Archive of historical materials
Idea: On the Theory of Positrons
OU1934-B9 (4 pages) Date: January 6, 1935
In 1929, Paul Dirac proposed the relativistic Dirac equation that described the behavior of electrons. The existence of positrons was predicted as a consequence of this equation, and their existence was confirmed by a cosmic ray experiment conducted in 1932. Dirac believed that a space in “vacuum” state was filled with an infinite number of electrons in negative-energy states. This was called the Dirac sea and implied an infinite negative electric charge filling all of space. Therefore, many people thought that the Dirac theory was incomplete.
Yukawa also addressed this issue. He believed that negative electric charges and positive electric charges should be treated symmetrically and that electrons and positrons had their specific fields. Based on that idea, Yukawa attempted to formulate a theory. Yukawa jotted down his ideas in this notebook. However, his attempt was unsuccessful and his endeavor faced deadlock. In page 4, he drew graffiti in bewildered frustration just as an ordinary person would. The ideas written in the note were eventually organized and summarized in “Density Matrix in the Theory of the Positrons” (See Archive OU1936-C1 and OU1936-C2). Today, electrons and positrons are described by the same Dirac field and it is known that the state of infinite negative electric charge does not manifest if quantized appropriately. (Written by Yutaka Hosotani)
