Olbers Paradox

Why is the sky black at night? If the Sun was on two times farther away than it is, then we would receive a quarter of the quantity of photons that we now receive, and also the Sun occupied a quarter of the angular surface of which they now occupy. All this suggests that the intensity of the radiation is constant. In the case of infinitely many stars, the sky area would be filled by the stars, so that the sky would shone as the sun during the day.

Olbers paradox is the paradox of dark night sky, which is in 1826th formulated by Hienrich Olbers (1758-1840). Olbers assumed that the universe is unchanging, static and uniformly filled with stars, whose number increases with distance. Therefore,there must be a star wherever we look and the sky would have to be glittering, but the night sky is still dark. However, the universe is neither immutable nor static, nor uniformly filled with stars, but stars are grouped in galaxies between which there is a huge empty space. The paradox is resolved when, besides the above, we detected expansion of the universe and the redshift, amount of light received already reduced by the square of the distance, and because of the removal of objects that radiate and removal of their redshift, emitted light lost even more energy and becomes visible in the microwave region, so the night sky is dark, not bright.