Universe

Discovered Universe in the History

It is still with the " miracle grec" that one owes the first signification advances in the comprehension of the world:

the philosophers Parménide, Plato, and Aristote had integrated the idea of a spherical ground , but they saw it in the center of the physical universe, whereas the Millet school represented the Earth punt.
Ératosthène is delivered then, on its side, with precise calculations: for example, it is mistaken perhaps only in 650 km in its measurement of the circumference of a terrestrial meridian line, that is to say hardly more than 1,5% of error. However, it expressed its result in stages, whose value varied from one place to another, and outdistances it between the towns of Alexandria and Syène, between which it took its measurement was known only in days of camel, which makes the measuring accuracy almost too suspect.
Aristarque de Samos is the first, seems it, to understand that the planetary system is héliocentré. This discovery then does not achieve the unanimity, for philosophical reasons especially in that such a cosmology is in dissension with the design Géocentrée of the world which was retained by large philosophers like Parménide, Plato, and Aristote. It calculates also the distance the Ground-Moon of which it finds a value very precise (60 terrestrial rays).
Hipparque continues this work: it recomputes the distance the Ground-Moon, counts 1.500 stars, roughly finds the period of precession of the equinoxes, which was already known Babylonian .

All this knowledge accumulated is taken again and preserved by the Arab at collapse of the world gréco-Roman, whereas the Christian world sinks in the obscurantism: Cosmas of Alexandria restores the flat world thus. It is necessary to await the Moslem conquests so that the Almageste of Ptolémée is redécouverte.

The Renaissance will carry to its apogee this representation of the world, thanks to explorations and with the great discoveries which took place of 13th at the 16th centuries, with geographical systems and cosmological very elaborate (Projection of Mercator).

The revolution known as copernician will upset this Cosmologie, in three stages:

Copernic redécouvre heliocentrism. However, this redécouverte is only partially revolutionist: indeed, Copernic remains attached to the supposed transparent spheres to support planets and to print their movement to them; it presents its system like a simple artifice intended to simplify calculations, which avoids to him troubles with the Clergé.
Dominican the Giordano Bruno defends the reality of the heliocentric model and extends it to all stars, opening the dimension of the physical universe ad infinitum.
Kepler, Galileo and Newton poses the fundamental bases of the Mécanique starting from the movement of the Planets, thanks to their studies respectively of the movement |elliptic of the Planet S around the Sun, the refinement of the astronomical observations with the definition of the movement uniformly accelerated, and the mathematical formalization of the force of gravity. The universe, however, remains confined in the Solar system.

Universe according to the theory of Big Bang

The expansion of the Universe, its age and Big Bang

The observations of the Décalage towards the red of the electromagnetic radiations coming from others Galaxie S suggest that those move away from our galaxy, at a radial speed of distancing presumedly proportional to this shift.

By studying the close galaxies, Edwin Hubble realized that in general the speed of distancing of a galaxy was proportional to its distance, which is known under the name of Loi of Hubble; such a law corresponds to a close universe in expansion.

Although the Constante of Hubble was revised in the past in important proportions (in a ratio from 10 to 1), the law of Hubble was extrapolated with the galaxies moved away, for which the distance cannot be calculated by means of the Parallaxe; this law is thus used to determine the distance from the most remote galaxies.

While extrapolating the expansion of the Universe in the past, one arrives at one time when this one has being much hotter and much denser than today. It is the model of the Big Bang which is an essential ingredient of the standard Modèle of current cosmology and has today a great number of experimental confirmations. The description of the beginning of the history of the Universe by this model starts however only after it had left one period called era of Planck during which the scale of energy of the universe was so large that the standard model is not able to describe the quantum phenomena which proceeded there. During this time, only a theory of the quantum Gravitation could explain the microscopic behavior of the matter under the important influence of gravity. But the physicists do not have yet (2006) such a theory. For reasons of coherence with the observations, after the era of Planck the model of Big Bang privileges today the existence of a phase of cosmic Inflation very short but during which the universe would have grown in an extremely fast way. It is following this phase that the main part of the particles of the universe would have been created with a high temperature, engaging a great number of important processes which finally led to the emission of a great quantity of light, called cosmological diffuse Fond, which can be observed today with a high degree of accuracy by a whole series of instruments (balloons, space probes).

It is the observation of this fossil radiation microwave, remarkably uniform in all the directions which constitutes today the capital element which assoit the model of Big Bang like correct description of the universe in its remote past. Many elements of the model still remain to be been refined but there is today consensus of the Scientific community around the model of Big Bang.

Within the framework of the Model ΛCDM, which is simplest incorporating all the elements that one has just evoked, the constraints resulting from the observations of the probe WMAP on the cosmological parameters indicate the most probable value for the age of the universe to approximately 13,7 billion years with an uncertainty of 0,2 billion years, which is in agreement with the data independent resulting from the observation from the globular Amas S like that of the white dwarf .

Cut Universe and observable Universe

See also: observable Universe

To date, nothing enables us to confirm that the universe either is finished, or Infini. Certain theorists lean for an infinite universe, others for a finished universe but not limited.

Observable universe being composed of all the places which could have affected to us since Big Bang, by holding account that the Speed of light is finished. The cosmic Horizon is at a distance from 13 to 14 billion light-years.

The current size (the Distance comobile) of the observable universe is larger, since the universe continued to extend during time that the light puts to reach us; it is estimated that it is of approximately 50 billion light-years (4,73×10²⁶m). The observable universe contains approximately 7×10²² star S, widespread in approximately 10¹¹ galaxies, themselves organized in cluster and supercluster of galaxies. The number of galaxies could be even larger, according to the deep Champ of Hubble observed with the Space telescope Hubble.

It will be noted that the popular and professional articles of research in cosmology often employ the term universe in the direction of observable universe .

We live in the center of the observable universe, in apparent contradiction with the Principe of Copernic which says that the universe is more or less uniform and does not have any center in particular. It is simply because the light does not move at an infinite speed and that the observations which we make thus come from the past. Indeed, while looking at more and more far, we see things which occurred at one time increasingly close to Big Bang. And since the light moves at the same speed in all the directions, all the observers live in the center of their observable universe (on Earth, we have practically all the same one).

From a philosophical point of view, the question of finitude or not-finitude of the Universe always worried the men.

The Universe containing by definition all that exists, including the Espace-temps (and it is an essential precision), cannot have “edge” such as we conceive this concept intuitively. Indeed, the existence of an edge would imply that beyond this edge, one would not be any more in the Universe, which is by absurdity definition. But if the Universe does not have an edge with the intuitive direction of this term, then its expansion is not intuitive either: if it were it, in what the Universe would be it expanding?

It is seen that this problem escapes our reasoning, which is always based on the false assumption that the Universe is galiléen. Ultimately, the concepts of finished and infinite cannot be applied to the Universe. The only data which seems intuitive and obvious, it is that the Universe always had, and will always have, a size “sufficient” for all its activities.

Form Universe

An important question of cosmology which remains unanswered is the Topologie of the Universe. is

the universe “flat”? I.e.: is the Théorème of Pythagore for the Triangle S rights valid with moreover large scales? Currently, the majority of the cosmologists believe that the observable universe is (almost) flat, just as the Earth is (almost) punt. Is
the universe simply related ? According to the standard model of Big Bang, the universe does not have any space border, but can nevertheless be of finished size.

This can be included/understood by a two-dimensional analogy: the surface of the ground does not have any edge, but has a well defined surface. You can also think of a Cylindre and imagine to stick the two ends of the cylinder together, but without folding the cylinder. It is also a two-dimensional space with a finished surface, but contrary to the surface of the Earth, it is flat, and can thus serve as better model.

Consequently, strictly speaking, should call us the stars and galaxies mentioned above “images” of stars and galaxies, since it is possible that the universe is finished and so small that we can see one or more time around him, and the true number of stars and physically distinct galaxies could be smaller. Assumptions of universe multiconnexe were proposed and are under study.

Future of the Universe

According to its average Density of Matter and energy, the universe will continue to extend indefinitely or it will be Gravitation nellement slowed down and will crumble on itself in a “Big-RIP” or “Big Crunch”. Currently, the state of our knowledge suggests not only that there is insufficiently mass and of energy to cause this collapse, but that the expansion of the universe seems to accelerate and will thus continue for always.

According to a theory of Stephen Hawking (in its book a short history of time ), if the universe indefinitely continues to extend, the particles resulting from successive explosions will not be rather any more close from/to each other to recreate stars after their explosion. Any activity in the universe will die out thus forever.

Quotations

Montesquieu:

“ Aujourd'hui we receive three different or contrary educations: those of our fathers, those of our Masters, that of the world. What one says to us in the last shift all the ideas of the first ”. George Bernard Shaw:

“ more than one millenium ago, Ptolémée set up a system of the world which lasted until the 17th century, reversed then by that of Newton, which lasted until being replaced there is little by that of Mr. Einstein, here present, of which I will not venture myself to try to predict what it will last ”.

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