[wisdom from a science geek]

Originally posted by dreamtamer007+--><div class='quotetop'>QUOTE(dreamtamer007)</div>
Theoretically all mass has some effect on other mass.[/b]
this is true. every object in the universe is gravitationally attracted to every other object in the universe. i don't think this is quite what you mean, though. you're talking about action/reaction, in which case it is still true. if i am floating in an empty void with only a pencil, and i push that pencil away from me, it will go floating off in the direction i push it (say North, which is aribtrary, since i'm in an empty void). i will go floating off in the opposite direction (South), although at a much slower speed. my momentum will be equal to the momentum i impart to the pencil, although in the opposite direction. since momentum is mass times velocity, and since i have a much higher mass than the pencil, i would necessarily have a much lower velocity.

<!--QuoteBegin-dreamtamer007
Even light which is said to have no mass. In the future spacecraft will accelerate hour after hour just buy using light to push it.
this is not quite accurate. light, of course, is energy. energy and mass are interchangable. remember the famous equation E=mc^2? although even saying they are interchangable is slightly misleading. it would be more accurate to say that they are identical. it's a radical concept, but according to quantum physics, at the most fundamental, sub-atomic level, there really isn't any difference between mass and energy. we can look at light as a particle (mass) or a wave (energy). both are equally valid, even though they seem mutually exclusive. too many people still look at the world from a classical/newtonian point of view. once quantum physics is better understood, we will have a radically different outlook on the world.

[/wisdom from a science geek]

sorry about that, i couldn't help myself. it just all came spilling out . . .