How Was The Universe Created And How Did It Formed ?
From the reflections of the philosophers of ancient Greece to the observations of current astrophysicists, the way in which men viewed the Universe has changed profoundly. But many questions remain unanswered. How was the universe created? How did the universe formed? How did everything start from nothing? So many mysteries which continues to baffle even the most scholarly modern scientists...
A universe first of all philosophical or religious
For a long time, it was not science, but philosophy and religion that demanded an explanation of the Universe. Thus, when in the 4th century BC, the Greek Eudoxus of Cnidus describes the Universe, he places the Earth, motionless, at its center. The Sun and the planets revolve around it, driven by a set of rotating spheres. As for the stars, they are located on the largest of the spheres, called “fixed stars”, and constitute the limits of the Universe. Perfected by the Greek scientist Ptolemy in the 2nd century AD, this model will remain the reference for almost 14 centuries.
The Earth and the Sun change places
In 1543, Nicolaus Copernicus revolutionized astronomy by placing the Sun at the center of the Universe. However, the heliocentric world of the Polish astronomer is still spherical, and still stops at fixed stars.
The universe did not really “open” until 1609, when Galileo first directed an astronomical telescope towards the sky. He then discovers that the Milky Way, considered until then as a kind of white nebula, is in fact composed of a multitude of stars which are as many suns. Relegated to the rank of star among the others, the Sun lost its place of center of the Universe in 1784, when William Herschel discovers that “our” star is on the edge of the Galaxy, whose visible part is the Milky Way, which is nothing but a disc full of stars.
The Universe neither immutable nor eternal
But the real revolution took place in the 20th century, thanks to observation using large telescopes and the big bang theory. The first gave the Universe its true dimension, and the second gave it a story.
At the beginning of the 20th century, in fact, scientists were still convinced that the Universe was immutable and eternal: it has always been and will continue to exist as it is today. But then why does the Universe, however dominated by the gravitational force which attracts all objects towards each other, not collapse on itself? And if the Universe is made up of an infinite number of stars that have always existed, why does it appear dark and not entirely bright?
The theoretical answer to these two questions is given between 1922 and 1927 by the Russian Alexander Friedmann and the Belgian Georges Lemaître, both at the origin of the big bang theory. The Universe is not static: it is expanding. The Universe has not been there forever: it was born 15 billion years ago. And, since that moment, it has gone from an extremely dense and hot state to the very dilute and cold state that we know today.
What observation very quickly confirms. As early as 1924, the American astronomer Edwin Hubble discovered that the Universe is made up of a multitude of galaxies comparable to ours, and then gives the Universe all its depth. In 1929, he noted that these galaxies are moving away from each other: the Universe is indeed expanding.
A solid scientific model, for the moment ...
Today, the big bang theory, although controversial by some astrophysicists, remains the most solid model. Numerous observations have come to confirm its predictions: the current abundance of elements, such as hydrogen and helium: the study of very distant galaxies, located nearly 15 billion light-years away; the discovery of background cosmological radiation by Arno Penzias and Robert Wilson in 1965, then its detailed study using the COBE satellite in 1992.
On Earth, particle physics experiments, carried out in large accelerators like that of CERN (European Organization for Nuclear Research), in Geneva, complemented these observations.
... but not all is resolved
The big bang theory does not, however, provide all the answers, particularly with regard to the future of the Universe. Will gravitation prevail over expansion, and will the Universe end in a “big crunch”, the reverse of the big bang? Or will the two forces balance and will the expansion be halted? The latest observations of supernova (star explosions) far away seem to indicate that the expansion is not about to stop: on the contrary, it would rather be accelerating.
But many other questions remain: Is the universe finite or infinite? What was there before the big bang? Was our Universe born from another larger Universe?
The big bang theory, a model to be completed
The evolution of the Universe in the first moments after the big bang is retraced on the basis of the acquired knowledge of particle physics. The primordial universe was a gas formed of particles and antiparticles animated by disordered movements at speeds close to that of light. At the mercy of incessant collisions, some particles were annihilated, while others appeared. Protons and neutrons began to combine a second after the big bang. In the following minutes, intense nuclear activity allowed the formation of light atomic nucleus (mainly hydrogen and helium). This stage lasted less than a quarter of an hour.
These exceptionally hectic first minutes were followed by a long, quiet period. It was not until 300,000 to 400,000 years later, when the temperature dropped below 3,000 degrees, that the radiation was finally able to propagate freely. The first galaxies would have formed about a billion years after the big bang, according to a process still poorly understood.
