# The cosmic variance of Omega - Astrophysics

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Abstract: How much can we know about our Universe? All of our observations arerestricted to a finite volume, and therefore our estimates of presumably globalcosmological parameters are necessarily based on incomplete information. Evenassuming that the Standard Model of cosmology is correct, this means that somecosmological questions may be unanswerable. For example, is the curvatureparameter Omega K positive, negative, or identically zero? If its magnitude issufficiently small, then due to cosmic variance no causal observation can everanswer that question. In this article, we first describe the gauge problemsassociated with defining the cosmic variance of cosmological parameters, thendescribe a solution involving the use of parameters defined on the surface oflast scattering, and finally calculate the statistical variance of idealmeasurements of the matter, radiation, and curvature density parameters. Wefind that Omega K cannot be measured to better than about 1.5x10^-5 1sigma, and that this limit has already begun to decrease due to the flatteningeffect of dark energy. Proposed 21 cm hydrogen experiments, for example, makethis limit more than just a theoretical curiosity.

Author: ** T. P. Waterhouse, J. P. Zibin**

Source: https://arxiv.org/