<P> The word observable used in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected . It refers to the physical limit created by the speed of light itself . Because no signals can travel faster than light, any object further away from us than light could travel in the age of the universe (estimated as of 2015 around 7010137990000000000 ♠ 13.799 ± 0.021 billion years) simply cannot be detected, as they have not reached us yet . In practice, the limit on observation is not 13.799 billion light - years for two reasons . The first reason is that space itself is expanding, so we can actually detect light from objects that were once close, but are now up to around 45.7 billion light years away (rather than up to 13.799 billion light years away as might be expected). The second reason is that before the recombination epoch, about 378,000 years after the Big Bang, the Universe was filled with a plasma that was opaque to light, and photons were quickly re-absorbed by other particles, so we cannot see objects from before that time using light or any other electromagnetic radiation . Gravitational waves and neutrino background would have been unaffected by this, and may be detectable from earlier times . The surface of last scattering is the collection of points in space at the exact distance that photons from the time of photon decoupling just reach us today . These are the photons we detect today as cosmic microwave background radiation (CMBR). However, with future technology, it may be possible to observe the still older relic neutrino background, or even more distant events via gravitational waves (which also should move at the speed of light). </P> <P> Sometimes astrophysicists distinguish 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 physical cosmology, the end of the inflationary epoch in modern cosmology). </P> <P> According to calculations, the comoving distance (current proper distance) to particles from which the CMBR was emitted, which represent the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light years), while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light years), about 2% larger . The radius of the observable universe is therefore estimated to be about 46.5 billion light - years and its diameter about 28.5 gigaparsecs (93 billion light - years 8.8 × 10 kilometres or 5.5 × 10 miles). The total mass of ordinary matter in the universe can be calculated using the critical density and the diameter of the observable universe to be about 1.5 × 10 kg . </P> <Table> <Tr> <Td> Part of a series on </Td> </Tr> <Tr> <Th> Physical cosmology </Th> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> <Ul> <Li> Big Bang Universe </Li> <Li> Age of the universe </Li> <Li> Chronology of the universe </Li> </Ul> </Td> </Tr> <Tr> <Td> Early universe (show) <Table> <Tr> <Td> <Ul> <Li> Inflation Nucleosynthesis </Li> </Ul> </Td> </Tr> <Tr> <Th> Backgrounds </Th> </Tr> <Tr> <Td> <Ul> <Li> Gravitational wave (GWB) </Li> <Li> Microwave (CMB) Neutrino (CNB) </Li> </Ul> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> Expansion Future (show) <Ul> <Li> Hubble's law Redshift </Li> <Li> Metric expansion of space </Li> <Li> FLRW metric Friedmann equations </Li> <Li> Inhomogeneous cosmology </Li> <Li> Future of an expanding universe </Li> <Li> Ultimate fate of the universe </Li> </Ul> </Td> </Tr> <Tr> <Td> Components Structure (hide) <Table> <Tr> <Th> Components </Th> </Tr> <Tr> <Td> <Ul> <Li> Lambda - CDM model </Li> <Li> Dark energy Dark fluid Dark matter </Li> </Ul> </Td> </Tr> <Tr> <Th> Structure </Th> </Tr> <Tr> <Td> <Ul> <Li> Shape of the universe </Li> <Li> Galaxy filament Galaxy formation </Li> <Li> Large quasar group </Li> <Li> Large - scale structure </Li> <Li> Reionization Structure formation </Li> </Ul> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> Experiments (show) <Ul> <Li> Black Hole Initiative (BHI) </Li> <Li> BOOMERanG </Li> <Li> Cosmic Background Explorer (COBE) </Li> <Li> Illustris project </Li> <Li> Planck space observatory </Li> <Li> Sloan Digital Sky Survey (SDSS) </Li> <Li> 2dF Galaxy Redshift Survey ("2dF") </Li> <Li> Wilkinson Microwave Anisotropy Probe (WMAP) </Li> </Ul> </Td> </Tr> <Tr> <Td> Scientists (show) <Ul> <Li> Aaronson </Li> <Li> Alfvén </Li> <Li> Alpher </Li> <Li> Bharadwaj </Li> <Li> Copernicus </Li> <Li> de Sitter </Li> <Li> Dicke </Li> <Li> Ehlers </Li> <Li> Einstein </Li> <Li> Ellis </Li> <Li> Friedman </Li> <Li> Galileo </Li> <Li> Gamow </Li> <Li> Guth </Li> <Li> Hawking </Li> <Li> Hubble </Li> <Li> Lemaître </Li> <Li> Mather </Li> <Li> Newton </Li> <Li> Penrose </Li> <Li> Penzias </Li> <Li> Rubin </Li> <Li> Schmidt </Li> <Li> Smoot </Li> <Li> Suntzeff </Li> <Li> Sunyaev </Li> <Li> Tolman </Li> <Li> Wilson </Li> <Li> Zel'dovich </Li> </Ul> <Ul> <Li> List of cosmologists </Li> </Ul> </Td> </Tr> <Tr> <Td> Subject history (show) <Ul> <Li> Discovery of cosmic microwave background radiation </Li> <Li> History of the Big Bang theory </Li> <Li> Religious interpretations of the Big Bang theory </Li> <Li> Timeline of cosmological theories </Li> </Ul> </Td> </Tr> <Tr> <Td> <Ul> <Li> </Li> <Li> Cosmology portal </Li> <Li> Astronomy portal </Li> </Ul> </Td> </Tr> <Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> </Table>

How many light years to the end of the universe
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