Are Neutrinos Their Own Evil Twins? Part 4: Majorana’s Mystery

In 1937, Ettore Majorana asked a question nobody else was even thinking about: does a particle have to have a distinct antiparticle? For neutrinos — which carry no charge — the answer might be no. They might be their own antiparticles. Deep underground right now, experiments are watching atoms decay, waiting for the signal that would prove it. So far: nothing. But the case is not closed.