Paul Dirac’s Seas and Bubbles

Abstract This chapter presents a revisionist history of Paul Dirac’s development of his famous “hole” theory of the positron, which proposed that the vacuum was an infinite “sea” of electrons. It argues that the deciding factor in Dirac’s plenum vacuum was his development of tools and practices from non-relativistic many-electron quantum theory. The chapter first demonstrates that Dirac’s early career consistently aimed at a relativistic and many-electron theory. Second, it uses new archival evidence to demonstrate the connection between Dirac’s approximate, many-electron formalism and positron theory. Third, it shows how the continued application of those tools, in collaboration with Rudolf Peierls, resulted in new vacuum phenomena, including vacuum polarization. This chapter argues that a paragon of “fundamental” relativistic theory was in fact (also) an approximate, non-relativistic theory. This was not a problem for Dirac, who felt that approximations could also be beautiful.