Ettore Majorana

Ettore Majorana was a brilliant and elusive member of Fermi’s group in Rome — the “Via Panisperna boys” — whose name attaches to one of the deepest open questions in neutrino physics.

A prodigious talent

Fermi regarded Majorana as a physicist of the very first rank, in the company of Galileo and Newton, but one who published sparingly and worked in near-isolation. His early studies touched on nuclear forces and the nature of the newly discovered neutron, and he commanded the mathematics of quantum theory with unusual depth.

The Majorana idea

In 1937 Majorana published a symmetric formulation of the theory of fermions in which a neutral particle could be its own antiparticle. Among the known elementary fermions, only the neutrino — being electrically neutral — could possibly be of this type. Whether it is remains unresolved. If the neutrino is a Majorana particle, then the never-observed process of neutrinoless double beta decay becomes possible, and the origin of neutrino mass differs fundamentally from that of every other particle.

A lasting mystery

In 1938, the year after that paper, Majorana withdrew his savings and boarded a ship between Palermo and Naples. He was never seen again — one of the enduring mysteries of twentieth-century science, the subject of investigations and speculation ever since.

A living legacy

His physics is very much alive. Experiments worldwide hunt for the neutrinoless double beta decay that would confirm the Majorana nature of the neutrino and reveal something new about why neutrinos have mass at all, a question taken up in Understanding the Neutrino, Part 6.