Feymman's theory, double slit experiment - Stephen Hawking

[jaumzaum]

Hi all,

I was studying Stephen Hawking's new book (very good, by the way). He was explainning Feymann's theory, that says a particle travels by all the ways possible to reach a given point. So single particles CAN have interference by themselves. Then he explain why, in the double slit experiment, if we try to take a picture of the particle at the moment it pass by the slit, to see in which slit it passes by, the interference disappears. SW says we change medium and its possible past(??) as we take a picture, and by far as I've understood, we change the medium because the photons collide with the particles, and changes its direction.

1. The first question is about this. I can't see why a single photon preclude all the other Freymann's trajectories the particle could have. Especially if they are big particles as fulerens.

And then SW explains John Wheeler experiment, where we take the picture only a moment before it collides with the screen.

2. As the particles have already passed by the slits, it should have already suffered interference, so why isn't there fringes anymore?

Thank you all by this exellent forum that helped me a lot!
And I'm really sorry if you notice some mistakes in my english. I'm brazilian :\

[]'s
John

 

[jaumzaum]

Nobody?

 

[San K]

SW says we change medium and its possible past(??) as we take a picture, and by far as I've understood, we change the medium because the photons collide with the particles, and changes its direction.

There is no need for time reversal, it is explainable without that.

1. The first question is about this. I can't see why a single photon preclude all the other Freymann's trajectories the particle could have. Especially if they are big particles as fulerens.

No one knows but there are various interpretations on/about that.

http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics