There is 13.7 billion years ago a tremendous explosion of light, Big Bang, gives rise to space, time, matter, burning chaos of unimaginable heat, a shapeless pulp will swell, expand in all directions and cool slowly. This term, Big Bang was coined in the 1950s by the English astrophysicist Fred Hoyle sarcastically to describe the concept of "original explosion" introduced in the cosmological model developed in the 1920s by the Belgian astrophysicist Georges Lemaître and the Russian physicist Alexander Friedmann. The history of Big Bang not prejudge the existence of an "initial moment" or a beginning. Today, it picks up in the sky a trace of this origin known as CMB or the sky, is a radiation of microwaves at low temperatures near absolute zero, reaching the surface Earth from all directions of the cosmos. It is so called because it forms a background to all the radio point sources that were detected by radio telescopes. It was detected for the first time by Arno Penzias and Robert Woodrow Wilson in 1965, which will be awarded the Nobel Prize for Physics in 1978. From the still hot cosmic soup of billions of degrees, elements of matter are weaving a web of structures more complex to finish in galaxies, hundreds of billions of galaxies of various shapes, moving away from each other. Observe these celestial objects is to measure the time it took light to reach us, but also see the state they were at that time. General relativity by Albert Einstein in 1915 marked the beginning of modern cosmology, where it becomes possible to describe the universe in its entirety as a physical system.
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For a long time
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Everything begins an insignificant split second after original explosion. Before, they nothing is known, it is "earthed up incognita", he has no zero time, the time does not exist.
The cosmic clock hits its first blow in 10-43 seconds. Universe is a lively space energy very dense terrifically warm, then he is assumed, he swells up shortly, it's the inflation.
The universe is expanding. In 10-32 seconds, first elements of matter accompanied with antimatter appear the elementary particles and their antiparticles, the quarks, the electrons, the neutrinos, the photons these grains of light in which bathe this cosmic soup.
Then comes into play a first force, a strong nuclear force, strong nuclear force It is the one who cements nucleons in pits. It is too who associates quarks 3 by 3 inside nucleons and give birth to the nuclear energy. 1 gram of nuclear fuel = 1 ton of dynamite. She acts on a distance of 10e-13 cm, she is 100 times as strong as the electromagnetic force and acts only on massive particles as the proton and the neutron 10e-24 grams weighty. The mass of a proton is equal to 1836 times the mass of the electron. who in time 10-6seconde, 1 millionth of second, is going to assemble quarks, 3 by 3 to give protons, neutrons may form pits, pits of hydrogen, many, heavier pits of helium, there is less.
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3 minutes only
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In 3 minutes, 98 % of the mass of the universe is constituted. Nothing again until 380 000 years, the end of the era radiative. Begin then the matter era and appears the second force, the electromagnetic force, the electromagnetic force This force, much superior to the force of gravity, acts only on particles in charge of particles loaded, either positively as protons, or negatively as electrons. It forms atoms by attaching electrons to pits, but it does not stop there. It welds atoms by obliging them to share their electrons to form molecules. It still urges molecules to harmonize in turn in long chains, the highest expression of these chains is the DNA which allows the life., it builds the atoms of hydrogen and helium by making turn electrons around pits.
Final act: in 1 billion years, an always expanding Universe and in cooling sees the gravitational force Discovered to the XVII th century by Newton, this attractive force acts on any masses. The weakest of four forces of the nature, but also the one who has the biggest reach, she acts on the whole universe, she is the glue of the cosmos. The intensity it this force depends on the mass of the object. It is that in the astronomical scale which the gravity really is felt, in enormous masses as that of the Earth (6x10e27 grams, in the Sun (10e33 grams), of a galaxy (10e44 grams), of a heap of galaxies (10e47 grams) or of the whole universe. to group atoms in more complex structures. It is the birth from the galaxies which in their hearts shelter the stars of the sky, the stars which evolve since 15 billion years.
In stars, protons merge to form pits of deuterium according to processes bound to the weak interactions, the weak nuclear force. It is it who allows the neutrons to be transformed into protons and vice versa when the conditions lend themselves to it. She does not act on particles immortal as electron, photon and neutrino. Although stronger than the gravity, it is 1000 times as weak as the electromagnetic force. It has influence only on a distance of 10-16 cm. It is in 1896, accidentally that the French physicist Henri Becquerel discovered this process of destruction, on a photographic patch. These pits are then of use to the construction of more massive pits. The clear energy is taken in 98 % in the form of brilliant energy by photons.
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According to the theoretical model of Big Bang, which describes the evolution of the Universe, the brilliance of thorough microwaves of the sky is a residue of the energy reigning at the time of the forming of the first stable atoms of the Universe as the brilliance becomes matter. It takes place 300 000 years after the essential explosion.
Data of the satellite COBE (Cosmic Background Explorer) showed that this brilliance is not as well uniform as believed it the scientists. This card of the cosmological brilliance in north half of the sky reveals, after computer treatment, zones of variable, appearing intensity each, arbitrarily, in different colors.
These fluctuations, which would correspond to the variations of density of the essential Universe and would so be at the origin of the forming of the galaxies, testify of the dynamics of the Universe in its debuts. Fluctuations in density of the order of 1/100000th of Kelvin are soaked in the brilliance fossil microwave in 2.73 K.
They show that approximately 300000 years after Big Bang there were diverse zones in the universe of a size included between 100 and 1000 Mpc.
Image: The bottom of the sky in these debuts (Mr Tegmark, Has. Of Oliveria-Costa, Mr Devlin, B. Netterfield, L. Page and E. Wollack, Astrophysical Journal, 474, L77)
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Notion of the distances and the space
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The astronomy works on a scale of distance that the man has difficulty in representing himself. So, the astrophysicists use the speed of light as standard measuring apparatus. Indeed, knowing that the light moves in 300 000 km/s in the space (the fastest existing speed in relativist physical appearance), when a time is indicated in speed-light, it is necessary makes understand a distance.
To approach the astronomy it is necessary to have first of all a notion of the distances and the space which separates celestial bodies. Then it is necessary to have a notion of the masses in presence. To give an image of the distances which separate the celestial bodies of our solar system, here is a model with a scale in 1/100 billionth, (1cm = 1 million km).
With this scale the solar system likes in the Big Stadium of France. The Sun, in the center of the stadium, would be 1,4 cm one diameter.
In 1,5 m of distance would be the Earth with a diameter of 0,1mm, Jupiter would be in 8m of the sun and would measure 1,4mm. Pluto would be in 59m of the Sun and would be one diameter of 0,05mm. The closest star Alpha Centauri CProxima Centauri (so sometimes called Alpha Centauri C) is a red dwarf of visible magnitude 11 too weak to be visible in the bare eye, situated in the constellation of the Centaur. It is one of three stars that form the Alpha Centauri system. It is the star the closest to the solar system in 4,22 years light. in neighborhood of Barcelona and Sirius (the same size as the Sun) would be in neighborhood of Lyon and.
Image: The speed of light is fixed to 299 792 458 m/s in 1983 by the weights and the measures, is a constant physics from which a precise value is obtained experimentally from the XVII th century by the Danish astronomer Ole Christensen Romer in 1676.
The speed of light was then esteemed at 200 000 kilometers per second, approximately 35 % below its true value because of the uncertainties of time on the size of the orbit of the Earth.
However, Cassini emitted doubts on the validity of the results of his colleague. James Bradley proposed then an estimation in km/s 300 000. Today, the speed of light constitutes one of the pillars of the theoretical physics.
Notion of the masses in presence
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The mass of our Galaxy amounts to approximately 40 billion sun masses. There is approximately 5 billion years the present matter in the space of our solar system condensed from a cloud of dust and gas.
Almost totality of the cloud disappeared to make place in the sun, planets being a residue of our star system. The Sun contains more than 99 % of the total mass of the solar system.
Jupiter the biggest dust of our system contains more matter than all the planets, the satellites, the asteroids, the comets, the dusts and the gas which constitute the rest of the solar system.
Together the Sun and the Jupiter appropriated 99,9 % of the mass of the system. The mass of Venus amounts to 0,2 % of the mass of Jupiter. The mass of the Earth amounts to 0,3 % of the mass of Jupiter.
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