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Hubble length

 
Measures and Units: Hubble length
 

astronomy. Symbol LH. The decimally rounded number of light years approximating the radius of the visible (from Earth) cosmos, = 1010 ly(94.605 36~ × 1021 km, 632.397 8~ × 1012 AU, 58.785 1~ × 1021 mi). The actual radius, which is about 40% greater, equals the ratio of the speed of light to the Hubble constant. (The use of the name for 109 ly, the distance travelled in an eon, was proposed in 1968 by Gamow.
[Gamow G. Nature Vol. 219, 765 (1968)])

Objects 1 LH distant are receding at 1 light year per year, hence at the limit to visibility. However, any objects still further away would be receding from us faster than light - an impossibility by current theory, save that the accepted view is that the fundamental structure of space-time is expanding, thereby carrying the galaxies further apart. The implication is that the sphere defined by the radius of visibility is identically the limit of the Universe which, despite all the conjectures about other planets having life like Earth's, would make Earth uniquely the centre of the Universe.

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Measures and Units. A Dictionary of Weights, Measures, and Units. Copyright © Donald Fenna 2002, 2004. All rights reserved.  Read more

 

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