Expansion of the universe | Wikipedia audio article
Channel: Subhajit Sahu
Date: 2018-12-08

This is an audio version of the Wikipedia Article:
Expansion of the universe


00:04:26 1 Cosmic inflation
00:07:19 2 Overview of metrics and comoving coordinates
00:09:50 2.1 Example: "Great Circle" metric for Earth's surface
00:12:06 2.2 Metric tensors
00:14:31 2.3 Comoving coordinates
00:15:34 3 Understanding the expansion of the universe
00:15:45 3.1 Measurement of expansion and change of rate of expansion
00:16:56 3.2 Measuring distances in expanding space
00:18:29 3.3 Topology of expanding space
00:23:01 3.4 Density of universe during expansion
00:26:28 3.5 Effects of expansion on small scales
00:27:02 3.6 Metric expansion and speed of light
00:31:14 3.7 Scale factor
00:33:40 3.8 Other conceptual models of expansion
00:35:02 4 Theoretical basis and first evidence
00:36:57 4.1 Hubble's law
00:37:07 4.2 Cosmological constant and the Friedmann equations
00:37:36 4.3 Hubble's concerns over the rate of expansion
00:38:30 4.4 Inflation as an explanation for the expansion
00:41:49 4.5 Measuring distance in a metric space
00:42:42 5 Observational evidence
00:44:05 6 Notes
00:47:45 7 Printed references
00:47:54 8 External links
00:48:43 undefined



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SUMMARY
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The expansion of the universe is the increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The  universe does not expand "into" anything and does not require space to exist "outside" it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale. Although light and objects within spacetime cannot travel faster than the speed of light, this limitation does not restrict the metric itself. To an observer it appears that space is expanding and all but the nearest galaxies are receding into the distance.
During the inflationary epoch about 10−32 of a second after the Big Bang, the universe suddenly expanded, and its volume increased by a factor of at least 1078 (an expansion of distance by a factor of at least 1026 in each of the three dimensions), equivalent to expanding an object 1 nanometer (10−9 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 1017 m or 62 trillion miles) long. A much slower and gradual expansion of space continued after this, until at around 9.8 billion years after the Big Bang (4 billion years ago) it began to gradually expand more quickly, and is still doing so today.
The metric expansion of space is of a kind completely different from the expansions and explosions seen in daily life. It also seems to be a property of the universe as a whole rather than a phenomenon that applies just to one part of the universe or can be observed from "outside" it.
Metric expansion is a key feature of Big Bang cosmology, is modeled mathematically with the Friedmann-Lemaître-Robertson-Walker metric and is a generic property of the universe we inhabit. However, the model is valid only on large scales (roughly the scale of galaxy clusters and above), because gravitational attraction binds matter together strongly enough that metric expansion cannot be observed at this time, on a smaller scale. As such, the only galaxies receding from one another as a result of metric expansion are those separated by cosmologically relevant scales larger than the length scales associated with the gravitational collapse that are possible in the age of the universe given the matter density and average expansion rate.
Physicists have postulated the existence of dark energy, appearing as a cosmological constant in the simplest gravitational models as a way to explain the acceleration. According to the simplest extrapolation of the currently-favored cosmological model, the Lambda-CDM model, this acceleration becomes more dominant into the future. In June 2016, NASA and ESA scientists reported that the universe was found to be expanding 5% to 9% faster than thought ea ...