Why is the night sky dark?

At the moment, the question of whether our Universe is infinite remains open. If we imagine that it is infinite and uniformly filled with stars, then wherever we point in the sky - there should be a star there, and therefore the night sky should glow brightly.

This is called Olbers' paradox. It can be resolved by the following explanations:

  1. The Universe is 13.8 billion years old, while its observable part has a radius of about 46 billion light-years (!). Space can expand faster than the speed of light. This means we only see that part of the Universe whose light has had time to reach us. We see far from all the light.
  2. The expansion of the Universe leads to redshift of light. This is not the Doppler effect, but something similar that makes light less bright. Expansion also leads to a decrease in visible stars and galaxies in the sky.
  3. Gas and dust are abundantly scattered throughout the Universe, called intergalactic and interstellar medium. They absorb part of the light.
  4. We also know that matter in the Universe is distributed unevenly. Large voids form between stars, galaxies, and their clusters.