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Inflationary epoch

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In physical cosmology, the inflationary epoch was the period in the evolution of the early universe when, according to inflation theory, the universe underwent an extremely rapid exponential expansion. This rapid expansion increased the linear dimensions of the early universe by a factor of at least 1026 (and possibly a much larger factor), and so increased its volume by a factor of at least 1078. Expansion by a factor of 1026 is 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 62 trillion miles).


Vacuum state is a configuration of quantum fields representing a local minimum (but not necessarily a global minimum) of energy.

Inflationary models propose that at approximately 10−36 seconds after the Big Bang, vacuum state of the Universe was different from the one seen at the present time: the inflationary vacuum had a much higher energy density.

According to general relativity, any vacuum state with non-zero energy density generates a repulsive force that leads to an expansion of space. In inflationary models, early high-energy vacuum state causes a very rapid expansion. This expansion explains various properties of the current universe that are difficult to account for without such an inflationary epoch.

Most inflationary models propose a scalar field called the inflaton field, with properties necessary for having (at least) two vacuum states.

It is not known exactly when the inflationary epoch ended, but it is thought to have been between 10−33 and 10−32 seconds after the Big Bang. The rapid expansion of space meant that any potential elementary particles (or other "unwanted" artifacts, such as topological defects) remaining from the time before inflation were now distributed very thinly across the universe.

When the inflaton field reconfigured itself into the low-energy vacuum state we currently observe, the huge difference in potential energy was released in the form of a dense, hot mixture of quarks, anti-quarks and gluons as it entered the electroweak epoch.

Detection via polarization of cosmic microwave background radiation[edit]

One approach to confirming the inflationary epoch is to directly measure its effect on the cosmic microwave background (CMB) radiation. The CMB is very weakly polarized (to a level of a few μK) in two different modes called E-mode and B-mode (by analogy to the E-field and B-field in electrostatics). The E-mode polarization comes from ordinary Thomson scattering,[1] but the B-mode may be created by two mechanisms:

  1. from gravitational lensing of E-modes; or
  2. from gravitational waves arising from cosmic inflation.

If B-mode polarization from gravitational waves can be measured, it would provide direct evidence supporting cosmic inflation and could eliminate or support various inflation models based on the level detected.

On 17 March 2014, astrophysicists of the BICEP2 collaboration announced the detection of B-mode polarization attributed to inflationary-related gravitational waves, which seemed to support cosmological inflation and the Big Bang,[2][3][4][5][6] however, on 19 June 2014 they lowered the confidence level that the B-mode measurements were actually from gravitational waves and not from background noise from dust.[7][8][9]

The Planck spacecraft has instruments that measure the CMB radiation to a high degree of sensitivity (57 nK). After the BICEP finding, scientists from both projects worked together to further analyze the data from both projects. That analysis concluded to a high degree of certainty that the original BICEP signal can be entirely attributed to dust in the Milky Way and therefore does not provide evidence one way or the other to support the theory of the inflationary epoch.[10][11][12][13]

See also[edit]


  1. ^ Tizchang, S.; Batebi, S.; Haghighat, M.; Mohammadi, R. (2016). "Cosmic microwave background polarization in non-commutative space-time". The European Physical Journal C. 76 (9): 478. arXiv:1605.09045. Bibcode:2016EPJC...76..478T. doi:10.1140/epjc/s10052-016-4312-5. S2CID 123613107.
  2. ^ "BICEP2 2014 results released" (Press release). National Science Foundation. 17 March 2014. Retrieved 18 March 2014.
  3. ^ Clavin, Whitney (17 March 2014). "NASA technology views birth of the universe" (Press release). NASA. Retrieved 17 March 2014.
  4. ^ Overbye, Dennis (17 March 2014). "Detection of waves in space buttresses landmark theory of Big Bang". The New York Times. Retrieved 17 March 2014.
  5. ^ Ade, P.A.R.; Aikin, R.W.; Barkats, D.; Benton, S.J.; Bischoff, C.A.; Bock, J.J.; et al. (BICEP2 Collaboration) (17 March 2014). "BICEP2 I: Detection of B-mode polarization at degree angular scales" (PDF). Physical Review Letters. 112 (24): 241101. arXiv:1403.3985. Bibcode:2014PhRvL.112x1101B. doi:10.1103/PhysRevLett.112.241101. PMID 24996078. S2CID 22780831. Archived from the original (PDF) on 17 March 2014.
  6. ^ Woit, Peter (13 May 2014). "BICEP2 News". Not Even Wrong. Columbia University. Retrieved 19 January 2014.
  7. ^ Overbye, Dennis (19 June 2014). "Astronomers hedge on Big Bang detection claim". New York Times. Retrieved 20 June 2014.
  8. ^ Amos, Jonathan (19 June 2014). "Cosmic inflation: Confidence lowered for Big Bang signal". BBC News. Retrieved 20 June 2014.
  9. ^ Ade, P.A.R.; et al. (BICEP2 Collaboration) (19 June 2014). "Detection of B-mode polarization at degree angular scales by BICEP2". Physical Review Letters. 112 (24): 241101. arXiv:1403.3985. Bibcode:2014PhRvL.112x1101B. doi:10.1103/PhysRevLett.112.241101. PMID 24996078. S2CID 22780831.
  10. ^ Adam, R.; Ade, P.A.R.; et al. (Planck Collaboration) (2016). "Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes". Astronomy & Astrophysics. 586 (133): A133. arXiv:1409.5738. Bibcode:2016A&A...586A.133P. doi:10.1051/0004-6361/201425034. S2CID 9857299.
  11. ^ Overbye, D. (22 September 2014). "Study confirms criticism of Big Bang finding". New York Times. Retrieved 2014-09-22.
  12. ^ Cowen, Ron (30 January 2015). "Gravitational waves discovery now officially dead". Nature. doi:10.1038/nature.2015.16830. S2CID 124938210.
  13. ^ Ade P. A. R.; et al. (BICEP2/Keck and Planck Collaborations) (2015). "Joint analysis of BICEP2/Keck array and Planck data". Physical Review Letters. 114 (10): 101301. arXiv:1502.00612. Bibcode:2015PhRvL.114j1301B. doi:10.1103/PhysRevLett.114.101301. PMID 25815919. S2CID 218078264.


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