This conceit works fine for simple phenomena like a planet's trajectory around the sun or a weight falling from the Leaning Tower of Pisa. But as scientists try to explain systems of greater complexity – a hurricane, the economy of Portugal, a human or even a reptilian brain – the calculations become ever more elaborate until one is left with an unwieldy array of symbols that do not explain much at all.

That is because the continuum is a fiction. Time doesn't flow, it ticks. Space is not a surface but a grid.

The key idea in the book is that simple, byte-size programs have the surprising ability to produce endlessly intricate behavior.