This book, which is now made public – when CBPF celebrates the 50th anniversary of the granting of the university mandate by the University of Brazil, which, in turn, completes 100 years of life – is the result of the commitment and persistence of more than two decades of Antonio Augusto Passos Videira, responsible for organizing thousands of documents, which the Austrian scientist Guido Beck bequeathed to CBPF as proof of his respect and esteem for this institution. Videira selected a set of letters that show the development of physics in various parts of the world between the 1920s and 1980s. These documents will contribute significantly to a better understanding of the processes by which physics has become a reality in places as different as Cordoba, Rio de Janeiro, Odessa, Leipzig, and Lyon.