: : : : : : It is just a thought exercise. As a practical matter, : : : it may not be possible to propel a large chunk of : : : matter (i.e. a space ship) to anything approaching : : : relativistic velocities (given current technology). : : : The question is though, does relativistic mass have the same : : : gravitational effect as rest mass?

: : : : Well, i would find it hard to believe that ships traveling at that rate would be able to. the mass of the object would be to great to actually to at that rate...come on..THINK ABOUT IT! : : : : Gaby

: : There is no such thing as mass "at rest", only at rest relative : : to some other matter.

: : Here is a kinda neet thought exercise... You could make a spaceship : : travel at the speed of light reletive to a much smaller object coming : : towards it, such as an atom in a particle excelarator. Relative to the particle : : the space ship could reach the speed of light.

: Yes, what would happen to the spaceship from the : perspective of particle? Would the spaceship : appear so massive as to seal itself off from : observation by the particle by forming an apparent : event horizon?

The question of an object with mass travelling at near the speed ot light is an interesting one. This is because the mass of the object does increase according to Lorentz transforms, hence what you say is a credible thought. Perhaps there is a maximum speed at which an object of certain mass can travel at before it cuts itself off from the rest of the universe. This maximum velocity would vary according to the mass of the object. So since light has no mass it can travel at the speed of light. So what would happen to small elementary particles travelling a close to c (they would attain a mass high enough to cut themselves off from the universe). Perhaps these particles can pop in and out of our universe because of this fact. I have actually read some studies which conclude that some elementarty particles don't actually fully exist in our unvierse.