Study of 1919 eclipse sparks talk of terms and terminology

Two items interestingly coincide in the March 2009 issue of Physics Today. Daniel Kennefick’s article (page 37) on the 1919 eclipse observations to test predictions of gravitational light deflection vindicated the traditional conclusion in favor of general relativity and Arthur Eddington’s role in the matter. Charles Day’s Search and Discovery story (page 14) concluded that a cosmological term in Albert Einstein’s equations can account for present data on the acceleration of cosmic expansion.

Eddington was a strong proponent of the cosmological term even after the discovery of the expansion of the universe removed Einstein’s original rationale for it and many physicists had rejected it dogmatically. He argued that the term had a fundamental character because its “cosmical constant” Λ provided a universal standard of length, and he asserted in his picturesque way that “to drop the cosmical constant would knock the bottom out of space.” ¹ (Italics in the original.)

The speculative theories Eddington developed in later life have tended to prejudice physicists against his views, but he was surely right that the cosmological term should not be regarded as a mere fudge factor. If Einstein had not introduced it to make a static universe possible, someone eventually would have realized that it was a legitimate addition to the original field equations. There are even purely affine generalizations of Einstein’s Riemannian theory, such as Schrödinger’s, that not only allow but demand a cosmological term. ² Wolfgang Pauli’s rejection of Schrödinger’s version precisely because it required a cosmological term is an example of the dogmatism I mentioned above. ³

I hope present observations of the acceleration of cosmic expansion will convince physicists to be more open-minded. Eddington may once again be vindicated.