In physical cosmology, the Copernican principle, named after Nicolaus Copernicus, is a working assumption that arises from a modified cosmological extension of Copernicus' heliocentric universe. Under the modified Copernican principle neither the Sun nor the Earth are in a central, specially favored position in the universe. In some sense, it is equivalent to the mediocrity principle. More recently, the principle has been generalized to the relativistic concept that humans are not privileged observers of the universe.