According to an audiobook i've been listening to about 'E=MC^2', at C (the speed of light) energy will not speed up an object and the energy will become 'mass'. Can anyone confirm this? Surely this also means that the amount of energy in the universe will be ever changing and that using the law of conservation of energy when working with energy in mechanics is incorrect? Perhaps the law of conservation of energy should be ammended to 'the total sum of mass and energy is a constant' ? Thanks for clearing this up.