How fine a granularity shall we use when
imposing the Copernican Principle?
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http://www.newscientist.com/blog/space/2008/07/are-we-living-in-giant-cosmic-void...
Friday, July 18, 2008
Are we living in a giant cosmic void?
Several of us at New Scientist recently came across an interesting paper by Timothy Clifton and colleagues at the University of
Oxford entitled "Living in a Void: Testing the Copernican Principle with distant supernovae".
The paper argues that if we are living in a giant void - that is, if our cosmic neighbourhood is significantly less dense than other
parts of the universe, then that could account for the fact that the universe's expansion appears to be accelerating. Astronomers
discovered this acceleration in the late 1990s when they found that distant supernovae appear dimmer, and thus farther away, than
expected.
Most cosmologists believe that a furtive anti-gravity-like force known as dark energy is to blame.
But no one can explain why the observed value of the dark energy is 120 orders of magnitude smaller than what's predicted from
quantum physics. In fact, the level of fine-tuning needed to produce such a specifically small but non-zero cosmological constant is
so absurd that the best explanation anyone's come up with is that our universe is merely one of an infinite number of universes.
According to Clifton, the problem may not lie with cosmologists' observations, but with their assumptions - namely, the Copernican
Principle, which says we don't occupy a special place in the cosmos, and that the distribution of matter is homogeneous, so any
given region of the universe is more or less the same as any other.
