New answers tagged

1

The conformal transformation $g'_{\mu\nu} = e^{-2\sigma}g_{\mu\nu}$, $sigma = sigma(x)$ leads to the transformation of the Ricci scalar $$ R' = e^{2\sigma}R - 12e^{2\sigma}(2\sigma_{,\mu}^{,\nu} - 2\sigma_{,\mu}\sigma^{,\mu} $$ Since $\phi' = e^{\sigma}$ then $$ \frac{1}{12}\phi'^2R' = \frac{1}{12}\phi^2 R - \phi^2(2\square\sigma - ...


9

Your question is not specific to inflation, and really applies to any case where a bosonic quantum field behaves semiclassically due to macroscopically large occupation numbers. One very simple example of this is the Stark effect in quantum mechanics, where a Hyrodgen atom is placed in a uniform electric field. The atom is treated as a quantum mechanical ...


1

As already explained in other answers and comments in General Relativity (GR) energy is not conserved. Some people and physicists say it is, it simply gets lost by the matter-energy and gained by the gravitational field, or viceversa; this is more pleasing to our sense of conservation of something, but it has problems in that the gravitational energy, is not ...


4

A fine tuning problem is only a problem if we require that the considered model is a good or complete model of how we think the universe behaves. In this case, it appears that we require the density of the universe to be as close as 1 part in $10^{64}$ to the exact density that will make it a flat universe that will expand forever, asymptotically coming to ...


3

The argument is that (mixing happens) => (inflation happens) => (mixed regions are out of causal contact, but have no way to change their local temperature) In this scenario, it doesn't matter when the photons are emitted. Their apparent homogenity is an effect of the left most step.


3

The process by which particles are created after inflation is known as "reheating". One needs a coupling between the inflaton and another particle's field for this to happen. Generally it occurs at the end of inflation when the inflaton is oscillating in the well of its potential and the expansion rate falls below the interaction rate between the inflaton ...


1

Firstly, you must know that there are many models for inflation which give different results to your a) and b) questions, and we still don't know which is the right one. I'll try to answer regarding the most accepted and simple models. a) During the period of inflation the distance between two separated points in the Universe increased at least ...



Top 50 recent answers are included