Entropy is not about speeds or positions of particles, the way temperature and pressure and volume are, but about our lack of information.

Information gently but relentlessly drizzles down on us in an invisible, impalpable electric rain.

This is not what I thought physics was about when I started out: I learned that the idea is to explain nature in terms of clearly understood mathematical laws; but perhaps comparisons are the best we can hope for.

As every bookie knows instinctively, a number such as reliability - a qualitative rather than a quantitative measure - is needed to make the valuation of information practically useful.

Claude Shannon, the founder of information theory, invented a way to measure 'the amount of information' in a message without defining the word 'information' itself, nor even addressing the question of the meaning of the message.

Entropy is not about speeds or positions of particles, the way temperature and pressure and volume are, but about our lack of information.

Numbers instill a feeling for the lie of the land, and furnish grist for the mathematical mill that is the physicist's principal tool.