Thoughts on the cosmological principle
  The cosmological principle says that the Universe is spatially homogeneous
and isotropic. It predicts, among other phenomena, the cosmic redshift of light
and the Hubble law. Nevertheless, the existence of structure in the Universe
violates the (exact) cosmological principle. A more precise formulation of the
cosmological principle must allow for the formation of structure and must
therefore incorporate probability distributions. In this contribution to the
Memorial Volume for Wolfgang Kummer, a great teacher and mentor to me, I
discuss how we could formulate a new version of the cosmological principle, how
to test it, and how to possibly justify it by fundamental physics. My
contribution starts with some of my memories of Wolfgang.
