Cosmological
Cosmology is the branch of astrophysics that studies the universe as a physical system.
Since the eighteenth century , cosmology was emancipated from metaphysics and theology : the distinction between scientific cosmology, the purpose of this article, and religious cosmology is discussed in the next paragraph. Other paragraphs deal with the angle of modern scientific cosmology.
The concept of universe has evolved over the history. While the Earth was generally regarded as a fixed point (theory -centric , advocated among others by Aristotle and Ptolemy ), the Renaissance saw the emergence of the idea that our planet did not occupy a privileged position in the universe ( Copernican principle ) and certainly was not the center. It is from the seventeenth century that the first astronomical observation instruments were introduced ( astronomical telescope of Galileo and the telescope of Isaac Newton ), to survey the cosmos, and to consider its structure, then , from the twentieth century , its history and its evolution.
Summary |
Cosmologies scientific and religious cosmologies
Cosmologies are divided into two groups: there are scientific cosmologies of religious cosmologies.
Until we have evidence of optical orbiting Earth, the eighteenth century (with the discovery of the aberration of stars by James Bradley ), cosmology was still part of the metaphysical. In the classification of Christian Wolff ( 1729 ), was indeed one of the three disciplines of "special metaphysics" with the theology (God) and psychology (the mind).
By nature, scientific cosmologies are confronted with the scientific method , and are scaffolded so as to be the most satisfactory theory compatible with observations at a given time. The quality of the observations to be improving, the theories are regularly refined in order to take account of these, according to the scientific and technological progress. In some cases they may be abandoned in favor of other theories if the observations are impossible to reconcile with them. Major paradigm shifts are still relatively rare in the history of cosmology (abandoned in favor of the geocentric theory of the heliocentric theory, discovery of interstellar distance scales, the structure of the Milky Way , and the expansion of the universe ). Less drastic changes to a given theory are more frequent (additions of cosmic inflation , the dark matter and the dark energy in the standard model of cosmology , for example).
Religious cosmologies, in turn, are the result of the basic texts of a religion given. These cosmologies generally have a profound coherence with other fundamental principles of that religion, particularly the moral , the ethical and the metaphysical. The question of whether the universe is the result of a creation of God is the subject of further discussions. Religious cosmologies are not now claim to construct scientific theories, or to impose any statement about the physical structure of the universe. They are rather seen as a social representation that is shared by the community of believers of one religion. Therefore, in order to avoid confusion, they must present a certain character of stability over time, which prevents inadvertent alterations of the basic texts.
We consider today that the interpretation ( hermeneutics ) texts Bible must be considered from a perspective symbolic , not literal. Also, the basic texts can be adjusted over time. That is the purpose of exegesis to find the right words to ancient texts go to their translation and interpretation in the contemporary context. Thus, we can see that certain passages of the cosmological Bible , if controversial seventeenth century (see the case of Galileo and the question of the heliocentric theory ), have been reformulated in a version that seems less confusing. Besides, the biblical passages are generally interested in the Earth and its inhabitants, or "heaven", while studying the scientific cosmology cosmos as a whole, our galaxy , the Milky Way galaxy being only one others.
Some radical religious dispute the interpretation only symbolic and argue that the truth of religious texts is an accepted fact, they describe the cosmology is also true. These critics and religious aspects of scientific cosmology who disagree with their religious cosmology. In some cases, they can deny the relevance of any scientific study that is not in the sense of religious cosmology, to the point of claiming the teaching of a par with the other (see creationism ). This attitude is universally regarded as unscientific in physics, and generally disowned by the vast majority of moderate practitioners of these religions.
The question of the origin of the world is also discussed in philosophy by the cosmogony. It develops several cosmological concepts, for example in the philosophy of Kant.
History of scientific cosmologies
Established scientific cosmology at a given time depends significantly on what is known about the universe. Before the nineteenth century , the known universe was essentially reduced to a single solar system , cosmology and only focuses on the formation thereof. Not until the first half of the nineteenth century that the distance to the star has been known relatives (from 1838 by Friedrich Wilhelm Bessel ). The study of the spatial distribution of stars in our galaxy was then carried out until the early twentieth century. Finally, in 1920 the extragalactic nature of what was then called " nebulae "(galaxies today) was discovered by Edwin Hubble. Shortly after, he has also discovered the expanding universe , that is to say that the galaxies in the universe moving away from each other, and more so quickly that they are far away. Cosmology as understood today is the study of the structure, history and evolution of a universe filled with galaxies of sight.
Attempting to define the conditions necessary and sufficient to implement the Big Bang is outside the scope of science. The link between a cosmology philosophical explanation, indicating the initial presence of the Being as a trigger and a new scientific approach to cosmological requires a new synthesis.
Modern cosmology
Distances The Earth is a planet relatively small (about 6370 km in radius ), in orbit around a star , the Sun. The Earth-Sun distance is used to define the astronomical unit , or about 150 million kilometers. Other planets orbiting the Sun. The furthest planet from the Sun (not counting the dwarf planets) is Neptune , a distance of about 4 and a half billion miles from the sun, thirty times the Earth-Sun distance.
The solar system is itself immersed in a structure, the Galaxy (in the case of our galaxy, the Milky Way), comprising several hundred billion stars. The nearest star to the Sun, Proxima Centauri , is located a little over 4 light years or 45 000 billion kilometers of it, or 10,000 times the Sun-Neptune distance. Most of the stars visible to the naked eye in the night sky are at distances of tens or even hundreds of light years. The Sun is in no way in the center of the Galaxy. It is about 25,000 light years, the Galaxy has a radius about 2 times larger than this distance, with a diameter of about 100 000 light years. These dimensions make it a typical galaxy in the universe.
If we except the dwarf galaxies that exist in large numbers in the neighborhood of our galaxy, the massive galaxy closest to us is the Andromeda galaxy , whose distance is just over 2 million light years. Our galaxy and the Andromeda are the two most massive representatives of a group of galaxies called the Local Group , off a few million light years. There are other larger structures in the universe, called galaxy clusters and superclusters. The cluster closest to the Local Group is the Virgo cluster (or Virgo cluster, the Latin name for the constellation ), itself located near the center of the Virgo supercluster. Superclusters are the largest structures in the universe, but their size does not exceed 200 to 300 million light years.
The size of the observable universe is, it is estimated at 43 billion light-years Masses The density of the Earth is about 5 tons per cubic meter. Given its size, its mass is about 6 Oct. 24kg. The Sun, which is a typical star is approximately 300 000 times more massive, or 2 10 30 kg. For larger objects (galaxies, clusters of galaxies), it is customary to use the solar mass as the unit of mass, the kilogram unit becomes too small given the numbers involved
Observations indicate that galaxies are significantly more massive than the stars within them. There is little doubt today that in addition to ordinary matter that we're done, there is another form of matter, now unknown in the laboratory, called dark matter. Unlike ordinary matter, dark matter does not interact with light and is therefore invisible. Moreover, it does not form compact structures like stars, planets or asteroids, but has a much more diffuse distribution in galaxies. The mass of dark matter in galaxies (and in the entire universe) is about six times higher than that of ordinary matter. The mass of our galaxy is a little more than a trillion solar masses.
The estimated mass of the supercluster is about about 10 15 solar masses. Reported to their size, the superclusters are objects extremely sparse: a few tens of atoms per cubic meter only. The mass of the observable universe is estimated at 1.4 10 24 masses solar .
Times
The period of revolution of the Earth around the Sun is one year (actually a tropical year ). The more distant planets are the Sun, the more their orbital period is high, a consequence of Kepler's third law. Thus, Neptune has a period of 165 years.
Orders of magnitude increases significantly if one looks at the period of revolution of Sun around the galactic center: it is about 200 million years. The stars are not immutable objects. They form, begin to shine, then fade for lack of nuclear fuel in their midst. The age of the Sun is about 4.5 billion years. The oldest stars in our galaxy about 10 billion years. It is also the age of our galaxy. The galaxies also born from huge clouds of gas. The universe itself as we know it is not eternal. He comes from a phase extremely dense and hot, the Big Bang , which occurred there about 13.7 billion years.
Contributions of general relativity
Main article: General relativity. Cosmology is to describe the universe and its formation, which can be initially represented by a relatively uniform distribution (large scale) of matter. It turns out that Newtonian mechanics is unable to describe a uniform distribution of matter and infinite. To describe the universe, it is essential to appeal to general relativity , discovered by Albert Einstein in 1915. Einstein is also the first to post a cosmological model modern solution to his newly discovered theory, but describing a universe homogeneous finite and static. This model is primarily motivated by both philosophical and physical, but introduces an extremely clever idea (and a bit risky at the time), the cosmological principle.
The discovery a few years later the expansion of the universe by Edwin Hubble calls into question the model of Einstein's static universe and ultimately lay the foundations of modern cosmology: the universe (or at least the region accessible to observations) is expanding, and described by general relativity. Its evolution is determined by this theory, as well as the physical forms of matter present in the universe. It is essentially based on recent cosmological theories that will emerge.
The observations indicate that the universe is expanding. It was denser and hotter in the past. That's the basic idea of Big Bang , the model has emerged in the mid- twentieth century. It indicates that the universe as we know it comes from a hot and dense phase (without pretending to know what happened at the beginning of this phase), after which he was in a extremely homogeneous state, that is to say without astrophysical objects (stars, galaxies, ...). These objects are subsequently formed by a process called gravitational instability. As astrophysical objects are formed, the physical conditions prevailing in the universe are changing, and eventually produce the universe as we know it. The details of these processes depends on many parameters, such as the age of the universe, density and properties of different forms of matter that coexist in the universe.
In practice, researchers develop cosmological models , that is to say a kind of scenario here describing the various phases through which the universe grew from and possibly during the Big Bang. In the 1990s, finally emerged the standard model of cosmology , which represents the simplest model able to explain all cosmological observations.
Main article: cosmological model. The standard model of cosmology
Main article: Standard Model of cosmology. The general relativity, quantum mechanics and quantum field theory , coupled with many astronomical observations can now outline a scenario of relatively reliable history of the universe on the last 13 or 14 billion years. It is customary now to speak of a standard model of cosmology , like the standard model of particle physics, although the latter is quantitatively better tested and better constrained. The standard model of cosmology is based on the concept of the expansion of the universe , and the fact that it was denser and hotter in the past (hence the term hot Big Bang). Its description is based on the use of general relativity to describe the dynamics of its expansion, and given its particular content in part by direct observation, partly by a set of theoretical and observational. We consider now that the universe is homogeneous and isotropic (that is to say that he always looks the same regardless of where it is observed and the direction in which the notes), its spatial curvature is zero (that is to say that the large-scale geometry is the geometry in space usual), and is filled with a number of forms of matter, namely:
- Of ordinary matter ( atoms , molecules , electrons , etc.), also called baryonic matter , returning to about 5% of the composition of the universe
- Another form of matter called dark matter (or dark matter), of non-baryonic, consisting of massive particles undetected so far, accounting for about 25% of the total composition
- Another form of energy whose nature is unknown, but could be a cosmological constant , and generically called dark energy , accounting for 70% in the composition of the material content of the universe
Added to this is the electromagnetic radiation , mostly in the form of a homogeneous background of photons from the hot, dense phase in the history of the universe, the cosmic microwave background. There is also a cosmic background of neutrinos , not detected to date, but whose existence is proven by a number of indirect observations (see article for details), and a cosmic background of microwave Gravitational also not detected, directly or indirectly.
It is likely that in the past, the material content was different. For example, there is no or only very little of antimatter in the universe, yet we think that in the past, matter and antimatter existed in equal quantities, but a surplus of ordinary matter was formed during a process, still poorly known, called baryogenesis. Currently, only the earliest times of the expansion phase of the universe are unknown. One reason for this is that it is not possible to directly observe these times, the most distant detectable radiation at the moment (the CMB ) has been issued about 380 000 years later. A number of scenarios describing some of the earlier periods are available, including the most popular is that of cosmic inflation.
The fate of the universe is not, at present, not known with certainty, but many elements suggest that the expansion of the universe will continue indefinitely (see acceleration of the expansion of the universe ). Another unresolved issue is the topology of the universe, that is to say its a very large scale structure, where various ideas have been proposed (see article Topology of the Universe ).
References and sources
Notes
- This distance is paradoxically higher than the path traveled by light since the Big Bang. See Horizon (cosmology) for explaining this phenomenon.
- This number exceeds the number of stars in the observable universe mentioned above for several reasons:
- All ordinary matter is condensed into stars (only 50% of our galaxy, for example),
- The mass of ordinary matter is a factor of 6 lower than that of dark matter,
- The total mass included in the observable universe has a component twice as large as that of dark matter, the dark energy.
See also
- Astronomy and History of Astronomy
- Astrophysics
- Big Bang
- Non-standard cosmology
- Expanding Universe
- Timeline of the Big Bang
- Standard model of cosmology
- Copernican , geocentric , heliocentric
- Table of astrophysical constants
- Universe
External Links
- National Programme of cosmology (formal coordination of cosmological research in France)
- (In) Ned Wright: Cosmology tutorial and FAQ
- Foundations of cosmology on the French site of the Planck mission
- Consumer Sites on cosmology
- Cosmology, Laboratory for the infinitely small on Futura-Sciences
- Extension of the main aspects of cosmology
Bibliography
The density of the Earth is about 5 tons per cubic meter. Given its size, its mass is about 6 Oct. 24kg. The Sun, which is a typical star is approximately 300 000 times more massive, or 2 10 30 kg. For larger objects (galaxies, clusters of galaxies), it is customary to use the solar mass as the unit of mass, the kilogram unit becomes too small given the numbers involved
Observations indicate that galaxies are significantly more massive than the stars within them. There is little doubt today that in addition to ordinary matter that we're done, there is another form of matter, now unknown in the laboratory, called dark matter. Unlike ordinary matter, dark matter does not interact with light and is therefore invisible. Moreover, it does not form compact structures like stars, planets or asteroids, but has a much more diffuse distribution in galaxies. The mass of dark matter in galaxies (and in the entire universe) is about six times higher than that of ordinary matter. The mass of our galaxy is a little more than a trillion solar masses.
The estimated mass of the supercluster is about about 10 15 solar masses. Reported to their size, the superclusters are objects extremely sparse: a few tens of atoms per cubic meter only. The mass of the observable universe is estimated at 1.4 10 24 masses solar .
Times
The period of revolution of the Earth around the Sun is one year (actually a tropical year ). The more distant planets are the Sun, the more their orbital period is high, a consequence of Kepler's third law. Thus, Neptune has a period of 165 years.
Orders of magnitude increases significantly if one looks at the period of revolution of Sun around the galactic center: it is about 200 million years. The stars are not immutable objects. They form, begin to shine, then fade for lack of nuclear fuel in their midst. The age of the Sun is about 4.5 billion years. The oldest stars in our galaxy about 10 billion years. It is also the age of our galaxy. The galaxies also born from huge clouds of gas. The universe itself as we know it is not eternal. He comes from a phase extremely dense and hot, the Big Bang , which occurred there about 13.7 billion years.
Contributions of general relativity
Cosmology is to describe the universe and its formation, which can be initially represented by a relatively uniform distribution (large scale) of matter. It turns out that Newtonian mechanics is unable to describe a uniform distribution of matter and infinite. To describe the universe, it is essential to appeal to general relativity , discovered by Albert Einstein in 1915. Einstein is also the first to post a cosmological model modern solution to his newly discovered theory, but describing a universe homogeneous finite and static. This model is primarily motivated by both philosophical and physical, but introduces an extremely clever idea (and a bit risky at the time), the cosmological principle.
The discovery a few years later the expansion of the universe by Edwin Hubble calls into question the model of Einstein's static universe and ultimately lay the foundations of modern cosmology: the universe (or at least the region accessible to observations) is expanding, and described by general relativity. Its evolution is determined by this theory, as well as the physical forms of matter present in the universe. It is essentially based on recent cosmological theories that will emerge.
The observations indicate that the universe is expanding. It was denser and hotter in the past. That's the basic idea of Big Bang , the model has emerged in the mid- twentieth century. It indicates that the universe as we know it comes from a hot and dense phase (without pretending to know what happened at the beginning of this phase), after which he was in a extremely homogeneous state, that is to say without astrophysical objects (stars, galaxies, ...). These objects are subsequently formed by a process called gravitational instability. As astrophysical objects are formed, the physical conditions prevailing in the universe are changing, and eventually produce the universe as we know it. The details of these processes depends on many parameters, such as the age of the universe, density and properties of different forms of matter that coexist in the universe.
In practice, researchers develop cosmological models , that is to say a kind of scenario here describing the various phases through which the universe grew from and possibly during the Big Bang. In the 1990s, finally emerged the standard model of cosmology , which represents the simplest model able to explain all cosmological observations.
The standard model of cosmology
The general relativity, quantum mechanics and quantum field theory , coupled with many astronomical observations can now outline a scenario of relatively reliable history of the universe on the last 13 or 14 billion years. It is customary now to speak of a standard model of cosmology , like the standard model of particle physics, although the latter is quantitatively better tested and better constrained. The standard model of cosmology is based on the concept of the expansion of the universe , and the fact that it was denser and hotter in the past (hence the term hot Big Bang). Its description is based on the use of general relativity to describe the dynamics of its expansion, and given its particular content in part by direct observation, partly by a set of theoretical and observational. We consider now that the universe is homogeneous and isotropic (that is to say that he always looks the same regardless of where it is observed and the direction in which the notes), its spatial curvature is zero (that is to say that the large-scale geometry is the geometry in space usual), and is filled with a number of forms of matter, namely:
- Of ordinary matter ( atoms , molecules , electrons , etc.), also called baryonic matter , returning to about 5% of the composition of the universe
- Another form of matter called dark matter (or dark matter), of non-baryonic, consisting of massive particles undetected so far, accounting for about 25% of the total composition
- Another form of energy whose nature is unknown, but could be a cosmological constant , and generically called dark energy , accounting for 70% in the composition of the material content of the universe
Added to this is the electromagnetic radiation , mostly in the form of a homogeneous background of photons from the hot, dense phase in the history of the universe, the cosmic microwave background. There is also a cosmic background of neutrinos , not detected to date, but whose existence is proven by a number of indirect observations (see article for details), and a cosmic background of microwave Gravitational also not detected, directly or indirectly.
It is likely that in the past, the material content was different. For example, there is no or only very little of antimatter in the universe, yet we think that in the past, matter and antimatter existed in equal quantities, but a surplus of ordinary matter was formed during a process, still poorly known, called baryogenesis. Currently, only the earliest times of the expansion phase of the universe are unknown. One reason for this is that it is not possible to directly observe these times, the most distant detectable radiation at the moment (the CMB ) has been issued about 380 000 years later. A number of scenarios describing some of the earlier periods are available, including the most popular is that of cosmic inflation.
The fate of the universe is not, at present, not known with certainty, but many elements suggest that the expansion of the universe will continue indefinitely (see acceleration of the expansion of the universe ). Another unresolved issue is the topology of the universe, that is to say its a very large scale structure, where various ideas have been proposed (see article Topology of the Universe ).
References and sources
Notes
- This distance is paradoxically higher than the path traveled by light since the Big Bang. See Horizon (cosmology) for explaining this phenomenon.
- This number exceeds the number of stars in the observable universe mentioned above for several reasons:
- All ordinary matter is condensed into stars (only 50% of our galaxy, for example),
- The mass of ordinary matter is a factor of 6 lower than that of dark matter,
- The total mass included in the observable universe has a component twice as large as that of dark matter, the dark energy.
See also
- Astronomy and History of Astronomy
- Astrophysics
- Big Bang
- Non-standard cosmology
- Expanding Universe
- Timeline of the Big Bang
- Standard model of cosmology
- Copernican , geocentric , heliocentric
- Table of astrophysical constants
- Universe
External Links
- National Programme of cosmology (formal coordination of cosmological research in France)
- (In) Ned Wright: Cosmology tutorial and FAQ
- Foundations of cosmology on the French site of the Planck mission
- Consumer Sites on cosmology
- Cosmology, Laboratory for the infinitely small on Futura-Sciences
- Extension of the main aspects of cosmology
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