Solve this variation of Thomas Kirkman’s famous 1850 puzzle by arranging girls in walking groups. And think fast — the clock is ticking.

# Multimedia

### What Happens if You Fall Into a Black Hole?

David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics.

### Interactive: What Is Space?

Imagine the fabric of space-time peeled back layer by layer.

### A ‘Rebel’ Without a Ph.D.

A conversation with the mathematical physicist Freeman Dyson on quantum electrodynamics, climate change and his latest pet project.

### Model Behavior: The Mathematics of Juggling

Juggling has advanced enormously in recent decades, thanks in part to the mathematical study of possible patterns.