When you look at the sky you can see many stars , but you can only see a small part of the universe.
The universe is made up of all space and time, all the matter and energy that exist, and the laws and physical constants that govern them. Before the universe appeared, there was neither time, nor space, nor matter.
The Astronomy is the science that studies the origin and evolution of the universe.
Astronomy or astrology?
La astronomía es la ciencia que estudia el origen y evolución del universo.
La astrología es una pseudociencia que trata de relacionar los eventos celestes con sucesos terrenales. Según la posición de la Tierra, la Luna, y otros cuerpos celestes en el momento del nacimiento de una persona, pretende interpretar y predecir el futuro de dicha persona.
Where does the word universe come from?
Models of the origin of the universe
Man, since ancient times, has always tried to explain how the universe could have been created, through mythological beliefs or scientific theories.
In the absence of a scientific basis that could explain it, mythological beliefs or cosmogony are based on the fact that the universe has been created by a superior being with infinite powers from nothing or through the ordering of chaos.
The Egyptians believed that there was a god in every part of the universe. The sky was the goddess Nut who, supported by Shu, the god of air, covered the Earth (the goddess Shibu).
For the Mayans, the universe was organized in three levels:
the sky (Caan),
the land (Caab), and
the underworld, Xibalba.
The universe is square and flat, and is surrounded by a lizard with planetary symbols. In each corner of the square a cardinal point is represented. In this square the three levels are located, and the center of the Earth born tree of life, whose branches rise to the 13 levels of the sky and its roots penetrate the 9 levels of the underworld.
There was only uniform chaos in the universe, nothing more. During 18000000 years, this chaos began to merge into a cosmic egg in which the opposite principles of yin and yang were balanced.
P'an Ku hatched from the egg and began to create the world. With his giant ax, he separated the yin from the yang, creating the Earth from the yin and the sky from the yang. To keep them apart, P'an Ku remained between heaven and earth, pushing the sky upward.
Scientific theories: big bang theory
Most scientists believe that the universe originated from a great explosion or big bang.
In 1929, the astronomer Hubble observed that galaxies are separating from each other, so he deduced that the Universe is continuously expanding. Therefore, if you were to go back in time, the galaxies would move closer to each other, until they were all at one point.
At that point all the matter and energy of the Universe would be concentrated. This initial moment, in which the big bang occurred, is believed to have occurred about 13.7 billion years ago.
The great explosion caused the initial matter to drift away great distances. Then, little by little, the galaxies, stars and planets that we know today were formed.
How is the universe going to disappear?
Although the most accepted theory about the origin of the universe is that of the Big Bang, there are several theories about how the universe can disappear.
If at some point the force of gravity with which galaxies are drawn outweighs the force that causes them to be moving apart, the universe will stop expanding and begin to contract. The galaxies will collide until producing the collapse of the universe or big crunch.
As the galaxies are moving apart, there will come a time when the density of the universe will be so small that it will make the force of attraction between the galaxies less than the force that separates them, so the continued expansion of the universe will cause it to separate all matter (big rip).