Small, dark, and very hard to see. This and far more indepth answers to every question you ever wanted to ask about black holes.
Pau Figueras explains how Einstein's theories predicted the existence of black holes, and how to describe them mathematically.
At the heart of modern physics lurks a terrible puzzle: the two main theories that describe the world we live in just won't fit together.
The story of George Boole is an extraordinary example of collaboration across the centuries.
Why do so many networks exhibit a similar kind of structure? It's because the rich tend to get richer!