The Copernican principle is a guiding foundation of cosmology. In short, it states that we are not in a privileged place in the Universe. A “random” observer will see the same Universe that we do. The cosmological standard model does satisfy this principle in space: at this moment, any other observer in the Universe should see the same Universe as we do (at large scales). Just like us, they see a smooth distribution of galaxies and a smooth CMB sky, with similar small anisotropies. However, we do live at a privileged time: in the history of the Universe, we just happen to be at the time when the dark energy density starts dominating over the dark matter density. This is known as the “coincidence” problem, and has been much discussed and agonized over.