I have always wondered about this question. How do 2 paritcles sitting at distance x come to know about each other? I know, you can say that they feel field from each other. But again, how does this field propagate? Remember electromagnetic or gravitational fields don't travel through a medium as pressure waves do. These fields don't require no medium at all. Then, what is it that they ride on? I read in one book - "The charges exert a force on one another by means of disturbances that they generate in the space surrounding them. These disturbances are called electric fields." Disturbances in space?? Sounds intriguing? Doesn't it mean that space is much more than what we see. This is just amazing. Any thoughts??? cheers, ~Manu ---------- Manu Garg http://manugarg.com "Truth will set you free!"