Testing cosmic homogeneity and isotropy using galaxy correlations
  Despite its fundamental importance in cosmology, there have been very few
straight-forward tests of the cosmological principle. Such tests are especially
timely because of the hemispherical asymmetry in the cosmic microwave
background recently observed by the Planck collaboration. Most tests to date
looked at the redshift dependence of cosmological parameters. These are subject
to large systematic effects that require modeling and bias corrections. Unlike
previous tests, the tests described here compare galaxy distributions in equal
volumes at the same redshift z. This allows a straight-forward test and
z-dependent biases are not a problem. Using ~10^6 galaxies from the SDSS DR7
survey, I show that re- gions of space separated by ~2 Gpc have the same
average galaxy correlation radii, amplitudes, and number density to within
approx. 5%, which is consistent with standard model expectations.
