Re: Again, a confusion between relativistic and restmass Crisp, I believe you are right about this, but considering that everything is relative, the restmass of an object compared to one observer would be different from that of an observer who was traveling at a different speed. Or am I interpreting rest mass wrongly? I thought rest mass was considered the mass an observer at same velocity would perceive. Also, I had asked what would happen if I could make an object appear to have no rest mass? Wouldn't it be possible to increase the speed of the object in proportion to the apparent reduction in rest mass? I am not sure (I need to look at Einstein's equations again, it's been a while) but I think a limiting factor would still be the speed of light, although if you could possibly appear to make the object's mass negative (I have no idea of the implications of that Please Register or Log in to view the hidden image!), you could potentially travel at the speed of light for almost no energy. I would definately like to hear your thoughts.