Re:If the universe is 13.8B years old, how can we see 46B li...
by cygx on Saturday December 07, 2019 @04:43PM
(#21732764)
Still not quite right: 13.8 Gly is the light travel distance, whereas proper distance at time of emission was less than that.
For example, for redshift z=9, light travel time is 13.17 Gy, proper distance at time of absorption (aka comoving distance) is 30.72 Gly and proper distance at time of emission (which, in a spatially flat universe, corresponds to angular diameter distance) is 3.07 Gly. The factor of 10 between these two distances is no coincidence as the ratio of the scale factor is given by 1+z.
For example, for redshift z=9, light travel time is 13.17 Gy, proper distance at time of absorption (aka comoving distance) is 30.72 Gly and proper distance at time of emission (which, in a spatially flat universe, corresponds to angular diameter distance) is 3.07 Gly. The factor of 10 between these two distances is no coincidence as the ratio of the scale factor is given by 1+z.
( The values have been calculated via http://www.astro.ucla.edu/~wright/CosmoCalc.html )