Cosmology has reached an era where precise calculations can be made of the contri-
butions of ordinary matter and radiation, dark matter, and dark energy, to the energy
density of the Universe. Our Universe at this time is thought to be dominated by dark
matter and dark energy, which together make up about 95% of the energy density. Or-
dinary matter and radiation make up the last 5%. In the following, Ω\Lambda is the current
value of the density of dark energy, and Ωm refers to the energy density of everything
else, i.e. all normal matter, dark matter, and radiation