# Density parameter Definition and 3 Discussions

The Friedmann equations are a set of equations in physical cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity. They were first derived by Alexander Friedmann in 1922 from Einstein's field equations of gravitation for the Friedmann–Lemaître–Robertson–Walker metric and a perfect fluid with a given mass density

ρ

{\displaystyle \rho }
and pressure

p

{\displaystyle p}
. The equations for negative spatial curvature were given by Friedmann in 1924.

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1. ### I Evolution of the Energy Density Parameters

I am busy with an effort to show how the energy density parameters evolve over time in an update of the LightCone7 calculator. See the posts on the thread Steps on the way to Lightcone cosmological calculator. As part of this effort, I ran into some difficulties with deciding how to find and...
2. ### Plotting Density Parameters as a Function of Redshift

I'm trying to plot the density parameters against redshift in Python, so I suppose this is kind of a cross over of programming and physics. I've been given the following two equations in order to do so $$r(z) = \lambda_H \int_{0}^{z} \frac{dz'}{E(z')}$$ E(z) = \frac{H(z)}{H_0} = \sqrt...
3. ### Cosmic Inventory

Homework Statement One of our homework problems asks us to state the density of Baryons, Cold Dark Matter, Radiation, Dark Energy, and the total density of the universe in terms of the critical density today. It also states to give the density of each quantity in dimensionless Omega units (the...