The actual matter density of the universe, accounting for all of the luminous matter and all of the dark matter known to exist in galaxies and clusters, is what fraction of the critical density?

Question

Quizplus · Accepted Answer

The critical density of the universe is the density required for the universe to be spatially flat. The actual matter density of the universe, including both luminous and dark matter, is estimated to be about 25 percent of the critical density. This means that the universe is likely to be spatially flat, as supported by observations of the cosmic microwave background radiation.

The Actual Matter Density of the Universe, Accounting for All