Complex sentence: Cosmologists normally work with a given space-like slice of spacetime called the comoving coordinates, the existence of a preferred set of which is possible and widely accepted in present-day physical cosmology.
Split into simpler sentences: Cosmologists normally work with a given space-like slice of spacetime called the comoving coordinates. However, the existence of a preferred set of comoving coordinates is possible and widely accepted in present-day physical cosmology.