Before you reach the speed of light in vacuum, matter becomes energy. At the speed of light in vacuum, the kinetic energy requirements for any mass are infinite. Any velocity above the exact* speed of light in vacuum (299,792,458 m/s) results in an imaginary kinetic energy.

* http://education.guardian.co.uk/egwe...144235,00.html

"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram