back-reaction
{{Refimprove|date=April 2017}}
In theoretical physics, back-reaction (or backreaction) is often necessary to calculate the self-consistent behaviour of a particle or an object in an external field.
Intuitive definition
When a particle is considered to have no mass or to have an infinitesimal charge, this can be described as saying that we deal with a probe and that back-reaction is neglected. However, a real object also carries (in general) a mass and a charge itself. These properties imply that the model of the original environment needs to be modified to reach self-consistency. For example, a particle can be described as helping to curve the space in general relativity. Taking into account the constraints implied on the model by the particle's properties – the back-reaction – is one way of reaching a more accurate model than if those constraints are ignored.
Cosmology
In inhomogeneous cosmology, in which structure formation is taken into account in a general-relativistic model of the Universe, the term "backreaction" is used for a measure of the non-commutativity of the averaging procedure
:
(which comes from the non-linearity of Einstein field equations) and the dynamical evolution of spatial slices of space-time.
{{As of|2017}}, the role of backreaction in possibly leading to an alternative to dark energy is an open question of debate among cosmologists. The existence of a homogeneity length scale can be considered to be that at which the calculations with and without backreaction give the same results. {{As of|2017}}, the existence of such a scale needs experimental confirmation.
References
{{reflist|30em|refs=
{{cite journal | last = Buchert | first = Thomas | title = Dark Energy from structure: a status report | journal = General Relativity and Gravitation | volume = 40 | issue = 2–3| pages = 467–527 | year = 2008 | arxiv = 0707.2153 | bibcode = 2008GReGr..40..467B | doi = 10.1007/s10714-007-0554-8 | s2cid = 17281664 }}
{{cite journal | last1 = Buchert |first1 = Thomas | last2 = Carfora |first2 = Mauro | last3 = Ellis |first3 = George F.R. |last4 = Kolb | first4 = Edward W. |last5 = MacCallum | first5 = Malcolm A.H. |last6 = Ostrowski | first6 = Jan J. |last7 = Räsänen |first7 = Syksy |last8 = Roukema |first8 = Boudewijn F. |last9 = Andersson | first9 = Lars |last10 = Coley |first10 = Alan A. |last11 = Wiltshire |first11 = David L. | author-link3 = George F. R. Ellis | author-link4 = Edward Kolb | title = Is there proof that backreaction of inhomogeneities is irrelevant in cosmology? | journal = Classical and Quantum Gravity | volume = 32 | issue = 21| pages = 215021 | date = 2015-10-13 | doi = 10.1088/0264-9381/32/21/215021 | arxiv = 1505.07800 |bibcode = 2015CQGra..32u5021B |s2cid = 51693570 }}
{{cite web|title=The Universe is inhomogeneous. Does it matter? |last1=Buchert |first1=Thomas |last2=Carfora |first2=Mauro |last3=Ellis |first3=George F.R. |last4=Kolb |first4=Edward W. |last5=MacCallum |first5=Malcolm A.H. |last6=Ostrowski |first6=Jan J. |last7=Räsänen |first7=Syksy |last8=Roukema |first8=Boudewijn F. |last9=Andersson |first9=Lars |last10=Coley |first10=Alan A. |last11=Wiltshire |first11=David L. |author-link3=George F. R. Ellis |author-link4=Edward Kolb |work=CQG+ |publisher=Institute of Physics |date=2016-01-20 |url=http://cqgplus.com/2016/01/20/the-universe-is-inhomogeneous-does-it-matter/ |access-date=2016-01-21 |archive-url=https://web.archive.org/web/20160123220203/http://cqgplus.com/2016/01/20/the-universe-is-inhomogeneous-does-it-matter/ |archive-date=2016-01-23 |url-status=live }}
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External links
{{cite web
|url=http://trenchesofdiscovery.blogspot.com.au/2015/07/cosmological-backreaction.html
|title=The Trenches of Discovery: Cosmological Backreaction
|author=Shaun Hotchkiss
|date=1 July 2015
|access-date=23 January 2016
}}
{{theoretical-physics-stub}}