I read somewhere that at 90% the speed of light the mass doubles. So does mass only nearly double at the speed of light and does mass not become infinite at the speed of light? I thought nothing with mass can travel at the speed of light because mass would become infinite at light speed. Also as per my understanding the relativistic mass increases at higher speeds but this increse in mass is temporary and when at rest the mass again returns to the normal value. Is this correct? Please answer these two questions.