Remembrances of Dirac

Graham Farmelo cites Paul Dirac’s 1939 speculations on the role of quantum jumps in primordial cosmology as an example of the man’s deep insights into physics. However, I think that is not a good example; Dirac probably was aware of the writings of Georges Lemaître, the first physical cosmologist, who by then had gained significant prominence. Most likely the credit for that insight should go to Lemaître, who published an amazing 1931 letter titled “The Beginning of the World from the Point of View of Quantum Theory.” ¹ In it he wrote, “Clearly the initial quantum could not conceal in itself the whole course of evolution; but, according to the principle of indeterminacy, that is not necessary.” It is remarkable how close Lemaître’s concept was to the contemporary notion of cosmology, in which the structure of the universe today arose from initial quantum fluctuations of a perfectly homogeneous, primordial vacuum.