Big Bang

The Big Bang ( pronunciation: [ ʔu ː ɐ̯ ˌ knal ], from ur " first " and pop ) is in modern cosmology of the early universe. As part of the Big Bang theory and the early universe is described, that is, the temporal evolution of the universe after the Big Bang. It occurred after the standard cosmological model ( Lambda - CDM model ) prior to about 13.8 billion years ago.

The big bang does not refer to an existing explosion in space, but the joint creation of matter, space and time from an initial singularity. Since no consistent theory of quantum gravity exists, there is in today's physics is no generally accepted theory for the state of the universe at very early times when the density of the Planck density corresponded. Therefore, the term " Big Bang " is the name of a formal point, which is reached by considering the cosmological model of an expanding universe beyond the scope of the underlying theory of general relativity beyond.

As the founder of the Big Bang theory is the theologian and physicist Georges Lemaître, who for the hot initial state of the universe, the term " primordial atom" or " primeval atom ", and later " cosmic egg " as used in 1931. The term Big Bang (English big bang, literally so, Big bang ') was coined by Sir Fred Hoyle, who wanted to appear credible as a critic and representatives of the competing steady-state theory this theory. The steady-state theory lost in the 1960s to consent, as astronomical observations are increasingly confirmed the Big Bang theory, and is now studied only by a minority of cosmologists.

3.1 Unified Field Theories
3.2 Inflation Theory

4.1 Primordial nucleosynthesis
4.2 Strongly Coupled Plasma
4.3 Radiation and matter era era

5.1 Expansion of the Universe
5.2 Frequency of the elements
5.3 Cosmic Background Radiation
5.4 formation of large-scale structures

6.1 Branenkosmologie
6.2 Loop Quantum Cosmology
6.3 Chaotic inflation

Survey

The term Big Bang to the starting point of the creation of matter and space-time is meant. Such a start is determined by cosmological theories, according to which the universe is expanding permanently. This observed by astronomers expansion of the universe has led to the concept of the Big Bang: The observed movement apart of the galaxies results in back-calculated a time at which they were concentrated in a narrow region of space. At the time of the Big Bang the energy density is formally infinite. Since physical theories presuppose the existence of space, time and matter, the actual big bang is impossible to describe them. The quantum field theory and general relativity have additional requirements that were not met immediately after the Big Bang. They are therefore suitable only for a description from a date to the back of the big bang is clearly more than one Planck time (about 5.391 · 10-44 seconds).

The main common characteristics and predictions of the Big Bang theories arising from the consideration of the first 300,000 years of evolution of the universe. In this article, therefore, the evolution of the early universe is described which leads to the main forecasts.

Basic assumptions

The Big Bang theories are based on two basic assumptions: The first assumption is that the laws of nature are universal and therefore can describe the universe with natural laws that apply close to Earth today. The second assumption is that the universe (but not at any time) looks at each place in all directions for great distances equal. This assumption is called the Copernican principle or cosmological principle. In the following these assumptions and basic conclusions are explained it.

Universality of the laws of nature

The adoption of universal laws of nature is essential for a description of the entire universe. All previous astronomical observations also point to a generality of the laws of nature.

From this universality of the laws of nature follows that can be described by the general theory of relativity evolution of the universe, which is currently the majority accepted theory of gravity and space-time. Here it is important to note that general relativity is incompatible with the theories of quantum physics. Since at very high matter density and thus very large spacetime curvature quantum effects are to be expected, therefore, the description of the early universe is subject to restrictions. The point of the Big Bang itself, and a very short subsequent period of one Planck time is with the current theories can not be written, and the term " Big Bang " can be understood as a label for this misunderstood part.

Cosmological principle

The cosmological principle states that the universe at the same time at any point in space and in all directions for great distances looks the same, and will also (spatial ) called homogeneity; the assumption that it look the same in each direction, ie (spatial ) isotropy. A view of the starry sky with the naked eye immediately shows that the universe is in the vicinity of the Earth is not homogeneous and isotropic, because there are irregularly distributed stars. On larger scale form the star galaxies, but these are also very unevenly distributed and form clusters of galaxies. On even greater scale, a honeycomb structure can be seen, which consists of so-called filaments and voids.

Turning to the cosmological principle on the general theory of relativity, the Einstein field equations simplify to the so-called Friedmann equations. The Friedmann equations describe therefore a homogeneous, isotropic universe. To solve the equations one goes out from the present state of the universe and followed the development backwards in time. The exact solution depends in particular on the measured values of the Hubble constant and density of various parameters that describe the mass and energy content of the universe. One finds then that the universe was once smaller ( expansion of the universe ); at the same time it was hotter and denser. Formally, the solution transferred to a time at which the value of the scale factor disappears, so the universe had no expansion and the temperature and density are infinitely large. This time is referred to as the " Big Bang ". It is a formal singularity of the solution of the Friedmann equations. This, however, no statement about the physical reality of such a singularity is made, since the equations of classical physics have only a limited scope and are no longer applicable when quantum effects play a role, as in the very early, hot and dense universe is assumed. To describe the evolution of the universe at very early times, a theory of quantum gravity is required.

The Early Universe

According to the Friedmann equations, the energy density of the universe was very high in its early phase. This means that the energies of the particles in the medium were very high. The very early phase of the universe is therefore the subject of theories that can not be verified with laboratory experiments.

Unified field theories

The beginning of recordable with the general theory of relativity, the universe follows the date on which the gravity separates from the other fundamental forces in the framework of a theory of a single elemental force. The properties of such a primal force and a universe that is dominated by such a, are unknown. Such a primal force model goes well beyond a theory of quantum gravity out, and do not currently given the existence of a generally accepted theory of quantum gravity can therefore be considered as a basis for the development of such a theory. In the context of string theory, it is hoped to develop a universal theory which would include a quantum gravity as well as theories of all fundamental forces. Whether and in what sense in such a theory, all four fundamental forces were unified, is unclear.

The other three fundamental forces, the strong nuclear force, weak nuclear force and the electromagnetic force are described in the framework of quantum field theory. Possible unified theories can therefore develop on the basis of existing theories. However, current experiments are not sufficient to test such theories sufficient. Due to the fact that there is a unified electroweak interaction, however, and suspect due to other theoretical arguments, many physicists that such a large unified theory (GUT: Grand Unified Theory ) exists.

The high temperature of the early universe had the consequence that different types of particles are constantly transformed into each other. At sufficiently high temperature, these conversion reactions occur with equal frequency from both directions, so that sets a thermal equilibrium. By the expansion of the universe, the temperature decreases with time; This leads to various reactions " freeze " when the temperature falls below a certain, characteristic for each reaction threshold. This means that the reaction in only one, namely ( after chemical parlance) " exothermic " direction runs, while the endothermic reverse reaction lacking the necessary energy. This leads gradually to the extinction of species of particles of high mass. Applied to a large unified interaction that would mean that in the very early phase of the universe unknown particles with a very large mass existed, which were divided into known lighter particles, which then " fused" to the heavy particles. Only when the average particle energy was decreased below the mass energy of the unknown heavy particles, they could not be produced by fusion of lighter particles and " died out ". The below this temperature limit and the associated extinction of massive particles is interpreted as spontaneous symmetry breaking.

There is in the universe observed asymmetry between matter and antimatter, ie while there are obviously matter very little anti-matter exists in the universe. Since the known interactions produce equal amounts of matter and antimatter, the well-known theories provide no explanation for this phenomenon (as of 2011 ). One potential explanation model provide the Sacharowkriterien that can be most easily satisfied by a CP violation in a GUT. Due to the freezing of reactions that do not receive the baryon number, can then end of the GUT era a small excess of matter compared to antimatter created, which forms the present-day, almost entirely composed of matter world after the matter -antimatter annihilation ( compare also to baryogenesis and leptogenesis ).

Inflation theory

According to the standard model of cosmology the Planck era was followed by an epoch in which the universe expanded very rapidly exponentially. During this so-called inflation, the universe expanded within 10-33 s to 10-30 s by a factor of 1030-1050. This superluminal expansion of the universe does not contradict the theory of relativity, since these do not, however, prohibits only a superluminal motion in space, a superluminal expansion of space itself. The area corresponding to the observable universe would now, according to the theory this must expand from a diameter which is less than the wide of a proton, to about 10 cm.

The exact details of inflation are unknown, but the measurements of the temperature fluctuations of the cosmic background radiation are by the WMAP satellite as a strong indication that inflation has occurred with certain properties. By means of the measurement results of the Planck space telescope, it could be possible to gain more detailed knowledge about the inflation epoch.

There are a number of models for the description of inflation. The most widely used models are one or more scalar fields which are referred to as Inflatonfelder, as a cause of the rapid expansion. Also unclear is the cause for the end of inflation. A possible explanation to slow roll models offer, in which the Inflatonfeld reached an energetic minimum and inflation therefore ends; and GUT models in which the end of inflation is explained by breaking of the GUT symmetry due to the cooling of the universe, and thus triggered disintegration of Inflatonfeldes. Due to the enormous expansion of the universe, this would have to cool down well below 1 K, so all endothermic particle reactions would have come to a standstill. Therefore, a " reheating " is believed process called at the end of the inflation phase of these large energies would have by the breaking of the GUT symmetry and the associated particle decay can deliver.

A period of inflation can explain several cosmological observations:

The global homogeneity of the cosmos ( the horizon problem)
The slight curvature of space ( flatness problem)
The fact that no magnetic monopoles are observed,
The large scale structure in the universe such as galaxies and clusters of galaxies,
The above-mentioned range of temperature fluctuations in the cosmic background radiation.

Evolution of the Universe

The period after the inflation and speculative refraction of a possible GUT symmetry, and the electroweak symmetry can be described by the known physical theories. The behavior of the universe at this stage is relatively largely determined by observations and differs for the various Big Bang models barely.

Primordial nucleosynthesis

As primordial nucleosynthesis, the formation of nuclei in the early universe is called. After the end of inflation, ie after about 10-30 s, the temperature dropped to 1025 K. It formed quarks and anti - quarks, the building blocks of today's heavy particles ( baryogenesis ). However, the temperature was so high and the time between two particle collisions so short that no stable protons or neutrons formed, but a so-called quark- gluon plasma from nearly free particles originated. The time to the formation of stable hadrons is also called quark era.

After 10-6 s, a temperature of 1013 K was present. Quarks could no longer exist as free particles, but united to hadrons, the building blocks of atomic nuclei. After 10-4 s, the temperature had dropped to 1012 K, so that no proton -antiproton or neutron Antineutron pairs were no longer formed. Most protons and neutrons were destroyed in collisions with their antiparticles - except for a small excess of one billionth. The density decreased to 1013 g/cm3. With decreasing temperature, crumbled the heavier hadrons and it eventually remained protons and neutrons and their antiparticles. Due to continuous transformations of protons into neutrons and vice versa, a large number of neutrinos created. In this so-called hadron era, there were the same number of protons as neutrons, since they could be transformed into each other. After 1 s, a temperature of 1010 K was reached. From this temperature could not be converted into neutrons protons.

Only after 10 seconds, at temperatures below 109 K, protons and neutrons combined by fusion to the first deuterium nuclei. These were converted for the most part in helium 4 nuclei. After about 3 minutes, the temperature and density of matter was removed to the extent that the nuclear fusion came to a standstill. The remaining free neutrons were not stable and disintegrate over the next few minutes into protons and electrons. Overall, formed in the first three minutes to 25 % helium -4 ( 4He ) and 0.001% deuterium and traces of helium -3 ( 3He), lithium and beryllium. The remaining 75 % presented protons subsequent hydrogen atom nuclei.

All heavier elements arose later inside stars. The temperature was still so high that the matter was present as plasma, a mixture of free atomic nuclei, protons and electrons with thermal radiation in the X-ray range.

Strongly Coupled Plasma

For neutrinos hardly interact with other particles, the density was low enough after 10-4 s - they were no longer in thermal equilibrium with the other particles, that is, they decoupled. After 1 s, a temperature of 1010 K was reached. Now destroyed and electrons and positrons - up on the surplus of a billionth of electrons. This was the formation of the building blocks of matter, from which the cosmos is still composed largely completed. The universe was now filled with a strongly interacting plasma of electrons, photons ( " particles of light " ) and atomic nuclei, mainly protons. In addition, there were neutrinos interacted mainly by gravity with the hot plasma. It is also assumed in the framework of the standard cosmological model, that there is also a large amount of dark matter was that also interacted only by gravity with the plasma.

It took about 400,000 years, until the temperature had dropped sufficiently that formed stable atoms and light could travel great distances without being absorbed. The mean free path of photons grew extreme, so the universe became transparent, more specifically took its optical density decreases very rapidly. This decoupling of light lasted about 100,000 years. During this period, some regions of the universe were already cooled down, that they were transparent, while in other regions predominated still hot plasma. There was at the time of decoupling much more photons than protons in the universe, the temperature of the universe was significantly lower than the ionization energy of the hydrogen, with the Boltzmann constant, namely at approximately, which corresponds to a temperature of about 4000 K. This means that the maximum of the radiation intensity at that time was in the visible spectrum. This radiation can be measured as cosmic background radiation today. However, it is due to the cosmological redshift is now much longer wavelength microwave radiation and corresponds to a temperature of 2.73 K.

The dynamics of the plasma is crucial for the development of the temperature fluctuations of the background radiation and the formation of structures of matter. The behavior of the plasma-filled universe can be described in the context of cosmological perturbation theory by means of the Boltzmann equation. Thus, certain basic characteristics of the spectrum of the temperature fluctuations can be explained. In particular it is in the plasma to pressure waves, so to speak, the sound waves that cause certain characteristic peaks in the range of temperature fluctuations. Could be measured that these peaks from the WMAP satellite with great accuracy, is a supportive evidence for these theories. The emergence of large-scale structures is qualitatively explained by the fact that dark matter accumulates in places where the plasma is denser and thus density imbalances so reinforced that the matter finally accumulated almost exclusively in relatively small areas of the universe.

Radiation and matter era era

The Friedmann equations are based on the model of perfect fluid matter. In this model, the material is described by two state variables, namely the energy density and pressure. The relationship between power and pressure is described by a state equation. The main cases for usual models of the universe with radiation, solid particles, often referred to as " dust," and with a cosmological constant with. For the different types of matter, the dependence of the energy density of the scale factor is very different, namely. The different time dependence in radiation and massive particles can also be understood clearly; in radiation decreases addition to dropping the number density of photons to the wavelength of the single photon by the cosmological redshift (due to the expansion of space ). This ensures that the energy density of radiation decreases more rapidly than that of the solid matter, so that a universe was radiation dominated at the beginning, is dominated by massive particles after some time, until at last would prevail a possible cosmological constant.

According to the Big Bang model, presented (electromagnetic ) radiation after inflation the majority of the energy density in the universe. At a time of about 70,000 years after the Big Bang were the energy densities of radiation and matter equal, then determined the massive matter, the dynamics of the universe. One speaks of the end of the radiation- dominated era and the beginning of the matter-dominated era.

Predictions of the big bang models

The Big Bang models with the characteristics described above are the most recognized models to explain the present state of the universe. The reason for this is that they make some of the key predictions that coincide well with the observed state of the universe. The main predictions are the expansion of the universe, the cosmic background radiation and the element distribution, in particular the proportion of helium in the total mass of the atoms. The main features of the temperature fluctuations of the cosmic background radiation are explained very successful in the context of the Big Bang cosmological models using perturbation theory. The theory of the temperature fluctuations also provides a model for the development of large-scale structures, namely of the filaments and voids that form the honeycomb structure described above.

Expansion of the universe

The expansion of the universe was observed in 1929 by Edwin Hubble first time. He discovered that the distance of galaxies of the Milky Way and its redshift are proportional. The red shift is explained by the fact that the galaxy from the observer to remove, so Hubble postulated an underlying proportionality between distance and recession velocity. It was at least since the work of Georges Lemaître in 1927 known that such proportionality of the Friedmann equations, it follows that also include the Big Bang. This observation was thus the first confirmation of the big bang models. Today, the Hubble law is well confirmed by measurements on a large number of galaxies. However, an approximate proportionality applies, as predicted by the Friedmann equations for a universe with solid matter, only for relatively nearby galaxies. However, very distant galaxies have escape velocities that are greater than would be expected in a matter-dominated universe. This is interpreted as an indication of a cosmological constant or dark energy.

Frequency of the elements

Most of the light atomic nuclei created in the first minutes of the universe during the Big Bang Nucleosynthesis. The description of this process in the context of the Big Bang model goes back to Ralph Alpher and George Gamow, Alpher - Bethe developed the - Gamow theory. In particular, the mass fraction of helium of about 25 % of ordinary matter (without dark matter ) is predicted by the Big Bang models consistently in very good agreement with the observed frequency. By measuring the frequency of rare nuclei such as deuterium, helium -3 and lithium -7 can be concluded that the density of ordinary matter in the universe. The measured frequencies of these elements is consistent within the existing models with one another and with other measurements of the material density.

Cosmic Background Radiation

The cosmic background radiation was predicted by Ralph Alpher, Robert Herman and George Gamow in 1948. They said subsequently various temperatures in the range of about 5 to 50 K before. It was not until 1964, the background radiation by Arno Penzias and Robert Woodrow Wilson was first identified as a real effect, having previously held several astronomers had measurements of the signal for antenna errors. The measured temperature is specified at 3 K, current measurements yield a temperature of 2,725 K. The background radiation is isotropic to a good approximation, that is, it has matching in each direction, temperature and intensity. Variations in the amount of 1% result from the Doppler effect due to the motion of the earth. The Milky Way is visible as a distinct disorder.

Rainer Kurt Sachs and Arthur Michael Wolfe said 1967 before that there were very small temperature fluctuations in the background radiation. The predicted effect of them was named in her honor Sachs - Wolfe effect. In 1993, the COBE satellite actually discovered fluctuations of 0.001 % in the temperature of the background radiation, the satellite WMAP this observation, as well as the Sachs - Wolfe effect confirmed. Other important characteristics of the spectrum of Temperaturanisotropien are the Silk damping and baryonic acoustic oscillations.

Formation of large-scale structures

By decoupling the radiation, the matter became stronger now under the influence of gravity. Inspired by the surrounding density fluctuations that may have occurred already in the inflationary phase by quantum fluctuations, large-scale structures formed after 1 million years in the cosmos. The matter began in the space areas with higher mass density as a result of gravitational instability and collapse to form mass aggregations. It formed first so-called dark matter halos, which acted as a gravitational sink, where later the visible matter collected for us. The radiation pressure underlying baryonic matter had sufficient density to clump together without the help of the dark matter so early large-scale structure that the resulting temperature variations can still be observed in the background radiation today. Without dark matter would be the emergence of large-scale structures, such as the honeycomb structure of voids and filaments, as well as the emergence of more smaller structures, such as galaxies, last much longer than the age of the universe, that results from the Big Bang models.

To study the properties of dark matter was tried to reproduce by simulation the process of structure formation. Various scenarios have been played out, and some could be ruled out with the help of such simulations as totally unrealistic. Today appear to be realistic so-called CDM scenarios, where this is the cosmological constant of Einstein's field equations, and CDM for cold dark matter (English: cold dark matter ) is. What type of particle is the dark matter that is currently (2011) still unknown.

The collapsing gas clouds had become compacted to the extent that the first stars formed. These were much more massive than our sun, so they were very hot and high pressures formed. As a result, heavier elements such as carbon, oxygen, and iron have been produced by nuclear fusion. Because of their large mass, the lifetime of these stars with 3-10 million years ago was relatively short, they exploded in a supernova. While the explosion of elements heavier than iron were formed by neutron capture (eg, uranium) and came into the interstellar space. The explosion pressure compressed adjacent gas clouds which thus could quickly produce new stars. Since the enriched metals gas clouds auskühlten faster incurred lower mass and smaller stars with weaker luminosity, but of longer life.

There were the first globular clusters from these stars, and finally the first galaxies from their precursors.

Further models

There are different models that match from a period of about 10 - 30s with the big bang models and aim to explain the very early universe without singularities. Such models can make in some cases, additional predictions compared to the usual big-bang models, or slight variations in the predictions, provided that these deviations are not refuted by the measurement accuracy. Such models are usually associated with the theories of quantum gravity and loop quantum gravity (loop quantum gravity ) as loop quantum cosmology.

Branenkosmologie

The Branenkosmologie is a theory which is closely related to string theory and concepts of this theory used. Models of Branenkosmologie describe a minimum five-dimensional space-time, in which the four-dimensional space-time as a " brane " (the word is derived from " membrane " ) is embedded. The modern treatment of this theory came from the 1999 Randall - Sundrum model developed. In this one Brane to model the observable universe. It provides a model of explanation for why gravity is much weaker than the other fundamental forces, but does not describe evolution of the universe. It contains no expansion of the universe and therefore neither redshift nor background radiation. It is therefore not a realistic model of the observable universe.

An advanced model of Branenkosmologie is the cyclic ekpyrotische Universe by Paul Steinhardt and Neil Turok, which is also based on the string theory and was developed in 2002. In this model, two four-dimensional branes collide in a five-dimensional space-time periodically, producing each time a state as he reigned after the Big Bang model in the very early universe. In particular, they form an alternative to inflation theory by measuring accuracy, in the context of today (2011 ) the same predictions. However, the ekpyrotische model makes different predictions about the polarization of the fluctuations of the background radiation, thus it is by future measurements, in principle, possible to falsify one of the two models.

Loop Quantum Cosmology

The Loop Quantum Cosmology is a theory that has evolved out of the loop quantum gravity ( including by Martin Bojowald ). Since in this theory the cosmological principle is taken for adoption, is not yet clear to what extent it is even compatible with the loop quantum gravity. The Loop Quantum Cosmology is an explanation for the cosmic inflation and the Big Bounce offers a cosmological model without big bang singularity. In this model, a predecessor universe collapses in a big crunch, but ensure the effects of quantum gravity that it does not collapse to a singularity, but only up to a maximum density. Then resumes expansion, stating the universe today. This model is currently (2011 ) Subjects of research and many questions are still unresolved. Among other things, it is not clear whether the history of the cyclic universe in each run repeated or varied identical. A further development of the model results in a cyclic universe that expands forever in exchange up to a maximum extent and collapses to a minimal extent.

Chaotic inflation

The theory of chaotic inflation was proposed by Andrei Linde in 1986 and is not associated with a particular quantum gravity theory. It says that the majority of the universe expands forever inflationary and only within different bubbles, inflation comes to a halt, so as to form a plurality of sub- universes. According to the model, the quantum fluctuations of Inflatonfelds ensure that the majority of the universe is eternal in the inflationary phase. Non- inflationary bubbles arise when the quantum fluctuations of Inflatonfeldes be locally small. Although the probability for the formation of these bubbles is very high, the high rate of inflation ensures that they can very quickly become much smaller compared to the rest of the universe by colliding very rare and the majority of the universe is characterized by eternal inflation.

The various sub- universes may have different values of the constants of nature and therefore different physical laws, if there are multiple stable states of the field. The theory is sometimes construed as Multiversumstheorie (for example, Alexander Vilenkin ), as many universes exist part that never can come into contact with each other. The inflationary multiverse is also known as quantum foam, as it does not agree in its properties with the observable universe. So on the theory that it contains neither matter nor radiation, but only the Inflatonfeld.

History of Research

The prerequisite for modern cosmology and thus also of the Big Bang model is the 1915, published by Albert Einstein general theory of relativity. 1922 put Alexander Friedmann and his description of the expanding universe the foundation for the Big Bang models. Although Einstein recognized that his model was compatible with the field equations, his work was initially covert, because no astronomical observations on an expansion of the universe hindeuteten and therefore static cosmological models have been preferred. Georges Lemaître developed in 1927 Friedmann's model independent of this again and developed it to a first big bang theory further, according to which the universe is the product of a single particle, the " primeval atom ". He led as a result of expansion of the universe already a proportionality of distance and escape velocity stellar objects ago. However, this work has received little attention.

1929 Edwin Hubble discovered by distance measurements on Cepheids in galaxies outside the Milky Way, that the redshift of the galaxies is proportional to their distance. This finding, which is now known as Hubble's law, he explained by the Doppler effect as a result of expansion of the universe. Hubble confirmed so Lemaître's prediction, but it was not known this and he does not refer in his writings on it. 1935 proved Howard Percy Robertson and Arthur Geoffrey Walker finally that the Friedmann - Lemaître - Robertson -Walker metrics are independent of the matter model, the only metrics that are compatible with the cosmological principle.

Ralph Alpher developed in 1948, George Gamow and Robert Herman, a theory of the origin of the universe from a hot initial state. Under this theory, they said both the abundance of helium in the early universe and the existence of the cosmic background radiation with blackbody spectrum before. For today's temperature of the background radiation they gave various estimates within the range of 5 K to 50 K. Arno Penzias and Robert Woodrow Wilson discovered accidentally in 1964 the cosmic microwave background radiation. Since they measured only on two frequencies, they could not find that the radiation has a blackbody spectrum. This was confirmed by additional measurements in the following years and the temperature was measured at 3 K. 1967 said Rainer Kurt Sachs and Arthur Michael Wolfe temperature fluctuations of the cosmic background radiation before. This effect is called after them as Sachs - Wolfe effect.

To explain the extremely homogeneous and isotropic initial state of the observable universe, which is inferred from the isotropy of the cosmic background radiation, beat Roger Penrose 1979 Weylkrümmungshypothese ago. This hypothesis also provides an explanation for the origin of the second law of thermodynamics. As a competing hypothesis to explain the homogeneity and isotropy of the early universe and to solve the horizon problem Alan Guth in 1981 developed the theory of the inflationary universe, which postulates a period of very rapid expansion in the early universe. The theory of the inflationary universe was later developed by Andrei Linde and others and eventually was able to prevail as an explanatory model.

Valerie de Lapparent, Margaret Geller and John Huchra discovered in 1986, the arrangement of clusters of galaxies in wall-like structures, in turn, large-scale bubble-like voids ( voids) enclose. Through the COBE satellite (1989-1993) and WMAP (2001-2010) was measured the cosmic background radiation with considerable accuracy. The fluctuation of the background radiation has been detected and measured its spectrum, so that the prediction of Sachs and Wolfe was confirmed. The measurement results of these satellites in conjunction with distance measurements allowed a more accurate determination of cosmological parameters, the evidence for an accelerated expanding universe arise.

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