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Encyclopedia > Big Bang nucleosynthesis
Physical cosmology
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edit Cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... Image File history File links Download high resolution version (2198x1274, 1278 KB)WMAP map of CMB anisotropy, from NASA.gov File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Nothing is certain as to the extent of either the age or size of the universe, but the age of the Universe, according to the Big Bang theory, is defined as the largest possible value of proper time integrated along a timelike curve from the Earth at the present epoch... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (bottom). ... The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. ... In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR) is a form of electromagnetic radiation discovered in 1965. ... In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. ... In cosmology, dark matter refers to matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. ... The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. ... The Friedmann equations relate various cosmological parameters within the context of general relativity. ... REDIRECT [[ --68. ... Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... ΛCDM or Lambda-CDM is an abbreviation for Lambda-Cold Dark Matter. ... The observable Universe is a term used in cosmology to describe a ball-shaped region of space surrounding the Earth that is close enough that we might observe objects in it. ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to that of the Sun (left). ... The shape of the Universe is a subject of investigation within cosmology. ... A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events that have occurred and will occur according to the scientific theory of the Big Bang. ... The timeline of cosmology lists the sequence of cosmological theories and discoveries in chronological order. ... The ultimate fate of our universe is a topic in physical cosmology. ... The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ... Spiral Galaxy ESO 269-57 // Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... For a non-technical introduction to the topic, please see Introduction to General relativity. ... Particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Quantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ...

In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. 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 He-3 and He-4, and the lithium isotope Li-7 (all of these nuclides are normally shown as NX where X = standard name of this element and N = the number of nucleons in the nucleus, but for this page they will simply be referred to as X-N) . // Cosmology, from the Greek: κοσμολογία (cosmologia, κόσμος (cosmos) world + λογια (logia) discourse) is the study of the Universe in its totality, and by extension, humanitys place in it. ... The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (bottom). ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Isotopes are forms of an element, therefore their nuclei have the same atomic number — the number of protons in the nucleus — but different mass numbers because they contain different numbers of neutrons. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of one atom in 6400 of hydrogen (see VSMOW; the abundance changes slightly from one kind of natural water to another). ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/gray Atomic mass 6. ... Nucleon is the common name used in nuclear chemistry to refer to a neutron or a proton, the components of an atoms nucleus. ...

Contents


Characteristic of Big Bang nucleosynthesis

There are two important characteristics of Big Bang nucleosynthesis (BBN):

  • It lasted for only about three minutes (during the period from 100 to about 300 seconds from the beginning of space expansion); after that, the temperature and density of the universe fell below that which is required for nuclear fusion. The brevity of BBN is important because it prevented elements heavier than beryllium from forming while at the same time allowing unburned light elements, such as deuterium, to exist.
  • It was widespread, encompassing the entire universe.

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 25% helium-4; about 1% of deuterium; trace amounts of lithium and beryllium; and no other heavy elements, leaving about 74% of H-1. That the observed abundances in the universe are consistent with these numbers is considered strong evidence for the Big Bang theory. The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... General Name, Symbol, Number beryllium, Be, 4 Chemical series alkaline earth metals Group, Period, Block 2, 2, s Appearance white-gray metallic Atomic mass 9. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of one atom in 6400 of hydrogen (see VSMOW; the abundance changes slightly from one kind of natural water to another). ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called nucleons), as well as a number of unstable, heavier particles (called hyperons). ...

Nucleosynthesis
Related topics

edit Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons). ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Cross section of a red giant showing nucleosynthesis and elements formed Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. ... Composite image of Keplers supernova from pictures by the Spitzer Space Telescope, Hubble Space Telescope, and Chandra X-ray Observatory. ... Cosmic ray spallation is a form of naturally occuring nuclear fission and nucleosynthesis. ... Spiral Galaxy ESO 269-57 // Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... The R process (R for rapid) is a neutron capture process for radioactive elements which occurs in high neutron density, high temperature conditions. ... The S process (S for slow) is a neutron capture process in the decay of radioactive elements that occurs in lower neutron density, lower temperature conditions. ... An induced nuclear fission event. ...

Sequence of BBN

Big Bang nucleosynthesis begins about one minute after the Big Bang, when the universe has cooled enough to form stable protons and neutrons, after baryogenesis. From simple thermodynamical arguments, one can calculate the fraction of protons and neutrons based on the temperature at this point. This fraction is in favour of protons, because the higher mass of the neutron results in a spontaneous decay of neutrons to protons with a half-life of about 15 minutes. 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. In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Baryogenesis is the generic designation for the physical processes that generate matter (more specifically, a class of fundamental particle called baryon) from an otherwise matter-empty state (such as it is generally believed to be the state of the Universe at its onset, the so-called Big Bang). ...


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. At the time at which nucleosynthesis occurs, the temperature is high enough for the mean energy per particle to be greater than the binding energy of deuterium; therefore any deuterium that is formed is immediately destroyed (a situation known as the deuterium bottleneck). Hence, the formation of helium-4 is delayed until the universe becomes cool enough to form deuterium (at about T = 0.1 MeV), when there is a sudden burst of element formation. Shortly thereafter, at three minutes after the Big Bang, the universe becomes too cool for any nuclear fusion to occur. At this point, the elemental abundances are fixed, and only change as some of the radioactive products of BBN (such as tritium) decay. A free neutron is a neutron that exists outside of an atomic nucleus. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of one atom in 6400 of hydrogen (see VSMOW; the abundance changes slightly from one kind of natural water to another). ... Tritium (symbol T or 3H) is a radioactive isotope of hydrogen. ...


History of Big Bang nucleosynthesis

The history of Big Bang nucleosynthesis began with the calculations of Ralph Alpher and George Gamow in the 1940s. Ralph Asher Alpher (born 1921) is a U.S. cosmologist. ... George Gamow (pronounced GAM-off) (March 4, 1904 – August 19, 1968) , born Georgiy Antonovich Gamov (Георгий Антонович Гамов) was a Ukrainian born physicist and cosmologist. ...


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. In cosmology, dark matter refers to matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. ...


Heavy elements

Big Bang nucleosyntheis produces no elements heavier than beryllium. There is no stable nucleus with 8 nucleons, so there was a bottleneck in the nucleosynthesis that stopped the process there. In stars, the bottleneck is passed by triple collisions of helium-4 nuclei (the triple-alpha process). However, the triple alpha process takes tens of thousands of years to convert a significant amount of helium to carbon, and therefore was unable to convert any significant amount of helium in the minutes after the Big Bang. In physics a nucleon is a collective name for the two baryons: the neutron and the proton. ... The triple alpha process is the process by which three helium nuclei (alpha particles) are transformed into carbon. ...


Helium-4

Big Bang nucleosynthesis predicts about 25% helium-4, and this number is extremely insensitive to the initial conditions of the universe. The reason for this is that helium-4 is very stable and so almost all of the neutrons will combine with protons to form helium-4. In addition, two helium-4 atoms cannot combine to form a stable atom, so once helium-4 is formed, it stays helium-4. 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 helium-4 abundance is important because 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. Cross section of a red giant showing nucleosynthesis and elements formed Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. ...


Deuterium

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 unstable and easy to destroy. Because helium-4 is very stable, there is a strong tendency on the part of two deuterium nuclei to combine to form helium-4. The only reason BBN does not convert all of the deuterium in the universe to helium-4 is that the expansion of the universe cooled the universe and cut this conversion short before it could be completed. One consequence of this is that unlike helium-4, the amount of deuterium is very sensitive to initial conditions. The denser the universe is, the more deuterium gets converted to helium-4 before time runs out, and the less deuterium remains.


There are no known post-Big Bang processes which would produce significant amounts of deuterium. Hence observations about deuterium abundance suggest that the universe is not infinitely old, in accordance with the Big Bang theory.


During the 1970s, there were major efforts to find processes that could produce 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 consists of protons and neutrons. In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ...


This inconsistency between observations of deuterium and observations of the expansion rate of the universe led to a large effort to find processes that could produce deuterium. After a decade of effort, the consensus was that these processes are unlikely, and the standard explanation now used for the abundance of deuterium is that the universe does not consist mostly of baryons, and that dark matter makes up most of the matter mass of the universe (though it is now believed (2006){citatation needed} that dark energy provides most (70%) of the energy density of the universe). In cosmology, dark matter refers to matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. ... In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. ...


It is very hard to come up with another process that would produce deuterium via nuclear fusion. What this process would require is that the temperature be hot enough to produce deuterium, but not hot enough to produce helium-4, and that this process immediately cools down to non-nuclear temperatures after no more than a few minutes. Also, it is necessary for the deuterium to be swept away before it reoccurs.


Producing deuterium by fission is also difficult. The problem here again is that deuterium is very subject to nuclear processes, and that collisions between atomic nuclei are likely to result either in the absorption of the nuclei, or in the release of free neutrons or alpha particles. During the 1970s, attempts were made to use cosmic ray spallation to produce deuterium. These attempts failed to produce deuterium, but did unexpectedly produce other light elements. An alpha particle is deflected by a magnetic field Alpha particles or alpha rays are a form of particle radiation which are highly ionizing and have low penetration. ... Cosmic ray spallation is a form of naturally occuring nuclear fission and nucleosynthesis. ...


Status and Implications of BBN

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.


As noted above, in the standard picture of BBN, all of the light element abundances depend on the amount of ordinary matter (baryons) relative to radiation (photons). Since the universe is homogeneous, it has one unique (but initially unknown to us) value of the baryon-to-photon ratio. To test BBN theory against observations thus is 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? In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called nucleons), as well as a number of unstable, heavier particles (called hyperons). ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ...


The answer at present is a qualified yes: the BBN light element predictions can be reconciled with observations for a particular range of baryon-to-photon values, when theoretical and particularly observational uncertainties are taken into account. This agreement is by no means trivial or guaranteed, and represents an impressive success of modern cosmology: BBN extrapolates the contents and conditions of the present universe (about 14 billon years old) back to times of about one second, and the results are in agreement with observation.


Non-standard BBN

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 neutrinos. A non-standard cosmology is a cosmological framework that fundamentally contradicts one of the basic aspects of the big bang model of physical cosmology. ... The neutrino is an elementary particle. ...


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, which is 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, standand 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. The neutrino is an elementary particle. ...


See also

The ultimate fate of our universe is a topic in physical cosmology. ...

External links

  • Burles, Scott, and Kenneth M. Nollett, Michael S. Turner (2001). "What Is The BBN Prediction for the Baryon Density and How Reliable Is It?". Phys.Rev. D 63: 063512. arXiv:astro-ph/0008495. Report-no: FERMILAB-Pub-00-239-A
  • Jedamzik, Karsten, "A Brief Summary of Non-Standard Big Bang Nucleosynthesis Scenarios". Max-Planck-Institut für Astrophysik, Garching.
  • 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.
  • R. A. Alpher, H. A. Bethe, G. Gamow, The Origin of Chemical Elements, Physical Review 73 (1948), 803. The so-called 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.
  • G. Gamow, 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.
  • G. Gamow, Nature 162 (1948), 680.
  • R. A. Alpher, "A Neutron-Capture Theory of the Formation and Relative Abundance of the Elements," Physical Review 74 (1948), 1737.
  • 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.
  • R. A. Alpher, R. Herman, and G. Gamow Nature 162 (1948), 774.
  • Java Big Bang element abundance calculator

  Results from FactBites:
 
Big Bang nucleosynthesis - Wikipedia, the free encyclopedia (2022 words)
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.
Big Bang nucleosynthesis predicts about 25% helium-4, and this number is extremely insensitive to the initial conditions of the universe.
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 consists of protons and neutrons.
Nucleosynthesis - Wikipedia, the free encyclopedia (586 words)
The subsequent nucleosynthesis of the elements occurs primarily either by nuclear fusion or nuclear fission.
Big Bang nucleosynthesis occurred within the first three minutes of the universe and is responsible for most of the helium-4 and deuterium in the universe.
The 4He, 3He, 2H and 7Li nuclei are fused in the cooling of the Big Bang from the primordial nucleons, which were created by the cooling of the quark-gluon plasma.
  More results at FactBites »

 
 

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