\begin{preface}

A meeting on Fermi and Astrophysics was  held at the University of Rome ``La Sapienza'' and the ICRANet Center in Pescara (October 3--6, 2001) in celebration of the hundredth anniversary of the birth of Enrico Fermi (1901--1954). During that anniversary year many events were organized covering the activities of Fermi in particle physics, nuclear physics, statistical mechanics and quantum statistics.  Besides these fundamental fields of physics,  I thought Fermi had also played a key role by pioneering ideas which, directly or indirectly, became crucial for the understanding of some basic conceptual aspects of astrophysics. 
This was the focus of our meeting in Pescara, where a set of lectures were presented,
and I delivered a concluding lecture  in the Aula Magna at the University of Rome ``La Sapienza": ``Fermi, General Relativity, Astrophysics and Beyond.'' 

I gave particular attention to the paradoxical situation of a paper by Fermi and Turkevich in the field of general relativity, cosmology and astrophysics as an example of an extremely rare circumstance in physics. Their results were not published under the authors' names at the time: they were quoted later in a 1950 review published by others together with a declaration of authenticity by the original authors. This fundamental work was not included in the collected papers of Fermi published in the West, whose numbered scheme classification of those papers will be referred to in the present 
volume.\footnote{
\textit{Enrico Fermi: Note e Memorie (Collected Papers)},  
Accademia Nazionale dei Lincei and The University of Chicago Press, Vol.~1, 1961, Vol.~2, 1965;
Volume 1 is available on-line at:\\
http://www.archive.org/details/collectedpapersn007155mbp.
}
It was, however,  included in his collected papers  published in the Soviet Union and it is definitely one of the cornerstone articles of relativistic cosmology and I tried to reach an understanding of how this highly unusual route to publication came about. 

This paper is fascinating from the point of view of its scientific logic and strategy: Fermi was attempting to prove George Gamow wrong, also reproaching him  for improperly using Einstein's theory of general relativity which he considered far from proven. As a matter of fact Fermi proves just the opposite. True, the work of Fermi and Turkevich did disprove some of Gamow's claims about the process of  cosmological nucleosynthesis, but it rigorously derived the correct equations to be used for describing cosmological nucleosynthesis in a  Gamow cosmology in an initially hot universe. Fermi  precisely  formulated the problem  within a Friedmann universe within Einstein's theory of general relativity, although with profound skepticism. The later observations of the cosmological background radiation led, precisely through the work of Fermi and Turkevich, to the triumph of Einstein's theory and of Gamow's theory of an  initially hot state of the universe!

I then realized that a variety of articles by Fermi had not yet been translated from Italian into English, especially those by the young Fermi when he was a student at the Scuola Normale Superiore in Pisa dealing mainly with electrodynamics and the special and general theories of relativity. This led to a lengthy process in which with the help of Emanuele Alesci, Donato Bini, Dino Boccaletti, Andrea Geralico, Robert Jantzen,  Simone Mercuri, we translated from Italian to English a selection of Fermi's papers, including the works of the Pisa period. There were also some other later papers related to astrophysics which, although they had been published in English, for a variety of reasons, had not yet reached the awareness they deserved from the scientific community at large.  
I was well aware of Fermi's skepticism towards the study of the interior structure of stars which he had expressed in a 
1927 lecture in Trento, some excerpts of which we have translated from the Italian in Chapter 1 to document this attitude, which had negative consequences for the Italian development of astrophysics. It was therefore rewarding to discover the scientific  meaning of a  crucial lecture that Fermi delivered later at the University of Rome in October 1949,  ``Theories on the origins of the elements'', recorded by Ettore Pancini,  which we have translated in its entirety into English. I suddenly  became aware of Fermi's deep but unexpected knowledge of cosmology,  in addition to the computation he performed with  Turkevich. We started assembling all of this material.

In the course of our work we also became aware of a scientific result published in a series of six papers   written by Fermi in 1922--1923 during his Pisa period while still a student and later in a temporary position at the University of Florence
and presented  in G\"ottingen in 1924. This result, which has been overlooked in nearly all textbooks, is his solution to the infamous so called ``4/3 problem'' that plagued the classical theory of the electron introduced by Abraham and Lorentz during the same period in which special relativity was born and which was wrongly interpreted by Poincar\'e as due to unidentified internal stresses holding the electron together. I discussed the scientific content of this topic for a few years with Donato Bini, Andrea Geralico and Robert Jantzen.

During the preparation of this material I have become more and more interested in the following points:

\begin{itemize}
  \item[a)] 
\textbf{Fermi's Rome Period}.\\
What were the reasons that Fermi, one of the first scientists to reach  a  deep understanding of Einstein's theory of general relativity and give profound contributions to the theory, already as a student in Pisa, after transferring to Florence in 1924 and in 1926 to Rome, never addressed any issue related to that theory? What could have happened during this Florence transition which inhibited his desire to pursue general relativity further?
In order to reach a better understanding I started to collect testimonies from people who had been  members of the Physics Institute to resolve this question.  I also collected some episodes relevant to understanding the further  history of Italian physics and of the Physics Institute in Rome. 
Of course many books and even movies exist which review
 the glorious achievements of the Fermi group in Rome. 
None of them addressed the specific issue that interested me:
 to better understand  Fermi's apparent lack of interest in general relativity and also in astrophysics  during the entire Rome period. Certainly three different components were present:

\begin{figure}
\begin{center}
\includegraphics[width =3.5in]{chap1_fermi_heisenberg_pauli.pdf}
\caption{E. Fermi, W. Heisenberg and W. Pauli (Como Conference, 1927).
}
\label{chap1_fig2}
\end{center}
\end{figure}


\begin{figure}
\begin{center}
%\includegraphics[width =3.5in]{chap1_fermi_heisenberg_pauli.pdf}
\caption{Finzi, Bleuler, Ruffini, and Tauber.
}
\label{preface_fig2}
\end{center}
\end{figure}

\begin{figure}
\begin{center}
\includegraphics[width =4in]{chap1_amaldi_fermi.pdf}
\caption{Fermi with some of his closest  collaborators in Rome: Oscar D'Agostino, Emilio Segr\'e, Edoardo Amaldi, Franco Rasetti and Enrico Fermi (from left to right).
}
\label{chap1_fig8}
\end{center}
\end{figure}


i) It is possible that Fermi's early interest in general relativity was overwhelmed by the powerful influence of Wolfgang Pauli, Werner Heisenberg and Pasqual Jordan
(see Fig.~\ref{chap1_fig2}) 
which led to his fundamental contributions to quantum statistics, quantum field theory and the theory of weak interactions. I often discussed this issue while  I was working in Hamburg with Jordan on boson stars, %see Fig 
with Heisenberg in Munich on electron-positron pair creation in overcritical electric fields and later with Wigner on observables from Black holes in Princeton. Many important testimonies  came also in discussions over many years with my close friend Arrigo Finzi (see Fig.~\ref{preface_fig2}), %see Fig 
who had been a student of Fermi in the Physics Institute and had as thesis advisor Tullio Levi-Civita in the Mathematics Institute.   
A lot I learned from Edoardo Amaldi, my teacher in Rome, who had been a close Fermi collaborator  (see Fig.~\ref{chap1_fig8}). %Fig 3 

ii) It also appears  that a fundamental role was played by
the outrageous anti-Semitic campaign which started in the early thirties in Germany and Italy and which by the end of the decade had led to the
 infamous racial laws of the Italian Fascist government and to the tragic expulsion from teaching  of some of the best scientific minds in Italy. The most dramatic case was certainly the one of Tullio Levi Civita. 
It was clear that this situation had made it impossible to pursue research on Einstein's theory during those years in Italy.

iii) There was also a third factor that the only observable effects of general relativity at that time were qualitatively very small, and had either been measured without sufficient accuracy to assert the uniqueness of the theory, namely the bending of light by the sun and the perihelion precession of Mercury, 
or it would be many decades later before 
and the predicted gravitational redshift could be observed. 
There were some fascinating possibilities that the point-like emission of a star would appear as a ``ring" (the Einstein ring) \cite{einsteinring} but no one could remotely imagine how to detect such a possibility then.
This was in sharp contrast with the almost daily success of experimental nuclear and atomic  physics. Moreover, general relativity as a theory was confronted with great mathematical difficulties and was drifting away from mainstream physics.
Examining Fermi's work during his Italian period one sees his initial  lack of  interest in  astrophysics that I spoke of above. 
I deciphered the reasons for this in an earlier speech given by Fermi in Trento to which I referred above. Unfortunately, such an attitude affected much of the further developments in the Rome school. It was an unfortunate  scientific missed opportunity not to have Fermi apply his genius to the early development of this  important field which was mainly developed by the English School in Cambridge. As we will see Fermi changed his mind towards the very end of his life.
 
\item[b)]
\textbf{Fermi's American period}.\\
Since Fermi's success in particle physics is well documented, I  
have limited my attention to three different aspects of this period:

i) To keep an eye open towards the Physics Institute in Rome and the evolution of its scientific interests, eagerly  searching for  any change in attitude or  a possible reconsideration of Einstein's ideas. Even marginal effects as the attribution of a name of a street can in this respect  have some significance in gauging the popularity and feeling for that research. 

ii) Fermi's novel interest in cosmology and astrophysics at the end of the Los Alamos war effort, expressed in  his joint work with Turkevich. 
This work was marked by a severe attitude of Fermi   towards  both Gamow and Einstein and to me the reason for his unwillingness to publish it himself still had to be explained. I try to justify his attitude towards Einstein's theory. 
  I have tried to justify his attitude toward Einstein's theory noting some equally
critical considerations of Richard Feynman towards that theory during the same time frame.  
I especially discussed this issue for many years with Yakov Borisovich Zel'dovich and  more recently a yet different point of view surfaced in discussions with  Riccardo Giacconi pointing to an even more extreme position. In  Riccardo's opinion Fermi did not attach any real astrophysical meaning to his computation and was considering his contribution  more as  a pedagogical example to teach Gamow how to be more careful in his work. 
On the other hand I could not avoid  noting  the deep chasm between Fermi's attitude towards cosmology and  the  equally fundamental work in that field  developed in the United States around the figures of  Einstein, Hermann Weyl, and Kurt G{\"o}del. I was of course very much influenced in this by the truly unique experience of my many discussions with G{\"o}del about his vision of cosmology.

iii)  Fermi's unexplained lack of interest in the work on neutron stars developed by George Gamow and Robert Oppenheimer and his school. A bitter confrontation between Einstein and Oppenheimer had developed  over the issue of the continued gravitational collapse of a neutron star with overcritical mass (see Fig.~\ref{fig:einopp}). 
Quite apart from the role of Fermi, this fundamental conceptual issue had been attracting my attention for years. Turning to Fermi,
 only in the very  last years  of his life did he begin to take an interest in white dwarfs and their critical mass, working as an adviser of the thesis by T.D. Lee. Indeed only in recent months have I have reached an understanding of the possible reasons why he was extraneous to this fundamental work of theoretical physics on neutron stars. 

\item[c)]
\textbf{The post Einstein-Fermi era and the birth of relativistic astrophysics}.\\ 
At the death of Einstein general relativity was still plagued by tremendous technical difficulties and by a profound detachment from the rest of physics, well expressed by Richard Feynman.
When Fermi died, his work with Turkevich was largely unknown and it would have been remembered as a severe criticism of Einstein and Gamow and at best as an exemplification  of an alternative more rigorous and cautious procedure in approaching an astrophysical problem. Its  special astrophysical significance and implications was certainly not clear  at the time. 
Heisenberg's work with Euler and the successive relativistic extension by Schwinger on vacuum polarization  was  still unsuccessful  in finding experimental support at the time: the  attempts to  discover electron-positron pairs created by overcritical fields, initially announced to be successful, were then disproved, and they will remain so for years to come in the routine analysis of  heavy ion collisions. 
While I was mulling over all these issues during the past decade I continued my work in relativistic astrophysics and was witnessing on a daily basis the tremendous relevance to the field of relativistic astrophysics of the classic papers of these three giants: Fermi, Einstein and Heisenberg.
\end{itemize}

\begin{figure}[h]
\centering
\includegraphics[width=3.5in,clip]{chap1_einopp.pdf}
\caption{In a classic paper, Einstein objected to the possibility of an object not rotating to approach asymptotically, as postulated by Oppenheimer and Snyder, its Schwarzschild horizon \protect\cite{eincluster}. Only recently it has been shown that the Einstein objections do not prevent the formation of a black hole (see our concluding remarks).}
\label{fig:einopp}
\end{figure}

From this thinking came the decision to structure all of this material in a book dedicated to 
Fermi, Einstein, Heisenberg and relativistic astrophysics.

The real revolution came with the birth and development of relativistic astrophysics. The discovery of the cosmic background radiation, the discovery of pulsars, the discovery of binary X-ray sources,  all offered the first possibility of realizing tremendous opportunities to test and further develop all of these theories. 
A new conceptual era for the study of the theory conceived by these three giants was made possible by multiple factors both in the theory and in observations.
The introduction of  novel concepts like that of a black hole as a physical and astrophysical entity was a crucial point and  its observation in a binary system in our galaxy has been critical.
Similarly the enormous technological and experimental   progress made possible in space in gamma-ray, X-ray, and optical astronomy, and the similar developments of ground-based and underground observatories  as well in the astroparticle physics domain were equally important. 
The greatest and most fundamental new results have come from  the utilization of their ideas not in the isolation that they had created between themselves while alive but in a profound new interaction unhampered by their personal prejudices: 


1) The discovery of the cosmic background radiation  was the first sign of the birth of the new era of relativistic astrophysics: the Fermi-Turkevich paper far from representing an academic exercise and a criticism of Gamow and Einstein theory has become the guiding theoretical work of cosmological nucleosynthesis  and the strongest proof both, now widely recognized,  of the validity of Einstein's theory and Gamow's prediction of an initially hot Friedman Universe.

2) The  Thomas-Fermi model, so often celebrated by Wigner, can also be used as an additional prototype:  quite apart from its daily utilization in atomic and solid state physics, it has become a leading component of a novel description of neutron stars. However, to reach this description it has been essential to generalize the this model to the realm of general relativity and introduce all the fundamental interactions in addition to just the gravitational one: it needed a unified approach based on the strong, weak, electromagnetic, and gravitational forces. The generalized model now represents  one of the  most difficult and rigorous system of equations ever introduced in physics and is leading to a new picture of white dwarfs and  neutron stars with novel observational properties. 

3) In a similar vein, in the description of vacuum polarization processes in overcritical electromagnetic fields, after many years of unsuccessfully attempting to observe the electron-positron pair creation in heavy-ion collisions, it has become possible to observe such a phenomenon on a grandiose astrophysical scale in the collapse to a black hole. The Heisenberg-Euler process is becoming observable in the gamma-ray bursts (GRBs), the most energetic and violent sources in the Universe, second only to the big bang. It had been necessary to further extend to  general relativity Schwinger's special relativistic formulation of the Heisenberg-Euler work in order to lead to a physical process of extraction of the blackholic energy of a black hole and create the expected electron-positron pair plasma, essential to the understanding of GRBs. This occurs in the process of gravitational collapse of an overcritical neutron star which is itself an outcome of the Thomas-Fermi equation properly extended to Einstein's theory of general relativity.


In these three  examples the greatest fruition of the separate ideas of Fermi and Heisenberg came from  joining them together with Einstein's theory of general relativity, which they had generally ignored, apart from Fermi in his earlier Pisa period. 
Similarly  the study of general relativity, confined to a very tiny number of specialists caught between the mathematical difficulties of solving Einstein's equations and the almost total absence of experimental support and motivation, was drastically  modified:

a) First  the introduction of numerical techniques to solve Einstein's equations and of algebraic manipulation techniques to handle their tensor formalism made an essential difference. 

b) The unexpected and revolutionary results of the discovery of gravitational waves made a tremendous difference in the astrophysical community: to see directly general relativistic effects in the evolution of a binary system.

c) The further step of introducing physical and astrophysical objects totally described by general relativity as black holes and the wealth of their observations in binary systems within our galaxy nearby galaxies as well as their observations in extragalactic active galactic nuclei signed the clear establishment of the field of relativistic astrophysics.

Even the work of Einstein on his Einstein clusters, originally developed as a counterexample to the work of Oppenheimer and Snyder on continued gravitational collapse,  has gained a new relevance and may lead to a new understanding  of the nucleus of our own galaxy. It has finally become clear that in his work on clusters, Einstein had already understood many of the properties  of the Schwarzschild solution, later attributed to Kaplan. 
Somehow he had not believed the results he had obtained with his correct theory and exact computations. Often  physicists make a mistake in writing  or solving  the field equations, but seldom  great physicists, as in this case,  write the correct equations, express the correct solutions but fail to accept the logical consequences of their own work!

All this could have never have been possible without the technological developments of the past half century since the beginning of the space age and the start of high energy physics studied in particle accelerators.  

In my short excursus  I have purposely avoided  entering into matters already extensively treated elsewhere, including in my own books,  and have focused on a historical perspective regarding some yet unpublished considerations and events which  I have either witnessed directly or reconstructed from other witnesses in Rome, Princeton, Cambridge, Moscow and in locations where relativistic astrophysics first began. 
The volume contains three chapters and three appendices including either commentary articles or reproductions of relevant historical and more recent articles.


%INSERT
\subsection*{Chapter 1}

After a general introduction I proceed to recall briefly our translation into English of Fermi's early papers  from those in general relativity written at the University of Pisa through the articles published in Florence and  those written upon his arrival at the Physics Institute in Rome, including his three classic papers on  quantum statistics, the Thomas-Fermi atom and establishing the foundation for the theory of weak interactions. 
These papers are  all contained in Chapter 2.

I then focus on some justification given by Fermi not to enter into the topic of the internal constitution of stars as contrasted with the superb contemporary work started in England by R.H. Fowler who had been the teacher of P.A.M. Dirac of applying the quantum Statistics to the solution of the enigma of the white dwarfs. I then recall the determination of the critical mass of white dwarfs  by H.C. Stoner based on the concept of ``exclusion principle'' for the electrons in white dwarfs, later known as the ``Pauli principle.'' I then recall the derivation of the critical mass by S. Chandrasekhar and independently by Landau using the Emden polytropic equations. 

I then return to general relativity and recall the difficult years from 1930 to 1960 in presence of a meager support from experiments, the field was kept alive thanks to the intervention of a few remarkable physicists and mathematicians  who save the message of Einstein for posterity. Next I turn to the situation in the University of Rome: the profound influence  the mathematicians in Rome had on the development of general relativity especially through the work of Levi Civita. 
The ambiance in the Physics Institute of Via Panisperna was clearly dominated by the work of Fermi in nuclear physics and has not be  my intention to cover any of these crucial  events  in the history of physics, covered by innumerous books. I only recall some of the discussions with Heisenberg who confirmed me his profound admiration for Fermi works and his exponential growth from a post doc in Gottingen and Leipzeig to a towering leader of the group in via Panisperna. What I recall, instead, is the devastating action of the racial laws of the Fascist government in Rome which soon led to the destruction of the Mathematics and Physics Institutes in Rome and indicate that nobody would have cared to work on Einstein theory under these circumstances.   
This was the moment of the awarding of the Nobel prize to Fermi, his departure from Rome, the beginning of Fermi American period and the European destruction by World War II. 

After the war, I first recall the situation at the University of Rome and the ambivalence there  with respect to Einstein's theory, and then one of the most significant contributions of the group of Oreste Piccioni for the properties of the mu meson as well the work Occhialini and Lattes in Brazil originally inspired by Fermi. These experiments signaled one of the greatest successes of the ``wild" physics originating in astrophysical observations and the birth and transition to the ``tamed" physics developed by  ``big" science  in  Earth-bound experiments.
In order to locate the contribution of Fermi after the Los Alamos in cosmology  I briefly recall the birth of cosmology as a precursor to relativistic astrophysics, the role of Einstein and G{\"o}del  and especially the contribution of the Soviet-Russian school on Cosmology: Landau, Lifshitz and Khalatnikov.  In particular, I recall some personal dialogue with G{\"o}del on this subject. 
I then enter in the matter of the Fermi-Turkevich paper:

a) I have not found any better way to illustrate the comprehension and motivation of this fundamental work then to use the words of Fermi in his 1949 lecture at the Marconi Physics Institute in Rome (see Par 1.13).

b) I have commented the main point of the Fermi-Turkevich paper using Fermi words and using the diagram and formulae from their original paper (see Par. 1.14).

c) The proof of the impossibility of building all elements by neutron capture in an early Friedmann universe  but just the light elements is then reached and the Fermi's negative conclusions of Gamow work and the use of Einstein Theory (see Par. 1.15).

I turn then to the reasons why the paper was not published and some of the most interesting reactions and less known reactions by Zel'dovich and the final flamboyant conclusion of George Gamow:

1) On the reason of not having the paper submitted for publication I quote two possible opinions by Ya.B. Zel'dovich and by Riccardo Giacconi. I also present a personal consideration and I leave the issue open to the judgment of the reader by simply quoting some final remarks by Fermi. 

2) I then recall the opposite view of an initially cold universe by Ya.B. Zel'dovich presented on an ideological conflict and his final approval of Gamow work.

3) The flamboyant adventure of George Gamow who had the incredible success of having Pope Pius the XII quoting the Gamow theory  in a speech as the correct cosmological theory and Gamow in turn citing Pope PIUS XII in a paper in {\it Physical Review}  as testimony of the correctness of his theory while Fred Hoyle, on the basis of his own theory of continuous creation,  was addressing derogatorily 
both Gamow and Pope Pius XII considering their theory just a ``Big Bang." In due time the derogatory word of Hoyle became the name of the new correct cosmology and the theory of continuous creation the interest of a steadily decreasing number of scientists reaching a set of measure zero in the physics community. 

The last papers of Fermi with S. Chandrasekhar previous to his death were dedicated to astrophysics, one of his last messages to Rosanna Cester: \lq\lq Go to astrophysics, there is the future of physics!'' 
After the death of Fermi and Einstein general relativity or better, the relativists had plunged in the lowest level of popularity in science well represented in the words of Richard Feynman. But again  as I have expressed the authentic resurrection of general relativity was just around the corner  and its reincarnation came in the field of relativistic astrophysics, where also the works of Fermi and Heisenberg within general relativity acquired new profound meanings.

In the description of the birth and development of relativistic astrophysics I am following the reconstruction of personal experiences since my earliest days as a student to my postdoc at Princeton and return to Rome. My first experience as a summer student at CERN was for me  important in clarifying my  own attitude toward ``caged" physics in accelerators versus ``wild" physics in the Universe and how from an initial sense of frustration, I drifted in my interests toward the knowledge of the universe made possible by the birth of relativistic astrophysics. I recall some of the  
precursors 
\\{\textbf precursors??}\\
in general relativity: Lifshitz and Khalatnikov, Regge and Wheeler, Kruskall and Kerr. I then recall the  three major breakthrough in observations: 
1) the birth of  X-ray astronomy, quoting a lucid  reconstruction of these events by Herb Gursky; 
2) the Discovery of the cosmic Background radiation made possible by the use of the Bell Labs antenna by Penzias and Wilson and 
3) the discovery of pulsars by Jocelyn Bell and Tony Hewish and their group in Cambridge England. 

I then turn again to some personal recollections: the completion of my thesis in Rome, my first post-doc in Hamburg with Pasqual Jordan  and the emergence of the work on boson stars. This very intense period was followed by my encounter in Paris with P.A.M. Dirac and J.A. Wheeler and  my transfer to Princeton  in September 1967. In Paris Wheeler was accompanied by Charles Misner and we had already at that time a discussion on the neutron star structure where I presented some doubts about the traditional approach. For those doubts to  become a reality took  some 35 years of further work as I will describe below!

Arriving in the United States in early September I went directly to the University of Maryland  to meet Joe Weber in view of the  keen interest Amaldi had in his work.  I soon returned to Princeton and I have recalled the visit in Princeton of Brandon Carter in the early December which had a profound impact, with his mathematical craftsmanship,  on my later work for years to come.  

What is also remarkable is that this absence of interest by Fermi for Einstein's theory continues throughout his entire American period: paradoxically the only work he did using Einstein's theory was the one by Fermi and Turkevich that he never published. Again there might have been many reasons for this decision not to publish these results. Some of these reasons are analyzed. Some of the words by Fermi himself given in the Rome lecture of 1949, now available in translation in this volume, may well clarify his scientific attitude. From that becomes clear a skepticism toward the use of Einstein's theory. The outcome of all this is that, independent of Fermi's personal attitude, cosmology and general relativity have made a tremendous leap forward using precisely that Fermi-Turkevich paper.
We then recall the particular interest Fermi had in astrophysics in the last years of his life 
and note the enormous impact of his work on some of the most recent developments of relativistic astrophysics.

Appendix A contains the reproductions of a number of classic articles relevant to these issues as well as more recent ones which carry to fruition earlier ideas of Fermi. It begins with the celebrated paper {\it On the theory of stars} by L.D. Landau,
and follow with two recent articles closely linked to Fermi's original work.
In the first the classic work of Fermi-Metropolis-Teller (FMT) at Los Alamos describing compressed atoms has been generalized to relativistic regimes both in the case of atoms and compressed nuclear matter. The FMT work was based on the Thomas-Fermi model of the atom appropriately modifying the boundary conditions to take into account compression. Generalizing this to astrophysical applications required the special relativistic generalization of their equations given in the first of these two papers. The second paper applies these considerations to the theory of white dwarfs and Fermi, having himself worked on this topic with T.D. Lee, would have enjoyed seeing this result. In particular these papers finally settle the multi year dispute between Chandrasekhar and Eddington from those days.

Next are two papers which illustrate the development of Fermi's school in Brazil following the transfer there of Giuseppe Occhiolini and his collaboration with Cesare Lattes, of Italian origin, and which recall the extraordinary activities of this small group of scientists. This is followed by an excerpt from Gamow's autobiography which deals with the scientific activities in Rio and then
a reminiscence by myself of his interactions with G\"odel in Princeton.
We then reproduce two papers on the role of neutrinos in cosmology which are linked to Fermi's beta decay paper (paper 80a) reproduced in Chapter 2)
where the idea of a massive neutrino was first proposed and it was shown explicitly how massive neutrinos would influence the original nucleosynthesis calculations of Fermi and Turkevich and lead to a new formulation of the Jean's instability put forth by Gamow in the formation of cosmic structure, and possibly lead to a cellular fractal structure of the universe.

The next article addresses the introduction of black holes by Ruffini and Wheeler and signal the coming of age of the field of relativistic astrophysics, followed by the review written by Ruffini for the Kerr Festschrift outlining the physics of gamma ray bursts, the most novel generalization of Fermi's work on electromagnetic structure in gravitating systems. As mentioned above, there is an underlying puzzle about Fermi's lack of interest in Einstein's theory in the latter part of this life. The last year of Einstein's life was also marked by a bitter disagreement between himself and Oppenheimer regarding the possible existence of continued gravitational collapse which later became known as black hole formation. Also motivated by the completion of this work explaining the complex relationship between Einstein and Fermi, we thought it appropriate to revisit Einstein's classic paper on Einstein clusters reproduced here as a reminder that his theoretical discussion offers no counterexample to black hole formation.

Finally as outlined in the reflections of Chapter 1, the greatest conceptual revolution in recent years has come from concepts originally introduced by Fermi and from concepts derived from general relativity. The description of fermions subject to a treatment taking into account all four fundamental interactions has characterized a new understanding of white dwarfs and neutron stars. It has also led to the understanding of the presence of ultracritical electrodynamical fields previously ignored in this self-gravitating system. These considerations are at the very foundation of recent developments in relativistic astrophysics. A series of six additional contributions along these lines are reproduced next. In the first of these describes the possibility of interpreting soft gamma ray repeaters and anomalous  X-ray pulsars in terms of rotating white dwarfs satisfying the new system of field equations mentioned above. The next article is particularly important since it represents the conceptual transition from the supercharged nuclei originally considered by Popov and Zel'dovich and the new concept of a neutron star treated as a very large nucleus with $10^{57}$ nucleons. The third article enters this topic in even greater detail. The last three articles address the conceptual aspects of the first self-consistent general relativistic solutions for a system of degenerate neutrons, protons and electrons in beta equilibrium, the first showing the impossibility of enforcing local charge invariance on such a self-gravitating system. The next article then points out the relevance of the Klein first integrals in an equilibrium system with electromagnetic, weak, strong and gravitational interactions. The conceptual alternatives to the traditional treatments of self-gravitating systems presented in these two articles are then applied in the final article to the computation of the neutron star equilibrium configurations within a fully relativistic theory taking into account all four fundamental forces of nature. The observational consequences of the new determination of the ranges of values of the mass, radius and moment of inertia  of a neutron star are outlined there. The article emphasizes how these results represent the maximum extension of the concepts introduced by Albert Einstein and Enrico Fermi and they have been made possible by the development of numerical and computer algebra computer techniques, motivated by a wealth of astrophysical observations which has grown exponentially since the birth of relativistic astrophysics in 1967 right up till the present moment.
I maintain that both in technology and in the theoretical understanding there is no simple rational planning: Nature always guides the progress of the results of  human understanding in spite of, and occasionally using, awkward human attitudes!

Next are reproduced the ``bare minimum'' of articles which helps us understand and place in context the Fermi-Turkevich contribution to cosmology:

\begin{itemize}

\item[1)]
four papers by George Gamow,

\item[2)]
the transcription of the lecture given by Fermi at the University of Rome (October 1949) as recorded by E. Pancini, followed by the celebrated contribution of Fermi and Turkevich as it appeared, inserted in the paper by Alpher and Herman (see below),

\item[3)]
a paper by Yakov Borisovich Zel'dovich.

\end{itemize}

In the first three papers 
(\textit{
R.A. Alpher, H. Bethe, G. Gamow: The Origin of Chemical Elements; 
G. Gamow: The Origin of Elements and the Separation of Galaxies; 
G. Gamow: The Role of Turbulence in the Evolution of the Universe}) 
Gamow  sketches his theory on the formation of the elements in an expanding universe and outlines a theory of the formation of galaxies.
The first paper is well known as the ``alphabetical article'' \footnote{
A witty clarification on the presence of Bethe among the authors is supplied by Gamow himself in his book ``The Creation of Universe'' (Viking Press, 1951) --- see p.~65 of the second printing, 1952. The same anecdote was told in advance --- two years before --- by Fermi in his lecture (see the  paper 240.3) in this chapter).
}.
The third paper 
(\textit{G. Gamow: The Role of Turbulence in the Evolution of the Universe}) 
is of an unusual nature: it starts with the famous citation ``It can be considered now as an unquestionable truth...'' from the address by Pope Pius XII to the Pontifical Academy of 
Sciences,\footnote{
Now one can read it in the volume Pontificia Academia  Scientiarum, Discorsi dei Papi all'Accademia delle Scienze (1936-1993), Citt\`a del Vaticano, MCMXCIV. The passages  quoted by Gamow are at pp.~89, 90, 91.
In Italian: 
``... risulta che, da uno a dieci miliardi di anni fa, la materia di tutte le nebulose spirali si trovava compressa in uno spazio relativamente ristretto, allorch\'e i processi cosmici ebbero principio.
... La densit\`a, la pressione e la temperatura debbono aver raggiunto gradi del tutto enormi, ... Solo con tali condizioni si pu\`o comprendere la formazione dei nuclei pesanti e la loro frequenza relativa nel sistema periodico degli elementi.''
}
and sketches the substantial fundamental ideas which later have come to be known as Gamow Cosmology and the theory leading to the discovery of the cosmological black body radiation and it outlines as well some very interesting ideas for the formation of structures in the early universe still of great interest today.

The fourth paper 
(\textit{G. Gamow: Expanding Universe and the Origin of Galaxies}) 
is, in a certain sense, the final version of the Gamow theory. In it, more than a decade before the observational discovery of the cosmic microwave background radiation, Gamow theoretically predicted the temperature of this radiation. His prediction was only based on general formulas of cosmological dynamics and in no way related to primordial nucleosynthesis. Thus, even if the calculations made by Fermi and Turkevich are shown to agree with the figures regarding the galaxies, the predicted temperature ($7^\circ K$) does not depend on nucleosynthesis. This fact has long been questioned by several authors but an actual error has never been demonstrated.
A.D. Chernin settled the question.\footnote{
See  
\textit{A.D. Chernin: How Gamow calculated the temperature of the background radiation or a few words about the fine art of theoretical physics}, \textit{Physics Uspekhi} {\bf 37} (8), 813--820 (1994).
}


There is no better way to appreciate Fermi's point of view in this matter than to read the text of the lecture Fermi gave at the University of Rome (1949) on the theory of the origin of the elements which we have translated here. In October 1949 Fermi was invited by the ``Fondazione Donegani" to deliver a series of lectures  in Italy on selected topics of atomic physics. The lecture presented here is particularly important since it is evidence of Fermi opinion of about the cosmological models of his time and the role he should have been able to play in the foundation of a relativistic theory of cosmology. This paper is indeed essential in understanding the point of view of Fermi on cosmology as discussed in detail in Chapter 1.
 
Reprinted here is an excerpt of pp.~193--197 from the celebrated  article  by Alpher and Herman in \textit{Reviews of Modern Physics} entitled \textit{Theory of the Origin and Relative Abundance Distribution of the Elements}. The section \textit{The formation of light nuclei} contains the authorized version (see the footnote on p.~194) of the Fermi-Turkevich calculation. 

Last but not least is the paper Ya.B. Zel'dovich: \textit{Pre-stellar state of matter} quoted and discussed in Chapter 1.


\subsection*{Chapter 2}
   
Chapter 2 reproduces the English translation of the papers originally published in Italian during Fermi's Pisa and Rome periods. The most famous of these introducing Fermi coordinates and Fermi transport (implicitly defining what later became known as Fermi-Walker transport, see a commentary article in Appendix C) was indeed a detour from Fermi's initial investigation of electromagnetic mass in special and general relativity that seems to have been largely ignored over the past ninety years. 
Appendix B  includes a commentary paper on Fermi's resolution of this ``$4/3$ problem" in the ratio between inertial mass and energy for the classical electron Coulomb field and a shorter journal article summarizing the natural completion of Fermi's original ideas about electromagnetic mass, 
followed by a historical context commentary paper. Finally we reproduce the related article from 1949 by B. Kwal which seems to be the only one to touch upon this topic until the independent work of Rohrlich in 1960, after which Fermi's original contribution was rediscovered.

\subsection*{Chapter 3}

Chapter 3 reproduces some of Fermi's classic papers from his American period regarding the origin of cosmic rays and the mechanism of their acceleration, the interstellar magnetic field and its importance in astrophysics (in this field, Fermi was a pioneer), and the famous Fermi-Pasta-Ulam paper on nonlinear problems.

Appendix C  reproduces a selection of the proceedings articles of the 2001 meeting \textit{Fermi and Astrophysics} held in Pescara and Rome. These are either commentary articles about particular articles by Fermi, or closely related applications thereof.

I am particularly grateful to my colleagues for their translation of the Fermi papers into English: 

Emanuele Alesci for papers 4c) and 5), Donato Bini and Andrea Geralico for papers (1), (2), and (3), Dino Boccaletti for papers (7), (10), (12), (13), (30), (38), (80a), and (240.3), and Simone Mercuri for paper (43), using the article labeling system from the two volume set of Fermi's collected works. Robert Jantzen has edited these translations for English expression. Andrea Geralico and Massimo Regi have given invaluable assistance in the typesetting process uniting original text and article reproductions in a single LaTeX document.



\begin{flushright}
{\it R. Ruffini} 
%and D. Boccaletti}
\end{flushright}
\end{preface}

\endinput
I have only recalled a less known aspect on the influence of Fermi on the start of modern physics in Brazil and the great discoveries there of Giuseppe Occhialini, Cesare Lattes and Gleb Wataghin. 
