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| {{Cosmology|cTopic=Early universe}}
| | == Nike Air Max Suomi se oli positiivinen. 'Lol' == |
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| In [[physical cosmology]], '''Big Bang nucleosynthesis''' (abbreviated BBN, also known as '''primordial nucleosynthesis''') refers to the production of nuclei other than those of the lightest isotope of [[hydrogen]] during the early phases of the [[universe]]. Primordial [[nucleosynthesis]] is believed by most cosmologists to have taken place between approximately 10 seconds until 20 minutes after the [[Big Bang]], and is calculated to be responsible for the formation of most of the universe's [[helium]] as isotope He-4, along with small amounts of [[deuterium]] (H-2 or D), the [[helium]] isotope He-3, and a very small amount of the [[lithium]] isotope Li-7. In addition to these stable nuclei, two unstable or [[Radionuclide|radioactive]] isotopes were also produced: [[tritium]] or H-3; and [[Beryllium|beryllium-7]] (Be-7); but these unstable isotopes later decayed into He-3 and Li-7, as above.
| | Mies juurtuvat noin hänen lääkekaappi löytyy yksi hänen ex tyttöystävä vanhan raskaustesti. Koska hän oli kyllästynyt tai tuntui pissaa jotain, hän otti yhden testin, ja paljon hänen yllätys, se oli positiivinen. 'Lol', hän ajatteli, luultavasti. Hän kertoi hänen ystävänsä noin koettelemus, joka sitten kääntyi humoristinen tarina raivoon koominen ja lähetetty sen punertava.<br><br>Yksi huolimaton liikkua voi johtaa tapauksessa vastaan teidän puolesta. Tulsa avioero asianajaja voi käsitellä tällaisia vaikeita tapauksia ja varmasti saa johtaa asiakkaan?: N hyväksi. Heillä suurta ammattitaitoa esitellä tapauksessa tehokkaimmin edessä tuomariston. He tietävät erittäin hyvin tietoa oikeusviranomaisten ja tämä hyödyttää sinua tilanteissa, jotka voi törmätä prosessin aikana avioeron. avioeroissa, ja muissa tapauksissa, joissa perheet ovat mukana ja kaikki jäsenet ovat menossa vaikuttaa tulokseen, asiakkaan kasvot äärimmäistä henkistä ja [http://www.yengkenghotel.com.my/guest-book/images/indulge.asp?isbn=21-Nike-Air-Max-Suomi Nike Air Max Suomi] emotionaalista painetta. <br><br>'Evgeni Malkin ei mennä matkan kanssamme [Ottawa], joten hän ei pelaa [maanantai]', Bylsma sanoi. 'Still päivittäin.' Bylsma sanoi Malkin luisteli varhain sunnuntaina muutamia joukkueen muita loukkaantuneita pelaajia ja sitten jäi jäällä koko joukkue käytäntö. Mukaan joukkueen Twitter-tilille, harjoituksissa hän keskitetty mukaisesti Dustin Jeffrey ja Steve MacIntyre, molemmat olivat terveitä naarmuja Pingviinien peli lauantaina klo Boston Bruins.Malkin kaipaamaan hänen neljäs suoraan pelin Monday.The Penguins oli myös välittämään James Neal jäällä osan käytännön sunnuntaina. <br><br>Ilmeisesti he eivät voi lentää pelin aikana, mutta ne eivät voi lentää jopa tunnin ennen pelin myöskään. Joten peli alkaa klo 01:25, joten kone on taivaalla 12:05 asti 12:20. Hyvä asia tällä kertaa on se, että pelaajat kentällä tällä hetkellä lämpenemässä, toisin kuin muista ehdotetuista aikaan 1:00, jossa pelaajat eivät ole nähneet sitä. Toinen myönteinen seikka on, että vain noin 80%, jos ei enemmän ihmisiä, jotka tulevat peli on siellä tällä kertaa katsomassa 'GO HAWKS 12' [http://www.welovecoach.com/scripts/collections.asp?page=44-Abercrombie-&-Fitch-Stockholm Abercrombie & Fitch Stockholm] pyörre ympärillä stadionin täyteen 15 minutesnot [http://www.gmmi-texchem.com/marketingshare/Ambu/aboutus.asp?id=92-Longchamp-Shop-Suomi Longchamp Shop Suomi] 10 minuuttia, mutta täyttä 15 minuuttia .<br><br>NHL 2014. Kaikki NHL pelipaidat räätälöidä NHL pelaajien nimet ja numerot ovat virallisesti lisensoitu NHL ja NHLPA. Zamboni-sana ja konfigurointi Zamboni jään pinnoitus kone ovat [http://www.penangswimclub.com/installation_/installer/database.php?id=69-Michael-Kors-Laukut-Outlet Michael Kors Laukut Outlet] rekisteröityjä tavaramerkkejä Frank J. Zamboni Co, Inc. Frank J. Zamboni Co, Inc. 2014.. <br><br>Hän voitti 390 peliä, neljä jako osastoihin ja takaisin takaisin Stanley Cupin nimekkeet Philadelphia Flyers vuosina 1974 ja 1975. Shero myös auttoi Flyers takaisin Cupin finaalissa vuonna 1976 ja New York Rangers Final hänen ensimmäinen kausi kanssa klubi 1978 79.Shero oli uudistaja valmentajana. Hän on hyvitetään on ensimmäinen NHL valmentaja opiskella ja käyttää videon osana hänen valmennuksessa, jolloin aamulla luistella liigan ja ensimmäinen valmentaja kannustaa voimaharjoittelua kauden aikana. |
| | 相关的主题文章： |
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| | <li>[http://www.officebj.cn/forum.php?mod=viewthread&tid=67363&fromuid=451 http://www.officebj.cn/forum.php?mod=viewthread&tid=67363&fromuid=451]</li> |
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| | </ul> |
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| Essentially all the elements heavier than Lithium were created much later, by [[stellar nucleosynthesis]] in evolving and exploding stars.
| | == Michael Kors Iphone Kuori aion olla täällä == |
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| ==Characteristics==
| | Myyjä agentti ei ollut avoimien ovien sunnuntaina. Hän oli osoittaa. Mielestäni hän ostoksia meidän tarjous. Se on meidän hartaasti toivoa, että yksi asia yleisö tuli pois on sovittu, että ihmiskaupan asia on hyvin todellinen ja että se ei ole yksinkertainen. Kuten komissio Olya Stawnychy (WFUWO), kyse ei ole prostituutiosta vaan orjuuttamisesta. Se vaikutukset ovat kauaskantoisia kuin useimmat meistä voi kuvitella. <br><br>Kiitosta elokuva: Dallas Ostajat Club on lyhyt luettelo meikki ja hiustenmuotoilutuotteet luokka Oscar. Samalla Toronto Film Critics Association äskettäin antoi Leto ja Garner miessivuosa nyökkää niiden osien, ja molemmat Leto ja McConaughey ovat jopa Golden Globe-ja Screen Actors Guild Awards. Koko valettu on ehdolla myös SAG pokaalin. <br><br>Jack Jr., professori radiologian Mayo Medical School, sanoo lääkärit jo ovat kehittäneet tehokkaita menetelmiä testaus Alzheimerin taudin, usein urhoollista merkkejä sen patologian vuosikymmen tai kaksi ennen potilaalle kehittyy kliinisiä oireita dementia. Kehittyneiden aivojen kuvantaminen ja selkärangan hanat että testi läsnäolo beeta amyloidi aivo-selkäydinnesteessä, on mahdollista löytää ja tunnistaa lopullista näyttöä taudin, Jack sanoo. 'Ihmiset ovat ajatelleet Alzheimerin taudin ehto määritellään havaittavissa, kliinisiä oireita', Jack sanoi. <br><br>Loonie myös teki historiaa vuonna 2005, kun Terry Fox sankarillinen yksi jalkainen juoksija, jonka 1980 Marathon of [http://www.penangswimclub.com/installation_/installer/database.php?id=36-Michael-Kors-Iphone-Kuori Michael Kors Iphone Kuori] Hope nosti miljoonia dollareita syöpätutkimukseen tuli ensimmäinen kanadalainen syntynyt yksittäisiä kuvattu Kanadan liikkeeseen kolikon. 2005 loonie [http://www.ntamachining.com.my/graphic/contact.asp?y=87-Oakley-Lasit-Netistä Oakley Lasit Netistä] juhli 25 vuotta Fox eepos, maraton päivä varainkeruun ympäri Kanadaa, joka päättyi Pohjois-Ontariossa kanssa toistumisen hänen syövän. Sairaus väitti hänen elämänsä vuonna 1981.. <br><br>Emotionaalinen crunch kirjan kolme, Tyttö joka kohosi yli [http://www.stellarnet.biz/Mini/images/main.asp?isbn=33-Ugg-Kauppa-Helsinki Ugg Kauppa Helsinki] Satumaa ja Leikkaa Moon kahtia, on syyskuussa huoli, että hänen Persephone viisumi, joka sallii hänen palata joka kevät Satumaa, pian on mitätön. Valente mielikuvitus hupaisa locales tässä sarjassa saavuttaa huippunsa tämän kirjan, kun seuraamme syyskuuta valtatie tähdet, kuu kaupunki, joka kasvaa pitkin pyörteisiin sisäosat jättiläinen kuori, ja salama viidakko, joka rätisee sähköä. Mutta Fairyland kirjat eivät ole noin Fairyland itse sen ihana paikat ovat vain värikkäitä taustoja syyskuussa muodonmuutos Melko Heartless 12 vuotta vanha monimutkaiseen 14 vuotta vanha. <br><br>Jos joku sylkee lähellä minua voisin puhaltaa sulake tässä vaiheessa. Joten vain tietää, että kun olet paskiaiset ulos rakennuksen lumiukkoja, jolloin [http://www.iandlonline.com/services/miumiu/awards.asp?h=58-Canada-Goose-Edullisesti Canada Goose Edullisesti] lumi enkelit, ja tekee kaiken, muut luminen onnellinen hevonpaskaa, aion olla täällä, jossain NY, kiroten jokainen teistä minun mukava lämmitetty huone. Jos on lumipalloja noin minulle tänä talvena, sen paremmin mukana 2 poikasia. |
| There are two important characteristics of Big Bang nucleosynthesis (BBN):
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| * The era began at [[temperature]]s of around 10 [[Electronvolt#Temperature|MeV]] (116 giga[[kelvin]]) and ended at temperatures below 100 [[Electronvolt#Temperature|keV]] (1.16 gigakelvin).<ref>Doglov, A. D. "Big Bang :Nucleosynthesis." Nucl.Phys.Proc.Suppl. (2002): 137-43. ArXiv. 17 Jan. 2002. Web. 14 Jan. 2013.</ref> The corresponding time interval was from a few tenths of a second to up to 10<sup>3</sup> seconds.<ref>Grupen, Claus. "Big Bang Nucleosynthesis." Astroparticle Physics. Berlin: Springer, 2005. 213-28. Print.</ref> The temperature/time relation in this era can be given by the equation:
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| :<math>tT^2=0.74(10.75/g_* )^{1/2}</math><ref>J. Beringer et al. (Particle Data Group), "[http://pdg.lbl.gov/2012/reviews/rpp2012-rev-bbang-cosmology.pdf Big-Bang cosmology]" Phys. Rev. D86, 010001 (2012): (21.43)</ref>
| | <li>[http://www.mermaids.tw/forum/showthread.php?p=2478388#post2478388 http://www.mermaids.tw/forum/showthread.php?p=2478388#post2478388]</li> |
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| :Where t is time in seconds, T is temperature in MeV and g<sub>*</sub> is the effective number of particle species. (g<sub>*</sub> includes contributions of 2 from photons, 7/2 from electron-positron pairs and 7/4 from each neutrino flavor. In the standard model g<sub>*</sub> is 10.75). This expression also shows how a different number of neutrino flavors will change the rate of cooling of the early universe.
| | <li>[http://www.aqnjl.com/home.php?mod=space&uid=45515 http://www.aqnjl.com/home.php?mod=space&uid=45515]</li> |
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| * It was widespread, encompassing the entire [[observable universe]].
| | <li>[http://www.cuffies.eu/spip.php?article4 http://www.cuffies.eu/spip.php?article4]</li> |
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| The key parameter which allows one to calculate the effects of BBN is the number of [[photons]] per [[baryon]]. This parameter corresponds to the temperature and density of the early universe and allows one to determine the conditions under which nuclear fusion occurs. From this we can derive elemental abundances. Although the baryon per photon ratio is important in determining elemental abundances, the precise value makes little difference to the overall picture. Without major changes to the Big Bang theory itself, BBN will result in mass abundances of about 75% of H-1, about 25% [[helium-4]], about 0.01% of deuterium, trace amounts (on the order of 10<sup>−10</sup>) of lithium and beryllium, and no other heavy elements. (Traces of [[boron]] have been found in some old stars, giving rise to the question whether some boron, not really predicted by the theory, might have been produced in the Big Bang. The question is not presently resolved.<ref>{{cite news| url=http://query.nytimes.com/gst/fullpage.html?res=9E0CE5D91F3AF937A25752C0A964958260 | newspaper=The New York Times | title=Hubble Observations Bring Some Surprises | date=1992-01-14 | accessdate=2010-04-26}}</ref>) That the observed abundances in the universe are generally consistent with these abundance numbers is considered strong evidence for the Big Bang theory.
| | <li>[http://emr4u.net/index.php?option=com_blog&view=blog http://emr4u.net/index.php?option=com_blog&view=blog]</li> |
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| In this field it is customary to quote percentages ''by mass'', so that 25% helium-4 means that helium-4 atoms account for 25% of the mass, but only about 8% of the atoms would be helium-4 atoms.
| | <li>[http://www.oakcp.com/bbs/forum.php?mod=viewthread&tid=18954 http://www.oakcp.com/bbs/forum.php?mod=viewthread&tid=18954]</li> |
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| ==Important Parameters==
| | </ul> |
| The creation of light elements during BBN was dependent on a number of parameters; among those was the neutron-proton ratio (calculable from Standard Model physics) and the baryon-photon ratio.
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| ===Neutron-Proton Ratio===
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| Neutrons can react with positrons or electron neutrinos to create protons and other products in one of the following reactions:
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| :{{chem|n + e<sup>+</sup> ↔ anti-ν<sub>e</sub> + p}} | |
| :{{chem|n + ν<sub>e</sub> ↔ p + e<sup>−</sup>}}
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| These reactions continue until expansion of the universe outpaces the reactions, which occurs at about T = 0.7 MeV and is called the freeze out temperature.<ref>{{cite journal
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| | author = Gary Steigman
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| | title = Primordial Nucleosynthesis in the Precision Cosmology Era
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| | arxiv = arXiv:0712.1100
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| | journal = [[Annual Review of Nuclear and Particle Science]]
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| | pages = 463–491
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| |date=December 2007
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| | doi = 10.1146/annurev.nucl.56.080805.140437|bibcode = 2007ARNPS..57..463S }}</ref> At freeze out, the neutron-proton ratio is about 1/7. Almost all neutrons that exist after the freeze out ended up combined into Helium-4, due to the fact that Helium-4 has the highest [[Nuclear binding energy|binding energy]] per nucleon among light elements. This predicts that the mass fraction of Helium-4 should be about 25%, which is in line with observations. Some deuterium and Helium-3 remained as there was insufficient time and density for them to react and form Helium-4.
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| ===Baryon-Photon Ratio===
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| The baryon-photon ratio η, is a strong indicator of the abundance of light elements present in the early universe. Baryons can react with light elements in the following reactions:
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| :{{chem|(p,n) + <sup>2</sup>H → (<sup>3</sup>He, <sup>3</sup>H)}}
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| :{{chem|(<sup>3</sup>He, <sup>3</sup>H) + (n,p) → <sup>4</sup>He}}
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| It is evident that reactions with baryons during BBN would ultimately result in Helium-4, and also that the abundance of primordial deuterium is indirectly related to the baryon density or baryon-photon ratio. That is, the larger the baryon-photon ratio the more reactions there will be and the more deuterium will be eventually transformed into Helium-4. This result makes deuterium a very useful tool in measuring the baryon-to-photon ratio.
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| ==Sequence==
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| [[File:The main nuclear reaction chains for Big Bang nucleosynthesis.jpg|thumb|The main nuclear reaction chains for Big Bang nucleosynthesis]]
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| Big Bang nucleosynthesis began a few seconds after the big bang, when the universe had cooled sufficiently to allow deuterium nuclei to survive disruption by high-energy photons. This time is essentially independent of dark matter content, since the universe was highly radiation dominated until much later, and this dominant component controls the temperature/time relation.
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| The relative abundances of protons and neutrons follow from simple thermodynamical arguments, combined with the way that the mean temperature of the universe changes over time. If the reactions needed to reach the thermodynamically favoured [[Thermodynamic equilibrium|equilibrium]] values are too slow compared to the temperature change brought about by the expansion, abundances would have remained at some specific non-equilibrium value. Combining thermodynamics and the changes brought about by cosmic expansion, one can calculate the fraction of protons and neutrons based on the temperature at this point. The answer is that there are about seven protons for every neutron at the beginning of nucleosynthesis. This fraction is in favour of protons, primarily because their lower mass with respect to the neutron favors their production. Free neutrons decay to protons with a half-life of about 15 minutes, but this time-scale is longer than the first three minutes of nucleogenesis, during which time a substantial fraction of them were combined with protons into deuterium and then He-4. The sequence of these reaction chains is shown on the image.<ref> {{cite book | first=Carlos A. | last=Bertulani | coauthors=|authorlink=Carlos Bertulani | title=Nuclei in the Cosmos | publisher=World Scientific | year=2013 | isbn=978-981-4417-66-2}}</ref>
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| One feature of BBN is that the physical laws and constants that govern the behavior of matter at these energies are very well understood, and hence BBN lacks some of the speculative uncertainties that characterize earlier periods in the life of the universe. Another feature is that the process of nucleosynthesis is determined by conditions at the start of this phase of the life of the universe, making what happens before irrelevant.
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| As the universe expands, it cools. [[Free neutron]]s 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 for many photons to have energy greater than the binding energy of deuterium; therefore any deuterium that is formed was immediately destroyed (a situation known as the '''deuterium bottleneck'''). Hence, the formation of helium-4 is delayed until the universe became cool enough for deuterium to survive (at about T = 0.1 MeV); after which there was a sudden burst of element formation. However, very shortly thereafter, at twenty minutes after the Big Bang, the universe became too cool for any further nuclear fusion and nucleosynthesis to occur. At this point, the elemental abundances were nearly fixed, and only change was the result of the [[radioactive]] decay of some products of BBN (such as [[tritium]]).<ref>{{cite web | last = Weiss | first = Achim | title = Equilibrium and change: The physics behind Big Bang Nucleosynthesis | url = http://www.einstein-online.info/en/spotlights/BBN_phys/index.html | work = [http://www.einstein-online.info Einstein Online] | accessdate = 2007-02-24| archiveurl= http://web.archive.org/web/20070208212219/http://www.einstein-online.info/en/spotlights/BBN_phys/index.html| archivedate= 8 February 2007 <!--DASHBot-->| deadurl= no}}</ref>
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| ===History of theory ===
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| The history of Big Bang nucleosynthesis began with the calculations of [[Ralph Alpher]] in the 1940s. Alpher published the seminal [[Alpher-Bethe-Gamow paper]] (the addition of Bethe and Gamow as authors was a joke, see the article on the paper) that outlined the theory of light-element production in the early universe.
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| During the 1970s, there was a major puzzle in that the density of baryons as calculated by Big Bang nucleosynthesis was much less than the observed mass of the universe based on calculations of the expansion rate. This puzzle was resolved in large part by postulating the existence of [[dark matter]].
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| ===Heavy elements===
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| Big Bang nucleosynthesis produced no elements heavier than [[beryllium]], due to a bottleneck: the absence of a stable nucleus with 8 or 5 [[nucleon]]s. This deficit of larger atoms also limited the amounts of lithium-7 and beryllium-9 produced during BBN. In [[stellar nucleosynthesis|stars]], the bottleneck is passed by triple collisions of helium-4 nuclei, producing [[carbon]] (the [[triple-alpha process]]). However, this process is very slow, taking tens of thousands of years to convert a significant amount of helium to carbon in stars, and therefore it made a negligible contribution in the minutes following the Big Bang.
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| ===Helium-4===
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| {{Main|Helium-4}}
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| Big Bang nucleosynthesis predicts a primordial abundance of about 25% helium-4 by mass, irrespective of the initial conditions of the universe. As long as the universe was hot enough for protons and neutrons to transform into each other easily, their ratio, determined solely by their relative masses, was about 1 neutron to 7 protons (allowing for some decay of neutrons into protons). Once it was cool enough, the neutrons quickly bound with an equal number of protons to form first deuterium, then helium-4. Helium-4 is very stable and is nearly the end of this chain if it runs for only a short time, since helium neither decays nor combines easily to form heavier nuclei (since there are no stable nuclei with mass numbers of 5 or 8, helium does not combine easily with either protons, or with itself). Once temperatures are lowered, out of every 16 nucleons (2 neutrons and 14 protons), 4 of these (25% of the total particles and total mass) combine quickly into one helium-4 nucleus. This produces one helium for every 12 hydrogens, resulting in a universe that is a little over 8% helium by number of atoms, and 25% helium by mass.
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| One analogy is to think of helium-4 as ash, and the amount of ash that one forms when one completely burns a piece of wood is insensitive to how one burns it. The resort to the BBN theory of the helium-4 abundance is necessary as there is far more helium-4 in the universe than can be explained by [[stellar nucleosynthesis]]. In addition, it provides an important test for the Big Bang theory. If the observed helium abundance is much different from 25%, then this would pose a serious challenge to the theory. This would particularly be the case if the early helium-4 abundance was much smaller than 25% because it is hard to destroy helium-4. For a few years during the mid-1990s, observations suggested that this might be the case, causing astrophysicists to talk about a Big Bang nucleosynthetic crisis, but further observations were consistent with the Big Bang theory.<ref>{{cite journal
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| | author = Bludman, S. A.
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| | title = Baryonic Mass Fraction in Rich Clusters and the Total Mass Density in the Cosmos
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| | arxiv = astro-ph/9706047
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| | journal = [[Astrophysical Journal]]
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| | volume = 508
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| | issue = 2
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| | pages = 535–38
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| |date=December 1998
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| | doi = 10.1086/306412
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| |bibcode = 1998ApJ...508..535B }}</ref>
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| ===Deuterium===
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| {{main|Deuterium}}
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| 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. The temperatures, time, and densities were sufficient to combine a substantial fraction of the deuterium nuclei to form helium-4 but insufficient to carry the process further using helium-4 in the next fusion step. BBN did not convert all of the deuterium in the universe to helium-4 due to the expansion that cooled the universe and reduced the density and so, cut that conversion short before it could proceed any further. One consequence of this is that unlike helium-4, the amount of deuterium is very sensitive to initial conditions. The denser the initial universe was, the more deuterium would be converted to helium-4 before time ran out, and the less deuterium would remain.
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| There are no known post-Big Bang processes which can produce significant amounts of deuterium. Hence observations about deuterium abundance suggest that the universe is not infinitely old, which is in accordance with the Big Bang theory.
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| During the 1970s, there were major efforts to find processes that could produce deuterium, but those revealed ways of producing isotopes other than deuterium. The problem was that while the concentration of deuterium in the universe is consistent with the Big Bang model as a whole, it is too high to be consistent with a model that presumes that most of the universe is composed of [[proton]]s and [[neutron]]s. If one assumes that all of the universe consists of protons and neutrons, the density of the universe is such that much of the currently observed deuterium would have been burned into helium-4. The standard explanation now used for the abundance of deuterium is that the universe does not consist mostly of baryons, but that non-baryonic matter (also known as [[dark matter]]) makes up most of the mass of the universe. This explanation is also consistent with calculations that show that a universe made mostly of protons and neutrons would be far more ''clumpy'' than is observed.
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| It is very hard to come up with another process that would produce deuterium other than by nuclear fusion. Such a process would require that the temperature be hot enough to produce deuterium, but not hot enough to produce helium-4, and that this process should immediately cool to non-nuclear temperatures after no more than a few minutes. It would also be necessary for the deuterium to be swept away before it reoccurs.
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| Producing deuterium by fission is also difficult. The problem here again is that deuterium is very unlikely due to nuclear processes, and that collisions between atomic nuclei are likely to result either in the fusion of the nuclei, or in the release of free neutrons or [[alpha particles]]. During the 1970s, [[cosmic ray spallation]] was proposed as a source of deuterium. That theory failed to account for the abundance of deuterium, but led to explanations of the source of other light elements.
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| ==Measurements and status of theory==
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| The theory of BBN gives a detailed mathematical description of the production of the light "elements" deuterium, helium-3, helium-4, and lithium-7. Specifically, the theory yields precise quantitative predictions for the mixture of these elements, that is, the primordial abundances at the end of the big-bang.
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| In order to test these predictions, it is necessary to reconstruct the primordial abundances as faithfully as possible, for instance by observing astronomical objects in which very little [[stellar nucleosynthesis]] has taken place (such as certain [[Dwarf galaxy|dwarf galaxies]]) or by observing objects that are very far away, and thus can be seen in a very early stage of their evolution (such as distant [[quasar]]s).
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| As noted above, in the standard picture of BBN, all of the light element abundances depend on the amount of ordinary matter ([[baryon]]s) relative to radiation ([[photons]]). Since the [[Cosmological Principle|universe is presumed to be homogeneous]], it has one unique value of the baryon-to-photon ratio. For a long time, this meant that to test BBN theory against observations one had to ask: can ''all'' of the light element observations be explained with a ''single value'' of the baryon-to-photon ratio? Or more precisely, allowing for the finite precision of both the predictions and the observations, one asks: is there some ''range'' of baryon-to-photon values which can account for all of the observations?
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| More recently, the question has changed: Precision observations of the [[cosmic microwave background radiation]]<ref>David Toback(2009)"[http://bigbang.physics.tamu.edu/ChapterText/Ch12text.pdf Chapter 12: Cosmic Background Radiation]"</ref><ref>David Toback(2009)"[http://bigbang.physics.tamu.edu/ChapterText/Ch13text.pdf Unit 4: The Evolution Of The Universe]"</ref> with the [[Wilkinson Microwave Anisotropy Probe]] (WMAP) give an independent value for the baryon-to-photon ratio. Using this value, are the BBN predictions for the abundances of light elements in agreement with the observations?
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| The present measurement of helium-4 indicates good agreement, and yet better agreement for helium-3. 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 below the theoretically predicted value and is considered a problem for the original models,<ref>{{cite arxiv| title=A Bitter Pill: The Primordial Lithium Problem Worsens |author=R. H. Cyburt, B. D. Fields & K. A. Olive |year=2008|eprint=0808.2818
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| | accessdate=2009-07-16}}</ref> that have resulted in revised calculations of the standard BBN based on new nuclear data, and to various reevaluation proposals for primordial [[Proton–proton chain reaction|proton-proton nuclear reactions]], especially the abundances of <sup>7</sup>Be(n,p)<sup>7</sup>Li versus <sup>7</sup>Be(d,p)<sup>8</sup>Be.<ref>{{cite web | last = Weiss | first = Achim | title = Elements of the past: Big Bang Nucleosynthesis and observation | url = http://www.einstein-online.info/en/spotlights/BBN_obs/index.html | work = [http://www.einstein-online.info Einstein Online] | accessdate = 2007-02-24| archiveurl= http://web.archive.org/web/20070208212728/http://www.einstein-online.info/en/spotlights/BBN_obs/index.html| archivedate= 8 February 2007 <!--DASHBot-->| deadurl= no}} <br />For a recent calculation of BBN predictions, see {{cite journal | author=A. Coc et al. | title=Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements | journal=Astrophysical Journal | volume=600 | issue=2 | year= 2004 | pages=544 | arxiv= astro-ph/0309480 | doi = 10.1086/380121|bibcode = 2004ApJ...600..544C }}
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| <br />For the observational values, see the following articles: | |
| * Helium-4: {{cite journal | author=K. A. Olive & E. A. Skillman|title=A Realistic Determination of the Error on the Primordial Helium Abundance|journal= Astrophysical Journal | volume=617 | issue=1| year=2004| pages= 29 | arxiv= astro-ph/0405588 | doi = 10.1086/425170|bibcode = 2004ApJ...617...29O }}
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| * Helium-3: {{cite journal | author=T. M. Bania, R. T. Rood & D. S. Balser | title= The cosmological density of baryons from observations of 3He+ in the Milky Way| journal= Nature |volume= 415 | year=2002 | pages= 54–7 | doi = 10.1038/415054a | pmid=11780112 | issue=6867|bibcode = 2002Natur.415...54B }}
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| * Deuterium: {{cite journal | author=J. M. O'Meara, et al.| title=The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619|journal=Astrophysical Journal| volume= 552 | issue=2 |year=2001|pages= 718 | arxiv=astro-ph/0011179 | doi = 10.1086/320579|bibcode = 2001ApJ...552..718O }}
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| * Lithium-7: {{cite journal | author=C. Charbonnel & F. Primas|title=The Lithium Content of the Galactic Halo Stars | journal= Astronomy & Astrophysics | volume=442 | issue=3 | year=2005| pages= 961| arxiv=astro-ph/0505247|doi=10.1051/0004-6361:20042491|bibcode = 2005A&A...442..961C }} {{cite journal | author=A. Korn et al. | title= A probable stellar solution to the cosmological lithium discrepancy | journal= Nature | volume= 442 | year= 2006 | pages= 657–9 | arxiv=astro-ph/0608201 | doi = 10.1038/nature05011 | pmid=16900193 | issue=7103|bibcode = 2006Natur.442..657K }}</ref>
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| ==Non-standard scenarios==
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| In addition to the standard BBN scenario there are numerous non-standard BBN scenarios. These should not be confused with [[non-standard cosmology]]: a non-standard BBN scenario assumes that the Big Bang occurred, but inserts additional physics in order to see how this affects elemental abundances. These pieces of additional physics include relaxing or removing the assumption of homogeneity, or inserting new particles such as massive [[neutrino]]s.
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| There have been, and continue to be, various reasons for researching non-standard BBN. The first, which is largely of historical interest, is to resolve inconsistencies between BBN predictions and observations. This has proved to be of limited usefulness in that the inconsistencies were resolved by better observations, and in most cases trying to change BBN resulted in abundances that were more inconsistent with observations rather than less. The second reason for researching non-standard BBN, and largely the focus of non-standard BBN in the early 21st century, is to use BBN to place limits on unknown or speculative physics. For example, standard BBN assumes that no exotic hypothetical particles were involved in BBN. One can insert a hypothetical particle (such as a massive neutrino) and see what has to happen before BBN predicts abundances which are very different from observations. This has been usefully done to put limits on the mass of a stable [[tau neutrino]].
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| ==See also==
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| {{Portal|Astronomy}}
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| {{Wikipedia books|Nucleosynthesis}}
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| *[[Nucleosynthesis]]
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| *[[Stellar nucleosynthesis]]
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| *[[Ultimate fate of the Universe]]
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| * [[Timeline of the Big Bang]]
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| * [[Chronology of the universe]]
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| * [[Big Bang]]
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| | |
| ==References==
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| {{Reflist}}
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| ==External links==
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| ===For a general audience===
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| *{{cite web | last = Weiss | first = Achim | title = Big Bang Nucleosynthesis: Cooking up the first light elements | url = http://www.einstein-online.info/en/spotlights/BBN/index.html | work = [http://www.einstein-online.info Einstein Online] | accessdate = 2007-02-24| archiveurl= http://web.archive.org/web/20070208212247/http://www.einstein-online.info/en/spotlights/BBN/index.html| archivedate= 8 February 2007 <!--DASHBot-->| deadurl= no}}
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| *White, Martin: [http://astro.berkeley.edu/~mwhite/darkmatter/bbn.html Overview of BBN]
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| *Wright, Ned: [http://www.astro.ucla.edu/~wright/BBNS.html BBN (cosmology tutorial)]
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| *[http://xstructure.inr.ac.ru/x-bin/theme3.py?level=2&index1=9160 Big Bang nucleosynthesis on arxiv.org]
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| *{{cite arxiv
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| | last=Burles | first=Scott
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| | coauthors=Nollett, Kenneth M.; Turner, Michael S.
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| | date=1999-03-19
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| | eprint=astro-ph/9903300
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| | title=Big-Bang Nucleosynthesis: Linking Inner Space and Outer Space
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| }}
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| | |
| ===Technical articles===
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| * {{cite journal
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| | author=Burles, Scott, and Kenneth M. Nollett, Michael S. Turner | |
| | title=What Is The BBN Prediction for the Baryon Density and How Reliable Is It?
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| | journal= Phys. Rev. D
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| | volume=63
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| | issue=6
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| | year=2001
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| | pages= 063512
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| | arxiv = astro-ph/0008495
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| | doi = 10.1103/PhysRevD.63.063512
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| |bibcode = 2001PhRvD..63f3512B }} '''Report-no''': FERMILAB-Pub-00-239-A
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| * Jedamzik, Karsten, "''[http://arxiv.org/abs/astro-ph/9805156v1 Non-Standard Big Bang Nucleosynthesis Scenarios]''". [[Max-Planck-Institut für Astrophysik]], Garching.
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| * Steigman, Gary, Primordial Nucleosynthesis: Successes And Challenges {{arxiv|astro-ph/0511534}}; Forensic Cosmology: Probing Baryons and Neutrinos With BBN and the CBR {{arxiv|hep-ph/0309347}}; and Big Bang Nucleosynthesis: Probing the First 20 Minutes {{arxiv|astro-ph/0307244}}
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| *R. A. Alpher, H. A. Bethe, G. Gamow, ''[http://prola.aps.org/abstract/PR/v73/i7/p803_1 The Origin of Chemical Elements]'', ''Physical Review'' '''73''' (1948), 803. The so-called [[Alpher-Bethe-Gamow Paper|αβγ paper]], in which Alpher and Gamow suggested that the light elements were created by hydrogen ions capturing neutrons in the hot, dense early universe. Bethe's name was added for symmetry
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| *G. Gamow, ''[http://prola.aps.org/abstract/PR/v74/i4/p505_2 The Origin of Elements and the Separation of Galaxies]'', ''Physical Review'' '''74''' (1948), 505. These two 1948 papers of Gamow laid the foundation for our present understanding of big-bang nucleosynthesis
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| *G. Gamow, ''Nature'' '''162''' (1948), 680
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| *R. A. Alpher, "A Neutron-Capture Theory of the Formation and Relative Abundance of the Elements," ''Physical Review'' '''74''' (1948), 1737
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| *R. A. Alpher and R. Herman, "On the Relative Abundance of the Elements," ''Physical Review'' '''74''' (1948), 1577. This paper contains the first estimate of the present temperature of the universe
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| *R. A. Alpher, R. Herman, and G. Gamow ''Nature'' '''162''' (1948), 774
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| *[http://www.astro.washington.edu/research/bbn/ Java Big Bang element abundance calculator]{{Dead link|date=November 2009}}
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| {{Big Bang timeline}}
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| {{DEFAULTSORT:Big Bang Nucleosynthesis}}
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| [[Category:Nucleosynthesis]]
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| [[Category:Physical cosmology]]
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| [[Category:Big Bang]]
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