Talk:Recombination (cosmology)

Recombination?
The "re" in recombination implies that the primordial (mostly hydrogen) plasma has previously existed in the combined or deionized state. The phase shift described here is the initial combination, the first condensation from the ionized state to the less energetic neutral state. The only reason to use the term "recombination" is that it is more familiar in the context of everyday chemistry, where most substances begin in the lower energy state. In the cosmic context (and in the context of protons and such generated by nuclear reactions), "deionization," "plasma (or ionic) condensation, or even "proton/electron capture" would be more appropriate.

I often use the phrase, "initial deionization of the primordial plasma" to describe this event, and add "what chemists might call 'recombination.'"Alan R. Fisher (talk) 07:51, 27 December 2010 (UTC)


 * And? That recombination is a misnomer is mentioned in a footnote. Recombination is what it the process is (unfortunately) called, and will continue to be called. So I am not sure what your point is. James McBride (talk) 08:33, 27 December 2010 (UTC)


 * In fact, "recombination" is a term borrowed from plasma physics. It's usage here is consistent with that field. It's simply the reverse process of ionization. So it's really not a 'misnomer.' I'll at least a week for comments before making any changes.MarkWayne (talk) 16:54, 1 July 2014 (UTC)


 * Well, it IS a misnomer, for the reasons previously stated. And sadly, that only makes a complex topic even more difficult to understand for the layperson.  Unfortunately, human nature being what it is, linguistic mistakes tend to last forever, long after the initial error is discovered.  Why the hell are Native Americans still called "Indians"??? Captain Quirk (talk) 03:20, 28 September 2014 (UTC)

Helium?
Is helium recombination worth a mention? Thanks.&mdash;RJH (talk) 19:04, 22 February 2010 (UTC)

Observational/experimental proof
Um, where is any mention of any observational or experimental proof of these events? If there are none, it should be noted that it is a hypothetical scenario. 76.15.238.242 (talk) 14:52, 26 February 2010 (UTC)
 * I suppose this could be made more explicit, but yes, there is the discussion of the cosmic microwave background in the Impact section, which would not have been emitted when it was if not for a recombination event just before. James McBride (talk) 19:58, 26 February 2010 (UTC)

Use of the word theoretical before 'big bang'
I think since the Big Bang theory is too often overstated as extremely solid and in fact presented as not a theory but a fact it creates a unscientific and unhealthy situation where people are massively unaware about the level of our knowledge and proof for it, as opposed to various other cosmological theories about the history of the universe for instance. For that reason I think it's preferable to precede the term big bang with 'theoretical' more often.

The fact that adding the word theoretical even prompts people to remove it again with the excuse that it 'add nothing' shows even more how polarized it became already, since even when you view it's not needed there is obviously no reason to not have the word there either. — Preceding unsigned comment added by Wwhat (talk • contribs) 02:55, 28 September 2011 (UTC)


 * No, it just shows how some people can't get accept that some things are considered facts by science. Adding a "theoretical" there is both misleading and distracting. Headbomb {talk / contribs / physics / books} 01:45, 5 October 2011 (UTC)
 * It's NOT a fact. That's 100% false. Being not a fact does not imply anything about religion which is what I assume people jump to. It just means it's not a fact. It's a model. Continually calling it a fact is an insecurity. 50.35.113.183 (talk) 17:32, 17 May 2023 (UTC)

Time line?
I don't see any mention of when the recombination era started, nor how long it lasted.77Mike77 (talk) 13:32, 23 October 2013 (UTC)

4000K is visible
The radiation from a 4000K blackbody includes some visible light (as we all know -- it's orange: The Sun isn't even that much hotter). This informs the description -- although not currently mentioned on this page -- of the subsequent Dark Ages. These are sometimes inaccurately described as having no visible light, but that's untrue until the temperature falls further, a million years or more of age. Jmacwiki (talk) 14:07, 2 June 2018 (UTC)

Where does 378 000 years come from?
It used to be "380 000 years", and new it has become even more "refined" ... But -exactly! - what is the origin of this value? For long I haven't thought much about it, but then I started wondering ...? I've looked around, but I have so far not found any other argument than that it is "380 000 years"!, sort of a fact brought, like a sore-eared white rabbit, right out of a black PhD hat. So "Source needed". But I don't want a source that claims - again - this value, or an even more refined value, but an explanation of: under what assumptions and in what context, based on what measurements, this particular value has been derived. (I think that is a rather modest request... ;-) Hilmer B (talk) 16:24, 6 October 2018 (UTC)

And while I am at it:

1) with such an "exact" date as 378 000 ABB you might wonder what happened then. I assume that nothing in particular dramatic occurred, rather it was a process that culminated around this date. This should be clarified in the article, otherwise this date is without meaning.

2) The exact relation between "age at recombination=378 000 y" and "z=1100" should be clarified. With a(t)=1/(z+1), where a(BigBang)=0 and a(now)=1: can it be stated that a(378 000)=1/(1100+1)? Hilmer B (talk) 22:28, 2 December 2018 (UTC)

The quoted density of H is just plain wrong?
The article states: total density of hydrogen (neutral and ionized) is given by $$n_p + n_H = 1.6 (1+z)^3 m^{-3}$$. Plank has measured Omega_b h^2 as 0.02205. If you multiply that by $$\rho_{cr}$$ (8.51e-24 g m^-3), you get $$4.14e^{-25} g m^{-3}$$. From BBN, we know that 0.75 of all baryonic mass is Hydrogen, so multiply that by 0.75. Finally, A hydrogen atom weighs 1.67e-24 g, so the density of H in the present day universe, assuming $$\rho_{cr} = 1.0$$, is 0.186 atoms per m-3, so the formula should read $$n_p + n_H = 0.186 (1+z)^3 m^{-3}$$.