Enrico Fermi: The Paper Nature Rejected
There is a useful lesson in the fact that the founding paper of weak-interaction physics was rejected by the most prominent journal of its day. Fermi published it elsewhere, in Italian and then in German, and it became one of the most consequential theoretical papers of the twentieth century. He also supplied the word everyone now uses: neutrino, the little neutral one, an Italian diminutive coined to distinguish Pauli's particle from the neutron.
Turning a Guess Into a Theory
Pauli had proposed a particle. That is not the same as having a theory. What was missing was a mechanism: how does a neutron inside a nucleus turn into a proton, an electron and this new neutral thing, and how often?
Fermi supplied it in 1934 by analogy with the emission of light. In electromagnetism, a photon is created at the moment an atom changes state - it does not exist beforehand. Fermi proposed that the electron and neutrino are likewise created at the moment of decay rather than sitting inside the nucleus waiting to leave.
He wrote this as a direct interaction between four particles at a single point, with a coupling strength that had to be measured rather than derived. That constant is now called the Fermi coupling, and its small value is what makes the weak nuclear force weak.
The theory made predictions. It gave the shape of the electron energy spectrum, which matched observation, and it related decay rates to the available energy. It was a working quantitative model of a force nobody had described before, built from an analogy and one measured number.
Too Remote From Reality
Fermi submitted the paper to Nature, which rejected it. The stated reason was that it contained speculations too remote from physical reality to be of interest to the reader. He published it in the Italian journal Il Nuovo Cimento and then in the German Zeitschrift fuer Physik, and it circulated from there.
The rejection is quoted often, usually as a joke at the referee's expense. It is more interesting read straight. In 1934 the neutrino had not been detected, the neutron was two years old, and the paper proposed a new fundamental force on the strength of an analogy. A cautious editor was not being unreasonable.
What made the difference was not that Fermi argued harder. It was that the theory produced numbers, those numbers matched measurements, and it kept doing so as measurements improved. The paper won on the only ground that ultimately counts.
It is worth holding both halves of that. The rejection was defensible at the time, and it was wrong. Peer review filters out most bad ideas and occasionally a good one, and the correction comes from evidence rather than from insistence.
The Rest of the Work
Fermi is unusual in having been first-rate at both theory and experiment, which was already rare in his lifetime and is close to extinct now. His 1938 Nobel Prize was for work on neutron-induced radioactivity and the discovery that slow neutrons are far more effective at inducing it.
The award had a second use. His wife Laura was Jewish, and Italy had introduced racial laws that year. The family travelled to Stockholm for the ceremony and continued to the United States rather than returning.
In Chicago on 2 December 1942 he directed the assembly of Chicago Pile-1 and achieved the first controlled, self-sustaining nuclear chain reaction, under the stands of a disused sports field. He later worked at Los Alamos.
He died in 1954 at the age of fifty-three. Fermions are named after him, along with an element, a laboratory, a class of estimation problem and the paradox about the absence of visible extraterrestrial civilisations.
Frequently asked questions
What did Fermi actually add to Pauli's idea?
A mechanism and a calculation. Pauli proposed a particle; Fermi proposed how the decay happens - electron and neutrino created at the moment of decay - and produced a theory that predicted the electron energy spectrum and decay rates.
Did Nature really reject the paper?
Yes, on the grounds that it contained speculations too remote from reality to interest the reader. Fermi published it in Italian and German instead, and it became the foundation of weak-interaction physics.
Where does the word neutrino come from?
From Fermi. It is an Italian diminutive meaning the little neutral one, coined to distinguish Pauli's proposed particle from the neutron, which had been discovered in 1932 and had taken the name Pauli originally used.
What was his Nobel Prize for?
For neutron-induced radioactivity and the discovery that slow neutrons are far more effective at producing it. It was awarded in 1938, and the journey to the ceremony allowed his family to leave Fascist Italy.
What is the Fermi coupling constant?
The measured strength of the interaction in his beta-decay theory. Its very small value is the reason the weak nuclear force is weak, and therefore the reason neutrinos interact so rarely.
