Closing in on the Ghost Particle

Can we weigh the lightest particle in the universe?

Photo by Paul Volkmer on Unsplash

At first physicists thought the neutrino, like the photon, was a massless particle. That, as Einstein told us, allows it to move through the cosmos at the speed of light. Observations seemingly confirmed this fact. Neutrinos do indeed move very fast, close to the speed of light (and not beyond, as one experiment mistakenly…