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Observable universe

Visualization of the 93 billion light year – or 28 billion parsec – three-dimensional observable universe. The scale is such that the fine grains represent collections of large numbers of superclusters. The Virgo Supercluster – home of Milky Way – is marked at the center, but is too small to be seen in the image. Key topics in Physical cosmology Universe · Big Bang Age of the universe Chronology of the universe Inflation · Nucleosynthesis GWB · Neutrino background Cosmic microwave background Redshift · Hubble's law Metric expansion of space Friedmann equations FLRW metric Shape of the universe Structure formation Reionization Galaxy formation Large-scale structure Galaxy filament Ultimate fate of the universe Future of an expanding universe Lambda-CDM model Dark energy · Dark matter Dark fluid · Dark flow Timeline of cosmological theories History of the Big Bang theory Discovery of cosmic microwave background radiation Observational cosmology 2dF · SDSS COBE · BOOMERanG · WMAP · Planck Newton · Einstein · Hawking · Friedman · Lemaître · Hubble · Penzias · Bharadwaj · Tolman · Wilson · Gamow · Dicke · Zel'dovich · Aaronson · Mather · Rubin · Penrose · Alfvén · Smoot · Bardeen · Ehlers · Ellis · Sunyaev · Schmidt · Suntzeff · de Sitter · Guth others   Astronomy Portal Category v t e In Big Bang cosmology, the observable universe consists of the galaxies and other matter that humans can in principle observe from Earth in the present day, because light (or other signals) from those objects has had time to reach the Earth since the beginning of the cosmological expansion. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction—that is, the observable universe is a spherical volume (a ball) centered on the observer, regardless of the shape of the universe as a whole. Every location in the universe has its own observable universe which may or may not overlap with the one centered on the Earth.The word observable used in this sense does not depend on whether modern technology actually permits detection of radiation from an object in this region (or indeed on whether there is any radiation to detect). It simply indicates that it is possible in principle for light or other signals from the object to reach an observer on Earth. In practice, we can see light only from as far back as the time of photon decoupling in the recombination epoch, which is when particles were first able to emit photons that were not quickly re-absorbed by other particles, before which the universe was filled with a plasma opaque to photons. The collection of points in space at just the right distance so that photons emitted at the time of photon decoupling would be reaching us today form the surface of last scattering, and the photons emitted at the surface of last scattering are the ones we detect today as the cosmic microwave background radiation (CMBR). However, it may be possible in the future to observe the still older neutrino background, or even more distant events via gravitational waves (which also move at the speed of light). Sometimes a distinction is made between the visible universe, which includes only signals emitted since recombination, and the observable universe, which includes signals since the beginning of the cosmological expansion (the Big Bang in traditional cosmology, the end of the inflationary epoch in modern cosmology). The comoving distance (current proper distance) to the particles which emitted the CMBR, representing the radius of the visible universe, is calculated to be about 14.0 billion parsecs (about 45.7 billion light years), while the comoving distance to the edge of the observable universe is calculated to be 14.3 billion parsecs (about 46.6 billion light years), about 2% larger.The age of the universe is about 13.75 billion years, but due to the expansion of space humans are observing objects that were originally much closer but are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the comoving distance at the present time) than a static 13.75 billion light-years distance. The diameter of the observable universe is estimated to be about 28 billion parsecs (93 billion light-years), putting the edge of the observable universe at about 46–47 billion light-years away. Cite error: There are tags on this page, but the references will not show without a {{Reflist}} template or a tag; see the help page.
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