This question is inspired by this more specific question where Cerelic wanted to know if conditions were suitable for liquid water to exist during an epoch when the characteristic temperature of the cosmic black body radiation was near room temperature. The answer is No, because the pressure was too low by then, but that raises the question of what the temperature of the medium was at a time when the pressure was near Earth sea-level pressure.

A log-log graph of temperature, pressure, and density of baryonic matter starting at the Big Bang would be quite interesting, especially if it were annotated with familiar references. It might need to have a special scale during the inflation era. Does such a thing exist in the literature?

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    $\begingroup$ I did find that this Wikipedia article has relevant information: en.wikipedia.org/wiki/Chronology_of_the_universe, but I think not enough detail to make this question a waste of time. $\endgroup$ Apr 14, 2021 at 15:19
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    $\begingroup$ Have you seen the links to scientific papers in the citations? $\endgroup$
    – WarpPrime
    Apr 15, 2021 at 16:31

1 Answer 1


It is well known that T has varied inversely to the scale factor R of the universe (from thermodynamics). The total mass/energy of it (assuming that the universe has critical density) increases as R, and the density of the total matter (if there is no mass increase) scales as R^-3, while in the case of growing matter (M proportional to R), it overall scales as R^-2. The pressure of each component depends on its equation of state. For non-relativistic matter (e.g. cold dust), the presure is 0.

  • $\begingroup$ This is downvoted because it isn't an answer to the question asked which wants the run of temperature, density and pressure with time. $\endgroup$
    – ProfRob
    Jan 22 at 13:05

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