Talk:Cosmic inflation

I added a section on the effect of the WMAP measurements on the acceptance of inflation vs topological defects. This based on Smeenk and it matches other things I've read. However the last bit of Smeenk on this topic suggests that the defect-after-phase-transition thing could operate in conjunction with inflation, something I've also read elsewhere. So I'd like to find a source that clarifies this story. Johnjbarton (talk) 22:53, 26 June 2025 (UTC)

"A distance of 1 cm expanded to a distance more than 20 times the distance from the Earth to the Moon.  All of the mass-energy in all of the galaxies currently visible started in a sphere with a radius around 4 x 10^-29m then grew to a sphere with a radius around 0.9m by the end of inflation."

At least one of these expansion examples is off by many orders of magnitude. Clive tooth (talk) 13:39, 2 August 2025 (UTC)

I did verify that the sources says this. The Earth Moon distance is 4x10⁸m times 20 works to 1.6x10¹⁰m which matches the source claim of 10 billion meters. The Cox/Forshaw uses a time of 4x10^-36s. The ratio the 1cm and 10 billion meters is ${\displaystyle 10^{12}}$, about 6-8 orders of magnitude too small. Earth - Sun would still be 3 orders short.

Ryden seems to use time equal to ${\displaystyle (N+1)t_{\textrm {GUT}}-t_{\textrm {GUT}}}$ where N is the number of "n-foldings" around 60 and the time is ${\displaystyle 10^{-36}}$. The minimum scale factor ratio for inflation is ${\displaystyle 10^{26}}$. Dodelson uses ${\displaystyle 10^{28}}$. Kolb and Turner have several different models, but they confirm the 60 e-foldings minimum. Zee gives similar numbers.

So the Cox/Forshaw must be a misprint/error. I will remove the Cox/Forshaw, thanks. Johnjbarton (talk) 00:06, 3 August 2025 (UTC)

When I saw your "about 6-8 orders of magnitude too small", it crossed my mind that changing a single letter the Cox/Forshaw quote would rescue it:

"A distance of 1 nm expanded to..."

Of course, I have no idea if this was their intention. 92.29.146.69 (talk) 18:07, 3 August 2025 (UTC)

Yes, in some source I read while double checking this I saw "subatomic distances" as the referent so maybe they meant 1nm.

It is very difficult to come up with a comparison for 26 orders of magnitude. The attractive feature of "Earth to Moon" is its seeming everydayness, but do you feel you know how far away the Moon is? An I'm not sure 1nm is helpful for the lower side for that reason.

Maybe "100 trillion-trillion times"? At least it seems been to me ;-) Johnjbarton (talk) 18:28, 3 August 2025 (UTC)

A nanometer would expand to about 10 light years during cosmic expansion.

But the nanometer is very far from "subatomic distances". And talking about a nanometer sphere expanding may give the impression that such a sphere existed at the start of cosmic expansion. Whereas we have no idea (and may never know) if such a huge sphere existed then.

A ball-park way of thinking of it is a sphere with a radius of about one trillionth of the radius of a proton expanding to a 1 meter radius sphere. 92.29.146.69 (talk) 21:48, 3 August 2025 (UTC)

[For some reason I had been writing "expansion" instead of "inflation".] 2.100.155.145 (talk) 07:58, 4 August 2025 (UTC)

I rewrote a sentence in Reheating as

• The energy density of this state is dominated by radiation gas, so prior to the end of reheating, the massive inflaton particles must have completely decayed.

But when I looked for a source, the (very detailed) sources we have gave a much more complex story. For example from Lozanov

• Despite all of these problems, the perturbative analysis in this section can be applied to the late stages of reheating, e.g., to the decay of remnant inflaton particles after most of the energy has been transferred into relativistic species. Note that such decay channels are crucial to include, so that the energy transfer can be completed. Otherwise, we can face another relic problem.

I think we should look for a better source for this last bit. Johnjbarton (talk) 22:33, 17 December 2025 (UTC)