Ok im no physicist, by any means but a thoughy struck me the otherday. If i where to build a box with a volume of 1 cubic plank length , and the inside of which was a perfect mirror, and i contained within it a photon or multiple photons, how would this affect the speed of light? I beleive i asked a similar question severeal years ago, and the trick to it was that photons being massless are theoretically infintessimally small. But would changing the volume of the box to a cubic plank length have any affect? Or is it the same situation? I appologise if this question seems primitive, im imagining a photon to be a particle like a pingpong ball, and I cant quite wrap my head around a particle not being able to be physically constrained My understanding is that a plank length is the smallest length of matter that can be understood with our models.