Modern Cosmology: Science or Folktale?
Current cosmological theory rests on a disturbingly small number of independent observations
Where Do We Stand Today?
Big Bang cosmology is not a single theory; rather, it is five separate theories constructed on top of one another. The ground floor is a theory, historically but not fundamentally rooted in general relativity, to explain the redshifts—this is Expansion, which happily also accounts for the cosmic background radiation. The second floor is Inflation—needed to solve the horizon and "flatness" problems of the Big Bang. The third floor is the Dark Matter hypothesis required to explain the existence of contemporary visible structures, such as galaxies and clusters, which otherwise would never condense within the expanding fireball. The fourth floor is some kind of description for the "seeds" from which such structure is to grow. And the fifth and topmost floor is the mysterious Dark Energy, needed to allow for the recent acceleration of cosmic expansion indicated by the supernova observations. Thus Dark Energy could crumble, leaving the rest of the building intact. But if the Expansion floor collapsed, the entire edifice above it would come crashing down. Expansion is a moderately well-supported hypothesis, consistent with the cosmic background radiation, with the helium abundance and with the ages inferred for the oldest stars and star clusters in our neighborhood. However, finding more direct evidence for Expansion must be of paramount importance.
In the 1930s, Richard Tolman proposed such a test, really good data for which are only now becoming available. Tolman calculated that the surface brightness (the apparent brightness per unit area) of receding galaxies should fall off in a particularly dramatic way with redshift—indeed, so dramatically that those of us building the first cameras for the Hubble Space Telescope in the 1980s were told by cosmologists not to worry about distant galaxies, because we simply wouldn't see them. Imagine our surprise therefore when every deep Hubble image turned out to have hundreds of apparently distant galaxies scattered all over it (as seen in the first image in this piece). Contemporary cosmologists mutter about "galaxy evolution," but the omens do not necessarily look good for the Tolman test of Expansion at high redshift.
In its original form, an expanding Einstein model had an attractive, economic elegance. Alas, it has since run into serious difficulties, which have been cured only by sticking on some ugly bandages: inflation to cover horizon and flatness problems; overwhelming amounts of dark matter to provide internal structure; and dark energy, whatever that might be, to explain the seemingly recent acceleration. A skeptic is entitled to feel that a negative significance, after so much time, effort and trimming, is nothing more than one would expect of a folktale constantly re-edited to fit inconvenient new observations.
The historian of science Daniel Boorstin once remarked: "The great obstacle to discovering the shape of the Earth, the continents and the oceans was not ignorance but the illusion of knowledge. Imagination drew in bold strokes, instantly serving hopes and fears, while knowledge advanced by slow increments and contradictory witnesses." Acceptance of the current myth, if myth it is, could likewise hold up progress in cosmology for generations to come.