Does this include dark matter?

Yes. The matter density parameter includes both baryonic (ordinary) matter and dark matter. About 85% of Omega_m is dark matter.

What happens if Omega_total exceeds 1?

An Omega greater than 1 implies a positively curved (closed) universe that may eventually re-collapse. Observations show Omega is very close to 1.

It depends on the Hubble constant: rho_crit = 3 H0² / (8 pi G). Different H0 values give slightly different critical densities.

Calculate the matter density parameter Omega_m = rho_m / rho_crit, indicating what fraction of the critical density is made up of matter.

Matter Density (rho_m)

kg/m³

Critical Density (rho_crit)

kg/m³

Matter Density Parameter (Omega_m)

0.279831

As Percentage27.983 %

Matter Density Parameter (Omega_m) vs Matter Density (rho_m)

The density parameter Omega_m tells us the fraction of the universe's critical density that is in the form of matter.

Omega_m = rho_m / rho_crit

*rho_m* is the average matter density

*rho_crit* is the critical density

If Omega_total = 1 the universe is geometrically flat. Current measurements give Omega_m about 0.31.

With rho_m = 2.65e-27 kg/m³ and rho_crit = 9.47e-27 kg/m³.