as I said, I am open to other possibilities as well.

Demystifier

As you can see from the first post on this thread, my argument is based on the fact that NEITHER of the self-consistent interpretations I am aware of implies that delayed choice affects past. As you can see, many of those interpretations are very far from being solipsistic.

jcsd

I have to say Demystifier, I do like your approach, which seems to be let's make ontology work for us, rather than us working for ontology.

Ken G

Well, I would have to say that on the surface, having an interpretation that is guided by deterministic particle trajectories certainly sounds like an external ontology-- which does not sound like an interpretation whose local elements are limited to the observers. Can you clarify that specific issue?

Demystifier

Have you actually read my paper? It's all explained there. In short, this particle ontology is not external but internal, describing only degrees of freedom which are ultimately responsible for emergence of consciousness. In a sense, it is assumed that consciousness is MADE of hidden point-particles.

Demystifier

Thanks! Yes, that's one way to see it.

Ken G

OK, I can see that connection. Many might balk at attempting that extrapolation, but it makes sense to me as one potentially valid angle from which to attack the essential issue: that of connecting the physics to the physicist.

bob900

But this interaction happens much later than when the signal particle is measured, so how can the guiding wave function resulting from this interaction possibly affect/guide the signal particle?

For reference, let's take the experimental setup depicted here. The first ("signal") photon is detected at D0, then, possibly at some much later time, its entangled partner ("idler") photon is detected one of the four detectors D1-D4.

Now going back to what you said :

But if there is some guiding function that guides the signal photon to its location within D0, this guiding function must take into account (i.e. be changed as the result of) the interaction between the apparatus (D1-D4). Let's say we set up the experiment so that the we release the photon at time t0, D0 measurement happens at some time t1, and the D1-D4 interaction happens a year from t1. So if the guiding function is to guide the photon from the source (the laser) to D0, it must, at time t0, have information from an interaction that will happen a year later. Is that not the same as saying that this information somehow travels back in time, to influence the guiding function at t0, so as to guide the signal photon to the proper place at D0?

Demystifier

That objection is not difficult to resolve. The signal photon is destroyed at D0 and ceases to exist. However, it doesn't mean that there is no longer any particle the idler photon could be entangled with. The destruction of signal photon does not destroy information carried by the signal photon (otherwise, QM would not be unitary). Instead, the information is transmitted from the signal photon to some of the particles of which the detector D0 is made of, so after a long time the idler photon is still entangled and correlated with those detector particles. Of course, the detector D0 is macroscopic, but it doesn't mean that it doesn't obey quantum laws. According to Bohmian mechanics, everything obeys quantum laws, even if sometimes these laws can be approximated by the classical ones.

San K

or perhaps it's entangled to only a microscopic part of the detector D0