The term universe stems from the concept latin universus and is sometimes used as a synonym for world, to the extent that it denote the set of all things created. Furthermore, a universe is all individuals or elements where one or more characteristics that are the subject of a statistical study are considered.
Another possible definition of universe refers to everything that exists physically. In this sense, the universe includes all forms of matter and energy, the physical laws that govern them and all of space and time.
The most accepted with regard to the origin of the universe theory is that of the Big Bang, or a species of explosion where all the matter and energy of the observable universe was concentrated at a point of infinite density. Following the Big Bang, the universe has started an expansion stage which is not yet complete.
Regarding this theory of the permanent expansion of the universe, some specialists consider that matter black (or dark) can exert enough gravity to hold the expansion, this after which material would be compress in a process known as the Big Crunch.
The universe is composed primarily of galaxies, which can be seen at first sight as points of light in the sky. Scientists distinguish between local galaxies (gravitationally United to the milky way, where the solar system) and external galaxies.
It is noted that the planet Earth is only part of the solar system, a galaxy that has 100,000 million stars and that is just one of the hundreds of thousands of millions of galaxies forming part of the universe.