Problem of the horizon

The problem of the horizon was for a long time a headache of the Cosmologie, of which it is commonly allowed today that the solution is offered by the Paradigme of the cosmic Inflation. A apparent Paradoxe was posed: how to make compatible the observation of the cosmological diffuse Fund which indicates that with very large scales the universe is isotropic Homogène and with the constraint resulting from the Relativité indicating that certain areas of the Univers are so distant that it would seem that they never could exchange information since the Big Bang?

Introduction

One knows since the discovery of the Expansion of the universe that areas now far away from cosmos were much closer in the past. Nevertheless, being given the speed of current expansion which is of type law of power, it would seem that even during the period of the Big Bang certain areas were causalement disconnected because of finitude from the Speed of light. This means that although speed of light is very large (approximately 300.000 km/s) and that the universe is very old (of the order of ten Billion Année S), the light would not have had time to traverse the distance necessary to link such regions. However since the discovery of the cosmological diffuse bottom one knows that with large scales the universe is with a high degree of accuracy (about $10^ {- 5}$ ) homogeneous and isotropic, it is necessary to find a mechanism by which these areas apparently disconnected from the point of view of relativity could exchange information at a certain period so that it can appear similar today.

A mechanism offering such a possibility was offered by the cosmic model of Inflation. It consists in supposing that shortly after Big Bang all the matter observed today was located in a small area so that it is reasonable to suppose that this one was homogeneous and isotropic then that the universe underwent one period of exponential Expansion which moved away very quickly the various components from this zone.

Cosmic horizon

Too remote objects

At the base, the problem of the horizon was almost discovered by chance: the astronomers realized that the galaxies seemed to be slightly too remote (and of the blow too young people) compared to the age of the universe (at least, the light which reaches us from there). According to the Law of Hubble, plus a galaxy moves away from us, plus it moves away quickly. That would like to thus say that the galaxies should be slightly closer if one believes calculations of them. The question is to know what pushed these galaxies further it should not. The answer is not in the present, but rather in the very first moments of the universe.

Cosmology inflationnaire

The cosmic Inflation, or inflation very short, brings a solution to this problem. During the very first moments of the universe, just after the Era of Planck, the universe would have grown suddenly, a short push of acceleration. All this time before inflation, of the areas still all close relations in the universe (cf Expansion of the universe), had " all their time " , to exchange their properties (like the Temperature for example). Just after that, inflation took place and of the very close zones then from/to each other were suddenly isolated.

Caption

We see it on the diagram, during a very short time, the universe increased to a significant degree. Of course, the point " big-bang" , by preoccupation with a clearness, was increased. In reality, this phase does not last longer than the era of Planck, located right front. Nevertheless even if, by convenience of presentation, the figure seems to allot to the universe a specific origin, it should well be carried out that the expansion of the universe, and inflation in particular, strictly speaking does not have a center. The expansion is a local phenomenon which takes place in way Homogène in any point of the paramount universe. It is necessary also to keep in mind that this diagram is a representation in time and not in space.

See too

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