[renormalised (Carl)]

OK....In your own reference frame, you will appear not to be gaining any mass, if you're accelerating towards c. But to someone watching you from the sidelines, you appear to be getting heavier and heavier as you approach c. The energy which manifests itself in your own reference frame is in the energy you're expending in order to push yourself towards c. The closer to c you get, the more energy you need to expend in order to maintain that acceleration. Think of yourself as flying a rocket. In order to accelerate to and attain c, you'd need to expend an infinite amount of energy to do so. So you'd have to carry an infinite amount of fuel. Remember, I said energy and mass are equivalent. Infinite energy is equivalent to infinite mass....you can never travel at the speed of light. Only photons can do that (and other particles with zero rest mass...e.g. gravitons).