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Posted by Bruce on March 25, 2001 20:52:25 UTC

The fact is the universe is homogeneous and isotropic with respect to large structure. This is a "known". Its not something we agree or disagree on because it is a fact. Isotropic: having the same values for properties measured along axes in any direction. Large structure would be your telescope at the origin of a coordinate system which is only bounded by a horizon in all directions. This horizon is the observable limit. This is like having your telescopes (or set of telescopes for observing all spectrums) at the center of a pie. Divide this pie into any number of pieces and sum the values of all measured properties for each section. Compare the sections and all sections are homogeneous and isotropic to within 1/100,000 th. If you look at small structure (which the other guy seems to think is large structure just because distances are measured in light years) then that section of the universe isn't homogeneous and isotropic with respect to other sections of the same area. Why is this? Because the universe has a quantum nature. During inflation there were quantum fluctuations (very minute deviations in thermal equilibrium and matter distributions). The universe was inflating many magnitudes greater than the speed of light. These variations were spread over large distances as space inflated. This allowed for areas with slightly greater initially energy density to eventually coalesce into 'such things as galaxies' due to local gravitational relationships. Calculations based on inflation theory show that these islands of greater and lesser energy density fit the random nature of small cosmological structure and they also correspond to were greater concentrations of matter should be. Lots of work has been done with the CMBR using COBE and Boomerang to evaluate the validity of different cosmological proposals. Cosmology isn't an exact science but for sure there is no center of mass in this universe.

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