text: According to general relativity, the “radius” of a spherical universe squared is equal to 2 over the product of curvature and this quantity.
full_question: 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.
first_sentence: According to general relativity, the “radius” of a spherical universe squared is equal to 2 over the product of curvature and this quantity.