Metric expansion of space
As expansion of the universe, the increase of the spatial expansion of the universe is called, which is expressed in the increase of the distance between two widely separated points distant in space. After the expansion of the Universe has slowed in the first billion years of its existence (after inflation shortly after its formation ), the expansion rate increases since then. The explanation of the observed accelerated expansion is the subject of current research and has led to the concept of dark energy.
Discovery history
Albert Einstein and Willem de Sitter described in 1917 for the first time the universe with the formalism of general relativity. However, they described a static, always consistent universe. The description of de Sitter later proved to be wrong. Alexander Friedmann gave in 1922 to the first relativistic description of an expanding or contracting universe ( Friedmann equations). This publication was hardly noted.
The American astronomer Vesto Slipher found in 1912 as first the red shift of the spectral lines of light from distant galaxies. Edwin Hubble published in 1925, the distance to M 31, the Andromeda nebula in which showed quite clearly that Andromeda far outside our Milky Way lies in 1926 he published distances to other galaxies.
The expansion of the universe was discovered in 1927 by Belgian Georges Lemaître. He discovered what had already found Friedman before him, that the basic equations of the theory of relativity produce a dynamic universe. This discovery he associated with Slipher redshifts and Hubble distances. He concluded that the universe is expanding. In its publication in the Annales de la Société Scientifique de Bruxelles in 1927, Lemaître was already the " Hubble law " to. Lemaître theoretically deduced that galaxies move away faster the further away they are from us (compare: Hubble constant ). This result he was confirmed in the observations. He found a value that has been largely confirmed by the work of Hubble in 1929 for the later named after Hubble constant. Lemaître stressed that the "escape" of galaxies ( in the context of the Shapley -Curtis debate also referred to the no longer used term " fog escape " ) not as a movement in a fixed space of us is to be understood away, but in the sense the general theory of relativity, as an expansion of space.
Hubble himself found the relationship, ie the relationship between the distances of the galaxies and interpreted as speeds redshifts (Doppler effect) in 1929. He indicated, however, not as an expansion of the universe, but in the sense of de Sitter's 1917 's proposed model of a static universe. Hubble has the model of the expanding universe never represented and - judging by his publications - probably never believed in it.
Had Einstein postulated even a static universe in his theories, he revised in light of this then-new theory of the expanding space its view. So Einstein had introduced a cosmological constant in the field equations to obtain static solutions of the universe. These solutions the structure of the universe, however, were unstable. Einstein called the idea of a cosmological constant later according to George Gamow as the "biggest blunder of my life ".
State of research
According to the most common theory today the cosmological redshift is not a Doppler effect in the strict sense, but due to the general increase of temporal intervals in the universe. This leads to the acceptance of the Big Bang, since the distances between the galaxies in this model vanish at a finite time in the past and, therefore, a state of infinitely high density exists.
For a long time it was unclear whether the expansion
- Continue indefinitely is ( open universe );
- Always slower, but still reach an asymptotic boundary condition is (flat universe );
- Eventually comes to a stop and back into a contraction passes ( closed universe ).
Observations of distant supernovae of type Ia, among others, as part of the Supernova Cosmology Project, for their evaluation astronomers Saul Perlmutter, Brian P. Schmidt and Adam Riess were awarded the Nobel Prize for Physics in 2011, show that the expansion of the universe accelerates today expires. These results are consistent with studies of the cosmic background radiation, for example by the WMAP satellite. The cause of dark energy is assumed a time-varying generalization of the cosmological constant. Dark energy could not yet be detected directly; their only currently observable effects related to the expansion of the universe and the structure formation in the universe.
Another hypothesis for the origin of the red shift is the distance-dependent photon - aging. They came up with the quantum theory, leaned on to the particle picture of light and is now been overtaken as scientific.
From some observations that can not be understood in the ordinary Friedmann - Lemaître - Robertson - Walker metric, one concludes that a phase of exponential expansion in the early universe. This expansion theories are called inflation theories.
There are also examines explanations in the framework of general relativity.