Answer:
*Doppler effect by the displacement or towards the red
*The microwave temperature of the universe
Step-by-step explanation:
The expansion of the universe can be visualized in various facts
* the stars and galaxies are moving away from us, this is observed in the Doppler effect by the displacement or towards the red of the hydrogen lines.
* The microwave temperature of the universe that comes from everywhere, this temperature is the rest of the temperature of an initial great explosion (big ban), for which the expanding universe must cool down.