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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.
We pursue a program to confront observations with arbitrarily inhomogeneous cosmologies beyond the FLRW metric. The main idea is to test the Copernican principle rather than assuming it a priori. We consider the $Lambda$CDM model endowed with a spher
A general cosmological principle -- Aleph -- is proposed as a substitute to the Anthropic principle. Furthermore, the universe, conceived as a world ensemble, is characterized by many (possibly infinite) X-Life world principles. The only known X-Life
One of the cornerstones of general relativity is the equivalence principle. However, the validity of the equivalence principle has only been established on solar system scales for standard matter fields; this result cannot be assumed to hold for the
This paper proposes a systematic study of cosmological signatures of modifications of gravity via the presence of a scalar field with a multiplicative coupling to the electromagnetic Lagrangian. We show that, in this framework, variations of the fine
According to the Cosmological Principle, the matter distribution on very large scales should have a kinematic dipole that is aligned with that of the CMB. We determine the dipole anisotropy in the number counts of two all-sky surveys of radio galaxie