Monday, January 24, 2011

Tethering the drifting balloons of imaginative cosmology ...

Claus Beisbart asks, "Can we justifiably assume the Cosmological Principle in order to break model underdetermination in cosmology?"

(I think he means something like this: Many proposed models of the universe today begin by assuming that basic observations so far are untrustworthy for other parts of the universe or multiverse - which justifies a number of theories that would otherwise be considered entertainment, not science. He hopes to use the Cosmological Principle as a ground rule.

The Cosmological Principle holds that
isotropy for all observers (all places in the Universe) implies homogeneity for all observers. ... A corollary to the cosmological principle is that the laws of physics are universal.

In other words, if it looks the same in all directions, that's because it really is the same, and the known laws of physics apply elsewhere in the universe.

Beisbart's Abstract
If cosmology is to obtain knowledge about the whole universe, it faces an underdetermination problem: Alternative space-time models are compatible with our evidence. The problem can be avoided though, if there are good reasons to adopt the Cosmological Principle (CP), because, assuming the principle, one can confine oneself to the small class of homogeneous and isotropic space-time models. The aim of this paper is to ask whether there are good reasons to adopt the Cosmological Principle in order to avoid underdetermination in cosmology. Various strategies to justify the CP are examined. For instance, arguments to the effect that the truth of the CP follows generically from a large set of initial conditions; an inference to the best explanation; and an inductive strategy are assessed. I conclude that a convincing justification of the CP has not yet been established, but this claim is contingent on a number of results that may have to be revised in the future.

A friend comments, "This is a very good article. The author also has done some work in
cosmology with Buchert, so he is a reliable guide in physics as well as philosophy."