More than anything else – the Universe itself, covering and including all planets, stars, galaxies, clusters, superclusters and cells. The range of modern telescopes reaches several billion light years.
Planets, stars, galaxies amaze us with an amazing variety of their properties, the complexity of the structure. And how is the whole universe, the universe as a whole?
Its main property is uniformity. This can be said more precisely. Imagine that we mentally allocated a very large cubic volume in the Universe, with an edge of 500 million light years. We calculate how many galaxies are in it. Let’s make the same calculations for other, but equally gigantic volumes located in different parts of the universe. If you do all this and compare the results, it turns out that each of them, wherever they are taken, contains the same number of galaxies. The same thing will happen when counting clusters or even cells.
The Universe appears to us everywhere the same – “continuous” and homogeneous. It’s easier than a device to come up with. I must say that people have long suspected this. Pointing out, for reasons of maximum simplicity of the device, to the general homogeneity of the world, the great thinker Pascal (1623-1662) said that the world is a circle, the center of which is everywhere, and the circle is nowhere. So with the help of a visual geometric image, he asserted the homogeneity of the world.
In a homogeneous world, all “places” are equal and any of them can claim to be the Center of the world. And if so, then it means that no center of the world exists at all.
The Universe has one more important property, but it was never even guessed about it. The universe is in motion – it is expanding. The distance between clusters and superclusters is constantly increasing. They seem to scatter from each other. And the mesh network is stretched.
At all times, people preferred to consider the Universe eternal and unchanging. This point of view prevailed until the 1920s. At that time, it was believed that it was limited by the size of our Galaxy. Paths can be born and die, the Galaxy still remains the same, just as the forest remains unchanged, in which trees are replaced generation after generation.
A real revolution in the science of the Universe was carried out in 1922-1924 by the work of the Leningrad mathematician and physicist A. Friedman. Based on the general theory of relativity just created by A. Einstein then, he mathematically proved that the world is not something fixed and unchanging. As a whole, he lives his dynamic life, changes in time, expanding or contracting according to strictly defined laws.
Friedman discovered the mobility of the stellar universe. It was a theoretical prediction, and the choice between expansion and contraction must be made on the basis of astronomical observations. In 1928-1929, Hubble, already known to us as a researcher of galaxies, managed to make such observations.
He found that distant galaxies and their entire collectives move, moving away from us in all directions. But so it should look, in accordance with the predictions of Friedman, the general expansion of the universe.
Of course, this does not mean that the galaxies scatter from us. Otherwise, we would return to the old views, to the pre-poker picture of the world with the Earth in the center. In fact, the general expansion of the Universe happens so that they all move away from each other, and from anywhere the picture of this scatter looks like we see it from our planet.
If the Universe is expanding, then, in the distant past, clusters were closer to each other. Moreover: from Friedman’s theory it follows that fifteen to twenty billion years ago there were no stars or galaxies yet and all the matter was mixed and compressed to a colossal density. This substance was then incredibly hot. From such a special state the general expansion began, which eventually led to the formation of the Universe, as we see and know it now.
General ideas about the structure of the universe evolved throughout the history of astronomy. However, only in our century could the modern science of the structure and evolution of the Universe – cosmology – appear.