Why is the night sky not completely white ?
In: 10
Because the universe is expanding.
This is actually an important question in the history of early 20th century physics and the theories of relativity and quantum mechanics that came out of that era. The question is called Olber’s paradox.
If the universe was infinite, uniform, and infinitely old as they believed at that time then every direction you look would end at a star, and the sky would be blinding.
In an expanding universe of finite age then the paradox goes away: light from distant stars hasn’t had time to reach us, and light is redshifted out of the visible spectrum. In some ways the Microwave Background is exactly what you describe: a nearly uniform light throughout the sky.
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