The fact that this quantity for the (*) Universe is extremely close to its critical value is the origin of the flatness problem, since at that critical value the Universe’s shape becomes flat.
According to general relativity, the “radius” of a spherical universe squared is equal to 2 over the product of curvature and this quantity. This quantity is raised to the “n+1 over nth” power and multiplied by a constant K in solutions to the Lane-Emden equation. This quantity’s namesake parameter is equal to it times 8 pi G over 3 times the Hubble constant squared. The fact that this quantity for the (*) Universe is extremely close to its critical value is the origin of the flatness problem, since at that critical value the Universe’s shape becomes flat. Polytropes express pressure as a function of this quantity, which is extremely high in neutron stars. For ten points, name this quantity which is roughly 5 atoms of hydrogen per cubic meter for the Universe.
According to general relativity, the “radius” of a spherical universe squared is equal to 2 over the product of curvature and this quantity.