Holographic cosmology is a phenomenological way to describe gravitational physics in early cosmology via a 3-dimensional Euclidean gauge theory. It is most relevant in an interesting new regime of a strong gravity analog of inflation, corresponding to perturbative gauge theory. The CMBR data is explained as well by it as standard inflation (they are indistinguishable), and we show that moreover, the standard puzzles of Hot Big Bang cosmology are also solved, as for inflation, sometimes in different and/or better ways. The cosmological constant problem is mapped in field theory to an understood property of RG flows. We comment on a way to obtain a top-down model that fits observations.