

https://en.m.wikipedia.org/wiki/Olbers's_paradox
Olbers’s paradox, also known as the dark night paradox or Olbers and Cheseaux’s paradox, is an argument in astrophysics and physical cosmology that says the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe.
The night sky being dark has some profound cosmological implications.
Yes. But why is there an absence of light?
If there are infinite stars, then every direction you look would encounter a star. (Things stay the same brightness per subtended angle as they get far away. Space dust doesn’t matter, as it would thermalize and radiate.)
So, the universe can’t have infinite luminous matter, be static and ageless, because if it were then the night sky would look like the surface of a sun.
This may all seem obvious, but it’s neat that you can figure that out with the naked eye.