Dark matter slowed by unknown force

摘要

A Mysterious force acts only on dark matter. That's the conclusion from observations of a huge galactic collision, and it hints that there could be a whole menagerie of particles and forces lurking at the edge of human perception. Dark matter is the invisible stuff that makes up 86 per cent of the mass in the universe. It famously refuses to interact with ordinary matter except via gravity, so theorists had assumed that its particles would be just as aloof with each other.