Hi, I'd like to ask what happens to energy/work that is expended to accelerate an object that is already traveling at lightspeed or at some appreciable fraction of lightspeed. My recollection is that continued application of force results in an asymptotic acceleration that tapers off as the limit approaches lightspeed. So as the acceleration under the applied force deviates from linearity, where is that difference in kinetic energy going? Is it being converted into something else? I forget -- is it being converted into radiation, or something?