The unpublished letters of an "ionized electron that once belonged to a neutral Lithium atom". Enrico Fermi writes to his physicist friend Aldo Pontremoli.

Enrico Fermi and Aldo Pontremoli met at the University of Rome, where the latter had graduated in physics in 1920 with full marks, becoming an assistant by Professor Orso Mario Corbino. Pontremoli, Milanese, from an illustrious and wealthy family; Fermi Roman, from a wealthy but not as illustrious family. The intermediary of their friendship may have been Enrico Persico, a year older than Fermi and his high school classmate, with whom he developed his knowledge in physics through continuous discussions and, after enrolling at the university, through exchanges of letters. and mathematics, already stimulated in both by their common high school physics teacher, Professor Filippo Eredia. It is no coincidence that it was the three of them who won, in 1926, the first three chairs of Theoretical Physics created in Italy. So a trio of friends who laid the foundations of modern physics at a very young age with their research. Fermi reaching the Nobel Prize in 1938; Pontremoli founding the Institute of Physics of the University of Milan, only to die tragically in 1928 on board Umberto Nobile's dirigil.

Here, however, we are at the beginning of their career. We are at the moment of their maximum and most intense scientific production, and these letters testify to the fruitful exchanges that take place between them. Exchanges that mainly concern the discussion on questions of theoretical and practical physics, but which then extend to more practical topics, in particular their future within the University. They are intense and beautiful letters, where you can feel the strength of thought moving inside one of the most brilliant scientific minds of the 20th century. The first were sent from Gottingen, where the young Fermi went after graduating in 1923 thanks to a scholarship obtained also through Professor Corbino. For six months he studied in Gottingen at Max Born's school, and here his scientific production was intense despite the inevitable problems of adjustment. And in one of the letters a reference to Einstein's theory of relativity illuminates this brief correspondence with an absolute light: Fermi comparing himself with Einstein on the theory that founded the modern known universe, a confrontation between giants which we can only witness in admiration. Fermi was just 22 years old, Einstein was exactly double, 44, but physics led them to dialogue on the same level.

Postcard from Gottingen, 13.1.1923 – addressed to Drs. E. Persico and A Pontremoli. Physical Institute – Via Panisperna Rome. Italian!
“Dear friends, I have now been in my new residence for a week, and in these first few days I have naturally found myself a little alone. However, I hope that with time this inconvenience will soon pass. I have already started attending university and getting to know the various professors, especially Max Born. And already now I have been able to understand that in this journey of mine I will have much more to learn than I thought. (…) How's the work with the spotlight going? (…) Affectionate greetings to you, with a prayer to extend them to everyone at the Institute, from this ionized electron that once belonged to a neutral Lithium atom.”Gottingen, 14.1.1923 Pontremoli:Gottingen, 14.1.1923 Pontremoli:He sends the drafts of his speech with a request to correct the errors and print the extracts, asking him for about thirty. He updates him on the work "on the effect of pressure on the broadening of the spectral lines", on the doubts he has, "without of course taking into account the increasingly mysterious mystery of such a large molecular field".Gottingen , 23.1.1923 in Pontremoli:He speaks again of the "cheating affair of the molecular field". “Here people do nothing but deal with quantum theory, so I found the right place for me. What really struck me was the high level of average culture of science students. Let's hope that over time we can improve it a little in Italy too! (…)”Gottingen, 16.5.1923 in Pontremoli:“Dear friend, I have read your notes on the last issue of the Lincei which have arrived here, and I congratulate them. In recent days I have sent to N.C. not one but three notes, one less uninteresting than the others. And so I will try to dirty some paper to present for the competition which I believe will be announced soon. In recent days, a paper by Einstein has been published on a "very general" theory of relativity; interesting especially because it is the first theory in which positive and negative electricity do not differ only in sign. We will see if its further development cannot eventually lead to solving the problem of the electron and the H nucleus. Warm regards. E. Fermi”Gottingen, 22.6.1923 in Pontremoli:He probably communicated to him - via telegram - that a competition had been announced for a university position in Florence-Rome (?) .Florence, 6.12.1925 in Pontremoli, typed letter signed:Deals with serious physical questions relating to the orbits of alkali metals etc. In the end there is talk of university competitions in Rome, Cagliari and Florence, where he is located.Florence, 14.2.1926 letter to Pontremoli:There is talk of university competitions, of baronial maneuvers and disappointments. “I have done theoretical work on the appearance of forbidden lines in an intense magnetic field, and I am doing, together with Carrara, an experimental one on the inverse of the photoelectric effect. (…)”Florence, 11.5.1926, letter to Pontremoli:“Dear Pontremoli, I have been thinking about the question of the possibility of having some experience at Monte Rosa. I didn't come up with any truly sensible ideas; a research that would be nice but is not, in my opinion, possible to carry out, would be a study of secondary corpuscular radiation. A search instead, relatively easy to carry out, but not particularly significant, would be the following. Study the discharge speed of a spectroscope located in a glacier crevasse, in its dependence on the inclination of the glacier; if such a dependence could be highlighted, it could serve to determine elements of the direction from which the radiation comes. (…)”Florence, 9.6.1926 – Letter to Pontremoli:Personal letter in which he communicates that the Theoretical Physics competition for Rome has been announced in the Official Gazette and asks him his opinion on the opportunity to "have as many physicists as possible on the commission". He proposes the names of Cantone and Maiorana.