"If a particle which has mass travel at the speed of light, the particle mass will reach infinity, which require infinity energy to move it, thus particle can't travel beyond the speed of light." I made an calculation about it.(And it turned out to be wrong) However, I couldn't find the mistake! This is my calculation: Let the mass = 1kg, and the velotion = c Kinetic energy gained while travelling=0.5mc^2 =0.5c^2 When these energy is fully converted into mass, Einstein's Equation:E=mc^2 0.5c^2=mc^2 m=0.5 The mass gained by the particle is 0.5, not infinity? Why?