Eddington's Tables, Quantum Mechanics and Realism

Steven French

Both advocates and critics of structural realism have conducted their debate under the shadows of Poincaré and Russell. However, if antecedents of a structural realism informed by quantum mechanics are to be looked for, then the historical focus should be shifted forward a few years, to the commentaries and reflective ontological work of Cassirer and Eddington. Here forms of structural realism can be found that are informed by the powerful mathematical framework of group theory that had been developed and applied to the new quantum mechanics by Weyl and Wigner. As Cassirer and Eddington both realized, one of the crucial features of modern physics is the increased significance of the role of symmetry and it is to this that group theory gives mathematical expression. OSR is informed by the role of symmetry and invariance in just the manner that Cassirer and Eddington advocated and the rest of the book is taken up in trying to articulate an appropriate metaphysics for such an informed perspective.

Hans Primas

G. C. Ghirardi

Miriam Cometto

Peter Kosso

Clive W. Kilmister

I conclude the first part of this book by carrying the story up to 1928, to the lightning flash in Eddington's mind produced by Dirac's paper on the wave equation of the electron. Setting out the context and Eddington's thinking about it is a very different matter for quantum mechanics and relativity. Both theories are commonly expressed in austere mathematical language. In the case of relativity the basic ideas behind the mathematics are now well understood and can be set out with little complication. These ideas were mostly already clear to Eddington. But for quantum mechanics the mathematics, yoked to the wealth of experimental results, drove the development of the theory at a breakneck speed, mostly without anyone pausing for deeper understanding. It is indeed only in the last decade that it has become generally accepted that quantum mechanics still lacks any coherent interpretation. To explain Eddington's context it is therefore necessary to say something about the mathematical formalism. It is true, as will become clear, that Eddington was a little more sceptical than most, but by and large the mathematics drove him as it did those directly working in the theory. I begin, then, with a description of that part of the early (pre-1925) history of quantum mechanics that was in Eddington's mind in 1923. Then I explain what happened in 1925–6 and Eddington's reaction to it. The chapter concludes with Dirac's relativistic wave equation of 1928 and Eddington's further reaction to that. The old quantum theory What is now called the old quantum theory arose at the turn of the century. Two related experimental contradictions with classical physics played important roles in this.