Hello, I've been trying to learn physics recently with the long term goal of understanding GR and cosmology. As a result, I have many questions, so I'll just get started.. In the famous double slit experiment, there is a coherent light source aimed at a double slit which produces an interesting interference pattern behind the slit. I'm wondering about the width of the light beam relative to the space between the slits. I assume that the beam must be wider than the gap between the slits.. Is that right? My real confusion comes from the experiment where you limit the beam power so that it emits one photon at a time. Doesn't each photon have its own trajectory that is determined at the moment it's emitted? I know that you can't measure exactly where it is without "collapsing the wave function", but wouldn't that uncertainty represent a very small physical size (on the order of nanometers, maybe, like visible light wavelengths), much smaller than the space of just one of the gaps? And then how would any one photon "know" about the other gap to produce the bulk interference pattern? Hope that all makes sense - I'm still at the phase where I'm not sure how to phrase the questions. Cheers!