I got to thinking about light while driving in the fog yesterday. I realized fog reveals the beam of light (the headlights send out) very well. Dust and other particles/objects have the same effect too.  I got to wondering, why don’t you see the beam of light unless it comes into contact with something? Think about it, the only time we see light is when its actually touching an object. Light is something that exists to us only because of physical objects. We would never know it was there if there were no physical objects for it to touch. Light seems to be something physical but only seen as a direct result from other things, and on the other hand things are only seen as a direct result from light touching it.