The shape of the universe depends on its density. If the density of the universe is greater than the critical density, then gravity will eventually win and the universe will collapse back on itself, the so called “Big Crunch”, like the graph's orange curve. If the mass and energy density of the universe is just right — at the so-called critical density — then the universe would be flat like a sheet, expanding at a steadily accelerating rate.

If the density is more than the critical density, the universe is closed and curves like a sphere; if less, it will curve like a saddle. One of the most fundamental ideas in theoretical cosmology is describing the matter or energy density of baryons, dark matter, dark energy, and radiation at different times during the history of the Universe.
The parameter that is used to measure the mass of the Universe is the critical density, Ω. Points to Remember. Most of the visible mass in the universe is composed of baryons (protons and neutrons). The 11th Density is the Universe itself. In this universe, there is sufficient mass in the universe to slow the expansion to a stop, and then eventually reverse it. The Hubble Parameter varies with time.. Where the symbols have their usual meanings. The Density Parameter is defined as the ratio of the actual (or observed) density to the critical density. The present day average density of the universe is only a few percent of the critical density, much less than the amount needed to close the universe. Matter consisted mainly of protons and neutrons. Approximately one second after the big bang, the universe was about 400,000 times as dense as water, and the temperature was 10 billion kelvins.

The critical density for the Universe is approximately 10-26 kg/m 3 (or 10 hydrogen atoms per cubic metre) and is given by:. Attempts to measure the actual density of the Universe have basically followed one of two methods: The geometry of the universe is often expressed in terms of the "density parameter", which is defined as the ratio of the actual density of the universe to the critical density that would be required to cause the expansion to stop. The evolution of the scale factor is determined by the Friedmann Equation.. H(z) is the red shift dependent Hubble parameter.

where H is the Hubble constant and G is Newton’s gravitational constant. Visual: Completing the torus of consciousness, Conscious Experience: Similar to 6th–7th density experience. Since the critical density is 140 billion solar masses per cubic Mpc, the mass-to-luminosity ratio of the Universe needs to be 700 solar if the Universe has the critical density.

The predicted density of protons and neutrons is about the same as the density that results if we spread out uniformly the mass visible in galaxies today.