Sometimes a simple question can lead to the deepest scientific conclusions. One of these questions is: why is the night sky dark?
At first glance, it seems that the answer is obvious: the stars are limited, they are removed, and darkness remains between them. However, such an answer is incorrect or at least insufficient. The solution to this phenomenon for a long time remained out of reach of scientists.
Cosmic darkness at night is not associated with the atmosphere of the Earth, which shines even in the darkest places. The reason lies in the very nature of the universe. Observations show that space space remains unlit, despite the presence of many stars and galaxies. Additional light sources, such as distant stars and galaxies, are too dim to be distinguished.
Historically, it was believed that the universe is endless in time and space, remaining unchanged. However, this idea gives rise to the problem: if the stars are evenly distributed in endless space, then the night sky should be bright due to the geometry of the distribution of light.
The problem is as follows: with an increase in the distance from the Earth, the number of stars in the spherical shell increases in proportion to the square of the distance. At the same time, the brightness of the light of the star decreases with the square of the distance. This means that the shells at any distances should radiate the same amount of light. In the endless Universe, each line of vision would certainly cross the star, making the whole sky as bright as the sun.
Some suggested that light could be blocked by gas and dust, but such clouds, heated from absorbed radiation, themselves become bright. This does not solve the problem.
This phenomenon was called Olbers paradox, in honor of the astronomer Henry Wilhelm Olbers, who wrote about this in 1823. However, such issues were discussed earlier, for example, Thomas Digges in the 16th century. The solution was found in the 19th century when Edgar Allan PO in his essay