Tuesday, November 25, 2008

We don't need no stinkin' Copernican Principle

I have often written that there are four ways to explain the fact that our universe is (at least apparently) fine-tuned.
  1. It really was fine tuned. That is, Goddidit.
  2. There are multiple universes, most of them sterile, but obviously ours is not. (A solution by large numbers.)
  3. The fine tuning is an illusion.
  4. Unimaginable luck.
It is interesting to see that some scientists are presenting a fifth possibility: the Copernican Principle is wrong.

The Copernican Principle is the cherished belief that we are not in any special place in the cosmos. It is essentially the same thing as the idea that the universe is homogenous--it looks the same, on a large scale, from any location. The article linked above discusses the non-homogeneous possibility that we are in fact in a very special low density bubble within the larger universe. Even more un-Copernican-like, we would have to be in the center of this bubble to explain the high degree of isotropy seen in the microwave background.

From the article:
This startling possibility [accelerated expansion] can be accommodated by the standard cosmological equations, but only at a price. That price is introducing dark energy - an unseen energy pervading space that overwhelms gravity and drives an accelerating expansion. Dark energy is problematic. No one really knows what it is. We can make an educated guess, and use quantum theory to estimate how much of it there might be, but then we overshoot by an astounding factor of 10120 [The so-called "worst" fine tuning problem in all of physics].

That is grounds enough, says George Ellis, a leading cosmology theorist based at the University of Cape Town in South Africa, to take a hard look at our assumptions about the universe and our place in it. "If we analyse the supernova data by assuming the Copernican principle is correct and get out something unphysical, I think we should start questioning the Copernican principle."

A cool, for some, Sophie's Choice: Which do you hate less, a fine tuned universe or the death of the Copernican Principle?

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