@jackm: this is incorrect. Were an atom of, say, Oxygen (8 protons, 8 electrons, 8 neutrons) to meet its anti-matter partner (8 antiprotons, 8 positrons, 8 antineutrons), the energy of both would be released (total conversion of matter to energy) following e=mc² (energy equals mass multiplied by the speed of light²)
As objects with mass approach the speed of light, it takes more and more energy to continue the acceleration. As the object continues to accelerate, the energy required to accelerate it increases geometrically, approaching infinite energy at C. Hence, it is impossible to accelerate something to the speed of light if it has mass.
@Cartman: I see that as simlar to the difference between travelling down a hill on foot or on a skateboard – you still travel the same distance, only at different speeds. Time travel using a wormhole would be equivalent to walking through a door at the top of the hill, and walking out the other side of the door at the bottom – the distance travelled is measurably different. Indeed, if the bottom of the hill were sufficiently far away – say 5 light seconds – you would be able to see yourself stepping through the door. Basically, a wormhole allows you to violate the classical principle of causality, ‘time travel’ through movement at relativistic speeds or through mass-derived distortion of spacetime does not – your grandchildren cannot come back to kill you, although you could meet them when you are biologically younger than they are.