Neutrinos are so tiny and inconspicuous that physicists believed for a long time they had no mass. Now, a massive device that scientists say will determine the mass of neutrinos has begun operation in Karlsruhe.

What is the exact mass of the three known kinds of neutrinos? Any answers? No? Well, don’t worry, because nobody knows. Not yet. Electron, muon and tau neutrinos are simply too difficult to grasp for scientists.