Martin Kruskal, a mathematician at Rutgers university in New Jersey, has two brothers, both of whom are also mathematicians. When my older brother’s oldest child was five, Kruskal recalls, he argued ...

Imagine Earth were to shrink to the size of a marble. We might be in trouble, but the planet would continue its smooth course around the sun while the moon would maintain its orbit, circling Earth ...

Think of a Number presenter Johnny Ball explains the concept of infinity to four-year-old Claudia Haworth. Claudia's mother Ellie wrote into the BBC's numbers programme More or Less to ask the team to ...