In 1867, physicist James Clerk Maxwell did something very naughty.

He proposed an apparent violation of the second law of thermodynamics so diabolically clever that other physicists have been trying to resolve it ever since.

His thought experiment invoked a ‘demon’ – a tiny, intelligent being stationed at a door between two chambers filled with gas, only allowing fast particles into one side and slow particles into the other – with the end result being warmth in one chamber and chill in the other.