Cosmogony

Cosmogony is the scientific discipline that explores the formation of the universe and the celestial bodies. There is agreement within cosmology that the universe came into being about 13–14 billion years ago with the so-called big bang. The nature of this event is beyond any physical interpretation due to the presumably immense temperatures close to the big bang, canceling any contemporary physical theory.

In the course of a symmetry break immediately after the big bang (BB) a very short-time explosive cosmic expansion occurred. One assumes this epoch of inflation to last for about 10“35 to 10”33 seconds after the BB. During this short phase the universe was undergoing expansion by a factor of 1030 to 1050; the amount posited depends on the mathematical description.

Inflation is of fundamental meaning for the formation of cosmological structure. Prior to inflation, the universe as a whole was subject to the laws of quantum mechanics. In particular these say that some uncertainty underlies the position and momentum of a particle; this must not be understood as a limitation of our perception and information, but rather as a natural, inherent property of matter and energy. As a consequence, the quantum fields during pre-inflation cannot be distributed over space in a perfectly homogenous manner. The very early universe is, rather, infused with quantum, fluctuations. While the universe expands exponentially during inflation, these quantum fluctuations are as well “inflated” to macroscopic size. The density variations arising in this way constitute the sprouts for any formations of large cosmological structures.

After the end of inflation the “normal” cosmic expansion begins, described by the general theory of relativity. For the first 10,000 years in the life of the universe, radiation energy density dominates over matter. This prevents any early increase in perturbations in the density of matter. The situation changes when matter gets the upper hand in the cosmic energy budget after some 10,000 years; the universe changes from being radiation dominated to being matter dominated. The reason is that radiation loses its energy more rapidly than matter due to the additional effect of redshift in an expanding space. From this moment of matter-radiation-equality on, matter density fluctuations are able to self-gravitationally amplify.

This effect of self-amplification concerns only so-called dark matter at first. This is some form of matter, the nature of which remains unknown at the time of this writing, that interacts only via the gravitational (and maybe the weak) force—this is also the reason for dark matter being hard to detect. Numerous observations show, however, that dark matter provides more than 80% of the substantial content of the universe. Only 15%−20% consists of “normal,” so-called baryonic matter that makes up all interstellar gas and dust, the stars and planets and ourselves. Whereas dark matter can now obey the process of self-gravitation to develop local density peaks unhindered, baryonic matter is still prevented from doing so by the influence of the ubiquitous high-energy background radiation; the temperature in the universe is still high enough to keep all baryonic matter in the state of a plasma, a hot gaseous mixture of negatively charged electrons and positive atomic nuclei. The high-energy background photons thus permanently interplay with the charge carriers. Any attempt of the baryons to accumulate within some region would be scotched by the effect of radiation pressure.

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