## gravity

Are the unchanging features of the Universe really unchanging?

*string theory*have nudged their way into public consciousness. It's a theory of everything in which everything's made of strings — or something like that. But why strings? What do they do? Where did the idea come from and why do we need such a theory?

**David Berman**has an equation-free introduction for beginners.

What goes up must come down — or does it? Find out how to cheat gravity with

**Julian Havil**.**Lewis Dartnell**explained how chaos on the brain is not only unavoidable but also beneficial. Now he tells us why the same is true for our solar system and sends us on a journey that has been travelled by comets and spacecraft.

*Plus*, we heard how a simple mathematical equation became the subject of a debate in the UK parliament.

**Chris Budd**and

**Chris Sangwin**continue the story of the mighty quadratic equation.