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Isotope of hydrogen with 1 neutronDeuterium, hydrogen-2, 2HGeneral2Hdeuterium, H-2, hydrogen-2110.0115% (Earth)2.11 +13135.720± 0.0012224.52± 0.20 keVDeuterium (or hydrogen-2, symbol 2HorD, also known as heavy hydrogen) is one of two of (the other being, or hydrogen-1). Haunted memories changing portraits. The of a deuterium atom, called a deuteron, contains one and one, whereas the far more common protium has no neutrons in the nucleus. Deuterium has a in Earth's of about one in 6420 of hydrogen.

Thus deuterium accounts for approximately 0.02% (0.03% by mass) of all the naturally occurring hydrogen in the oceans, while protium accounts for more than 99.98%. The abundance of deuterium changes slightly from one kind of natural water to another (see ).The name deuterium is derived from the Greek deuteros, meaning 'second', to denote the two particles composing the nucleus. Deuterium was discovered and named in 1931. When the neutron was discovered in 1932, this made the nuclear structure of deuterium obvious, and Urey won the in 1934 “for his discovery of heavy hydrogen”. Soon after deuterium's discovery, Urey and others produced samples of ' in which the deuterium content had been highly concentrated.Deuterium is destroyed in the interiors of stars faster than it is produced.

Other natural processes are thought to produce only an insignificant amount of deuterium. Nearly all deuterium found in nature was produced in the 13.8 billion years ago, as the basic or primordial ratio of hydrogen-1 to deuterium (about 26 atoms of deuterium per million hydrogen atoms) has its origin from that time.

This is the ratio found in the gas giant planets, such as Jupiter. The analysis of deuterium–protium ratios in comets found results very similar to the mean ratio in Earth's oceans (156 atoms of deuterium per million hydrogen atoms). This reinforces theories that much of Earth's ocean water is of cometary origin.

The deuterium–protium ratio of the comet, as measured by the, is about three times that of earth water. This figure is the highest yet measured in a comet.Deuterium–protium ratios thus continue to be an active topic of research in both astronomy and climatology. Deuterium discharge tubeDeuterium is frequently represented by the D. Since it is an isotope of with 2, it is also represented by 2H. Allows both D and 2H, although 2His preferred. A distinct chemical symbol is used for convenience because of the isotope's common use in various scientific processes.

Also, its large mass difference with ( 1H) (deuterium has a mass of 2.014 102, compared to the hydrogen of 1.007 947 u, and protium's mass of 1.007 825 u) confers non-negligible chemical dissimilarities with protium-containing compounds, whereas the isotope weight ratios within other chemical elements are largely insignificant in this regard.Spectroscopy In the energy levels of electrons in atoms depend on the of the system of electron and nucleus. For the, the role of reduced mass is most simply seen in the of the atom, where the reduced mass appears in a simple calculation of the and Rydberg equation, but the reduced mass also appears in the, and the for calculating atomic energy levels.The reduced mass of the system in these equations is close to the mass of a single electron, but differs from it by a small amount about equal to the ratio of mass of the electron to the atomic nucleus. For hydrogen, this amount is about 1837/1836, or 1.000545, and for deuterium it is even smaller: 3671/3670, or 1.0002725. The energies of spectroscopic lines for deuterium and light hydrogen therefore differ by the ratios of these two numbers, which is 1.000272. The wavelengths of all deuterium spectroscopic lines are shorter than the corresponding lines of light hydrogen, by a factor of 1.000272.

In astronomical observation, this corresponds to a blue Doppler shift of 0.000272 times the speed of light, or 81.6 km/s.The differences are much more pronounced in vibrational spectroscopy such as and, and in rotational spectra such as because the of the deuterium is markedly higher than that of protium. In, deuterium has a very different frequency (e.g. 61 MHz when protium is at 400 MHz) and is much less sensitive. Deuterated solvents are usually used in protium NMR to prevent the solvent from overlapping with the signal, although on its own right is also possible.Big Bang nucleosynthesis.

Main article:Deuterium is thought to have played an important role in setting the number and ratios of the elements that were formed in the Big Bang. Combining thermodynamics and the changes brought about by cosmic expansion, one can calculate the fraction of protons and neutrons based on the temperature at the point that the universe cooled enough to allow formation of nuclei. This calculation indicates seven protons for every neutron at the beginning of nucleogenesis, a ratio that would remain stable even after nucleogenesis was over.

This fraction was in favor of protons initially, primarily because the lower mass of the proton favored their production. As the universe expanded, it cooled. And protons are less stable than helium nuclei, and the protons and neutrons had a strong energetic reason to form helium-4. However, forming helium-4 requires the intermediate step of forming deuterium.Through much of the few minutes after the big bang during which nucleosynthesis could have occurred, the temperature was high enough that the mean energy per particle was greater than the binding energy of weakly bound deuterium; therefore any deuterium that was formed was immediately destroyed. This situation is known as the deuterium bottleneck. The bottleneck delayed formation of any helium-4 until the universe became cool enough to form deuterium (at about a temperature equivalent to 100 keV). At this point, there was a sudden burst of element formation (first deuterium, which immediately fused to helium).

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, with the only change as some of the products of big bang nucleosynthesis (such as ) decay. The deuterium bottleneck in the formation of helium, together with the lack of stable ways for helium to combine with hydrogen or with itself (there are no stable nuclei with mass numbers of five or eight) meant that an insignificant amount of carbon, or any elements heavier than carbon, formed in the Big Bang. These elements thus required formation in stars. At the same time, the failure of much nucleogenesis during the Big Bang ensured that there would be plenty of hydrogen in the later universe available to form long-lived stars, such as our Sun.Abundance Deuterium occurs in trace amounts naturally as deuterium, written 2H2 or D 2, but most natural occurrence in the is bonded with a typical 1Hatom, a gas called (HD or 1H2H).The existence of deuterium on Earth, elsewhere in the (as confirmed by planetary probes), and in the spectra of, is also an important datum in. Gamma radiation from ordinary nuclear fusion dissociates deuterium into protons and neutrons, and there are no known natural processes other than the, which might have produced deuterium at anything close to its observed natural abundance (deuterium is produced by the rare, and occasional absorption of naturally occurring neutrons by light hydrogen, but these are trivial sources).

There is thought to be little deuterium in the interior of the Sun and other stars, as at these temperatures the that consume deuterium happen much faster than the that creates deuterium. However, deuterium persists in the outer solar atmosphere at roughly the same concentration as in Jupiter, and this has probably been unchanged since the origin of the Solar System.

The natural abundance of deuterium seems to be a very similar fraction of hydrogen, wherever hydrogen is found, unless there are obvious processes at work that concentrate it.The existence of deuterium at a low but constant primordial fraction in all hydrogen is another one of the arguments in favor of the theory over the of the universe. The observed ratios of hydrogen to helium to deuterium in the universe are difficult to explain except with a Big Bang model. It is estimated that the abundances of deuterium have not evolved significantly since their production about 13.8 billion years ago.

Measurements of Milky Way galactic deuterium from ultraviolet spectral analysis show a ratio of as much as 23 atoms of deuterium per million hydrogen atoms in undisturbed gas clouds, which is only 15% below the estimated primordial ratio of about 27 atoms per million from the Big Bang. This has been interpreted to mean that less deuterium has been destroyed in star formation in our galaxy than expected, or perhaps deuterium has been replenished by a large in-fall of primordial hydrogen from outside the galaxy.

In space a few hundred light years from the Sun, deuterium abundance is only 15 atoms per million, but this value is presumably influenced by differential adsorption of deuterium onto carbon dust grains in interstellar space.The abundance of deuterium in the atmosphere of has been directly measured by the as 26 atoms per million hydrogen atoms. ISO-SWS observations find 22 atoms per million hydrogen atoms in Jupiter. And this abundance is thought to represent close to the primordial solar system ratio.

This is about 17% of the terrestrial deuterium-to-hydrogen ratio of 156 deuterium atoms per million hydrogen atoms.Cometary bodies such as and have been measured to contain relatively more deuterium (about 200 atoms D per million hydrogens), ratios which are enriched with respect to the presumed protosolar nebula ratio, probably due to heating, and which are similar to the ratios found in Earth seawater. The recent measurement of deuterium amounts of 161 atoms D per million hydrogen in Comet (a former object), a ratio almost exactly that in Earth's oceans, emphasizes the theory that Earth's surface water may be largely comet-derived. Most recently the deuterium–protium (D–H) ratio of as measured by Rosetta is about three times that of Earth water, a figure that is high. This has caused renewed interest in suggestions that Earth's water may be partly of asteroidal origin.Deuterium has also observed to be concentrated over the mean solar abundance in other terrestrial planets, in particular Mars and Venus.Production. This section does not any.

Unsourced material may be challenged and.Find sources: – ( February 2019) Deuterium is produced for industrial, scientific and military purposes, by starting with ordinary water—a small fraction of which is naturally-occurring —and then separating out the heavy water by the, distillation, or other methods.In theory, deuterium for heavy water could be created in a nuclear reactor, but separation from ordinary water is the cheapest bulk production process.The world's leading supplier of deuterium was until 1997, when the last heavy water plant was shut down. Canada uses heavy water as a for the operation of the design.Another major producer of heavy water is India. All but one of India's atomic energy plants are pressurised heavy water plants, which use natural (i.e., not enriched) uranium. India has eight heavy water plants, of which seven are in operation. Six plants, of which five are in operation, are based on D–H exchange in ammonia gas. The other two plants extract deuterium from natural water in a process that uses hydrogen sulphide gas at high pressure.While India is self-sufficient in heavy water for its own use, India now also exports reactor-grade heavy water.Properties Physical properties The physical properties of deuterium compounds can exhibit significant and other physical and chemical property differences from the protium analogs., for example, is more than. Chemically, there are differences in bond energy and length for compounds of heavy hydrogen isotopes compared to protium, which are larger than the isotopic differences in any other element.

Bonds involving deuterium and are somewhat stronger than the corresponding bonds in protium, and these differences are enough to cause significant changes in biological reactions. Pharmaceutical firms are interested in the fact that deuterium is harder to remove from carbon than protium.Deuterium can replace protium in water molecules to form heavy water (D 2O), which is about 10.6% denser than normal water (so that ice made from it sinks in ordinary water). Heavy water is slightly toxic in animals, with 25% substitution of the body water causing cell division problems and sterility, and 50% substitution causing death by cytotoxic syndrome (bone marrow failure and gastrointestinal lining failure). Organisms, however, can survive and grow in pure heavy water, though they develop slowly. Despite this toxicity, consumption of heavy water under normal circumstances does not pose a to humans. It is estimated that a 70 kg (154 lb) person might drink 4.8 litres (1.3 US gal) of heavy water without serious consequences.

Small doses of heavy water (a few grams in humans, containing an amount of deuterium comparable to that normally present in the body) are routinely used as harmless metabolic tracers in humans and animals.Quantum properties The deuteron has +1 (') and is thus a. The frequency of deuterium is significantly different from common light hydrogen. Also easily differentiates many deuterated compounds, due to the large difference in IR absorption frequency seen in the vibration of a chemical bond containing deuterium, versus light hydrogen. The two stable isotopes of hydrogen can also be distinguished by using.The triplet deuteron nucleon is barely bound at E B = 2.23 MeV, and none of the higher energy states are bound. The singlet deuteron is a virtual state, with a negative binding energy of 60 keV. There is no such stable particle, but this virtual particle transiently exists during neutron-proton inelastic scattering, accounting for the unusually large neutron scattering cross-section of the proton. Nuclear properties (the deuteron) Deuteron mass and radius The nucleus of deuterium is called a deuteron.

It has a mass of 2.013 553 212 745(40) u (equal to 1875.612 928(12) MeV)The of the deuteron is 2.127 99(14).Like the, measurements using deuterium produce a smaller result: 2.125 62(78). Ionized deuterium in a reactor giving off its characteristic pinkish-red glowDeuterium is used in, usually as liquid D 2O, to slow neutrons without the high neutron absorption of ordinary hydrogen. This is a common commercial use for larger amounts of deuterium.In, liquid D 2 is used in to moderate neutrons to very low energies and wavelengths appropriate for.Experimentally, deuterium is the most common nuclide used in reactor designs, especially in combination with, because of the large reaction rate (or ) and high yield of the D–T reaction. There is an even higher-yield D– fusion reaction, though the of D– 3Heis higher than that of most other fusion reactions; together with the scarcity of 3He, this makes it implausible as a practical power source until at least D–T and D–D fusion reactions have been performed on a commercial scale. Commercial nuclear fusion is not yet an accomplished technology.NMR spectroscopy. Emission spectrum of an ultravioletDeuterium is most commonly used in hydrogen in the following way. NMR ordinarily requires compounds of interest to be analyzed as dissolved in solution.

Because of deuterium's nuclear spin properties which differ from the light hydrogen usually present in organic molecules, NMR spectra of hydrogen/protium are highly differentiable from that of deuterium, and in practice deuterium is not 'seen' by an NMR instrument tuned for light-hydrogen. Deuterated solvents (including heavy water, but also compounds like deuterated chloroform, CDCl 3) are therefore routinely used in NMR spectroscopy, in order to allow only the light-hydrogen spectra of the compound of interest to be measured, without solvent-signal interference.Nuclear magnetic resonance spectroscopy can also be used to obtain information about the deuteron's environment in isotopically labelled samples. For example, the flexibility in the tail, which is a long hydrocarbon chain, in deuterium-labelled lipid molecules can be quantified using solid state deuterium NMR.Deuterium NMR spectra are especially informative in the solid state because of its relatively small quadrupole moment in comparison with those of bigger quadrupolar nuclei such as chlorine-35, for example.Tracing In, and, deuterium is used as a non-radioactive, for example, in the. In and, deuterium behaves somewhat similarly to ordinary hydrogen (with a few chemical differences, as noted). It can be distinguished from ordinary hydrogen most easily by its mass, using. Deuterium can be detected by spectroscopy, since the mass difference drastically affects the frequency of molecular vibrations; deuterium-carbon bond vibrations are found in spectral regions free of other signals.Measurements of small variations in the natural abundances of deuterium, along with those of the stable heavy oxygen isotopes 17O and 18O, are of importance in, to trace the geographic origin of Earth's waters.

The heavy isotopes of hydrogen and oxygen in rainwater (so-called ) are enriched as a function of the environmental temperature of the region in which the precipitation falls (and thus enrichment is related to mean latitude). The relative enrichment of the heavy isotopes in rainwater (as referenced to mean ocean water), when plotted against temperature falls predictably along a line called the (GMWL). This plot allows samples of precipitation-originated water to be identified along with general information about the climate in which it originated.

Evaporative and other processes in bodies of water, and also ground water processes, also differentially alter the ratios of heavy hydrogen and oxygen isotopes in fresh and salt waters, in characteristic and often regionally distinctive ways. The ratio of concentration of 2H to 1H is usually indicated with a delta as δ 2H and the geographic patterns of these values are plotted in maps termed as isoscapes. Stable isotopes are incorporated into plants and animals and an analysis of the ratios in a migrant bird or insect can help suggest a rough guide to their origins. Contrast properties techniques particularly profit from availability of deuterated samples: The H and D cross sections are very distinct and different in sign, which allows contrast variation in such experiments. Further, a nuisance problem of ordinary hydrogen is its large incoherent neutron cross section, which is nil for D. The substitution of deuterium atoms for hydrogen atoms thus reduces scattering noise.Hydrogen is an important and major component in all materials of organic chemistry and life science, but it barely interacts with X-rays. As hydrogen (and deuterium) interact strongly with neutrons, neutron scattering techniques, together with a modern deuteration facility, fills a niche in many studies of macromolecules in biology and many other areas.Nuclear weapons This is discussed below.

It is notable that although most stars, including the Sun, generate energy over most of their lives by fusing hydrogen into heavier elements, such fusion of light hydrogen (protium) has never been successful in the conditions attainable on Earth. Thus, all artificial fusion, including the hydrogen fusion that occurs in so-called hydrogen bombs, requires heavy hydrogen (either tritium or deuterium, or both) in order for the process to work.Drugs. Main article:A deuterated drug is a medicinal product in which one or more of the atoms contained in the drug molecule have been replaced by deuterium. Because of the, deuterium-containing drugs may have significantly lower rates of, and hence a longer. In 2017, became the first deuterated drug to receive FDA approval.

Reinforced essential nutrients Deuterium can be used to reinforce specific oxidation-vulnerable C-H bonds within essential or conditionally, such as certain, or (PUFA), making them more resistant to oxidative damage. Polyunsaturated, such as, slow down the chain reaction of that damage living cells. Deuterated ethyl ester of linoleic acid , developed by Retrotope, is in a in and has successfully completed a Phase I/II trial in. History Suspicion of lighter element isotopes The existence of nonradioactive isotopes of lighter elements had been suspected in studies of neon as early as 1913, and proven by mass spectrometry of light elements in 1920. The prevailing theory at the time was that isotopes of an element differ by the existence of additional protons in the nucleus accompanied by an equal number of. In this theory, the deuterium nucleus with mass two and charge one would contain two protons and one nuclear electron.

However, it was expected that the element hydrogen with a measured average atomic mass very close to 1 u, the known mass of the proton, always has a nucleus composed of a single proton (a known particle), and could not contain a second proton. Thus, hydrogen was thought to have no heavy isotopes.Deuterium detected. Harold UreyIt was first detected spectroscopically in late 1931 by, a chemist at. Urey's collaborator, five of to 1 of liquid, using the low-temperature physics laboratory that had recently been established at the National Bureau of Standards in Washington, D.C.

The technique had previously been used to isolate heavy isotopes of neon. The cryogenic boiloff technique concentrated the fraction of the mass-2 isotope of hydrogen to a degree that made its spectroscopic identification unambiguous. Naming of the isotope and Nobel Prize Urey created the names protium, deuterium, and tritium in an article published in 1934. The name is based in part on advice from who had proposed the name 'deutium'.

The name is derived from the, Greek deuteros (second), and the nucleus to be called 'deuteron' or 'deuton'. Isotopes and new elements were traditionally given the name that their discoverer decided. Some British scientists, such as, wanted the isotope to be called 'diplogen', from the Greek diploos (double), and the nucleus to be called diplon.The amount inferred for normal abundance of this heavy isotope of hydrogen was so small (only about 1 atom in 6400 hydrogen atoms in ocean water (156 deuteriums per million hydrogens)) that it had not noticeably affected previous measurements of (average) hydrogen atomic mass. This explained why it hadn't been experimentally suspected before.

Urey was able to concentrate water to show partial enrichment of deuterium. Lewis had prepared the first samples of pure heavy water in 1933. The discovery of deuterium, coming before the discovery of the in 1932, was an experimental shock to theory, but when the neutron was reported, making deuterium's existence more explainable, deuterium won Urey the in 1934. Lewis was embittered by being passed over for this recognition given to his former student. 'Heavy water' experiments in World War II. Main article:Shortly before the war, and moved their research on neutron moderation from France to Britain, smuggling the entire global supply of heavy water (which had been made in Norway) across in twenty-six steel drums.During, was known to be conducting experiments using heavy water as moderator for a design. Such experiments were a source of concern because they might allow them to produce for an.

Ultimately it led to the operation called the ', the purpose of which was to destroy the deuterium production/enrichment facility in Norway. At the time this was considered important to the potential progress of the war.After World War II ended, the Allies discovered that Germany was not putting as much serious effort into the program as had been previously thought. They had been unable to sustain a chain reaction. The Germans had completed only a small, partly built experimental reactor (which had been hidden away). By the end of the war, the Germans did not even have a fifth of the amount of heavy water needed to run the reactorpartially due to the Norwegian heavy water sabotage operation. However, even had the Germans succeeded in getting a reactor operational (as the U.S. Did with a graphite reactor in late 1942), they would still have been at least several years away from development of an with maximal effort.

The engineering process, even with maximal effort and funding, required about two and a half years (from first critical reactor to bomb) in both the U.S. And, for example.In thermonuclear weapons. A view of the Sausage device casing of the, with its instrumentation and cryogenic equipment attached. This bomb held a cryogenic Dewar flask containing room for as much as 160 kilograms of liquid deuterium. The bomb was 20 feet tall.

Note the seated man at the right of the photo for the scale.The 62-ton device built by the United States and exploded on 1 November 1952, was the first fully successful '. In this context, it was the first bomb in which most of the energy released came from stages that followed the primary stage of the.

The Ivy Mike bomb was a factory-like building, rather than a deliverable weapon. At its center, a very large cylindrical, insulated or, held liquid deuterium in a volume of about 1000 (160 kilograms in mass, if this volume had been completely filled).

Then, a conventional (the 'primary') at one end of the bomb was used to create the conditions of extreme temperature and pressure that were needed to set off the.Within a few years, so-called 'dry' hydrogen bombs were developed that did not need cryogenic hydrogen. Released information suggests that all built since then contain of deuterium and lithium in their secondary stages. The material that contains the deuterium is mostly, with the lithium consisting of the isotope. When the lithium-6 is bombarded with fast from the atomic bombis produced, and then the deuterium and the tritium quickly engage in, releasing abundant energy, and even more free neutrons.Modern research In August 2018, scientists announced the transformation of gaseous deuterium into a.

This may help researchers better understand, such as Jupiter, Saturn and related, since such planets are thought to contain a lot of liquid metallic hydrogen, which may be responsible for their observed powerful.

.The Big Bang theory is a of the from the through its subsequent large-scale evolution. The model describes how the from an initial state of very high and high, and offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of, the (CMB), and – the farther away are, the faster they are moving away from Earth. If the observed conditions are extrapolated backwards in time using the known, the prediction is that just before a period of very high density there was a. Current knowledge is insufficient to determine if the singularity was primordial.first noted in 1927 that an expanding could be traced back in time to an originating single point, calling his theory that of the 'primeval atom'. For much of the rest of the 20th century scientific community was divided between supporters of the Big Bang and the rival, but a wide range of empirical evidence has strongly favored the Big Bang, which is now universally accepted.

Concluded from analysis of galactic in 1929 that galaxies are drifting apart; this is important observational evidence for an expanding universe. In 1964, the CMB was discovered, which was crucial evidence in favor of the hot Big Bang model, since that theory predicted the existence of a background radiation throughout the universe.The known laws of physics can be used to calculate the characteristics of the universe in detail back in time to an initial state of extreme density and temperature. Detailed measurements of the expansion rate of the universe place the Big Bang at around 13.8 years ago, which is thus considered the. After its initial expansion, the universe cooled sufficiently to allow the formation of, and later. Giant clouds of these primordial elements – mostly, with some and – later coalesced through, forming early and galaxies, the descendants of which are visible today.

Besides these primordial building materials, observe the gravitational effects of an unknown surrounding galaxies. Most of the in the universe seems to be in this form, and the Big Bang theory and various observations indicate that it is not conventional that forms atoms. Measurements of the redshifts of supernovae indicate that the, an observation attributed to 's existence. Contents.Features of the modelThe Big Bang theory offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of, the,. The theory depends on two major assumptions: the universality of physical laws and the. The universality of physical laws is one of the underlying principles of the. The cosmological principle states that on large scales the is and.These ideas were initially taken as postulates, but later efforts were made to test each of them.

For example, the first assumption has been tested by observations showing that largest possible deviation of the over much of the age of the universe is of order 10 −5. Also, has passed stringent on the scale of the and.The large-scale universe appears isotropic as viewed from Earth. If it is indeed isotropic, the cosmological principle can be derived from the simpler, which states that there is no preferred (or special) observer or vantage point. To this end, the cosmological principle has been confirmed to a level of 10 −5 via observations of the temperature of the CMB.

At the scale of the CMB horizon, the universe has been measured to be homogeneous with an upper bound 10% inhomogeneity, as of 1995. Expansion of space. Main articles: andThe expansion of the Universe was inferred from early twentieth century astronomical observations and is an essential ingredient of the Big Bang theory. Mathematically, general relativity describes by a, which determines the distances that separate nearby points. The points, which can be, or other objects, are specified using a or 'grid' that is laid down over all spacetime.

The cosmological principle implies that the metric should be homogeneous and isotropic on large scales, which uniquely singles out the. This metric contains a, which describes how the size of the universe changes with time.

This enables a convenient choice of a to be made, called. In this coordinate system, the grid expands along with the universe, and objects that are moving only because of the, remain at fixed points on the grid. While their coordinate distance remains constant, the physical distance between two such co-moving points expands proportionally with the scale factor of the universe.The Big Bang is not an explosion of moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distances between comoving points. In other words, the Big Bang is not an explosion in space, but rather an expansion of space. Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our universe only on large scales—local concentrations of matter such as our galaxy do not necessarily expand with the same speed as the whole Universe.

Main article:An important feature of the Big Bang spacetime is the presence of. Since the universe has a finite age, and travels at a finite speed, there may be events in the past whose light has not yet had time to reach us.

This places a limit or a past horizon on the most distant objects that can be observed. Conversely, because space is expanding, and more distant objects are receding ever more quickly, light emitted by us today may never 'catch up' to very distant objects. This defines a future horizon, which limits the events in the future that we will be able to influence.

The presence of either type of horizon depends on the details of the FLRW model that describes our universe.Our understanding of the universe back to very early times suggests that there is a past horizon, though in practice our view is also limited by the opacity of the universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the universe continues to, there is a future horizon as well. See also: andExtrapolation of the expansion of the universe backwards in time using general relativity yields an and at a finite time in the past. This irregular behavior, known as the, indicates that general relativity is not an adequate description of the laws of physics in this regime.

Models based on general relativity alone can not extrapolate toward the singularity — beyond the end of the so-called. This primordial singularity is itself sometimes called 'the Big Bang', but the term can also refer to a more generic early hot, dense phase of the universe. In either case, 'the Big Bang' as an event is also colloquially referred to as the 'birth' of our universe since it represents the point in history where the universe can be verified to have entered into a where the laws of physics as we understand them (specifically general relativity and the of ) work. Based on measurements of the expansion using and measurements of temperature fluctuations in the cosmic microwave background, the time that has passed since that event — known as the 'age of the universe' — is 13.799 ± 0.021 billion years. The agreement of independent measurements of this age supports the (ΛCDM) model that describes in detail the characteristics of the universe.

Despite being extremely dense at this time—far denser than is usually required to form a —the universe did not re-collapse into a singularity. This may be explained by considering that commonly-used calculations and limits for are usually based upon objects of relatively constant size, such as stars, and do not apply to rapidly expanding space such as the Big Bang. Likewise, since the early universe did not immediately collapse into a multitude of black holes, matter at that time must have been very evenly distributed with a negligible. Inflation and baryogenesis.

Main articles: andThe earliest phases of the Big Bang are subject to much speculation, since astronomical data about them are not available. In the most common models the universe was filled homogeneously and isotropically with a very high and huge temperatures and, and was very rapidly expanding and cooling. Approximately 10 −37 seconds into the expansion, a caused a, during which the universe grew and temperatures dropped by a factor of 100,000. Microscopic that occurred because of were amplified into the seeds that would later form the large-scale structure of the universe.After inflation stopped at around the 10 −33 to 10 −32 seconds mark, reheating occurred until the universe obtained the temperatures required for the of a as well as all other. Temperatures were so high that the random motions of particles were at, and of all kinds were being continuously created and destroyed in collisions. At some point, an unknown reaction called violated the conservation of, leading to a very small excess of and over antiquarks and antileptons—of the order of one part in 30 million.

This resulted in the predominance of matter over antimatter in the present universe. Panoramic view of the entire sky reveals the distribution of beyond the. Galaxies are color-coded by.The universe continued to decrease in density and fall in temperature, hence the typical energy of each particle was decreasing.

Phase transitions put the of physics and the parameters of elementary particles into their present form. After about 10 −11 seconds, the picture becomes less speculative, since particle energies drop to values that can be attained in. At about 10 −6 seconds, quarks and combined to form such as.

The small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. The temperature was now no longer high enough to create new proton–antiproton pairs (similarly for neutrons–antineutrons), so a mass annihilation immediately followed, leaving just one in 10 10 of the original protons and neutrons, and none of their. A similar process happened at about 1 second for electrons and positrons. After these annihilations, the remaining protons, neutrons and electrons were no longer moving relativistically and the energy density of the universe was dominated by (with a minor contribution from ).A few minutes into the expansion, when the temperature was about a billion and the density of matter in the universe was comparable to the current density of Earth's atmosphere, neutrons combined with protons to form the universe's and in a process called (BBN). Most protons remained uncombined as hydrogen nuclei.As the universe cooled, the density of matter came to gravitationally dominate that of the photon.

After about 379,000 years, the electrons and nuclei combined into (mostly ), which were able to emit radiation. This relic radiation, which continued through space largely unimpeded, is known as the cosmic microwave background. The may have begun during a habitable epoch when the universe was only 10–17 million years old. Structure formation.

Main article:Independent lines of evidence from Type Ia supernovae and the CMB imply that the universe today is dominated by a mysterious form of energy known as, which apparently permeates all of space. The observations suggest 73% of the total energy density of today's universe is in this form. When the universe was very young, it was likely infused with dark energy, but with less space and everything closer together, predominated, and it was slowly braking the expansion.

See also: Etymologyis credited with coining the term 'Big Bang' during a talk for a March 1949 broadcast, saying: 'These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past.' It is popularly reported that Hoyle, who favored an alternative ' cosmological model, intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models.

'The big bang picture is too firmly grounded in data from every area to be proved invalid in its general features.' The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by BBN. More recent evidence includes observations of, and the distribution of, These are sometimes called the 'four pillars' of the Big Bang theory.Precise modern models of the Big Bang appeal to various exotic physical phenomena that have not been observed in terrestrial laboratory experiments or incorporated into the Standard Model of particle physics. Of these features, is currently the subject of most active laboratory investigations. Remaining issues include the and the of cold dark matter.

Dark energy is also an area of intense interest for scientists, but it is not clear whether direct detection of dark energy will be possible. Inflation and baryogenesis remain more speculative features of current Big Bang models. Viable, quantitative explanations for such phenomena are still being sought. These are currently unsolved problems in physics.Hubble's law and the expansion of space.

The spectrum measured by the FIRAS instrument on the satellite is the most-precisely measured spectrum in nature. The and on this graph are obscured by the theoretical curve.In 1964, and serendipitously discovered the cosmic background radiation, an omnidirectional signal in the band. Their discovery provided substantial confirmation of the big-bang predictions by Alpher, Herman and Gamow around 1950. Through the 1970s, the radiation was found to be approximately consistent with a spectrum in all directions; this spectrum has been redshifted by the expansion of the universe, and today corresponds to approximately 2.725 K. This tipped the balance of evidence in favor of the Big Bang model, and Penzias and Wilson were awarded the 1978.The surface of last scattering corresponding to emission of the CMB occurs shortly after, the epoch when neutral hydrogen becomes stable. Prior to this, the universe comprised a hot dense photon-baryon plasma sea where photons were quickly from free charged particles. Peaking at around 372 ±14 kyr, the mean free path for a photon becomes long enough to reach the present day and the universe becomes transparent.

9 year WMAP image of the cosmic microwave background radiation (2012). The radiation is to roughly one part in 100,000.In 1989, launched COBE, which made two major advances: in 1990, high-precision spectrum measurements showed that the CMB frequency spectrum is an almost perfect blackbody with no deviations at a level of 1 part in 10 4, and measured a residual temperature of 2.726 K (more recent measurements have revised this figure down slightly to 2.7255 K); then in 1992, further COBE measurements discovered tiny fluctuations in the CMB temperature across the sky, at a level of about one part in 10 5. And were awarded the 2006 Nobel Prize in Physics for their leadership in these results.During the following decade, CMB anisotropies were further investigated by a large number of ground-based and balloon experiments.

In 2000–2001, several experiments, most notably, found the to be spatially almost flat by measuring the typical angular size (the size on the sky) of the anisotropies.In early 2003, the first results of the Wilkinson Microwave Anisotropy Probe were released, yielding what were at the time the most accurate values for some of the cosmological parameters. The results disproved several specific cosmic inflation models, but are consistent with the inflation theory in general. The space probe was launched in May 2009. Other ground and balloon based are ongoing.Abundance of primordial elements. Main articles: andDetailed observations of the and distribution of galaxies and quasars are in agreement with the current state of the Big Bang theory. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the Big Bang, and since then, larger structures have been forming, such as and.Populations of stars have been aging and evolving, so that distant galaxies (which are observed as they were in the early universe) appear very different from nearby galaxies (observed in a more recent state).

Moreover, galaxies that formed relatively recently, appear markedly different from galaxies formed at similar distances but shortly after the Big Bang. These observations are strong arguments against the steady-state model. Observations of star formation, galaxy and quasar distributions and larger structures, agree well with Big Bang simulations of the formation of structure in the universe, and are helping to complete details of the theory.

Primordial gas clouds. Of under a microscope - used to search for polarization in the CMB.In 2011, astronomers found what they believe to be pristine clouds of primordial gas by analyzing absorption lines in the spectra of distant quasars.

Before this discovery, all other astronomical objects have been observed to contain heavy elements that are formed in stars. These two clouds of gas contain no elements heavier than hydrogen and deuterium. Since the clouds of gas have no heavy elements, they likely formed in the first few minutes after the Big Bang, during BBN.Other lines of evidenceThe age of the universe as estimated from the Hubble expansion and the CMB is now in good agreement with other estimates using the ages of the oldest stars, both as measured by applying the theory of to globular clusters and through of individual stars.The prediction that the CMB temperature was higher in the past has been experimentally supported by observations of very low temperature absorption lines in gas clouds at high redshift. This prediction also implies that the amplitude of the in clusters of galaxies does not depend directly on redshift.

Observations have found this to be roughly true, but this effect depends on cluster properties that do change with cosmic time, making precise measurements difficult. Future observationsFuture might be able to detect primordial, relics of the early universe, up to less than a second after the Big Bang. Problems and related issues in physics.

See also:As with any theory, a number of mysteries and problems have arisen as a result of the development of the Big Bang theory. Some of these mysteries and problems have been resolved while others are still outstanding. Proposed solutions to some of the problems in the Big Bang model have revealed new mysteries of their own. For example, the, the, and the are most commonly resolved with inflationary theory, but the details of the inflationary universe are still left unresolved and many, including some founders of the theory, say it has been disproven.

What follows are a list of the mysterious aspects of the Big Bang theory still under intense investigation by cosmologists and.Baryon asymmetry. Main article:It is not yet understood why the universe has more matter than antimatter. It is generally assumed that when the universe was young and very hot it was in statistical equilibrium and contained equal numbers of baryons and antibaryons. However, observations suggest that the universe, including its most distant parts, is made almost entirely of matter. A process called baryogenesis was hypothesized to account for the asymmetry. For baryogenesis to occur, the must be satisfied.

These require that baryon number is not conserved, that and are violated and that the universe depart from. All these conditions occur in the Standard Model, but the effects are not strong enough to explain the present baryon asymmetry.Dark energy. Main article:Measurements of the redshift– relation for type Ia supernovae indicate that the expansion of the universe has been accelerating since the universe was about half its present age. To explain this acceleration, general relativity requires that much of the energy in the universe consists of a component with large negative pressure, dubbed 'dark energy'.Dark energy, though speculative, solves numerous problems. Measurements of the cosmic microwave background indicate that the universe is very nearly spatially flat, and therefore according to general relativity the universe must have almost exactly the of mass/energy. But the mass density of the universe can be measured from its gravitational clustering, and is found to have only about 30% of the critical density. Since theory suggests that dark energy does not cluster in the usual way it is the best explanation for the 'missing' energy density.

Dark energy also helps to explain two geometrical measures of the overall curvature of the universe, one using the frequency of, and the other using the characteristic pattern of the large-scale structure as a cosmic ruler.Negative pressure is believed to be a property of, but the exact nature and existence of dark energy remains one of the great mysteries of the Big Bang. Results from the WMAP team in 2008 are in accordance with a universe that consists of 73% dark energy, 23% dark matter, 4.6% regular matter and less than 1% neutrinos. According to theory, the energy density in matter decreases with the expansion of the universe, but the dark energy density remains constant (or nearly so) as the universe expands. Therefore, matter made up a larger fraction of the total energy of the universe in the past than it does today, but its fractional contribution will fall in the as dark energy becomes even more dominant.The dark energy component of the universe has been explained by theorists using a variety of competing theories including Einstein's cosmological constant but also extending to more exotic forms of or other modified gravity schemes. A, sometimes called the 'most embarrassing problem in physics', results from the apparent discrepancy between the measured energy density of dark energy, and the one naively predicted from. Shows the proportion of different components of the universe – about 95% is and.During the 1970s and the 1980s, various observations showed that there is not sufficient visible matter in the universe to account for the apparent strength of gravitational forces within and between galaxies.

This led to the idea that up to 90% of the matter in the universe is dark matter that does not emit light or interact with normal baryonic matter. In addition, the assumption that the universe is mostly normal matter led to predictions that were strongly inconsistent with observations. In particular, the universe today is far more lumpy and contains far less deuterium than can be accounted for without dark matter. While dark matter has always been controversial, it is inferred by various observations: the anisotropies in the CMB, galaxy cluster velocity dispersions, large-scale structure distributions, gravitational lensing studies, and of galaxy clusters.Indirect evidence for dark matter comes from its gravitational influence on other matter, as no dark matter particles have been observed in laboratories. Many particle physics candidates for dark matter have been proposed, and several projects to detect them directly are underway.Additionally, there are outstanding problems associated with the currently favored cold dark matter model which include the dwarf galaxy problem and the cuspy halo problem. Alternative theories have been proposed that do not require a large amount of undetected matter, but instead modify the laws of gravity established by Newton and Einstein; yet no alternative theory has been as successful as the cold dark matter proposal in explaining all extant observations. Horizon problem.

Main article:The horizon problem results from the premise that information cannot travel. In a universe of finite age this sets a limit—the particle horizon—on the separation of any two regions of space that are in contact. The observed isotropy of the CMB is problematic in this regard: if the universe had been dominated by radiation or matter at all times up to the epoch of last scattering, the particle horizon at that time would correspond to about 2 degrees on the sky. There would then be no mechanism to cause wider regions to have the same temperature.: 191–202A resolution to this apparent inconsistency is offered by inflationary theory in which a homogeneous and isotropic scalar energy field dominates the universe at some very early period (before baryogenesis). During inflation, the universe undergoes exponential expansion, and the particle horizon expands much more rapidly than previously assumed, so that regions presently on opposite sides of the observable universe are well inside each other's particle horizon.

The observed isotropy of the CMB then follows from the fact that this larger region was in causal contact before the beginning of inflation.: 180–186Heisenberg's uncertainty principle predicts that during the inflationary phase there would be, which would be magnified to a cosmic scale. The overall is determined by whether the is less than, equal to or greater than 1.

Shown from top to bottom are a with positive curvature, a with negative curvature and a with zero curvature.The flatness problem (also known as the oldness problem) is an observational problem associated with a FLRW. The universe may have positive, negative, or zero spatial depending on its total energy density. Curvature is negative if its density is less than the critical density; positive if greater; and zero at the critical density, in which case space is said to be flat.

Observations indicate the universe is consistent with being flat.The problem is that any small departure from the critical density grows with time, and yet the universe today remains very close to flat. Given that a natural timescale for departure from flatness might be the, 10 −43 seconds, the fact that the universe has reached neither a nor a after billions of years requires an explanation. For instance, even at the relatively late age of a few minutes (the time of nucleosynthesis), the density of the universe must have been within one part in 10 14 of its critical value, or it would not exist as it does today. Ultimate fate of the universe. Main article:Before observations of dark energy, cosmologists considered two scenarios for the future of the universe. If the mass density of the universe were greater than the critical density, then the universe would reach a maximum size and then begin to collapse.

It would become denser and hotter again, ending with a state similar to that in which it started—a Big Crunch.Alternatively, if the density in the universe were equal to or below the critical density, the expansion would slow down but never stop. Star formation would cease with the consumption of interstellar gas in each galaxy; stars would burn out, leaving, and black holes. Collisions between these would result in mass accumulating into larger and larger black holes. The average temperature of the universe would very gradually asymptotically approach —a. Moreover, if protons are, then baryonic matter would disappear, leaving only radiation and black holes.

Eventually, black holes would evaporate by emitting. The of the universe would increase to the point where no organized form of energy could be extracted from it, a scenario known as heat death.Modern observations of accelerating expansion imply that more and more of the currently visible universe will pass beyond our and out of contact with us. The eventual result is not known. The ΛCDM model of the universe contains dark energy in the form of a cosmological constant.

This theory suggests that only gravitationally bound systems, such as galaxies, will remain together, and they too will be subject to heat death as the universe expands and cools. Other explanations of dark energy, called theories, suggest that ultimately galaxy clusters, stars, planets, atoms, nuclei, and matter itself will be torn apart by the ever-increasing expansion in a so-called. MisconceptionsOne of the common misconceptions about the Big Bang model is that it fully explains the. However, the Big Bang model does not describe how energy, time, and space was caused, but rather it describes the emergence of the present universe from an ultra-dense and high-temperature initial state. It is misleading to visualize the Big Bang by comparing its size to everyday objects.

When the size of the universe at Big Bang is described, it refers to the size of the observable universe, and not the entire universe.Hubble's law predicts that galaxies that are beyond Hubble distance recede faster than the speed of light. However, special relativity does not apply beyond motion through space. Hubble's law describes velocity that results from expansion of space, rather than through space.Astronomers often refer to the cosmological redshift as a Doppler shift which can lead to a misconception. Although similar, the cosmological redshift is not identical to the classically derived Doppler redshift because most elementary derivations of the Doppler redshift do not accommodate the expansion of space. Accurate derivation of the cosmological redshift requires the use of general relativity, and while a treatment using simpler Doppler effect arguments gives nearly identical results for nearby galaxies, interpreting the redshift of more distant galaxies as due to the simplest Doppler redshift treatments can cause confusion.

Pre–Big Bang cosmology. Detailed information of and references for tests of general relativity are given in the article. There is no consensus about how long the Big Bang phase lasted. For some writers, this denotes only the initial singularity, for others the whole history of the universe. Usually, at least the first few minutes (during which helium is synthesized) are said to occur 'during the Big Bang'. It is commonly reported that Hoyle intended this to be pejorative.

However, Hoyle later denied that, saying that it was just a striking image meant to emphasize the difference between the two theories for radio listeners. Strictly, dark energy in the form of a cosmological constant drives the universe towards a flat state; however, our universe remained close to flat for several billion years before the dark energy density became significant.References. For an annotated list of textbooks and monographs, see.; (August 1988). 'Reflections on Early Work on 'Big Bang' Cosmology'.

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Retrieved 23 December 2019.; Boslough, John (1996). New York:. Riordan, Michael; (May 2006). Vol. 294 no. 5. (PDF) from the original on 30 November 2014. (1993) Originally published 1977. (Updated ed.).

New York:. 1st edition is available from the. Retrieved 23 December 2019.External links.