Does the Delayed Choice Experiment Challenge Classical Intuition?

[debra]

Delayed Choice Revisited.

Here is a very cut down summary of Wheeler's delayed choice experiment (hope I got it essentially correct):

When a wave packet is half way between the screen and the double slits, a decision is made by the observer as to whether to look for a photon or a wave.

If a wave is chosen to observe, then its intensity is due to the interference between the two paths from the slit - no problems.

If the particle is chosen to observe, by essentially looking directly down both paths to the two slits, then a photon is indeed observed, which went down just one slit path as only a particle can do - no problems.

The confusion, is caused, by the conflict between a particle going along a fixed single path, and a wave which 'must have been' in two paths at once. It appears as a contradiction.

But using Copenhagen Interpretation, there is no contradiction because a wave packet is neither a wave or a particle, only a probability of observing one or the other. Only if the wave packet *interacts* with something on the way will decoherence take place. If it does not interact there is nothing to say what happened on the way, because on the way the position and momentum remain unobserved - in superposition.


It was a wave packet that made the journey, and that would have been in both paths at once!

Then if a particle was observed that is the result of probability (wf collapse) at the receiving end.
Likewise, the interference wave result is also the result of summation of wave amplitudes at the receiving end for waves in both paths.

 

[azntoon]

So no matter what was chosen to observe, the result was due to the wave packet that made the journey, and more importantly, the result was determined upon arrival. The delayed choice of whether to observe a particle or a wave at the receiving end is actually the same as the decision whether to interact with the wave packet on its journey - and this decides whether decoherence has taken place or not. This delayed choice also determines whether the wave packet behaves like a wave (no interaction) or a particle (interaction) when it reaches the double slits.