The universe tends towards disorder. But how come nobody knows why?

By Michael Brooks

ALL the King’s horses and all the King’s men couldn’t put Humpty together again. Everyone knows the sorry tale of Humpty Dumpty, but have you ever noticed that the rhyme makes no mention of an egg? In fact, the ill-fated protagonist only assumed egg-man form when he met Alice in Lewis Carroll’s Through the Looking Glass, after which broken eggs became indelibly associated with irreversible damage. So perhaps Carroll deserves to shoulder a share of the blame for scrambling our ideas about entropy.

Entropy is typically thought of as a measure of disorder or randomness, and it is bound up with thermodynamics – the branch of physics that deals with heat and mechanical work. Its propensity to increase forever has granted it exalted status as the pithiest answer to some deep questions, from what life is to how the universe evolved and why time moves ever forward like an arrow. And yet just like Humpty, entropy gets messy as soon as you crack its surface.

For a start, there is no single definition. But even if we understand it broadly as a measurement or quantity, our current conception of entropy doesn’t work to describe the things it purports to, not least the universe. “It’s all very confusing,” says Anthony Aguirre at the University of California, Santa Cruz.

Now, Aguirre and others are going back to the drawing board in search of a universally valid version of entropy anchored in our most fundamental theory: quantum mechanics. They hope to put our understanding of the universe’s mystifying directionality on firmer footing – or nudge it off a wall.

We might even be …