> The answer they found: if the Earth’s oceans had twenty times more deuterium than they actually contain, they could be ignited by a 20 million megaton bomb (which is to say, a bomb with the yield equivalent to 200 teratons of TNT, or a bomb 2 million times more powerful than the Tsar Bomba’s full yield).

A factor of twenty in the elemental composition of hydrogen, and a factor of a million in the fission efficiency of uranium. We’ve been lucky with regard to untested physical constants so far, but there’s no promise that that will hold going forward!