The life of the physicist, historian of science and major scientific administrator Sergei Ivanovich Vavilov (1891–1951) is unusual. Perhaps, when viewed from the 21st century, both his scientific achievements and his heroic, selfless activity as president of the Academy of Sciences (which, moreover, occurred during the years of the shameful defeat of genetics and other similar ideological campaigns) will no longer seem too significant. However, the personal diary that Academician Vavilov kept secretly for many years, recently published for the first time, opens up a surprising new dimension to his intellectual life. In it, historical reality coexists with the world of dreams, daydreams and reflections on deep issues of consciousness, faith, and death. The historian of science A.V. Andreev in his book describes this unexpected side of the personality of S.I. Vavilov and makes an attempt to study his original philosophy.