We’ve seen particles that are massless only in one direction

Strange particles that have mass when moving in one direction but no mass when moving in another were first theorized more than a decade ago. Now, these particles that change the mass limit have been observed 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’re going straight, you’re very light, you’re massless. But turn 90 degrees east or west, and you become very massive,” he says…