2.6. Redshift and temperature
The redshift measures the expansion of the Universe via the stretching of light
Redshift can be used to describe both time and distance. As a time, it
simply refers to the time at which light would have to be emitted to have
a present redshift z. As a distance, it refers to the present
distance to an object from which light is received with a redshift z.
Note that this distance is not necessarily the time multiplied by the
speed of light, since the Universe is expanding as the light travels
across it.
As the Universe expands, it cools according to the law
In its earliest stages the Universe may have been arbitrarily hot and
dense.