Talk:Chronology of the universe

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Nucleosynthesis[edit]

RE: At this time, there are about three times more hydrogen ions than helium-4 nuclei.

This is a subtle mis-statement. At the end of the nucleosythesis period, Helium nuclei (almost all He4 and the tiniest amount of He3), account for approximately 25% of the MASS of ordinary matter in the universe - excluding the left over supersymmetric matter.

This proportion is well known. It can be directly observd in various ways, because the proportion of different nuclei only changes in the interior of stars,and in gas clouds ejected by previous generations of stars within galaxies. Everywhere else, the proportion remains almost the same, only disturbed by antiprotons from the decay of the lightest supersymmetric particle. (A topic on which I published a Physical Review Letter with John Hagelin and his student in 1989).

Because most of the hydrogen is in the form of protons, H1, and very little as deuterons, H2 deuterium nuclei, the statement above would mean that the total mass of Helium nuclei (alpha particles) would be 33% more than the total mass of protons (Hydrogen nuclei)!

The sentence would be better rewritten as:

At this time, there are approximately three times more hydrogen ions by mass than helium-4.

Alex Hankey, Physicist — Preceding unsigned comment added by 122.167.131.202 (talk) on 14:30, 24 July 2007

Incomplete Timeline[edit]

There is no mention of what happened before the Big Bang. This needs to be mentioned to complete the time...LINE. Wait... If time is infinite, then how are we here now? This inconsistency should be mentioned, as well.108.85.152.134 (talk) 23:03, 13 December 2015 (UTC)

What makes you think that time is infinite? Dbfirs 23:38, 13 December 2015 (UTC)
Space-time is considered to have manifested together at the Big Bang, hence time did not yet exist before the singularity, at least in this universe. 76.10.128.192 (talk) 04:02, 20 January 2016 (UTC)


Before the Big Bang: According to the Kalam argument, everything which has a beginning has a cause. Thus, if we accept the Big Bang as the beginning of the universe, then we need to postulate a cause i.e. something before the Big Bang. I re-state the Kalam argument as follows: If anything exists, then there could never have been 'nothing'. In this statement, 'nothing' implies no matter, energy, force, or potential. Since the universe exists, there could never have been 'nothing'. So it is fair to ask the question "What happened before the Big Bang?". — Preceding unsigned comment added by Dr Reg Broekmann (talkcontribs) 05:53, 16 January 2017 (UTC)

The Kalam argument and quantum mechanics aren't on speaking terms. But that's irrelevant, the big bang was a singularity (in the mathematical sense), information does not cross such a boundary, even if there was anything "before" that. In reality, we can't even observe back to the big bang, our instruments are limited to at the very earliest getting information from the Recombination period, when the universe became transparent. The cosmic microwave background derives from that era. Tarl N. (discuss) 06:53, 16 January 2017 (UTC)

Inconsistencies within Electroweak Epoch[edit]

Under 'Very Early Universe - Electroweak epoch', the following is stated: "the electroweak epoch began 10−36 second after the Big Bang". Directly in the next sentence, it is stated: "the electroweak epoch began when the inflationary epoch ended, at roughly 10−32 second." and this completely contradicts the previous sentence. Which one is it? Did the Electroweak epoch begin 10-36 seconds after the big bang or did it begin 10-32 seconds after?

JamesYeoman (talk) 10:36, 30 August 2016 (UTC)

What you're missing is that the two timeframes are according to two different theories: "traditional big bang cosmology" vs. "inflationary cosmology". See a slightly more detailed explanation at Electroweak epoch. Tarl N. (discuss) 12:40, 30 August 2016 (UTC)

Very early universe[edit]

This hyperlink redirects to the same page the user came from. — Preceding unsigned comment added by 71.191.3.123 (talk) 19:27, 2 October 2016 (UTC)

There are further circular links in the article, such as the one for the Dark Ages in the table. Awkward. They should be removed and the terms bolded. --Florian Blaschke (talk) 00:49, 7 October 2016 (UTC)

Size of observable universe[edit]

I think it's useful to give an idea how large the volume (or radius) of what become today's observable Universe was at other times. I found it not that easy to find. I'm not looking for particularly precise numbers, so I looked up Friedmann equations and what they say about scale factor a(t). For matter-dominated Universe (which is the case from 47ka since BB up to today), and if Universe is spatially flat or close to it, a(t) is proportional to t^(2/3). Let's check, will this give correct size of 42 mly at recombination from today's radius of 46 Gly? 46000000kly / (13800000ka/380ka)**(2.0/3) = 41946 kly. Good.

Now, earlier times are trickier: at 47ka, Universe transitioned from radiation dominated to matter dominated. Before 47ka, in radiation-dominated universe, a(t) is proportional to t^(1/2). Transition period would require some interpolation for good precision. But let's make a rough estimate by simply using t^(2/3) for 47ka, then using t^(1/2) before that. At 47ka, we get radius 46000000kly / (13800000ka/47ka)**(2.0/3) = 10413 kly. Now, what would be the radius at 1 sec (neutrino decoupling)? Using t^(1/2) here: 10413000ly / (47000*365*24*60*60sec/1sec)**(1.0/2) = 8.55 ly. I'll go with "about 10 light-years".

Where you wrote mly, you apparently meant Mly. - Patrick (talk) 20:31, 5 September 2017 (UTC)
Regardless, 213.175.37.10 (who neglected to sign his contribution) is engaged in WP:OR. Unless we find a citation which specifies size of the universe at those times, we'll have to delete those entries. Tarl N. (discuss) 01:19, 6 September 2017 (UTC)
The 42 Mly radius at recombination is not a number I invented/calculated to put on this page. You can google it. Hmm... Google also found it on "Observable_universe" page.

Inconsistency in dating of the Dark Ages[edit]

The table says that the Dark Ages lasted from 0.38–150 Ma, but the text says 150–800 Ma (without citation). Moreover, in the following paragraph, Loeb (2014) gives 10–17 Ma for the "Habitable Epoch" he postulates, which is consistent only with the value in the table. The epoch from 150 Ma on already belongs to the "Reionization" epoch according to the following sections, and the table. The material immediately following the 150–800 Ma is inconsistent and seems to conflate (erroneously) the reionization epoch with the Cosmic Dark Ages; all the mentioned galaxies (not only the first one) appear to belong to the later reionization epoch, not the Dark Ages, and if this is so, this material is not germane to the Dark Ages section anyway and should be moved to the "Reionization" section. The hatnote linking to List of the most distant astronomical objects also seems to belong there and not to the Dark Ages section. (As far as I understand, the "Dark Ages" span the time between the end of the recombination epoch 0.38 Ma and the beginning of the reionization epoch 150 Ma, when the first stars were formed, hence the reionization epoch is also considered the beginning of the Stelliferous Era, and the formation of the oldest galaxies clearly does not belong to the Dark Ages.) However, I cannot exclude that the article is misleading as to the dating of the relevant epochs – I'm not an expert and therefore I hesitate to change the article myself. --Florian Blaschke (talk) 00:40, 7 October 2016 (UTC)

@Drbogdan and Dbfirs: You appear to be knowledgeable about this subject – can you look into the issue I've brought up? --Florian Blaschke (talk) 23:40, 9 October 2016 (UTC)

@Florian Blaschke and Dbfirs: Thank you for your comments - and noted concerns - yes - agreed - some of the material you mentioned may need to be improved - for my part, I've tried to improve some of the text/refs I had added earlier (beginning 4 December 2014) - however, other material (ie, that related to "150–800 Ma" - and onward) may have been added by other editors some time ago (beginning 25 October 2010?) - it's *entirely* ok with me if you would like to improve the material further of course - in any case - Thanks again for your comments - and - Enjoy! :) Drbogdan (talk) 03:29, 10 October 2016 (UTC)

Habitable epoch inconsistency[edit]

The Habitable epoch section contains inconsistencies with material contained elsewhere on the page. The Habitable epoch section states: the background temperature was between 373 K and 273 K, allowing the possibility of liquid water, during a period of about 6.6 million years, from about 10 to 17 million after the Big Bang and speculated that primitive life might in principle have appeared during this window. Later in the Chronology of the universe page in the Star Formation section it clearly states that elements heavier than Lithium where first formed in this period and so the elements necessary for life and water such as Oxygen and Carbon were not formed until 560 million year after the Big Bang. In the first 20 minutes of the Big Bang (Nucleosynthesis) only Hydrogen, Helium and Lithium were formed. So 10 to 17 million after the Big Bang it is impossible for there to be liquid water as claimed. The suggestion that primitive life formed during this period is surprising. All references for the above are contained on the Chronology page. The Nature article referred to in the section appears to have inadequately peer reviewed. DJM1961Br (talk) 23:48, 8 January 2017 (UTC)

The article wasn't in Nature, but in the Journal of Astrobiology. The paper is available at ArXiv (here). He speculates that hyper-massive stars could have been created and lived their entire lifspans by then, creating the heavier elements in question. Not to say that the article isn't speculative - formation of non-incandescent planets out of supernova remnants that early is decidedly unlikely. Tarl N. (discuss) 02:25, 9 January 2017 (UTC)

Agreed the article was not published in Nature. I very much doubt the paper represents the mainstream or standard view of the cosmological community on the formation of the early universe. The section is inconsistent with later material on star formation. — Preceding unsigned comment added by DJM1961Br (talkcontribs) 04:49, 9 January 2017 (UTC)

I also think the article is fairly speculative, and should not be mentioned in this article. Deleting this fragment... — Preceding unsigned comment added by 2A00:CA8:A14:6A01:4685:FF:FE33:1E8B (talk) 20:52, 28 August 2017 (UTC)

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