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The Nine Schoolgirls Challenge
Solve this variation of Thomas Kirkman’s famous 1850 puzzle by arranging girls in walking groups. And think fast — the clock is ticking.
The Particle That Broke a Cosmic Speed Limit
Physicists are beginning to unravel the mysteries of ultrahigh-energy cosmic rays, particles accelerated by the most powerful forces in the universe.
A Surprise for Evolution in Giant Tree of Life
The largest evolutionary tree ever compiled leads researchers to conclude that chance mutation — not natural selection — drives the development of new species.
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.