  Recollections about a few episodes from the history of physics of vacuum,
connected with the names of Pomeranchuk, Landau, Zeldovich, Sakharov and
Kirzhnits. The text of the talk will be published in the Proceedings of the
International Conference ``From the Smallest to the Largest Distances'',
Tribute to Jean Tran-Thanh-Van, May 24-26, 2001 (``Surveys in High Energy
Physics'', Taylor and Francis, 2002, v.16, No.3).
