"The best science online" according to someone who really ought to know: Henry Reich, creator of MinutePhysics.

Albert Einstein's famous equation E=mc² explains, of course, why a nuclear power reactor can generate so much electricity in such a relatively tiny space, while using such a relatively tiny amount of fuel. Electricity from other forms of energy, say tidal or wind motion, sunlight, chemical bonds (burning things)... well, nuclear fission and fusion, thanks to E=mc², are definitely in their very own league.