Why can't we see light?

A peculiar question indeed! You might think it needs complex physics and maths involved to be answered. But no it is not so the answer is quite simple and can be explained by means of simple logic.

Suppose a genius inventor somehow builds a high tech camera capable of shooting at some trillion frames per second and sets it up for an experiment to observe light or supposedly the particles which compose light, the photons.

So, he uses a simple torch as the source of light which he intends to fire up on a screen in front of it and will record the path of light on his camera expecting to see the photons and their interactions in slow motion. He also ensures absolute vacuum conditions between the torch and the screen so that he can get a clear observation of the photons. Finally he turns the room completely dark and fires his torch and records this action on the camera.

Now,he runs towards his camera to watch the less than 1 second footage that was recorded. He runs the footage at the slowest possible rate that the camera is capable of. But, he finds nothing. Nothing but the illuminated screen and the burning torch.

The reason is quite clear. When the torch is turned on, photons are emitted and are scattered to all directions and some of them reach our eye and some of them reach the screen. Our intention is to view the photons that are moving towards the screen. We know that we are only able to see things when the photons reach our retina after bouncing off the thing (actually this is not exactly that happens. This is just an over simplification). So, to view them, they need to reach our eye first of all (or the camera lens in this case). Also as photons are massless they cannot interact with each other. So, one photon cannot also bounce off another photon to enable us to see it.

Thus, we only see the objects that light illuminates (in this case- the screen) or the sources from which it is produced (in this case- the torch) but not light itself. Simply speaking we cannot observe something that that is itself required for observation.