Question

In a typical photon experiment the photon is depicted as moving across the page, say from right to left. Suppose we were actually able to witness such an experiment, from the side (to position of reader to a page). If the photon is actually moving from left to right can I, standing at 90 degrees to the motion, see the photon?

Answer 1

Dear , the pictures are drawn to indicate that the photons are there. They are there even if you don't see them. There are many things that we can't see - or we can't see directly or at a given moment - but they still exist. And of course, you don't see the photons (with a wrong direction) by normal methods - you would have to collide them against something else that you could observe but that would change the propagation of the photons on the page.

However, if you want to be fancy, the answer is that you can actually see photons by other photons. Because of quantum effects (with a virtual box-like loop of an electron, and four attached photons), the electromagnetic waves are slightly non-linear. So light can collide with other light so you could actually "shine" a very powerful beam of light to see another beam.

You can't do it in your kitchen but this phenomenon has actually been tested experimentally at SLAC, California. It works: see this thread:

Scattering of light by light: experimental status