Oh, My God, It’S Full Of Stars. Sorry, Photons!

2021-01-26   |   by CusiGO

Heaven and its secrets have attracted many people, some of whom are professional in searching for the mystery of how the universe works, some of whom are amateurs, but are also moved by the same curiosity. We’re all trying to explore the universe.

Heinrich Wilhelm Matthias olbers is a man who is not specialized in astronomy, but has become history because of his contribution. Albers is a doctor, and despite years of health education at Gottingen University, he spent some time studying kites. Later, he discovered asteroids, some of which are called Vesta, the second largest planetary belt, and the brightest asteroids on our planet. However, at least among astrophysicists studying the universe and galaxy formation, Albers is most famous for the famous Albers paradox or dark night, which is a relatively simple reasoning, usually as an introduction to any cosmology course, and was explained by German doctors in 1823.

Isaac Newton defended a static and infinite universe in which the gravitation between objects is balanced. Albert Einstein also “liked” such a universe. The basis of the Albers paradox is the contradiction between the assumption that the universe follows known cosmological principles, except that it is static and infinite, and the fact that the sky is a dark night. According to the principle of cosmology, the universe is homogeneous and isotropic. This is an axiom, which we have discussed in this article. This is the basis of all the sciences that study the origin and evolution of the whole universe, that is, the so-called cosmology. So no matter where we look, our line of sight must intercept an infinite number of stars. Distant stars make us feel weaker, but if we see an infinite number of stars, the end result is that no matter where we see, we will see light as strong as the sun, and the night sky should be bright. But obviously not, right? So, like all paradoxes, something in logical argument must have failed. The universe either does not follow cosmological principles, or it is not static, or it is not infinite. Even the failure of reasoning may go beyond what is clearly expressed in a sentence, but it implies that we can discuss the meaning of infinity, whether it is infinite in space or time (can the two be separated?) Or about the exact meaning and validity of the principles of the universe.

Today, we do not discuss either the premise of the albus paradox or the solution usually given by cosmological arguments, such as the finite age of the universe. We want to talk about the hypothesis in that argument: night is dark.

Is it really night? Obviously, if we call darkness “the lack of light to perceive things” and regard light as electromagnetic radiation perceived by human eyes, then night is dark. However, if we regard the physical definition of light as all electromagnetic radiation, including optics, X-ray, infrared and so on, as we said in previous articles, if we use super powerful telescopes, the answer is completely different: the night is not dark, photons constantly come in from us, that is, there is light during the day and at night.

Not only is the night not dark, but the universe is not dark, because it is full of photons and electromagnetic radiation. There are basically two types of photons that fill the universe, and there are two origins. First of all, any object will emit electromagnetic radiation at a certain temperature. Well, if we think of the universe as an object, it will emit photons (or we won’t complicate it) and fill the space-time. This is the so-called background cosmic radiation. Its existence was predicted around 1950. We first detected it in 1964, which is one of the major tests for the correctness of the big bang theory. It is estimated that there are almost one-fifth of photons (1 and 90 zeros) in the whole universe, which is about a quarter of the volume of milk. Is that more or less? Everything is relative. Compared with the amount of sand grains on all the beaches in the world, it is estimated to be about 1000 trillion (1 and 21 zeros), because it is very large. Compared with the number of protons and neutrons in the universe, even if we multiply by 3 to get the number of quarks, or we add the number of electrons, the total number of photons in the cosmic background radiation is still one billion times the number of particles. In quantity, photons dominate the universe.

The second origin of photons bathed in the whole universe comes from the matter of all the stars and all the black holes around in the history of the universe. They all send photons, especially optical photons, into space. Some of them are absorbed by nearby objects, such as gas clouds or planets, which are heated and emit photons into the infrared. The collection of all these photons is called extragalactic background light, and their research is very important, not only because it describes all the stars and black holes in the universe, but also because it is a kind of radiation, sweeping the whole universe, By studying it, we can know everything that exists or ever existed in it, including dark matter, just like some candidate particles of dark matter called axions. It is estimated that the number of such photons in the entire universe is about a quarter (1 and 84 zeros), equivalent to just over 10% of the volume of four bricks of milk.

No matter where we go, we can see photons. Compared with the photons from the sun, there are not many photons. There are 1-45 zeros per second, and there is not much energy. But “God, the universe is full of photons”, as explained by David Bowman’s 2001 space odyssey.

Pablo G.P é rez Gonz á lez is a researcher at the center for Astrobiology of the advanced scientific research council and the National Institute of Aerospace Technology (CAB / csic-inta)

Patricia s á nchez BL á zquez is a professor at the University of complutens (UCM) in Madrid

The cosmic vacuum is a part of our understanding of the universe in a qualitative and quantitative way. Its purpose is to explain the importance of understanding the universe, not only from a scientific point of view, but also from a philosophical, social and economic point of view. The name “cosmic vacuum” refers to the fact that most of the universe is and is now in a vacuum, with less than one atom per cubic meter, although in our environment, paradoxically, there are more than 500 million atoms per cubic meter, which leads to a reflection on our existence and the existence of life in the universe.

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