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Further to the claim that “our sun is just a typical star,”a friend wondered what this paragraph in Chas A. Egan’s “Dark Energy, Anthropic Selection Effects, Entropy and Life” means:
It is with great esteem that we remember these pioneers of modern science, who taught us that observational evidence trumps philosophical aesthetics. However, upon pedantic inspection, the Copernican idea leads to untrue predictions. For example, if we did occupy a mediocre vantage point then the density of our immediate environment would be ~10^-30 g cm^-3 However the density of our actual environment is g cm ^ 3>. A napkin calculation considering the density and size of collapsed objects suggest the chance of us living in an environment as dense or denser by pure chance is around 1 in ~10^30 —a significant signal.
Physicist Rob Sheldon offers a translation, and it turns on the Copernican Principle, popularized by Carl Sagan among others:
The Copernican principle suggests that we are not finely tuned, but everything around us is quite average: average sun, average planet, average moon, average solar system, average galaxy, average universe. You get the point.
If you take the mass of the universe (about 100 billion galaxies worth of matter) and divide by the size of the universe (13.7 billion light years in radius) then the average density of the universe is about one proton per liter. Now the air you are breathing is about 10^24 protons/liter (treating oxygen as 16 protons), and the water you are drinking is another 10000 times more dense than that. So in reality, we don’t live in an average density spot in the universe.
But it is worse than that. For our spot to be so dense, the amount of empty space in the universe must be 10^30 more frequent. So we not only live in an unusually dense spot, but also in a very specific location.
So right off the bat, the Copernican principle fails on matter, space and density. So why should we believe it on anything else? Isn’t what is being claimed “we are very average after we have controlled for the non-average variables”, which is right up there with “you are 99% chimpanzee after we remove the non-chimp parts”.
See also: The Science Fictions series at your fingertips (cosmology).
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