I know this may sound strange, given that we cannot really work out where in space a photon is because it cannot be completely stopped. But here's a thought. Let us assume that a photon has been emitted in vacuum going in a straight line. At any given moment in time, this photon will have travelled a distance of Code (Text): c * t from the source, where c is the speed of light and t the time since its emission. So technically, our Δx is in fact equal to zero. Theoretically speaking, it does not matter now what Δp is, because 0 * n will always equal zero, and not a value greater than Code (Text): hbar / 2 But we might even bring Δp down to 0. Assume that the photon has been emitted from a monochromatic laser. Such a photon will have a known frequency and wavelength. Given that for a photon, Code (Text): h / λ gives us its momentum, we can know its momentum with an uncertainty of Δp=0. Does the uncertainty principle apply at all to such a photon?