Horizons are weird. They delimit what we can see in the distance, but they are also always personal: Walk 10 miles to the west and your horizon line moves 10 miles to the west with you.
Remarkably, this local, personal character of horizons also extends to black holes, the most enigmatic objects in the cosmos. Going beyond that horizon towards a new understanding of space, time and black holes is the principal goal of physicist Carlo Rovelli's wonderful new book White Holes.
