QED, partial reflection, Feynman, FTL

[Myslius]

I would like to discuss partial reflection of the photons and how thickness of the material (let's say glass) affects reflection (originally from Feynman, QED).
Let's say we have a glass 1m apart from the detector, and another glass 100m apart. The thickness of second glass affects probability waves and the percentage of the light reflected. I find this paradoxical. Let's say we shoot some photons to the glass. It takes 1m/c + 1m/c time to detect reflection from the first glass (highest probability wave peak).
My question is, how after 2m/c time we can know if there is another glass 100m apart? That's kinda FTL.

 

[Valerie Park]

The answer to your question lies in the fact that the photons aren't actually travelling at a speed faster than light. It is just that the probability of the photon being detected upon reflection is higher after two metres than it is after one metre. When the photon is reflected off the first glass, it has a certain probability wave associated with it. This wave is then affected by the presence of the second glass, which increases the probability of the photon being detected or reflected. This means that even though the photon has not actually travelled through the glass, the probability wave can detect the presence of the second glass. So even though the photon has only travelled two metres, the probability wave has already accounted for the presence of the second glass and its effect on the reflection of the photon.