Physical cosmology

Cosmology (from the Greek κοσμολογία - here: " the doctrine of the world " ) deals with the origin, development and the fundamental structure of the universe ( cosmos ) as a whole and is a branch of astronomy, which is closely related to astrophysics.

The cosmology describes the universe by physical laws. It is particularly observed today, uneven distribution of galaxies and clusters of galaxies in the vicinity of the otherwise spatially, but not temporally homogeneous and isotropic, expanding universe to understand. The significant clustering, with large intervening empty spaces ( voids), means that one speaks of a " lumpy " universe. The largest ever discovered structure, the Sloan Great Wall, is about 1.37 billion light years long.

Furthermore, the cosmology has the total existing flatness ( Euclidean space ), the time- varying structures (radiation, quasars, galaxies), the cosmic background radiation, which interpreted as an expansion of the universe redshift of light, the numerical values ​​of the constants of nature and the frequency of the chemical elements recapulated in the universe.

Standard Model

The standard Big Bang model or sees the beginning of the universe in an almost point-like state from which it evolved into a big bang expansion called for today observable cosmos. The standard model is compatible with the general theory of relativity. It is confirmed by three observations:

According to the standard model of cosmology results in roughly the following sequence:

  • Planck era; to 10 - 43s; all four forces are still united;
  • Inflationary phase; ending after 10 - 33s to 10 - 30s; extreme expansion by a factor of 1030-1050;
  • Quark era; to 10 - 7s; are formed quarks, leptons and photons; the imbalance of matter and antimatter created in the baryogenesis;
  • Hadron era; to 10 - 4s; Protons, neutrons and their antiparticles arise; also muons, electrons, positrons, neutrinos and photons;
  • Lepton era; to 10 s; Muons decay, electrons and positrons are annihilated;
  • Primordial nucleosynthesis; to 3 min; Hydrogen, helium, lithium arise;
  • Radiation era; about 300,000 years;
  • Matter era; to this day; Universe becomes transparent arise galaxies.

Important tools for the exploration of the universe are now carried by satellites and space probes: The Hubble Space Telescope, ROSAT, Hipparcos and WMAP.

To explain the observed expansion and the flat geometry of the universe in the large the Big Bang model is now complemented by ideas of Alan Guth that it came through a symmetry breaking in the early universe to a very strong short-term expansion, which the uniformity of the universe and at the edge the observable range ( horizon ) is explained.

The biggest challenge to the cosmological theory is today but probably the mismatch between observable matter and its distribution and the observed mean velocity of propagation of the universe represents the usual explanation makes for unobservable by means of electromagnetic radiation components of the required matter density of dark matter (about 23 %) and dark energy (about 73 % ) is responsible. Their exact composition, however, is open today. However, it is often assumed that it is independent of the cosmology postulated by physicists elementary supersymmetric partners of already known elementary particles in the dark matter. If there is this, they are likely to eventually be proven beyond a doubt due to the expected energy levels and the available particle within the next 5 to 10 years. Alternatively, a change in the Einstein field equations have been proposed.

Steady State Theory

The steady-state theory ( stationary behavior, such as " uniform expansion ") was developed in 1949 by Fred Hoyle, Thomas Gold and others as an alternative to the Big Bang theory. During the 1950s and into the 1960s, this theory has been accepted by most cosmologists as a possible alternative.

The ' steady state theory ' has been postulated on the basis of calculations that showed that a purely static universe with the assumptions of the general theory of relativity would not be tolerated. In addition, observations of Edwin Hubble showed that the universe is expanding. The theory postulates now that the universe does not change its appearance, although it is larger. For this matter must constantly be re- formed to keep the average density equal. Since the amount of newly formed matter is very small ( only a few hundred hydrogen atoms per year in the Milky Way ), the formation of new matter can not be observed directly. Although this theory violates the conservation of energy, she had, among other things, the attractive feature that the universe has no beginning and ask for the before and after due to the commencement of the expansion are superfluous.

The difficulties of this theory began in the late 1960s. Observations showed that the universe is temporally actually changed, the stationarity condition is thus explicitly violated: quasars and radio galaxies were found only in distant galaxies. Halton Arp interpreted the available data since the 1960s differently and stated that there would be quasars in the nearby Virgo cluster. The decline of the steady-state theory has been accelerated by the discovery of the cosmic background radiation, which was predicted by the Big Bang theory.

Since then, not the steady-state theory, but the big bang theory is true in the majority of astronomers as a successful standard model of cosmology. In most publications on astrophysics it is implicitly assumed.

History of Cosmology

Beginnings and Ptolemaic world view

Records of mythical cosmologies are from China ( I Ching, Book of Changes ), from Babylon ( Enuma Elish ) and Greece ( Theogony of Hesiod ) is known. Cosmological ideas had in Chinese culture, especially in Taoism and Neo-Confucianism a high priority. The Babylonian myths - which probably go back to older Sumerian myths and in turn are likely to be a template for the biblical Genesis again - and sky observations have probably influenced the later Greek cosmological ideas, which became the basis of medieval Western cosmology. - Cosmological recordings were made not only from the Babylonian, but also by the Egyptian priesthood. In the Pyramid Texts the world of the gods is associated with cosmic beings in connection which are mainly related to the sun, but also to the moon and numerous stars. It is therefore also an astronomical background clearly. This is also evident from the relief of the Code of Hammurabi, which shows the cosmopolitan -minded king before the enthroned sun god.

Earlier cosmologies were subject to the principle of recording astronomical data and subsequent interpretation of the data. From the interpretations and prophecies, the mythologies developed. In addition, provided the astronomical records useful information for the past calendar represents, for example, Ur - 3 calendar, by which the processes were arranged in agriculture. The Greek scholar Thales of Miletus, but especially in Anaximander ( 6th century BC), the process of rationalization began. Anaximander first time designed a world view, which was based on legitimate causal relationships and objects in the sky then assigned a physical nature. According to Anaximander the infinite universe is the source of an infinite number of worlds of which our world is only one that had split off and did their parts collected by rotation. In the same vein, the cosmological drafts of the atomists Democritus and Anaxagoras went.

The ideas of Anaximander Anaximenes worked out further and looked at the air as primordial matter. Pythagoras - were for whom are all things, in fact numbers or numerical relationships - took the view that the sky had inhaled the infinite, to form groups of numbers.

Another important development was the first historically traditional system in which the earth was not the center, which was designed by Philolaus, a Pythagorean, in the 5th century BC.

In the cosmology of Plato (5th / 4th century BC), which he describes in the Timaeus, he described the celestial objects than personal, equipped with intellect divine beings. The earth was in Plato's idea a ball that rested in the center of the cosmos.

Plato's pupil Aristotle disagreed in his cosmology partially considers his teacher regarding the divine nature of celestial objects. The heavenly bodies, he also called divine and gifted with intellect; they consist of the " fifth element " and be explored by the " first philosophy." The movements of the heavenly bodies and spheres are ultimately caused by a first unmoved mover (in the sense of modifiers ). Aristotle advocated a model of the universe, which assumed a central fire ( he meant explicitly not the sun ), to which the celestial bodies ran in circles.

Eudoxus of Knidos designed beginning of the 4th century BC, a sphere model, which was further developed by Callippus and could describe the retrograde loop motions of the planets for the first time and influenced the both Aristotle and the Ptolemaic worldview. Measurements of Eratosthenes, the BC the circumference of the Earth particular in the 3rd century with good accuracy, and also of Aristyllus and Timocharis however, showed variations of planetary motions of the calculated according to Eudoxus ' method positions. Apollonius of Perga developed in the 3rd century BC a method of calculating the orbits of planets using epicycles, that is, he made circular motions of the planets, the center of which was itself again on a circular path.

A heliocentric model represented Aristarchus of Samos (3rd / 2nd Century BC). He was therefore accused of impiety; his model of the world could not prevail.

Ptolemy described in the 2nd century in his Almagest a geocentric cosmology, which was to bring with most observations of his time in line and was generally accepted until the enforcement of the Copernican worldview.

The Copernican Revolution

Already in the 15th century were by the German polymath and Cardinal Nicholas of Cusa ( 1401-1464 ) anticipated important ideas for his cosmology and made the Ptolemaic world view in question by rejecting the idea of ​​a limited universe, in the center of which the immovable earth is located. In contrast, the universe described by Copernicus in 1543 in his De revolutionibus orbium Coelestium was limited and finally by a material sphere of fixed stars. This, however, was too large to explain the lack of stellar parallax by Copernicus ' ideas. Important to the Copernican system was the loss of the special position of the earth and the introduction of a heliocentric universe with circular orbits of the planets around the sun. Only Thomas Digges ( 1576, A Perfit Description of the Caelestiall Orbes ) represented a modified Copernican world view without material sphere of fixed stars with infinite Euclidean space. Also of Giordano Bruno (1548-1600) an infinite universe with an infinite number of suns and planets has been proposed in which the fixed stars are distant suns observed. Because of this and other statements that contradicted the Catholic beliefs, he was condemned as a heretic and put to death at the stake.

Other important reasons for the rejection of the Ptolemaic world view were observed by Tycho Brahe supernova of 1572 and his evidence that a comet observed in 1577 was located outside the moon's orbit, making the sky as described by Aristotle, was not immutable. Tycho Brahe increased the precision of the planetary observation considerably. His assistant Johannes Kepler realized after his death in the analysis of observational data that the planetary orbits are not as assumed by Copernicus circular, but elliptical. He formulated the laws of planetary motion, which are now known as the Kepler 's laws. Kepler tried to explain planetary motion by a magnetic force. He turned so that a mechanistic picture of planetary motion to where the planets were not more animated as in Ptolemy. However, Kepler believed in a finite universe, and tried to show this by arguments which were later known as olberssches paradox. The Copernican system was supported also by Galileo's discovery of Jupiter's moons, the observation of the lunar surface and its proof that the fixed stars are seemingly point-like.

By Isaac Newton ( Philosophiae Naturalis Principia Mathematica, 1687 ) were with his theory of gravitation and cosmology, the mechanics for the first time linked. This brought a Newton physics to cosmology, in which the same laws for celestial ( planetary motion ) and terrestrial areas (gravity) were considered. Only by the Newtonian mechanics the Copernican system was compared with the Ptolemaic system excellent, as the common center of gravity, not exactly located in the center of the Sun, but still within the sun. An important step in this development was the previous development of mechanics, in particular the concept of inertia ( Galileo, Descartes ).

Thomas Wright did not stop the sun for the center of the universe, but for a fixed star among many. He rejected the assumption of a homogeneous distribution of stars and the Milky Way identified as consisting of individual stars disc in the plane of the Sun is. He also looked at the fog observed by astronomers as other galaxies. Immanuel Kant developed in 1755 in the Universal Natural History and Theory of Heaven not only a cosmology similar to that of Thomas Wright, but also a cosmogony in which an initially chaotic distributed matter is highly concentrated under gravitational effect to the observed celestial bodies. A similar development scheme was developed by Laplace. Also, the astronomer William Herschel tried to derive by classifying stars and galaxies a chronological development scheme.

Of gods and myth to science

The transitions from philosophy to science were made depending on the different attitude to metaphysics. However, the cosmos has also been used in philosophy as the model and example to show the people a reasonable course of action. The harmonious order of the universe was an example for Greek philosophy and served as both the ideal of a contemplative life and in particular also the ideal of scientific setting, the BIOS theoretikos. This cosmic order could be adapted by mimesis, see also originating from Greek antiquity the liberal arts. The forces that were conceived in the Greek cosmological tradition as gods and superhuman powers, has the philosophy later viewed as forces of the soul. Hence the connection and sometimes equating astronomy and astrology stirred until the late Middle Ages and beyond, until the 18th century. Hannah Arendt sees still in watches parable of a similar world view, which tends to subject- object split due to imperfect knowledge of nature. Corresponding mystification then explain the attempt to overcome this split and cause the " objectivist bill " criticized by Jürgen Habermas. Cosmos as a Greek word that means something like jewelry, ornament, order, organization, institution, type world order and space, on the one hand and on the other hand has aesthetic technical and practical aspects. This term conveys the right for Greek ideals of employment with the beautiful frame concept that lay behind the old ontology based and a kind of sacred attitude included. This is followed also like the following Kantian build " decision ":

" Two things fill the mind with ever new and increasing admiration and awe, the oftener and more steadily we reflect busy. The starry heavens above me and the moral law within me "

Copernican, and Cosmological Anthropic Principle

The assumption of an essentially homogenous cosmos was later called to Copernicus ' honor " Copernican principle ". The specific additional requirement of isotropy leads to the cosmological principle.

There are a number of possible theories of universe. The anthropic principle states that a theory must not stand in contradiction to that today exists Intelligent Human Life. You must ensure the appropriate development conditions and living conditions, otherwise it is false.

Problem: Loss of information

The standard theory is essentially dependent on information gained from the universe itself ( existence of other galaxies, redshift, background radiation, chemical abundances, etc.). This information is lost as the expansion of the universe over time.

  • It forms an ever- extended event horizon, however in comparison to the expansion of the universe is getting smaller. Objects beyond which, for example, other galaxies, the escape observation.
  • The cosmic background radiation is always longwave. At a wavelength of 300 km, it is no longer able to penetrate into the Milky Way, it is reflected by the dust.
  • Through the nucleosynthesis in stars the traces of primordial nucleosynthesis are becoming more blurred. The proportion of helium in the universe ( primordial ) to 28% (today) to rise ( in a trillion years ) from 24% to 60 %.
  • Milky Way, Andromeda Galaxy and some smaller nearby galaxies will unite into a single super star clusters.

All of this means that there is already looks like in 100 billion years for an observer in this super star clusters, as this would represent the entire universe. Also, no more conclusions can be drawn on the Big Bang. Astronomers who live then possibly would, therefore an entirely different picture of the structure and evolution of the universe get as living today.

This has also led to the question of how such information loss has already occurred under certain circumstances, and thus also to the question of the reliability of cosmological theories.

After all, it has already given the inflationary phase of such a loss of information. Due to the inflation of the universe wide ranges have been moved beyond the observable.

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