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When it is said, for example, that grand unification took place "Between 10−43 second and 10−36 second after the Big Bang", how are these figures of time derived?

Moreover, do these figures have any meaning, considering that during these epochs, spacetime was incredibly warped, and immediately after inflation, matter was at an incredibly high energy state and moving at relativistic speeds?

Amphibio
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    the times come from the energy scale. For a rough guide, see Weinberg's "The First Three Minutes". – Peter Diehr Mar 03 '16 at 11:54
  • Why would spacetime have been "incredibly warped"? And what does "incredibly high energy state" supposed to mean? Was it hot for your taste? Sure... but you weren't around, so what you think of as "just the right scale" doesn't matter. The scale dictates the physics and locally the physics wasn't all that exciting... which is actually what we are trying to explain... just why was it so incredibly homogeneous and boring? – CuriousOne Mar 03 '16 at 11:59
  • @CuriousOne, I don't find it boring at all. Why should I? – Amphibio Mar 03 '16 at 12:04
  • The first one, $10^{-43}\text{ s}$, is called the Planck time. It is typical time of all forces unification. We believe in that because we assume that the high energy description of our world is based on three theories: general relativity with dimensionful parameter $G$, special relativity with dimensionful parameter $c$, and quantum mechanics with dimensionful parameter $\hbar$. We expect that at the energy scale which corresponds to the time of order of Planck one these theories are unified into the one. Below this scale the gravity decouples from the hypothetical strong-electroweac GUT. – Name YYY Mar 03 '16 at 12:06
  • The second one, $10^{-36} \text{ s}$ (or to $E \sim 10^{16}\text{ GeV}$), corresponds to the hypothetical scale of unification of electroweak and strong theory into strong-electroweak GUT. This scale is expected to be so large based on analysis of running constants in some of explicit models of GUT. – Name YYY Mar 03 '16 at 12:06
  • Precisely, if QCD and electroweak running couplings match one point at some scale, then corresponding theory becomes to be describable by only one coupling constant, which means that the SM symmetry group becomes to be enclosed in simple Lie group $G$. Some GUT theories, like minimal supersymmetry, gives the value of such scale - $10^{16} \text{ GeV}$. – Name YYY Mar 03 '16 at 12:06
  • And therein lies the misconception. The observational data demands that the universe had to be extremely boring, while you seem to be assuming that it was a huge inhomogeneous mess. – CuriousOne Mar 03 '16 at 12:16
  • @NameYYY: All of that is model dependent, though, isn't it? If there is no GUT because there is another scale which we don't know about, yet, then it's all out the window, isn't it? – CuriousOne Mar 03 '16 at 12:17
  • @CuriousOne, I don't find the concepts of symmetry, unification, and the planck scale boring in the slightest. If you happen to be feeling disenchanted, don't apply that to the physics. – Amphibio Mar 03 '16 at 12:24
  • I am only fascinated by what has been measured and none of that is more than a story for highly educated children right now. Curiously, what you are imagining about the early universe has already been ruled out by measurements. :-) – CuriousOne Mar 03 '16 at 12:28

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