We must try to understand that the universe is something really gigantic, bigger than anything you can imagine! Even researchers who study this subject every day have trouble understanding what the universe looks like.
We often imagine it as a kind of huge balloon filled with galaxies but a balloon that has no wall, no center and nothing around him, no outside. Everyone says it, but in reality no one understands exactly what it looks like. You saw like me that the universe contains planets, stars, galaxies, quasars, black holes and maybe even extraterrestrials, but it’s not is not sure.
The universe also contains a lot of gas and dust floating randomly in space. Some elements are from the formation of the universe but others were ejected by stars at the time of their explosion in supernova.
As far as we look in the universe with a large telescope, we see galaxies, and still galaxies. Regardless of the direction in which we look and whatever the magnification, we see galaxies by thousands, as if the universe was homogeneous and unlimited.
Astronomers have discovered galaxies more than 10 billion light-years away and believe that they still exist far more distant. Recently, indeed, some physicists have estimated that the radius of the universe measured a.l., a 1 followed by a thousand billion zeros! All this space is probably full of galaxies.
But one wonders what is the point of having such a vast universe if one does not have the means or the time to explore it? And nobody knows anything! The universe exists, a point that’s all. Who did it and why? As no one knows, some people think it’s God but no one knows either.
So astronomers have tried to understand how the universe was formed, if there was a beginning or if it has always been there, how it evolves and whether or not it will ever disappear. Today nobody knows the answer but several theories have been proposed.
In 1929, the American astronomer Edwin Hubble discovered that all the galaxies were moving away from each other, sometimes to more than 1000 km / s (3.6 million km / h)! First of all it was thought that they all deviated from the Milky Way. But we did not understand why they were all running away from us. In fact it was an optical illusion because in reality it is the universe that is expanding and growing continuously. The galaxies only follow this movement like pellets stuck on a balloon that would inflate continuously.
Then, in 1965, thanks to radio telescopes, astronomers discovered that the universe was not quite cold and that there was a tiny bit of heat in the space. Its temperature is +2.73 K is -270.42 ° C. It is obviously very cold but it is a little hotter than the absolute 0 ° (0 K) which is -273.15 ° C. According to calculations and laboratory experiments, the universe has cooled over time and had to reach a temperature of several billion billion degrees about 13.8 billion years ago! But what phenomenon has caused this heat and why the universe continues to grow? Looks like there was an explosion.