## Articles

Euclid's fourth axiom says that all right angles are equal. But isn't that obvious?

Why there is a limit to how much better computer chips can get and what it's got to do with black holes.

In 2004 Stephen Hawking famously conceded that black holes do not devour all information when they swallow matter — seemingly resolving the black hole information paradox that had perplexed physicists for decades. But some argue that the paradox remains open and we must abandon our simple picture of spacetime to unravel it.

Does light have weight? Newton thought so. His laws predicted that gravity would bend light, two centuries before Einstein's revolution.

An impossible equation, two tragic heroes and the mathematical study of symmetry.

This week would have been the 100th birthday of Martin Gardner, who is deservedly credited with turning on several generations of people worldwide to the pleasures of maths! To mark the occasion here are some favourite puzzles that, apart from being fun, also lead to some serious maths.