Imagine a charged particle moving in vacuum with relativistic velocity. It emits electromagnetic wave with some known energy. This energy can be detected and used somewhere else. I guess this energy should come from particle’s kinetic energy, thus particle should slowly decelerate over time. However, General Relativity states all inertial points of view are identical. If an observer moves near the particle with the same constant speed, he will believe particle stays still and emits no energy. From his point of view, particle should not decelerate. Will the particle decelerate, after all? I came up with the following assumption to resolve this paradox: if radio detector exists somewhere nearby, moving electrons n it’s antenna will attract to the moving particle by electromagnetic force, so particle will decelerate. If there is no radio detector nearby, particle will keep its speed. However, then comes the next question: electromagnetic wave is a photon. Photon can be seen as a particle. Logically, it can not exist for some observers and does not exist for another observer.