The Physics of Ettore Majorana: Theoretical, Mathematical, and Phenomenological, Salvatore Esposito, Cambridge U. Press, 2015. $85.00 (382 pp.). ISBN 978-1-107-04402-9 Buy at Amazon
When Paul Dirac proposed what we now call the Dirac equation, he apparently had gone through a dozen alternatives, which he discarded, even from his filing cabinet. To this day no one knows why he chose the simplest construction rather than the most obvious one or, indeed, any of the others that ended up filling his wastebasket. It is extraordinary that he even stumbled on his final formulation, simple and beautiful as it was, given that it was so far removed from the prevalent mathematics of his day, and also so full of physical oddities.
About a decade after the 1928 publication of the Dirac equation, the quirky Sicilian genius Ettore Majorana published a variation whose wavefunction solutions—Majorana fermions—are real. The truth is that Dirac’s equation is bizarre, and plenty of alternatives existed even after Dirac’s publication. The alternatives are in a way more curious. That some of them made it into the mainstream of physics—after originally being badly misinterpreted—just goes to show the inherent anarchy of the process of producing new science.
If you find this sort of thing interesting, you will love The Physics of Ettore Majorana: Theoretical, Mathematical, and Phenomenological, in which author Salvatore Esposito delves deep into Majorana’s notebooks and published work. The book goes back to the time when relativistic quantum mechanics, quantum field theory, and particle physics were still embryonic. To read about the hits and misses, the clashes, the missed opportunities, the tensions between physics and mathematics, can be nothing but humbling. The chapter on alternatives to the Dirac equation is perhaps the most poignant; the whole book is imbued with the feeling of sailing through uncharted seas.
Majorana was one of the first to think about fundamental theories of nature in terms of group theory and symmetry. At the time, no one around him understood what he was doing. The Majorana fermion and the possibility that the neutrino might be such a particle were some of the offshoots of his work. I have always been enthralled by Majorana’s ability to think out of the box, to oppose trends, and to open up new avenues of reasoning. His mind was unique, and if reading his papers can be challenging, mainly for notational reasons, plodding through his notebooks can feel like a trek in the jungle. Esposito’s book, however, provides the perfect guided tour through his brief but prolific career, in modern language and with proper contextualization.
A few years ago I wrote A Brilliant Darkness (Basic Books, 2009) on the science and person of Majorana because I did not like the pervasive Jekyll and Hyde descriptions of him. For the international physics community, his name conjures thoughts of neutrinoless double beta decay, representation theory, and atomic and nuclear physics. In Italy he has rock-star status because of a stunt he pulled towards the end of his known life. Majorana’s final antic has become a popular detective story, revisited by the Italian press on a roughly biannual basis.
On the night of 26 March 1938, at the young age of 31, Majorana boarded a ship and was never seen again. He left behind notes and telegrams that may be construed as suicide letters, but he also took with him his passport and a large amount of cash. He may have jumped overboard, but his body was never recovered. He was later “sighted” on several occasions, leading to all manner of conspiracy theories. More fascinating, to my mind, is the drama and psychology behind his “vanishing,” whatever might actually have happened on that night.
Majorana’s story is one in which unconventional science mimics unconventional character, and the two aspects should be presented in tandem as much as possible. But if your interests lie in science rather than scientists, up until now you would mainly regret the gaping hole in the literature regarding Majorana’s scientific output. His singular thinking was largely left to specialists happy to trudge through archives and old journals, as well as somewhat unreadable reprints of his papers, often not in English. This book fills the gap and celebrates his legacy in its full glory.
João Magueijo is a professor of theoretical physics at Imperial College London. He works in cosmology and quantum gravity and is best known for his contributions to the varying speed of light theory and to varying-constant models of the early universe.
