From the point of view of astronomy, the Universe is considered the largest object available for observation. In fact, it turns out that the border of the visible cosmos coincides with the border of the Universe and everything that is further away is available only for theoretical research by physicists.
How does the universe work according to astronomers? Our Earth is one of the planets of the solar system. The sun is in the Milky Way galaxy , and the Milky Way galaxy is in a cloud of other galaxies. Many clouds of galaxies form a structure called a metagalaxy. The metagalaxy occupies the entire visible region of the universe. Therefore, the universe consists of a very rarefied interstellar gas; stars unevenly distributed in space and forming clusters and galaxies; planets, comets, clouds of dust and other cold objects falling into the gravitational field of stars and star clusters. This is how the macrocosm looks.
But the approximate picture described above of how the universe works is not complete. It does not take into account that beyond the visible boundary of the cosmos there may exist other objects that differ from those that are observed inside. The fact is that the point of view about the infinity of the Universe is not entirely correct. The universe must have some kind of boundary, albeit very far removed. This follows at least from the most popular theory of how the birth of the universe occurred - the theory of the Big Bang.
Based on the Big Bang theory, the emergence of the Universe is due to the existence of some superdense substance, which exploded. As a result of the explosion in the first three minutes all the elementary particles of the Universe appeared, which were grouped into larger formations. But you can still observe the consequences of the explosion: the space of the Universe is expanding, and galaxies fly apart in all directions from each other.
It is logical to assume that the initial substance (or energy) had to have a finite volume and be in some other space, which, possibly, still exists and is located outside the Universe.
What is called infinity in physics is, in fact, mathematical infinity. It arises where equations and theory cannot describe an existing phenomenon. Therefore, it remains only to speculate on how the Universe is arranged there, where the most powerful telescopes and the mathematical apparatus of theorists cannot peer. In particular, we cannot know exactly what the boundary of the universe looks like.
Physicists believe that in answering the question of how the universe is arranged, the study of elementary particles should help. Experiments show that the "most elementary" subatomic particles behave like clumps of energy. And besides energy there is nothing more. Even space, which has long been considered an independent entity, is now regarded as a reservoir of energy. But there is a very large distance between elementary particles, for example, protons and neutrons in the nucleus of an atom. Therefore, from the perspective of the microworld, the Universe looks like dotted energy clusters scattered at a very great distance from each other.