Properties Spanning the First 500 kyr

Key properties tracked for the first Gyr.

Concordance model parameters. All columns are linear in time, with redshift marked on the left. The first two columns are simply the age and scale factor (log): at these times the universe is only 0.01% - 0.1% of its current size. Columns 3 and 4 give the matter (dark matter plus baryons) and radiation (photons and neutrinos) densities, expressed in gm/cm3 (log plus 24), so they are typically a few thousand protons masses per cm3. Notice how the radiation density increases faster and passes the matter density near z ~ 3300, or 50,000 years -- the famous period of equality. Column 5 gives the temperature -- increasing from ~3000K at the CMB up to 10,000K at equality. Column 6 gives the velocity of a galaxy currently moving at 72 km/s at distance 1 Mpc. At this early time that matter was moving at a few thousand km/s and was only a few 100 pc distant. The final column gives the apparent angular diameter of 10 kpc physical size: a few arcminutes. Note that the CMB wall of fog is at z ~ 1100, so one cannot in practice see anything beyond that. However, the scale at the CMB is about 15 arcsec per kpc.

Figure made for this course.