A massless particle, a.k.a. Weyl fermion, predicted nearly 100 years ago, has been found in another corner of physics. Electrons in a semimetal can behave like these particles. They are either right-handed or left-handed—they are mirror images like our hands. Theory predicted that Weyl semimetals could produce handedness-dependent electrical current by shining circularly polarized infrared light onto it. Scientists then confirmed and measured this current. Changing from right- to left-handed light switched the direction of the current, meaning they could determine the handedness of these electrons.