While most cultures base their cosmologies on familiar units such as few hundreds or thousands of years, the Hindu concept of time embraces billions and trillions of years. Hindu sages describe time as cyclic, an endless procession of creation, preservation and dissolution.
This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. March Learn how and when to remove this template message Deuterium is in some ways the opposite of helium-4, in that while helium-4 is very stable and 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.
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.
During the s, 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 protons and neutrons.
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 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. 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 s, 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.
Lithium Lithium-7 and lithium-6 produced in the Big Bang are in the order of: 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.
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 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 quasars.
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 presumed to be homogeneousit 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: Or more precisely, allowing for the finite precision of both the predictions and the observations, one asks: More recently, the question has changed: Precision observations of the cosmic microwave background radiation   with the Wilkinson Microwave Anisotropy Probe WMAP and Planck 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?
The present measurement of helium-4 indicates good agreement, and yet better agreement for helium The discrepancy is a factor of 2. These should not be confused with non-standard cosmology: These pieces of additional physics include relaxing or removing the assumption of homogeneity, or inserting new particles such as massive neutrinos.
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. One can insert a hypothetical particle such as a massive neutrino and see what has to happen before BBN predicts abundances that are very different from observations.
This has been done to put limits on the mass of a stable tau neutrino.Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology: Authors: Serpico, Pasquale D.; Raffelt, Georg G.
Affiliation: It is the only unknown parameter characterizing the thermal medium at the primordial nucleosynthesis epoch. Nuclear fusion is the only process reasonably capable of powering the sun, and one product of this fusion is invisible particles called 'neutrinos'.
But why don't we observe as . In physical cosmology, Big Bang nucleosynthesis (abbreviated BBN, also known as primordial nucleosynthesis, arch(a)eonucleosynthesis, archonucleosynthesis, protonucleosynthesis and pal(a)eonucleosynthesis) refers to the production of nuclei other than those of the lightest isotope of hydrogen (hydrogen-1, 1 H, having a single proton as a nucleus) during the early phases of the Universe.
Primordial Nucleosynthesis in the Precision Cosmology Era by Gary Steigman [Ann. Rev. Nucl. Part. Phys. 57, ()] Primordial Nucleosynthesis: from precision cosmology to fundamental physics by F. Iocco et al. [/09]. Energetic hadronic and electromagnetic showers in the keV era of the hot big bang are produced by the decays of long lived particles.
These showers initiate a new phase of nucleosynthesis. The abundance ratios of D, /sup 3/He, /sup 6/Li and /sup 7/Li are given by fixed points of rate equations. Big Bang Nucleosynthesis (BBN) begins in earnest when the Universe is a few minutes old and ends less than half an hour later when the nuclear reactions are quenched by the low temperatures and densities.