“Natalie Wolchover brings us up to date on efforts to understand the origin of the highest energy cosmic rays — single particles that have about the same energy as “a bowling ball dropped on a toe,” as she memorably puts it.”

The Particle That Broke a Cosmic Speed Limit | Quanta Magazine

Physicists are beginning to unravel the mysteries of ultrahigh-energy cosmic rays, particles accelerated by the most powerful forces in the universe.