You cannot acelerate an electron to the speed of light without infinite energy right? ditto for a positron. And if you succeeded, who would know. the infinite mass would cause the visible universe to disappear up its own navel. However, an electron and a positron can annihilate to form a gamma ray (given something at this end to balance the momentum), the gamma ray can move some distance at the speed of light, encounter some thing else and split back into an electron and positron.. So the net result is that some mass has 'transported' itself at the speed of light without 'moving' at the speed of light. How can such a subtle distinction prevent the universe from ending?