Happy New Year! To get 2008 off to a bang, I will be kicking off a series on the big bang and the expanding universe (also known as "inflationary cosmology"). An excellent way to do so, in my view, is by reviewing John Farrell's 2005 book, The Day Without Yesterday: Lemaitre, Einstein, and the Birth of Modern Cosmology.
As noted in the title, the book is about Georges Lemaitre (1894-1966), a Belgian astrophysicist (Ph.D. from MIT) and priest. It is Lemaitre who, with some later modifications by others, laid the groundwork for the modern big bang theory of an expanding universe, at a time when there was widespread belief among scientists in a static universe.
A few weeks ago, I had seen an episode of the History Channel series, The Universe, which introduced me to Lemaitre for the first time. Shortly thereafter, I found The Day Without Yesterday in a bookstore, and it seemed to be a perfect way for me to expand my knowledge from what I had seen in the documentary.
With access to letters and photographs from the Lemaitre and Einstein archives, Farrell weaves, to my mind, the perfect blend of scientific exposition and personal story. The duality of Lemaitre's scientific and theological commitments is discussed somewhat, toward the end of the book, and the overwhelming sense is that he kept the two quite separate. At a little over 200 pages, the book is a quick read, easily capable of being finished in a few sittings.
As the book conveys, Lemaitre's ideas stemmed from his thoughtful responses to Einstein's general relativity and Willem de Sitter's initial elaborations on Einstein's theory. In fact, Farrell quotes one of Einstein's letters to Lemaitre, as follows (p. 169):
"I doubt that anybody has so carefully studied the cosmological implications of the theory of relativity as you have."
Further, as the book discusses, development of the big bang theory from roughly 1925-1950 went through at least three stages:
First, having learned of data from astronomical observations suggestive of receding objects, Lemaitre introduced the idea of an expanding universe. Writes Farrell:
It's important to note here that Lemaitre was not yet interested in discussing a temporal beginning of the cosmos in any sense of the term, as has often been inaccurately stated in many books about twentieth-century cosmology. His 1927 paper suggested an expansion of the universe beginning from an initial static Einstein state -- not a big bang, not an explosion of matter from nothing (p. 90).
As a second stage, quoting from Farrell (p. 91), Lemaitre's "further theory of a primeval atom, or initial cosmic origin, would come later, once he realized the physical deficiencies of beginning with Einstein's model."
Third, Lemaitre predicted that there would be a physical residue of the initial expansion of the universe, but his version consisted of a "cold" process of radioactive decay, involving cosmic rays. A later alternative by George Gamow and colleagues, involving a "hot explosion" and the cosmic microwave background as the residue, along with the eventual detection of the background, ended up providing major support for the big bang theory (Farrell, pp. 101-109, plus Chapter 7).
One other topic from Farrell's book that is worth noting is the argument about sociological factors playing a large role in what types of theories the scientific community would find acceptable at any given time (back in October 2005, I reviewed a book titled Constructing Quarks, which dealt with similar issues).
Focusing on Einstein's seeming obsession with preserving the idea of a static universe -- even going so far as to insert a "cosmological constant" into his equations to ensure such -- Farrell offers the following observation:
It's somewhat odd to see in retrospect how conservatism and hesitation manifest themselves in the history of science... Perhaps because of the general nature of this conservatism, it's unfair to ask why Einstein was content to plug the cosmological constant into his equations -- in reaction to their clear suggestion that the universe as a whole could not be static. Einstein was preceded by generation after generation of thinkers who believed the same thing (pp. 52-53).
As this series continues, future topics I plan to discuss include redshifts, Hoyle's steady-state theory, the cosmic microwave background, the cosmological constant, and Guth's inflationary cosmology.