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 Automatic translation  Automatic translation Category: universe
Updated Febrary 22, 2015
  Size of the visible universe

Image: the visible universe can be cut into slices observable. Cutting a slice universe located 5 billion light years from us, we see all objects whose light has gone there are 5 Ga. By cutting a slice of universe located to 10 billion-years light, we see all objects whose light has gone there are 10 Ga. By cons in a slice universe located 15 billion light years away, we see nothing but black because all the objects light has gone there are 15 Ga are located behind the horizon and unfortunately for most of them, they will never be visible. The oldest light we see come from 13.8 Ga. In 1.2 Ga we will see those has gone there are 15 Ga. The visible universe grows a year, every year. However the universe continues to expand, and some objects will never be visible as they move away from us faster than the speed of light. Credit:

nota: The age of the universe was redefined in 2014 thanks to the observations of the Planck mission. Cosmological parameters indicate a probable value for the age of the visible universe, about 13.798 (± 0.037) billion years.
The observable universes in the universe as a whole... by astronoo
  Observable Universe seen by the Planck mission

Image: The first light of the observable universe seen by the Planck mission (March 2013). This picture shows the most distant signals we receive. False colors, red (hot regions) to blue (cold areas) represent the temperature fluctuations of the cosmic microwave background. Image Credit: ESA Planck collaboration.

Quantum mechanics describes the fundamental physical phenomena at work at the atomic and subatomic scale. It was developed in the early twentieth century by a dozen physicists whose Planck, Einstein, Heisenberg, Bohr, de Broglie, Schrödinger, Feynman to solve various problems such as black body radiation, the photoelectric effect, or existence of spectral lines. Quantum mechanics proved so fruitful that it solved the mystery of the structure of the atom. It also describes the behavior of elementary particles and is the foundation of modern physics. General relativity is a relativistic theory of gravitation developed mainly between 1907 and 1915 by Albert Einstein. Marcel Grossmann and David Hilbert are also associated with this achievement for helping Einstein to cross the mathematical difficulties of the theory. General relativity says that gravity is the manifestation of the curvature of space-time generated by the distribution of matter and energy. The measurement of the mean curvature of space-time is equal to the extent of the energy density (Gij = χ Tij) Gij is the Einstein tensor that represents the curvature of space-time at one point, Tij is the energy-momentum tensor represents the contribution of all matter and energy to the energy density at that point of the gravitational field. χ is a simple dimensional factor to express the equation in the usual units to match the equation to physical reality and the observed value of the gravitational constant. Quantum field theory is used in elementary particle physics, it provides a theoretical framework to describe the degrees of freedom of the fields and systems with a large number of bodies. It allows to quantify the interactions between the particles. The forces between the particles are actually exchanges other virtual particles called mediators. The electromagnetic force between two electrons is caused by an exchange of photons. The weak interaction is caused by an exchange of W and Z bosons The strong interaction is caused by the exchange of gluons. Gravity is not described by an exchange of particle but many theories anticipate the existence of a graviton which would be the mediator. The observable universe is the visible part of our universe. Each observer is at the center of a "luminous sphere" whose surface is on the cosmological horizon. Other observers elsewhere in the universe have their own observable sphere with the same radius as our sphere. Thus each light sphere has a finite radius of 13.8 billion light years because the light from celestial objects beyond the horizon has not had time to reach us. But the observable universe grows over time, the radius of the visible universe is growing every year, a light year, and even a bit more considering the expansion of the Universe. Today some invisible objects will become visible but other very distant objects, because of the expansion of the universe are receding from us at a speed greater than the speed of light. These distant objects "will never be visible" and does not violate the principle which says that no object can not exceed the speed of light, since it is the space between objects that swells. The cosmological horizon is the limit of the observable universe from a given point of a "real universe". Light having a finite speed (≈300 000 km / s), this horizon is located 13.8 billion light-years is the limit where electromagnetic radiation may come from. Some regions of the universe are inaccessible to observation because they are behind the cosmological horizon of the observer. The most distant signals we receive come from the cosmic microwave background. The last scattering surface is the region of space from which was issued last photons, those which have not been reabsorbed by the matter. Thus the oldest electromagnetic radiation of the universe is gone, that last scattering surface is the cosmic microwave background that is observed today throughout our universe. The Hubble radius approximately corresponds to the radius of the observable portion of an expanding universe. Ie the size of the observable universe is of the same order of magnitude as the Hubble radius. However, the relationship between the size of the observable universe and the Hubble radius depends on the cosmological model considered.

1997 © − Astronomy, Astrophysics, Evolution and Earth science.

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