In independent works at the beginning of the 20th century Albert Einstein proposed his Theory of General Relativity in which it follows that the universe should not be static, but that it is in expansion, however, this did not coincide with what was believed to be really a static universe, in this way Einstein introduced in its formula the cosmological constant to adapt it to current theories.
Vesto Slipher, a member of the Lowell Observatory under the orders of the famous Percival Lowell, was commissioned to study the circular movement of gas clouds during the formation of stars, a theory that was defended by his boss. He found apart from the rotation of these nebulae a persistent redshift in his spectra, this finding was due to the fact that the Doppler effect indicates that the wavelengths emitted by an object that moves away from the observer, lengthen by running towards the red in the spectrum studied. However, Slipher did not find the explanation for his finding.
It was again Hubble who when measuring the distances of 25 galaxies found a direct correlation between their distance and the degree of shift or in other words the speed at which they move away. I had just discovered the expansion of the Universe.
The Man who united the findings of Slipher, Hubble and Einstein was a mathematician priest named Georges Lemaitre, who in 1927 published an article where he developed the relationship of redshift with an expanding universe.
Later, when his article was promulgated among the scientific community, it began to be thought that if the universe is ever expanding, everything must have been united at a point of light which it called singularity or "primordial atom" and its expansion "Great Noise". Later astronomer Fred Hoyle, who was opposed to this proposal, call it disparagingly "Big Bang." This is how the most accepted theory is currently known as the origin of the universe.
In the second half of the twentieth century, advances in physics provided new types of astronomical instruments, some of which have been placed on satellites that are used as observatories in the Earth's orbit. These instruments are sensitive to a wide variety of radiation wavelengths, including gamma rays, X-rays, ultraviolet, infrared and radio regions of the electromagnetic spectrum.
Astronomers not only study planets, stars and galaxies, but also plasmas (hot ionized gases) that surround double stars, interstellar regions that are the birth places of new stars, invisible cold dust grains in the optical regions, energy nuclei They may contain black holes and microwave background radiation, which can provide information on the initial phases of the history of the Universe.
Today we know that we live in a solar system located on the periphery of the Milky Way composed of billions of suns, which is part of a galactic complex called a local group, which, in turn, is located in a supercluster of galaxies distributed by a universe of more than 15 billion light years that is expanding.
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