The equivalence of mass and energy means that an object (having mass) can not reach the speed of light. As it approaches the speed of light, the mass of the object would become infinite thereby taking an infinite amount of energy. Therefore, only something without any intrinsic mass (like light or a wave) can go the speed of light.
See also:
- A Brief History of Time
- The universe expands faster than the speed of light, but doesn’t actually have a speed. The universe is not infinite.
- In omega point universes, perhaps you could have infinite energy