Cosmological parameters and their correspondence with recent data are very important, so I have two basic questions, what is the exact meaning and definition of the number of e-folds, and for what purpose was it introduced? And why the slow roll parameters should be very small in the inflationary period

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    $\begingroup$ $H=\frac{d}{dt}\ln a$ is the rate of $e$-folds in $a$. Could you restate your question about slow roll parameters in terms of notation such as e.g. used here? $\endgroup$
    – J.G.
    Jan 3, 2023 at 12:46
  • $\begingroup$ Thanks, but I want a non-mathematical definition of it. What does it mean to say 50 or 60 e-folds? without an equation? $\endgroup$
    – Saber
    Jan 3, 2023 at 15:07
  • $\begingroup$ Does "the universe's length scale multiplying by $e^{50}$ or $e^{60}$" count as "without an equation"? $\endgroup$
    – J.G.
    Jan 3, 2023 at 15:34


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