Dear All, I have a couple questions on the double slit experiment I hope you can help shed some light (or photons) on. =) Arrival Timing of Photons In a normal double-slit experiment like the above setup, do photons always arrive at the detector at a constant speed (basically, speed of light), or does the arrival time experience fluctuation (albeit an extremely minute one)? Since the interference pattern is a result of many troughs of (probability) waves, and troughs seem to have a certain order in its propagation (just like in waves, some troughs are in front and some behind), does that mean if a photon is detected at a position created by interference of troughs further back, it would actually arrive at the detector at a slightly later time? I understand that the "wave" is not physical, but if the interference resembles the characteristics of normal waves, wouldn't that also signify a correlation to the spatial and temporal sequence of troughs? Reflection Interference If we change some parts of P (please refer to photo below) to become a mirror, so that the photon is either reflected back or detected there, would the reflection's backward "wave" interfere with the forward "waves", or perhaps even cancel it out since it's an opposing "motion"? Thank you for your guidance.