Tachyons before tachyons: Lev Strum (1890–1936) and superluminal velocities

No particle or signal carrying information can travel at a speed exceeding that of light in vacuum. Although this has for a long time been accepted as a law of nature, prior to Einstein’s 1905 theory of special relativity the possibility of superluminal motion of electrons was widely discussed by Arnold Sommerfeld and other physicists. Besides, it is not obvious that special relativity rules out such motion under all circumstances. From approximately 1965 to 1985, the hypothesis of tachyons moving faster than light was seriously entertained by a minority of physicists. This paper reviews the early history concerning faster-than-light signals and pays particular attention to the ideas proposed in the 1920s by the little-known Ukrainian physicist Lev Strum (Shtrum). As he pointed out in a paper of 1923, within the framework of relativity it is possible for a signal to move superluminally without violating the law of causality. Part of this article is devoted to the personal and scientific biography of the undeservedly neglected Strum, whose career was heavily—and eventually fatally—influenced by the political situation in Stalin’s Soviet Union. Remarkably, to the limited extent that Strum is known today, it is as a literary figure in a novel and not as a real person.