(Budapest, March 12th, 1912 – Budapest, March 2nd, 1978)
The reputation and personality of Lajos Jánossy has enticed generations to enter the physicists' profession.
Since the age of 6, he lived abroad: he attended university in Vienna and, later, in Berlin. For a few years, he worked with Kohlhörster in Berlin, and, then, with P. M. D. Blackett - who later became a Nobel Prize winner (1948) - in the field of cosmic radiation at Birbeck College in London and, then, at Manchester University. He moved in 1947 to Ireland and was appointed to a professorship at the Dublin Institute for Advanced Studies. He worked there as the leader of the Cosmic Radiation Laboratory for nearly three years.
In 1940 and 1941, he discovered the penetrative showers of cosmic radiation and identified their most important properties and their relationship to the extended particle showers present in the air.
Based on this, the view was established that, under the effect of the primarily high-energy cosmic particles, an extremely large number of particles - primarily mesons - with high penetration capability are created in the upper layers of the atmosphere. As a result of repeated interactions, a very large number of particles (showers) reach the surface of the earth.
Invited by the Hungarian government, Jánossy returned home in 1950, not only for reasons of promised scientific possibilities, but also because his foster-father (György Lukács philosopher) and his mother had also returned home from their emigration in Moscow.
Jánossy was charged with the task of managing the Cosmic Radiation Department at the Central Research Institute for Physics (Hungarian abbreviation: KFKI) founded in 1950. He was very active in scientific organisation, education and public life. He was appointed deputy director of the KFKI from 1950 to 1956, and the director from 1956 to 1970. In addition, he was also active in university education; the Department of Nuclear Physics at Loránd Eötvös University was established for him.
Until the fifties, the most important field in the research of high-energy particles was the examination of cosmic radiation. But as the large accelerators started to take over the leading role, Jánossy turned away from the examination of cosmic radiation and took the theoretical problems of quantum mechanics, the dual character of light as well as the theory of relativity in hand. The measurements he carried out in connection with the dual character of light supplied results that were expected on the basis of quantum mechanics; yet, due to the requirements of extremely high accuracy, measurements of this kind had not been carried out before Jánossy. In relation to his famous photon experiment, Schrödinger was not slow to write a letter in which he emphasised the importance of the result. In both the measurement of cosmic radiation and the low intensity interference experiment, the correct evaluation of results is of fundamental importance, which justified Jánossy's interest in the statistical evaluation of measurements.
In the last one and a half decades of his theoretical activity, he was engaged in the hydrodynamic model of quantum mechanics and the interpretation problems of the theory of relativity.
Memberships: Member (1950) and, later, vice-president (1961 to 1973) of the Hungarian Academy of Sciences; member of the Bulgarian Academy of Sciences, the Irish Academy of Sciences, the Mongolian Academy of Sciences and the Academy of Sciences of the German Democratic Republic.