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Sorry if this question to too silly for the experts here. But how do cosmologists assign a temperature and a time to each important cosmic event in the history of evolution of the universe such as electroweak symmetry breaking, QCD phase transition etc and to more speculative events such as grand unification, inflation etc? Please feel free to use some equations. For a tabular summary see Chronology of the universe.

I emphasize that I know how to calculate things like the photon or neutrino decoupling temperature and decoupling time i.e. by equating interaction rate $\Gamma(T)$ which keeps them in equilibrium to the Hubble rate $H(T)$. Thus we can solve for $T$, and then use time-temperature relationship. But my question is how to use similar idea to find the time of, say, the electroweak symmetry breaking.

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    $\begingroup$ Please tell me why this has got a close vote so that I can work on it. $\endgroup$ Commented Jan 1, 2020 at 13:18
  • $\begingroup$ I think these temperatures (QCD phase transition, electroweak symmetry breaking, etc) come from particle physics, not cosmology. $\endgroup$
    – Allure
    Commented Jan 1, 2020 at 14:03
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    $\begingroup$ @Allure That is true but how? How to show that the EWSB occurred at time $10^{-32}$ seconds. Particle physics tells the scale of EWSB is about 100 GeV. $\endgroup$ Commented Jan 1, 2020 at 14:11
  • $\begingroup$ EWSB occurred at $10^{-12}$ s, not $10^{-32}$ s. See Wikipedia. $\endgroup$
    – G. Smith
    Commented Jan 8, 2020 at 3:42
  • $\begingroup$ I believe this answers your question: nicadd.niu.edu/~bterzic/PHYS652/Lecture_13.pdf $\endgroup$
    – G. Smith
    Commented Jan 8, 2020 at 3:50

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From facts about particle physics and thermodynamics, we get an equation of state, which describes the stress-energy tensor. The stress-energy determines the pressure and density, which show up in the Friedmann equations. You solve the Friedmann equations, and you get predictions for, e.g., when the CMB will have had a certain temperature.

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  • $\begingroup$ How to show that the EWSB occurred at time $10^{-32}$ seconds. Particle physics tells the scale of EWSB is about 100 GeV. $\endgroup$ Commented Jan 2, 2020 at 5:42

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