Observable universe

The observable universe is in the standard model of cosmology the part of the universe, which is accessible in principle from the earth from our observation. Assuming that the universe is isotropic, which has from Earth observable universe the shape of a sphere with the Earth at the center. This is independent of the shape of the universe as a entire. Every place in the universe has its own observable universe which may overlap with ours, but not necessarily.

Observation horizon

The observation horizon limits the part of the universe of which may have reached us since the Big Bang information. Areas beyond the observation horizon can not be observed, because there is insufficient time since the Big Bang in order to get out of there light can. Likewise, the speed of transmission of information or the movement of matter ( particles) by the speed of light is limited, so can us about events behind the observation horizon reach no information (see also light beam ).

However, the current distance to the observation horizon is not the age of the universe (about 13.7 billion years ) multiplied by the speed of light given, not 13.7 billion light years, but larger; it is currently estimated as part of the Big Bang standard model at about 46.6 billion light years. Indeed, it is to consider that the universe has continued to expand, while the light from the observation horizon moving to us, that is, already made routes are subsequently become longer.

Often the equivalent, reversal of approach to definition is used: The particle horizon is then the sphere would be penetrated up to the speed of light radiation, if it had been sent out to our point immediately after the Big Bang and would have unhindered spread.

Calculation

The distance to the particle horizon can be calculated according to the following formula:

The speed of light and the time ( during the Big Bang is equal to zero, and now the same age of the world ). The size is the scale factor, a dimensionless quantity, the course over time indicates the expansion of the universe and is equal to one (,) today. If the integral diverges for a given, the corresponding universe has no particles horizon.

Cosmic background radiation as a boundary

In practice, electromagnetic radiation at the wavelengths of the most slightly closer observation horizon because the Early Universe was impermeable to light. The most past information and thus the information about the most distant areas obtained via electromagnetic waves, dates from the time of about 400,000 years after the Big Bang, when the universe became transparent. This radiation is known as the cosmic background radiation and therefore originates from the edge of the observable universe today. At the time of its release some 14 billion years ago the distance was only 30 million light-years, the ratio of these distances z = 1500 is the factor of expansion of the universe over this period, while the redshift.

Redshift

Due to the expansion of the universe, the radiation is redshifted more strongly by an object, the closer is this the observation horizon; the observation horizon, the redshift is infinite. However, the assumption is wrong, that objects in the observation horizon move today with the speed of light away from us, as one might think for a simple (wrong) interpretation of the cosmological redshift as a Doppler effect in a static universe. "Move" objects on the observation horizon today apparently made ​​off with more than 3 times the speed of light from us. However, this does not contradict the theory of relativity, because the expansion of the universe is no movement in the room, but an expansion of space itself, ie, the kinetic energy (and therefore mass) of the object itself does not change. Today, no transmission of information from an object on the observation horizon to us ( or vice versa) is possible.

Event horizon

In contrast to the observation horizon that indicates how far objects can be removed current maximum, so that their light reaches us today, are at the event horizon, how far an object can be maximum of us today, so that his light upon us in a theoretical limit can reach just in principle in the infinite future. An acceleration of the expansion due to dark energy leads to more events and objects behind the cosmological event horizon in no causal relationship with us and can penetrate any information from there more to us. The event horizon is due to the accelerated expansion of the universe, such as the observation horizon, at a finite distance but much closer than the observation horizon. In the standard model of the event horizon about 16.2 billion light-years corresponding to a redshift of z = distance from us, 1.8.

Hubble radius

The Hubble radius refers to the distance at which galaxies backoff speed of c, the speed of light, have. He is 14.2 billion light-years away from us, which corresponds to a redshift of z = 1.46. In a universe with increasing expansion velocity objects located today within the Hubble radius can disappear behind the Hubble radius, which can reach us by them emitted light no longer, due to the accelerated expansion in the future.