Strange particles that have mass when moving in one direction but no mass when moving in the other direction were first theorized more than a decade ago. Now, these mass-changing particles have been glimpsed in a semimetal exposed to extreme conditions.

“This (particle) is very strange. You can imagine walking down the streets of New York and if you go straight you’re super light, you’re massless. “But when you turn 90 degrees east or west, you become supermassive.”