Dark energy | Wikipedia audio article
Channel: wikipedia tts
Date: 08/12/2018

This is an audio version of the Wikipedia Article:
Dark energy


00:01:39 1 History of discovery and previous speculation
00:01:50 1.1 Einstein's cosmological constant
00:03:26 1.2 Inflationary dark energy
00:06:27 1.3 Change in expansion over time
00:07:55 2 Nature
00:09:37 2.1 Technical definition
00:10:38 3 Evidence of existence
00:11:16 3.1 Supernovae
00:13:28 3.2 Cosmic microwave background
00:14:47 3.3 Large-scale structure
00:16:06 3.4 Late-time integrated Sachs-Wolfe effect
00:16:44 3.5 Observational Hubble constant data
00:18:41 4 Theories of dark energy
00:19:13 4.1 Cosmological constant
00:22:03 4.2 Quintessence
00:24:41 4.3 Interacting dark energy
00:25:28 4.4 Variable dark energy models
00:26:09 4.5 Observational skepticism
00:27:14 5 Other mechanism driving acceleration
00:27:24 5.1 Modified gravity
00:28:20 6 Implications for the fate of the universe
00:32:23 7 In philosophy of science
00:32:57 8 See also



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SUMMARY
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In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe.  Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate.
Assuming that the standard model of cosmology is correct, the best current measurements indicate that dark energy contributes 68% of the total energy in the present-day observable universe. The mass–energy of dark matter and ordinary (baryonic) matter contribute 27% and 5%, respectively, and other components such as neutrinos and photons contribute a very small amount. The density of dark energy (~ 7 × 10−30 g/cm3) is very low, much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the mass–energy of the universe because it is uniform across space.Two proposed forms for dark energy are the cosmological constant, representing a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant can be formulated to be equivalent to the zero-point radiation of space i.e. the vacuum energy. Scalar fields that change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow.