An Anecdote by C. N. Yang

The question of the gauge-field mass problem was raised by Pauli when Yang was invited to present the Yang-Mills results at the Princeton Institute in February 1954. As Yang relates:

Wolfgang Pauli (1900-1958) was spending the year in Princeton, and was deeply interested in symmetries and interactions.... Soon after my seminar began, when I had written on the blackboard,

( - i

B)

Pauli asked, "What is the mass of this field B ?" I said we did not know. Then I resumed my presentation but soon Pauli asked the same question again. I said something to the effect that it was a very complicated problem, we had worked on it and had come to no definite conclusions. I still remember his repartee: "That is not sufficient excuse". I was so taken aback that I decided, after a few moments' hesitation, to sit down. There was general embarrassment. Finally Oppenheimer said, "We should let Frank proceed". I then resumed and Pauli did not ask any more questions during the seminar.

Wolfgang Pauli and C. N. Yang

Thus Pauli also was aware of the non-triviality of the mass problem. But some other interesting information is revealed by the following sequel to the episode:

I do not remember what happened at the end of the seminar. But next day I found the following message:

February 24, Dear Yang, I regret that you made it almost impossible for me to talk to you after the seminar. All good wishes. Sincerely yours, W. Pauli.

I went to talk to Pauli. He said I should look up a paper by E. Schrodinger... it was a discussion of space-time dependent representations of the

matrices for a Dirac electron in a gravitational field. Equations in it were, on the one hand, related to equations in Riemannian geometry and, on the other, similar to the equations that Mills and I were working on. But it was many years later when I understood that these were all different cases of the mathematical theory of connections on fibre bundles.