The paper is dedicated to the statistical (ensemble) interpretations of quantum mechanics which appeared in the USA and USSR before War II. The author emphasized a remarkable similarity between statements which arose in different social, economical and political contexts. The comparative analysis extends to the scientific and philosophical traditions which lay behind American and Soviet statistical interpretations of quantum mechanics.

The American movement was launched by the young and prominent physicist John Slater and his erstwhile teacher at Harvard, E. C. Kemble. The physicist and philosopher Henry Margenau, who with Robert Lindsay published the first American book on the foundations of modern physics, also pushed the ensemble approach. K.V.Nikolsky and L.I.Mandelstam were the main figures in the USSR. K.V.Nikolsky worked at Lebedev Physics Institute of the Academy of Sciences and, according to recollections and archival material, his quantum endeavors were supported by institute director S.I.Vavilov (who became President of the Academy of Sciences after War II). L. I. Mandelstam, professor at Moscow State University and one of the leaders of Soviet physics, presented his ensemble approach in his authoritative lectures in 1939. In the U.S. the ensemble approach was also proposed by Wendell Furry, while in the USSR it was supported by the Marxist philosopher B.M.Hessen, who took the command positions at the Moscow State University and Lebedev Physics Institute in 1930-1936.

There were cross references in the American writings. In fact, the young Slater attended Kemble’s lectures on quantum mechanics and as a mature physicist he was planning to collaborate with Kemble in elaborating the foundations of quantum theory. The Harvard University Archives and the APS Archives show that Kemble and Margenau exchanged letters in 1935. In 1936 Furry stated the concept of ensemble by referring to the Kemble 1935 article. Although Nikolsky arrived at his ensemble approach independently from the Americans, he referred to Kemble in his 1941 book. After 1934 Nikolsky and Mandelstam both worked at the Lebedev Physics Institute and may have communicated. Mandelstam supervised Hessen’s PhD work at the Communist Academy and subsequently Hessen was his administrative chief at the Moscow State University and the Academy of Sciences. The ensemble approach was touched in the addresses to the seminars which were held at the Moscow State University and the Communist Academy.