mechanics. In the last chapter of this book, Pauli discusses the Dirac equations. He
writes that Dirac equations have weak points because they yield improbable and even
1. These equations assume that, besides an electron, there exists a positively charged
particle, the positron, which no one ever observed.
2. Moreover, the electron behaves strangely upon meeting the positron. The two
annihilate each other and form two photons.
xvi Israel M. Gelfand
And what is completely crazy:
3. Two photons can turn into an electron–positron pair.
Pauli writes that despite this, the Dirac equations are quite interesting and especially
the Dirac matrices deserve attention.
I(I.M.Gelfand) asked Dirac, “Paul, why, in spite of these comments, did you not abandon your equations and continue to pursue your results?’’
“Because, they are beautiful.’’
(from Gelfand memorial volume)