I
The Big Bang
Chapter 1
Summary
The standard
model of Big Bang can be summarized in a few lines.
Approximately
fifteen billion years ago, the universe was born from a violent explosion. The
primordial universe was at a very high temperature, higher than 10^26,
10^28 Kelvin degrees. To 1/100 of
second, the universe, with very high density and very high temperature (more
than 10 ^11 Kelvin degrees), consisted of an undifferentiated soup of matter
and light (photons, electrons and positrons, neutrinos and antineutrinos,
protons and neutrons), dominated by radiations. Then, the temperature decreased
very quickly with the expansion of the universe (Weinberg 1980).
After 3 minutes
and 45 seconds, the temperature being sufficiently low, the cores of deuterium,
and then of helium took shape. After 380.000 years, the temperature having fallen
to several thousands from Kelvin degrees, the first atoms of hydrogen and light
elements (deuterium 2H, helium 3H, helium 4H, lithium 7Li) could be formed.
The expansion
going on, the galaxies and the stars appeared followed by the great structures
of the universe (galaxies clusters, superclusters of galaxies, large walls,
etc...). The heavier chemical elements occurred in stars.
The theory of
inflation, worked out to solve a certain number of serious problems posed by
the model of Big Bang, is a prolongation of it but is also independent of it.
The standard
model of Big Bang rests on a certain number of principles, facts, assumptions,
presupposed and consequences, that we can enumerate and that we will analyze:
redshifts of the remote galaxies and the constant of Hubble Ho; the expansion
of the universe, general relativity and the cosmological principle; the theory
of inflation; the Cosmic Microwave Background Radiation; the primordial
nucleosynthesis and the ratio baryons/photons at the beginning of Big Bang; the
age of the universe; great structures of the universe; critical density and the
geometrical shape of the universe. The problems of the dark mass, the
cosmological constant and quintessence can be added to it.
Next : 2 The Big Bang model
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