What It Takes To Weigh a Neutrino

You've probably heard of neutrinos–tiny, almost massless particles that can zip through the entire Earth without striking anything. They're not quite massless though, and that's led physicists to go to incredible lengths to weigh them.

The photo below shows part of the experiment that scientists used recently to nail down the neutrino's mass. 

An experiment nearly two decades in the making has finally unveiled its measurements of the mass of the universe’s most abundant matter particle: the neutrino.

The neutrino could be the weirdest subatomic particle; though abundant, it requires some of the most sensitive detectors to observe. Scientists have been working for decades to figure out whether neutrinos have mass and if so, what that mass is. The Karlsruhe Tritium Neutrino (KATRIN) experiment in Germany has now revealed its first result constraining the maximum limit of that mass. The work has implications for our understanding of the entire cosmos, since these particles formed shortly after the Big Bang and helped shape the way structure formed in the early universe.

The mass turns out to be no more than 1.1 electron volts. Compare that to an electron, which has a mass of about 500,000 eV.

You can read more about the KATRIN experiment on Wikipedia.