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The size of the universe is unknown.

The diameter of the observable universe (where "observable" refers to the universe that can theoretically be observed since the light coming from that area has had time to reach us since the Big Bang) is estimated to be about 93 billion lightyears (about 29 billion parsecs or about \(8.8 \times 10^{23}\) kilometers).[1] As nothing can exceed the speed of light, some nonastronomers and laymen assume that the observable universe is actually 13.8 billion light-years in size, as this is the scientifically hypothesized age of the universe in years. The curvature of the universe makes it much larger than this.[2]

The size of the observable universe is determined by how far light can travel given the total elapsed time since the Big Bang. There are most likely galaxies outside the observable universe that cannot be seen yet because they are too far away for their light to have traveled to Earth, and no conceivable technology by modern means can change that.

The diameter of the actual universe is unknown. One source estimates that the whole universe is at least 250 times larger (3,450 billion light-years) than the observable universe,[3] whereas other sources give lower bounds of \(10^{10^{10^{122}}}\) times.[4]

Linde and Vanchurin (2010) estimated possible number of universes in the multiverse as \(10^{10^{10^7}}\).[5]

If the universe's geometry is flat (i.e. it has zero curvature), it will be infinite in size. NASA confirmed with Wilkinson Microwave Anisotropy Probe (WMAP) that the universe is flat with only a 0.4% margin of error as of 2013.[6]

For the size of the universe in time, although history of the universe is agreed on among scientists to some degree, the ultimate fate of the universe cannot be predicted with certain, and there are several scenarios depending on various undetermined factors. There are some predictions on far-future events in the universe.

Sources[]

  1. I. Bars and J. Terning (2009) Extra Dimensions in Space and Time Springer Science & Business Media p.27
  2. Edward L. Wright (2006) Why the Light Travel Time Distance should not be used in Press Releases Update 2013-08-02. Retrieved 2023-09-15.
  3. Vanessa Janek Universe Could be 250 Times Bigger Than What is Observable Universe Today. 2011-02-08.
  4. D. N. Page (2007) Susskind's challenge to the Hartle–Hawking no-boundary proposal and possible resolutions Journal of Cosmology and Astroparticle Physics JCAP01(2007)004. Preprint
  5. A. Linde and V. Vanchurin. (2010) How many universes are in the multiverse? Phys. Rev. D 81, 083525. Preprint.
  6. NASA. Will the Universe expand forever? WMAP's Universe. 2014-01-24.
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