The cofounder of quantum field theory: Pascual Jordan

B. Schroer

H. Capellmann

Bert Schroer

After recalling episodes from Pascual Jordan's biography including his pivotal role in the shaping of quantum field theory and his much criticized conduct during the NS regime, I draw attention to his presentation of the first phase of development of quantum field theory in a talk presented at the 1929 Kharkov conference. He starts by giving a comprehensive account of the beginnings of quantum theory, emphasising that particle-like properties arise as a consequence of treating wave-motions quantum-mechanically. He then goes on to his recent discovery of quantization of ``wave fields'' and problems of gauge invariance. The most surprising aspect of Jordan's presentation is however his strong belief that his field quantization is a transitory not yet optimal formulation of the principles underlying causal, local quantum physics. The expectation of a future more radical change coming from the main architect of field quantization already shortly after his discovery is certainly quite startling. I try to answer the question to what extent Jordan's 1929 expectations have been vindicated. The larger part of the present essay consists in arguing that Jordan's plea for a formulation without ``classical correspondence crutches'', i.e. for an intrinsic approach (which avoids classical fields altogether), is successfully addressed in past and recent publications on local quantum physics.

George W. Stickel, Society for the Advancement of American Philosophy

Domenico Costantini, Carlo Ferigato

Abstract Pascual Jordan was the first to propose the law of interference of probability amplitudes as a principle of quantum mechanics. We analyze the role of probabilistic ideas played in this proposal from a historical perspective. In particular, we point out the relation between the usual theory of probability that Jordan called elementary and quantum mechanics. Jordan was the first to stress the analogy between the law of total probability and the law of interference. In this regard, we speculate about the intellectual path Jordan might have followed in order to arrive at the interference law. We do not oppose the usual probability to quantum probability. Instead, we are convinced, as Jordan was, that the rules of quantum mechanics are the rules of a probability theory that has ceased to be elementary.