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2.7. The history of the Universe

Presently the matter content of the Universe is dominated by non-relativistic matter, but because radiation reduces more quickly with the expansion, this implies that at earlier times the Universe was radiation dominated. During the radiation era temperature and time are related by

Equation 19 (19)

The highest energies accessible to terrestrial experiment, generated in particle accelerators, correspond to a temperature of about 1015 K, which was attained when the Universe was about 10-10 sec old. Before that, we have no direct evidence of the applicable physical laws and must use extrapolation based on current particle physics model building. After that time there is a fairly clear picture of how the Universe evolved to reach the present, with the key events being as follows:

A more precise time-line is given in many textbooks, e.g. [3].

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