 Physical cosmology has achieved a consensus Standard Model (SM), based on extending the local physics governing gravity and the other forces to describe the overall structure of the universe and its evolution. According to the SM, the universe has evolved from an extremely high temperature early state, by expanding, cooling, and developing structures at various scales, such as galaxies and stars. This model is based on bold extrapolations of existing theories—applying general relativity, for example, at length scales 14 orders of magnitude larger than the those at which it has been tested—and requires several novel ingredients, such as dark matter and dark energy. The last few decades have been a golden age of physical cosmology, as the SM has been developed in rich detail and substantiated by compatibility with a growing body of observations. Here we will briefly introduce some of the central concepts of the SM to provide the minimal background needed for the ensuing  discussion.[2] 