Talk:Big Bang nucleosynthesis

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Falicious Times for Early Universe Events are Obtained with Non-Relativistic Models[edit]

I suspect that the universe started with roughly dead galaxies falling in with a total mass of approximately solar masses that were composed largely of white dwarf material that slammed together a bit like the pieces of a uranium bomb. The infalling material was primarily cooled white dwarf remanant material with a small admixture of neutron stars, and when it slammed together the radiation-dominated era began immediately. Calculations show that the initial fireball was radially unstable, such that the energy required to compress it against radiation pressure for a meter was just equal to the work done by the gravitational field in shrinking the fireball radius another meter. Thus the universe was eventually compressed to its limiting density, that of a nucleon, as it coasted in from the ignition perimeter at , initially at white dwarf density, without gaining additional energy. This would have yielded a lower spherical radius limit at nucleon density about equal to the radius of the orbit of Mars. The black body radiation field switched on at a temperature determined roughly from


containing many billions of times as much mass-energy ε from the infall kinetic energy as the entire nucleonic rest mass-energy. It was a bit like a man jumping on an elevator going down at constant velocity in the presence of radiation pressure ε/3. The energy release was rapid and ultimately explosive when the hard-core nucleonic potential caused a reflection shock wave that turned the infall around. Composed of dead galaxies of cold white dwarf material of the approximate density kg/m3, the universe mass fell into a sphere of radius 2000 AU, or meters, just 0.0316 light-years, before lighting up and coasting down to nucleon density radius over a period of several months at v < c. Subsequent calculations have shown that it took over 26.7244 years for the fireball to expand and cool enough for deuterium and helium to form, kicking in fusion energy, and the galaxies formed well over years after the reflection from nucleonic density, following the end of the radiation-dominated era at the time when radiation was decoupled from matter and the matter-dominated era began. These times are longer than many times you may read about elsewhere that were computed from approximate, non-relativistic models for the expansion of a universe of constant density. We find easy closed-form solutions to the approximate equations like

, with (matter-dominated era) and

, with (radiation-dominated era).

For both cases, it is easy to specify early times such that v >> c. These difficulties yielding short times to key early-universe events vanish when we use [16]


as the basis of our calculations, neglecting a pressure term at first. Here the force is equal to the time-derivative of the special relativistic momentum , and gravitating mass is equal to inertial mass . Note that the equal falling of objects of different mass is preserved, so the principle of equivalance may still be applied. On the other hand, solutions are difficult to obtain in closed form then. However, one can easily show that velocities with v > c are never realized. We have gas- and radiation-ball theorems that give the radius R as a function of the temperature T in the form R(T). Then the expression t > R(T)/c gives the time for the expansion of the fireball to radius R(T) for any given early universe event temperature.

Our infall-before-bounce scheme insures that the basic conservation laws always hold true. I note that matter always falls in before supernovae, novae, or plantary nebula ejection occur, so it is natural to extend this to the Big Bang, equipping it with a preliminary Big Crunch and Crunch-Bang or Squeeze-Boom cosmic cycles. The matter-dominated era nucleons in the subsequent cooled Big Bang fireball are thought to be conserved across cosmic cycles hundreds of billions of years in length. - James A. Green, May 6, 2006 JamesAGreen 17:07, 6 May 2006 (UTC). See for more on the Big Bang and the Big Crunch.

Why is it written:

It is believed to be responsible for the formation of hydrogen (H-1 or simply H), its isotope deuterium (H-2 or D), the helium isotopes ... etc

H-1 was not formed by nucleosynthesis, it is just protons, formed much earlier during the Big Bang. Right? BIL 20:20, 12 October 2006 (UTC)

It's spelled "fallacious" 2001:48F8:1001:0:0:0:0:E54 (talk) 20:41, 11 June 2017 (UTC)

p + p → d + π[edit]

Over on Plasma cosmology#Light elements abundance, Eric Lerner's theory is cited, that deuterium was formed by the above reaction between cosmic rays and cold protons. This article (BBN) makes it sound like everything had already been considered in the 70s. If anyone has a reference that specifically says this reaction was considered and rejected, it would make a very nice addition to the plasma cosmology article. (Of course, if a generation of cosmologists really overlooked this possibility, that would be even more delicious.) --Art Carlson 13:23, 7 November 2006 (UTC)


When were all the other elements created? Gold, iron and the other metals? Could someone point me in the right direction? Thansk


Citation needed[edit]

The citation needed in the helium-4 section about ending the Big Bang nucleosynthesis crisis could be this from the Astrophysical Journal, University of Pennsylvania:

Since I'm not familiar with the template for inserting sources that are periodicals, I hope someone will enter this reference. --Sir48 11:28, 12 February 2007 (UTC)

Request for comments: cited articles/article for general audience[edit]

A while ago, I made some changes to this article, adding a reference to the new WMAP measurements to the "Observational Tests" section and stressing the race between equilibrium and external change by expansion in the "Sequence of BBN section", adding as references two web articles by Achim Weiss (from the Max Planck Institute of Astrophysics in Munich). I also split the external links into technical links and those suitable for a general audience, and added a more general article by Weiss to the latter section.

Those were pretty much my first contributions to Wikipedia, and I hadn't progressed in reading the "How to" pages as much as I probably should have - anyway, I realize now that I should have declared a conflict of interest, since the three articles by Weiss are published on a website which I edit (Einstein Online). I think that my behaviour was as cautious and neutral as the guidelines suggest, and that I might be overdoing it by making this grand declaration here, but hey, I guess that's not up to me to decide - hence this request for comments. Markus Poessel 12:06, 5 April 2007 (UTC)

This really does not seem like a conflict of interest to me. Also, the material that was inserted seems reasonable, although I am not an expert on Big Bang nucleosynthesis. You may want to add references to refereed journal articles to supplement the existing references, but that is my only suggestion. Dr. Submillimeter 14:03, 5 April 2007 (UTC)
Thanks for your comment. At least for the observational tests, I've now added references to journal articles. Markus Poessel 19:49, 5 April 2007 (UTC)
Thanks for the help! I don't see any serious conflict of interest here, assuming we're not going to have *all* articles from your website down the road. Don't sweat the "grand declaration." It's considerate of you to check. Just don't let it stop you from being bold! Cheers, Gnixon 15:46, 6 April 2007 (UTC)
Thanks for the reassurance. I was certainly not planning on linking *all* articles, but I think a number of them would make good external links for the topics they address - don't worry, though, I'll follow proper procedure regarding those, proposing the additions on the respective talk pages and letting other Wikipedians decide. Markus Poessel 19:11, 7 April 2007 (UTC)

Statement disagreeing with itself?[edit]

It lasted for only about three minutes (during the period from 1 to about 100 seconds from the beginning of space expansion)

So, how long was it? Three minutes, or 100 seconds? 18:55, 11 May 2007 (UTC)

The starting time is inconsistent, too. There's one mention of 3 minutes and several of 1 second after the BB:

[BBN] lasted for only about seventeen minutes (during the period from 3 to about 20 minutes from the beginning of space expansion)

Big Bang nucleosynthesis begins about one second after the Big Bang (talk) 23:11, 22 March 2008 (UTC)

The end of the process is gradual so it depends where you draw the line. This page on nucleosynthesis from Prof. Wright shows the reactions and has graphs of the relative abundances which might make the timescale clearer. Other than the slow decay of some species, the abundances had virtually stabilised by 1000s or around 16 minutes.
George Dishman 11:10, 31 January 2010 (UTC)

On 9/24/11, the article still had errors in the timing for Big Bang nucleosynthesis. It says that it started 3 minutes after the Big Bang. According to "The Essential Cosmic Perspective" by Bennett et al, the Era of Nucleosynthesis went from 0.001 seconds to 5 minutes after the Big Bang. The temperatures changes significantly between O.001 seconds and 3 minutes. — Preceding unsigned comment added by (talk) 03:58, 25 September 2011 (UTC)

Also, there exists a confusingly-worded sentence in the section titled, "Characteristics"; it says, "The corresponding time interval was from a few tenths of a second to up to 1000 seconds." Does this mean that the corresponding time interval is estimated to have spanned anywhere from a few tenths of a second to up to 1000 seconds, or that the time interval started at roughly 0.1 seconds after the Big Bang and then continued until roughly 1000 seconds after the Big Bang? I'd guess the latter were the case, but I'm not sure. Popa910 (talk) 17:58, 19 November 2015 (UTC)


I believe a trace amount of Lithium-6 was synthesized in BBN. See Frank Levin's recent book Calibrating the Cosmos. Eroica 10:22, 5 August 2007 (UTC)


Is H-1 a proper notation for the hydrogen atom? It is not used in the Hydrogen atom article . It is also not mentioned in the disambiguation page H-1. --George100 (talk) 13:18, 12 July 2008 (UTC)


Last section of Observational Tests and Status of Big Bang nucleosynthesis:

But for lithium-7, there is a significant discrepancy between BBN and WMAP, and the abundance derived from Population II stars. The discrepancy is a factor of 2.4―4.3.[7]. This level of agreement is by no means trivial or guaranteed, and represents an impressive success[peacock term] of modern cosmology...

The statement is obviously not neutral according to WP:NPOV but instead tries to misrepresent a discrepancy as a success. Forgive me for being sharp, but this kind of talk doesn't befit wikipedia editors. We present facts as they are, and we aren't cosmologists, so if we keep cool and sceptical towards the Big Bang Theory, our academical careers (if we have such) won't suffer. A correct attitude to a discrepancy between observation and theory is that it is a (IMHO minor, but yet) problem for the theory. ... said: Rursus (mbork³) 11:10, 27 October 2009 (UTC)

Rewrote. Someone might add clarifying sentences, such as that measuring primordial abundancies is very hard and error prone, so that a discrepancy is not a serious problem, unless it persists however much the scientists change models and make new refined observations. ... said: Rursus (mbork³) 11:53, 27 October 2009 (UTC)

The problem of "missing" Lithium 7 appears to be getting bigger (perhaps 2x bigger) rather than better observations making it disappear. synthesis of lithium isotopes in the hot tori formed around stellar mass black holes. Perhaps it is time to give the Lithium 7 problem it's own section in this article? Bern1005 (talk) 10:23, 10 September 2012 (UTC)

There must be something wrong with that theory[edit]

The abundances of helium and hydrogen are almost the same as observed in the Sun today. But, part of the hydrogen formed helium by nuclear fusion inside the Sun, so that the abundance of helium must be higher today. -- (talk)

Indeed the amount of helium created in the estimated lifetime of the Sun

is about 7 percent of its mass. Moreover heavy elements are created, while only very few helium at the same time. —Preceding unsigned comment added by (talk) 22:28, 10 November 2009 (UTC)

mass of helium atom = 4 x 1.66E-27 kg, energie per formed helium atom = 27 MeV = 27 x 1.6E-13 J, luminosity of the Sun = 4E26 J/s, age of the Sun = 4.5E9 years = 4.5E9 x (365x24x60x60) s

mass of produced helium = (4 x 1.66E-27 kg)*(4E26 J/s x 4.5E9 x (365x24x60x60) s) / (27 x 1.6E-13 J) —Preceding unsigned comment added by (talk) 10:02, 11 November 2009 (UTC)

What does Google say?[edit]

((4 * 1.66E-27 * kg) * (4E26 * (J / s) * 4.5E9 * (365 * 24 * 60 * 60) * s)) / (27 * 1.6E-13 * J) = 8.72496 × 1028 kilograms

That means: 8.7E28 kg helium was produced inside the Sun in 4.5 billion years. That is 4.4 percent of the mass of the Sun (2E30 kg). Sorry, Google calculated it more correctly as I did yesterday. (talk) 10:13, 11 November 2009 (UTC)

Read Sun#Chemical composition to understand why that extra helium doesn't show up at sun's surface. Dauto (talk) 23:40, 11 November 2009 (UTC)

Origin of nucleosynthesis theory[edit]

I was watching the History channel and they had a "The Universe: Big Bang" episode in which it states Fred Hoyle was the one who came up with the idea of the nucleosynthesis of elements (as well as his Steady State theory). Obviously steady state fell out of favor, but it was said in the program that his idea of nucleosynthesis in stars was continued and improved on by Alpher et al. Anyone know more about this? Because the article does not mention Hoyle at all as it stands today. jlcoving (talk) 20:12, 11 December 2009 (UTC)

Hoyle is more appropriately covered in the article on stellar nucleosynthesis, which was the theory he actually proposed (and which turned out to be partly correct). Remember, Hoyle famously never believed in the Big Bang.SBHarris 05:53, 28 September 2011 (UTC)

Never say never[edit]

It is wrong to say that strictly no heavy elements were created in the big bang. The processes making heavy elements are unlikely, but pretty much any process that can occur (no matter how unlikely) will occur. It would be better to quote the limit on the abundance of heavier elements due to BBN. My recollection is that the theoretical number ratio for the combined total of all elements heavier than Li to H is something like ~10-16, i.e. quite a bit smaller than the 10-10 for Li but not strictly 0. Unfortunately, I can't seem to find an appropriate reference at the moment. If someone can find a reference, I would appreciate seeing a more accurate limit rather than simply saying no heavy elements where created. Dragons flight (talk) 05:16, 21 October 2010 (UTC)

Be and B are ~ 10-18 ( ) Dan Watts (talk) 15:05, 28 September 2011 (UTC)

I've wondered for some time if the quantity of heavier elements was truly zero or just minute, even undetectably low. Those with more knowledge of physics and chemistry might correct me, but I suspect that BBN or processes occurring at the same time might have produced extremely small quantities of every element, though even the tiniest traces would have been equivalent to the masses of galaxies, stars, certainly planets. Or was it even less? As you move up the periodic table would the quantity of certain elements become some low that at some point for some heavier element might there have literally only been a single atom (!?) of it in the entire universe with the mass production or it and heavier elements from fusion and supernova occurring many millions of years later. A somewhat goofy speculation, I know, but I have a hard time accepting that there were only the first 5 elements and absolutely nothing beyond existed. — Preceding unsigned comment added by (talk) 00:35, 12 March 2013 (UTC)

I think it would have to be very, very little, because older stars have substantially less of the elements heavier than He, and if the very first stars had had even as much metal as the surviving oldest stars, they would still be burning and detectable today. The reason why the oldest detected stars are younger than the predicted time when the first stars ignited, is that those first stars contained nothing heavier than He, burned much faster, and died much younger than later generations of stars. If the Big Bang had produced any significant quantity of heavier elements, some of those first (Population III) stars would still be around.2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 19:06, 5 March 2017 (UTC)

Deuterium is the opposite of helium-4?[edit]

"Deuterium is in some ways the opposite of helium-4 in that while helium-4 is very stable and very difficult to destroy, deuterium is only marginally stable and easy to destroy."

Is the bold part of the statement really necessary? (talk) 19:12, 11 March 2012 (UTC)

No. SBHarris 21:13, 10 September 2012 (UTC)

Could it be the entire Helium-4 and Deuterium sections of this article were subsequently lifted verbatim and republished uncredited in Anderson, R. W., The Cosmic Compendium: The Big Bang & the Early Universe (Raleigh: Lulu Press, 2015), pp. 53-54?—BardRapt (talk) 22:38, 23 November 2016 (UTC)

Are you saying those two sections are in fact plagiarized? If you do recognize the text and know it to be plagiarized please say so and add a Template:Copypaste label to the plagiarized sections, otherwise other editors who don't recognize them can't help replace them. We can't read the page you linked to because Google books does not display that page. 2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 18:50, 5 March 2017 (UTC)
I was able to get Google books to load it this time. Looking at the references, the book credits the whole Big Bang nucleosynthesis section to Wikipedia. Looking at pp. 50-54 of that book, the whole thing appears to be just an earlier version of this very article. So I don't think the article here is plagiarized.2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 19:00, 5 March 2017 (UTC)

Blatant error[edit]

The article states that "It lasted for only about seventeen minutes" and thereafter "It was widespread, encompassing the entire observable universe. There is a huge problem with these statements. If we presume that the observable universe refers to what the observable universe is currently, 13.75 billion light-years in radius, after the Big Bang, particles would have had to travel at a speed faster than the speed of light to reach the edge of the observable universe. I don't know what this article is trying to say, but I think someone should describe what they mean better. The observable universe refers to what we humans can see currently. There were no humans observing the universe after the Big Bang so how can we even say that the universe was observable? By whom? If the Big Bang theory is true, the universe must have had been tiny back then (started from a single point by explosion), if by universe we refer to matter (not space that could be infinite). --Hartz (talk) 20:01, 2 November 2012 (UTC)

The universe was tiny back then-- only about 20 light minutes in radius (about the distance across the asteroid belt in our own Solar system now). This included not only matter but also space: in theory there was nothing "outside" that. By "observable universe" we mean the universe that we can observe now (though now it's quite a lot bigger). It is thought that the universe outside the boundary we can observe is quite a lot larger than the universe inside it (see the size discussion in universe). SBHarris 02:01, 3 November 2012 (UTC)
Yes, makes sense. Space and matter are not the same thing and matter is situated in space in the same way you are situated in a room - unless space, the vast vacuum, would have been compressed with matter into a single point. However, how can the article talk about the observable universe minutes after the Big Bang? --Hartz (talk) 06:00, 3 November 2012 (UTC)
The "observable universe" is the part of the universe that we could currently "see" (in principle). i.e. the part of the universe from which signals could have reached us. So, the observable universe minutes after the big bang, is the part of the minute old universe that we can currently obtain information about.TR 12:40, 3 November 2012 (UTC)
If that is the case, this clarification should be added to the article to avoid confusion. --Hartz (talk) 06:21, 4 November 2012 (UTC)
Does anyone know a good source for just how tiny the observable universe was when it was 10^3 seconds old? I wanted to add a clarification to that section, but realized I can't say anything particularly intelligent about it. 2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 19:34, 5 March 2017 (UTC)

Need clarification[edit]

I'm trying to make the writing a little clearer but need help understanding the intention of the writer in the following cases:

"It would also be necessary for the deuterium to be swept away before it reoccurs."

Not sure what "it" is. I suspect it would be clearer as: "it would also be necessary for the deuterium to be swept away before it could be fused in to an excess of helium." Zedshort (talk) 22:26, 15 March 2013 (UTC)

And in the following para, I assume it should be ratios of 7Be/7Li verses 7Be/8Be.

"The discrepancy is a factor of 2.4―4.3 below the theoretically predicted value and is considered a problem for the original models,[9] that have resulted in revised calculations of the standard BBN based on new nuclear data, and to various reevaluation proposals for primordial proton-proton nuclear reactions, especially the abundances of 7Be(n,p)7Li versus 7Be(d,p)8Be." Zedshort (talk) 22:52, 15 March 2013 (UTC)

Time still contradictory July 31, 2013[edit]

Introduction claims nucleosynthesis started "moments" after the Big Bang. Characteristics claims it started " from a few tenths of a second to up to 10^3 seconds.". Sequence claims "Big Bang nucleosynthesis began a few minutes after the big bang". The discrepancies need to be explained or eliminated. Also the equation in Characteristics is USELESS. Why insert what is essentially garbage? {[ My claiming that mass has no energy content, because D = rô ÷ Σ² where r is average hadron distance, and Σ is mass in MeV sheds NO light on my (incorrect) claim. An equation out of context does not advance understanding. (I could have just as well claimed that mass has energy because of the same (meaningless) equation.)}] (talk) 21:10, 31 July 2013 (UTC)

I agree about the equation that begins tT2. The surrounding material does not explain what time is meant by t nor what temperature is meant by T. The explanation about g* makes it seem that g* = 10.75, so the equation simplifies to tT2 = 0.74. As it stands, the entire bullet point reads like gibberish to the uninitiated. Solo Owl 22:56, 2 December 2014 (UTC)
This is still a problem in March 2017. The different sections say it began 10 seconds, or 10 milliseconds, or a few seconds after the Big Bang.2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 17:11, 5 March 2017 (UTC)
I wonder if some of the inconsistency is due to measuring the beginning by different standards: are the early dates (10 milliseconds) for when proton-proton fusion first became possible, or for when deuterium was stable long enough to create nuclei that lasted long-term? In either case, 10 milliseconds is 10^-2 seconds, which would put the beginning in the Hadron Epoch. But elsewhere Wikipedia and other sources appear to date the entire nucleosynthesis to the Photon Epoch, which began at ~10 seconds.2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 18:40, 5 March 2017 (UTC)
The ending time is also self-contradictory. In Characteristics the nucleosynthesis is said to have ended at 1000 seconds, which is 16.67 minutes. Elsewhere in this article and at both Universe and Timeline_of_the_formation_of_the_Universe articles, nucleosynthesis is said to have ended at 20 minutes. I understand that may be a matter of precise vs. rounded figures, but if so this article should clarify that. Also that Timeline article has nucleosynthesis beginning at 3 minutes, which contradicts this article. 2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 19:42, 5 March 2017 (UTC)

Isotopes' notation in the intro[edit]

Should we use a proper way for that? For example, as in here? 3
, 4
, etc.? Lincoln Josh (talk) 12:13, 19 September 2013 (UTC)

some other isotopes produced in very minute traces in BBN[edit]

Beryllium-9, through the reaction 7Li(T,n)9Be (abundance relative to 1H: 10−13). Note however that a more recent paper linked above gives the abundance as around 10−18, with a similar figure for 10B and 11B combined.

CNO isotopes through the odd triple-alpha (12C 10−14; 13C and 14N 10−15; 14C gets to 10−17 and then its decay becomes significant; 16O 10−18; 15N 10−19; 18O 10−22, later increasing to 10−21 because the also produced 18F decays into it; 17O 10−21. All too low to observe, but predicted.

If so BBN is then predicted to produce everything up to fluorine, but C–F simply do not appear in enough quantity to be detectable. Be and B are perhaps on the borderline between observation and nonobservation. Double sharp (talk) 14:21, 29 September 2014 (UTC)

Baryon photon ratio[edit]

This section of the article does not give any estimate for this ratio, nor any reference to a source that discusses this ratio. BuzzBloom (talk) 16:02, 4 May 2015 (UTC)

T + 3He[edit]

Why is there no discussion of the T + 3He => 6Li interaction? — Preceding unsigned comment added by (talk) 21:39, 29 July 2015 (UTC)

I am by no means an expert in this subject, but my best guess is that the amounts of T and 3He are extremely small, so the total number of times they interact and form 6Li would probably be almost entirely negligible.Popa910 (talk) 17:54, 19 November 2015 (UTC)

External links modified[edit]

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Article needs improvement[edit]

This article needs to be detailed and clear. There is no reason to use shorthand, describing two reactions with a single equation. There is plenty of space. All equations describing creation of isotopes should be included. The figure of nuclear reactions is by itself unsatisfactory. The language is imprecise in places:

"As the universe expands, it cools. Free neutrons and protons are less stable than helium nuclei, and the protons and neutrons have a strong tendency to form helium-4. However, forming helium-4 requires the intermediate step of forming deuterium. Before nucleosynthesis began, the temperature was high enough...."

This is an example of a needlessly unhelpful sentence.

Also, the text is poorly organized, e.g. a couple of lines "history of the theory" in the middle of a discussion of nucleosynthesis.

I am speaking as an educator who wants tu use this article as a resource for the creation of educational material. I find this article of limited use and am forced to look elsewhere for the information I was hoping to find here. Asgrrr (talk) 15:55, 1 June 2016 (UTC)

I agree parts of this article are unclear. But can you please explain a bit more why the particular sentence you cited is unnecessary? I think it is necessary, but is it unclear? It explains why, even though proton-proton fusion was possible at an earlier time, nucleosynthesis could not truly get started until the temperature cooled further and deuterium became stable.2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 18:44, 5 March 2017 (UTC)

I am pleased that others are interested in improving this important article, and I thank 2601:441:4102:9010:6C02:87A4:248A:9E70 for the warning template. Besides recently adding two 2016 Academic articles that may be citable inline during improvements, I had accumulated a list of concerns in the hope of working on them. I am happy(!) to share this list with others. It may be useful to discuss and clarify reasons for edits to come. My apologies for any redundancy with issues mentioned before on this talk page.

  1. Inconsistencies about time period of process: While it's only a imprecise concept, these discrepancies seem too large. lede: "from 10 seconds to 20 minutes" cf. Section Characteristics: "about 10 milliseconds to up to [sic] 1000 seconds" cf. "0.1 to 10,000s" cf. Frampton, page 5 and Mark Paris, page 7: "1s to 100s":
  2. Should be made clear that the BBN analysis is a fit to experimental data (specified), with certain free parameters (specified) determined by the fit. (right?) Anyway, some brief summary of the extraction procedure would be nice.
  3. Explain why photon abundance (flux) is crucial to the relative yields, distinguished from photon temperature.
  4. Is photon density determined by scaling CMB? Based on any mentionable assumptions? But CMB photons have atomic origin. BBN temperature is characteristic of nuclear (MeV) photons. Mention relationship via equilibrium argument?
  5. Not clear that all uses of the word "parameter" are typical of physics community. Distinguish any determined by the BBN fit from those derived from other data outside this BBN analysis. If the latter, from where?
  6. Mention that cross sections used in the BBN fit were measured in laboratories on earth (or theoretically estimated in some cases?)
  7. Which input(s) dominate the uncertainties of the predicted abundances?
  8. Section Characteristics seems quite problematic:
    1. Specify explicitly number of active neutrino flavours used in fit
    2. Why only "observable" universe? Sources don't have this qualification. Any evidence for BNN inconsistency at large red shifts? cf Subsection History of theory: "observed mass of the universe" — should be mass density? Otherwise not just observable universe.
    3. "corresponds to the baryon density": Explain why sometimes expressed here like this, sometimes as ratio to photons. Mention why not include CMνs with photons: already frozen out by BBN lower density
    4. "from this we can derive elemental abundances": Doesn't this belong in Intro?
    5. "little difference to the overall picture": What is considered in this "overall picture" aside from abundances?
    6. What is distinguished by "Big Bang theory itself"?
    7. Clarify that relative abundances given here are % of what: all baryonic matter at end of BBN era. (Now only in metal-poor regions!)
    8. "observed abundances in the universe": Actually wrong: now observable only in metal-poor regions, assumed to be representational. Since all of the BBN results are summarized just 2 sentences earlier, why not also provide the observed values here, with a link for the non-trivial methods of observation/extraction?
  9. Subsection Neutron–proton ratio: "expansion of the universe outpaces the reactions" needs more explanation. In fact, need to explain causes of both neutrino and photon "freeze-out".
  10. Some place, maybe should mention whether neutrino oscillations could affect the n/p ratio.
  11. Subsection History of theory: "calculations of the expansion rate": should be measurement or "extraction" of expansion rate, specifying how — via WL?
  12. Was there significant re-heating from the exothermic fusion reactions?
  13. Mention one of the most important implications of BBN results: on page 5 — "It is thus impossible, given the BBN constraint, that baryonic material make up all, or even a majority, of the dark matter." This source is not fully peer-reviewed, so prefer a better one.[a]
  14. Near the bottom of the first page of the RPP review (now ref. [3]), it sez: "baryon mass density today". As a BBN neophyte, I'm not sure if this includes stuff that fell into black holes since BBN. I suppose it must, in which case that wording seems sub-optimal, and should be avoided in our article. Hopefully we won't need to mention "today" at all.
A comment on the start-time: the times < 1 second relate to neutron-proton conversion; around 1 sec the reactions like p + e -> n + neutrino became too slow to maintain thermodynamic equilibrium (but free neutrons can still decay). But there were negligible nuclei with 2 or more nucleons.  The start time of 10 seconds is an approximate time when the deuterium abundance became non-negligible (i.e. nucleons started fusing together). TychosElk (talk) 23:07, 6 March 2017 (UTC)
So 10 milliseconds is intended to indicate the start of neutron > proton genesis? I don't think neutron decay should be confused with nuclear fusion in this article. 2601:441:4102:9010:C10C:F189:988F:CE2D ([[User talk:2601:441:4102:9010:2601:441:4102:9010:C10C:F189:988F:CE2D (talk) 20:40, 13 March 2017 (UTC)

I've addressed the shorthand reactions and "describing two reactions with a single equation" by fully writing out all the reactions. I request somebody versed in particle physics to review and double-check my work in case I goofed up a reaction. 2601:441:4102:9010:6578:26E8:C88C:47BE (talk) 17:57, 18 March 2017 (UTC)


  1. ^ Perhaps one of you can explain why a small group of rebels has published dozens of papers and two books, exploring forms of baryonic matter as dark matter, apparently unaware or unbelieving of this widely accepted result of BBN. They don't seem to mention BBN in their papers, e.g., most recently here and here. Some of them are peer-reviewed, so one hopes the referees raised the question! It's difficult to understand why referees wouldn't insist on BBN being addressed in their papers.

Layzeeboi (talk) 05:12, 6 March 2017 (UTC)

Deuterium but no Brown Dwarfs?[edit]

The Deuterium section talks at length about how nothing but Big Bang Nucleosynthesis could possibly create deuterium, without one single mention of brown dwarfs -- probably more common than stars, and apparently fusing protons into deuterium for the early part of their existence. This fact should be accounted for in the discussion of deuterium abundance today and what that abundance says about the Big Bang. I would add a paragraph about brown dwarfs myself, but I don't know how much deuterium they produce or how that relates to overall deuterium abundance and what that says about the Big Bang.2601:441:4102:9010:6C02:87A4:248A:9E70 (talk) 17:13, 5 March 2017 (UTC)

The abundances in question here are those that have been unprocessed by any stars — "unastrated". So the observations are made in very selective regions of low metallicity — almost nothing visible heavier than helium, hence primordial. Layzeeboi (talk) 10:47, 6 March 2017 (UTC)
Layzeeboi is basically correct. Also, brown dwarfs (above about 13 Jupiter masses) actually fuse deuterium into helium (until D runs out and they cool down). Anyhow, they live longer than the age of the universe so their fusion products never get out. TychosElk (talk) 22:50, 6 March 2017 (UTC)

Thank you. I clearly don't understand this topic very well. I removed the needs-update tags I had added. So here is my attempt to understand it and make a rough draft of some language that could help clarify the Deuterium section for lay readers:

Deuterium is easier to destroy than it is to create. The energy necessary to fuse 2D into some isotopeLi or 3He is less than the energy necessary to fuse P into 2D. This is why brown dwarfs, astronomical objects smaller than stars but larger than planets, can destroy deuterium but aren't hot enough to create more of it. Stars, which can create deuterium, tend to destroy it faster than they can create it. The early universe expanded and cooled so rapidly that nucleosynthesis ended before the all of the primordial 2D was destroyed, but stars

And something about stars being in hydrostatic? equilibrium and having lifespans longer than 16-17 minutes. I think I understand that more massive stars have less core convection and burn a smaller fraction of their hydrogen, which makes them shorter-lived, so they would be more likely to create net D and to explode it into the interstellar medium. But I don't know if that is balanced solely by D being destroyed faster than it's created or what else explains it. 2601:441:4102:9010:B5D3:FD7:2650:2FA1 (talk) 22:49, 10 March 2017 (UTC)