When you look up at the night sky, you can see stars twinkling in the darkness, but considering that there are countless brightly shining stars and galaxies in the universe, it would not be strange if the night sky was as bright as the day with starlight. But why does space seem dark?
The question of whether the sky would be covered in dazzling light is known among astronomers and physicists as Olbers’ paradox. According to UCSC astrophysicist Tenley Hutchinson-Smith, this paradox is explained by the expansion of the universe.
He said that because the universe we are in is expanding faster than light, the light from galaxies that are too far away may have delayed wavelengths and be converted into radio waves such as infrared and microwaves that are invisible to our eyes. In other words, the light of distant stars cannot be seen by the human eye. This is why the universe appears dark.
If what he says is true, the universe is filled with invisible light. However, this light is actually observed as the cosmic microwave background, also known as the afterglow of the Big Bang. One expert said that all stars emit light against the cosmic microwave background, and that this includes light invisible to humans, such as ultraviolet or infrared light. Therefore, if humans could see microwaves, the entire universe would appear dazzlingly bright.
Another reason why space appears dark is that there is no material like Earth’s atmosphere in space. For example, the reason the Earth’s sky appears blue is because molecules such as nitrogen and oxygen that make up the atmosphere scatter the blue and purple light contained in sunlight in all directions. This phenomenon is called Rayleigh scattering.
However, in a vacuum, light arrives in a straight line from the source to the observer. Strictly speaking, there is no vacuum in outer space because there are interstellar gas particles, but since there are almost no substances that scatter light, the phenomenon that appears to brighten the Earth’s sky does not occur and appears dark.
Recent research also suggests that the universe may not be as dark as scientists previously thought. According to a paper published in April 2021 by the U.S. National Optical Astronomy Observatory’s observation team, the cosmic background light, which removed known star and galaxy light from the data observed by the space probe, was photographed and found to be twice as bright as expected. The reason why the universe was brighter than expected is a subject of future research. In this respect, the universe may be dark gray rather than pitch black. Related information: this placeYou can check it here.
