Firstly, I'd like to say that I'm not exactly well versed in physics, so this may seem like a silly question, but I'm kind of interested. :P I was watching some videos and doing some research on the "double slit experiment", and I started thinking about light. Why is it that if you would shoot light through two slits you just get the two bands of light? If light is actually waves, wouldn't you get that interference pattern? The only thing I can think of is that photons don't interact with one another, but then it's claimed that photons have mass, even if it's minuscule. So it should be possible for photons to be bouncing off one another, no? EDIT: Actually, I was wrong, perhaps I should have looked up photons before I asked. :P Though I thought I heard somewhere that photons have mass. Anyway, I guess I should change the question to "Do photons interact with one another?"