Alexandru Proca

Alexandru Proca (October 16, 1897, Bucharest - December 13, 1955, Paris), great Romanian physicist, author of the modern approach of the nonzero photon mass and the superluminal radiation field, of the theory of strong interactions, of the Proca massive vector boson field, co-author of the Maxwell-Proca and Einstein-Proca theories.

Alexandru Proca was born in Bucharest in 1897 into a family of intellectuals. A brilliant school boy, mastering a few modern languages as well as Latin and some old Greek as was the curricula of any modern high school at that time, he showed an early appetite for mathematics. Soon after graduation, in the middle of World War I, he was mobilized (1917) and, after a brief instruction in a Military School, was sent to the front. 1918 was a triumphant year for his country, Romania, which saw most of its historic and ethnic borders settled. However the infrastructure for higher education, especially in the sciences and engineering, was quite weak and many young people used to go abroad, mainly to France and later to Germany, to acquire a proper training and qualification. Proca graduated from the newly inaugurated Polytechnic School (PS) in 1922 as an Electromechanical Engineer. He was employed by the Electrical Society Câmpina, a company at the centre of a rich oil field. At the same time he served as assistant professor at the chair of Electricity of the PS, which was headed by Professor Vasilescu-Karpen, a celebrity among many generations of engineers.

The young Proca felt however that he was betraying his natural aptitude for the fundamental sciences, mathematics and physics. Already familiar with Einstein’s papers he anticipated a major breakthrough and thought that he had something to say in this field. It is amazing that as early as 1920, still a student in engineering, he wrote a first paper on relativity, one of not many in the world at that time. So he left a promising and lucrative career to go to Paris (1923), full of expectations. Here, to his disappointment, he discovered that his diploma was useless. What he had to do was to matriculate from a French University and to pass the examinations for the 4-years curricula. This he did brilliantly and one year later he was Licencié en Sciences at Sorbonne, Paris.

In 1925 Marie Curie offered him his first job in her Institut du Radium where he was assigned to make measurements of β rays emitted by thorium descendants. He completed successfully the subject with a publication in Comptes Rendus (Nov.1926), but that marked the end of his experimental investigations. Though he enjoyed much sympathy and appreciation from Mme Curie, she allowed him to pursue his natural calling towards theoretical physics that persisted during all these years in spite of his official daily duties. He was attracted by fundamental problems, such as the intimate nature of light quanta, the atomicity of entropy and even of time; he was one of the first thinkers about a discontinuous spatio-temporal frame. It was however de Broglie who directed him towards the mainstream of theoretical pursuits at that time, namely the Dirac equation and the quantum relativistic fields that had just started to take shape in the pioneering works of Born and Jordan,Dirac himself and Heisenberg. Proca engaged seriously in the programme and after a series of six papers devoted to the Dirac equation published in C. R Acad. Sci. Paris, (1930-33), and two more on the properties of the photon, he submitted an exceptional doctorate thesis to a commission: JeanPerrin, Louis de Broglie, Léon Brillouinand, Aimé Cotton. In 1930 Proca received French citizenship and married Marie Manolesco with whom he had a son, George Proca.

From 1929, when Les Annales de l’Institut Henri Poincaré was founded, Proca was the editor of this famous journal. In 1934 he spent one year with E. Schrödinger in Berlin and a few months with N. Bohr in Copenhagen, where he met Heisenberg and Gamow. From 1936 to 1941 he developed his masterpiece work, the theory of massive vector (spin 1) boson fields governing the weak interaction and the motion of spin-1 mesons. Prestigious scientists such as Yukawa, Wentzel, Taketani, Sakata, Kemmer, Heitler, Fröhlich and Bhabha, reacted favourably to his equations in 1938. W. Pauli mentioned Proca’s theory in his Nobel lecture. As a particular sign of his world-wide recognition one can mention his invitation to attend in 1939 the Solvay Congress. To his misfortune, this Congress could not take place due to the outbreak of World War II. During the war he was for a short time Chief Engineer of the French Radio broadcasting Company. In 1943 he moved to Portugal where he lectured at the University of Porto. In 1943-45 he was in the United Kingdom at the invitation of the Royal Society and the British Admiralty to join the war effort.

After the war he started in 1946 the Proca seminar series in Paris with many prestigious invited speakers from France and abroad including A.Einstein, H.Yukawa and W.Pauli. This seminar contributed very much to the education of young French particle physicists. He accepted to organize with P. Auger in 1950 the Theoretical Physics Colloquium of CNRS and in 1951 to be the French delegate at the General Meeting of the International Union of Physics. By that time the Proca equation was indeed famous as the only sound theoretical basis of the Yukawa meson.

Starting in 1953 Proca began a fight with a laryngeal cancer that lasted until December 13, 1955 when he passed away. He left a major heritage in theoretical physics that by its actuality goes beyond historical interest.