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THE RELATIVISTIC QUANTUM theory of fields was born some 35 years ago through the paternal efforts of Dirac, Heisenberg, Pauli and others. It was a somewhat retarded youngster, however, and first reached adolescence 17 years later, an event which we are gathered here to celebrate. But it is the subsequent development and more mature phase of the subject that I wish to discuss briefly today.
Julian Schwinger (1966) studied this question.