A good introduction to the fluid equation is in Introduction to Cosmology by Barbara Ryden (references here to 1st edition). The idea is that the first law of thermodynamics (conservation of energy) joined to the Friedmann equation gives an equation about how the universe expands (p. 52). This leads to equations of state (p. 54). A few more steps and assumptions implies for a matter dominated universe a time t_0 = (2/3) (1/ H_0) (p. 75). Why 2/3? That is what the equation of state implies. But one would expect t_0 = 1 / H_0. Moreover, t_0 = (2/3) (1/ H_0) seems to underestimate the age of the universe compared to astronomical observations (p. 91).
For a radiation dominated universe, , t_0 = (1 / 2) (1/ H_0) (p. 76). According to cosmology, it seems the universe was first radiation dominated (an initial plasma) and later matter dominated.
Does that mean that the way the universe ages depends on what is in it? How does the universe (if we anthropomorphize) know when to transition from 1 / 2 to 2/3? How is it able to shift gears like that? Does aging (time) depend on whether there is radiation or matter? And 2/3 gives a wrong answer anyway.
If the fluid equation is treated merely as a heuristic, then cosmology may be in the dark when it comes to theoretical bases for the age of the universe. If the fluid equation is treated as an essential cosmological inference, then are the assumptions joined to it in doubt?
Hello Robert Shour,
To answer your question, yes, cosmology must rely on fluid mechanics.
Indeed, by studying Einstein's equation, we note that it expresses the existence of aether, a superfluid non-Newtonian space-time.
For more details, I invite you to read my article, and would be happy to answer your questions.
Preprint Stress Energy Tensor Study in Fluid Mechanics
Regards,
BAUDRIMONT Roman
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