:: You seem to be implying that this is some sort of internal contradiction. But why? There is nothing contradictory about the fact that speeding up a particle is progressively harder, even if you try to do it orthogonally to its present velocity relative to you. The basic fact is that for momentum to be conserved under the Lorentz transformation, you need a factor of gamma in the momentum (which, again, is loosely interpreted as a "relativistic mass", since p=mv*gamma combined with a classial p=mv leads people to see m*gamma as the "mass" part. I find that interpretation more confusing than useful, but it has many adherents.) --[[User:NgSmith|NgSmith]] | :: You seem to be implying that this is some sort of internal contradiction. But why? There is nothing contradictory about the fact that speeding up a particle is progressively harder, even if you try to do it orthogonally to its present velocity relative to you. The basic fact is that for momentum to be conserved under the Lorentz transformation, you need a factor of gamma in the momentum (which, again, is loosely interpreted as a "relativistic mass", since p=mv*gamma combined with a classial p=mv leads people to see m*gamma as the "mass" part. I find that interpretation more confusing than useful, but it has many adherents.) --[[User:NgSmith|NgSmith]] |