Delayed choice experiment

[rajeesh]

Why is that in the delayed choice experiment it is argued that the choice of observation in the present decides what had happened in the past?

Why cannot it be put down to simply state that the photon in the past, had looked into the future and determined the choice of observation (wether there is a screen or a telescope trained on the slits) and behaves accordingly.

 

The photon could be looking into the future and if it finds a screen it will decide to act as a wave. If on the other hand it finds a telescope pointed onto the slits it decides to behave as a particle.

[swansont]

There is no "the" delayed choice experiment, there is a class of experiments that involve delayed choice, so one cannot always make a statement that universally applies. Generally speaking, though, you don't choose the option that violates causality or any other physical principle when interpreting an experiment, and that experiment hasn't excluded interpretations that jibe with accepted physics.

[rajeesh]

There is no "the" delayed choice experiment, there is a class of experiments that involve delayed choice, so one cannot always make a statement that universally applies. Generally speaking, though, you don't choose the option that violates causality or any other physical principle when interpreting an experiment, and that experiment hasn't excluded interpretations that jibe with accepted physics.

 

The photon seems to know whether there is a screen or a telescope focused on the slits. Can we measure this knowledge somehow by placing an array of detectors between the slits and the screen/telescope. What would happen if we placed such a detector?

[swansont]

The photon seems to know whether there is a screen or a telescope focused on the slits. Can we measure this knowledge somehow by placing an array of detectors between the slits and the screen/telescope. What would happen if we placed such a detector?

You have to diagram the experiment. As I pointed out, there is no "the" delayed choice experiment.

[rajeesh]

You have to diagram the experiment. As I pointed out, there is no "the" delayed choice experiment.

 

Consider the below (figure 1), an electron gun is made to emit electrons one by one through two slits S1 and S2.

There is a screen at the other side and a pair of telescopes (with electron detectors inside them) T1 and T2 trained on the slits S1 and S2 respectively.

We can choose to bring down the screen even after the electron has crossed the slits.

 

If we choose to keep the screen up, we get an interference pattern as more and more electrons move through the slits.

But if we choose to remove the screen the electron is always detected either at T1 or T2 with a 50:50 chance.

 

Now if we choose to insert an array of detectors in between the slits and the screen/telescopes (figure 2), the electron will be detected in atleast one of the detectors in the array as it moves from the slits to the screen.

How does it affect the entire set up?

 

Consider that we have the screen up. Since we have the detectors the interference pattern should disappear.

If we have the screen down, then the electron shows up only at either of the telescopes.

So wouldn't the electron be detected at the detectors which are in line with the telescopes T1 and T2.

 

The question is whether there would be any difference in which detector (inside the array) the electron shows up depending on whether the screen is up or down?

 

 

 

Edited September 3, 2012 by rajeesh

[rajeesh]

Also Please let me know if attempts have been made to conduct such an experiment.

[swansont]

I can try and decipher papers on this, but if it's not from an experiment that's been done, I'm not prepared to try and guess what the results are going to be. Too far outside of what I do.

[rajeesh]

I can try and decipher papers on this, but if it's not from an experiment that's been done, I'm not prepared to try and guess what the results are going to be. Too far outside of what I do.

 

Thanks. The point I was trying to make was that if the system has to be causal, then there should not be any difference in the detection pattern at the detector array irrespective of whether the screen is up or down. Because if there is a difference, then we can predict whether the screen is going to be up or down in the future.

 

Or is the whole thing more complicated than this?

[Delta1212]

What detector would you be using for this? Anything capable of detecting and providing you with information about a photon is going to affect that photon.

[rajeesh]

What detector would you be using for this? Anything capable of detecting and providing you with information about a photon is going to affect that photon.

A normal detector. You mean to say that it will affect the photon's behaviour in the future?

[ACG52]

A normal detector. You mean to say that it will affect the photon's behaviour in the future?

 

A detector works by the photon impacting either the molecules of the film or the electronic sensor. There's no way to detect a photon flying by and not hitting the detector.