Planck scale: Difference between revisions
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In [[particle physics]] and [[physical cosmology]], the '''Planck scale''' (named after [[Max Planck]]) is an [[energy scale]] around 1.22 × 10<sup>19</sup> [[GeV]] (the [[Planck energy]], corresponding to the [[mass–energy equivalence]] of the [[Planck mass]], 2.17645 × 10<sup>−8</sup> kg) at which [[quantum effects]] of [[gravity]] become strong. At this scale, present descriptions and theories of sub-atomic particle interactions in terms of [[quantum field theory]] break down and become inadequate, due to the impact of the apparent [[renormalization|non-renormalizability]] of gravity within current theories. |
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==Relationship to gravity== |
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At the Planck scale, the strength of gravity is expected to become comparable with the other forces, and it is theorized that all the fundamental forces are unified at that scale, but the exact mechanism of this unification remains unknown. The Planck scale is therefore the point where the effects of quantum gravity can no longer be ignored in other [[fundamental interactions]], and where current calculations and approaches begin to break down, and a means to take account of its impact is required.{{citation-needed}} |
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While physicists have a fairly good understanding of the other fundamental interactions of forces on the quantum level, [[gravity]] is problematic, and cannot be integrated with [[quantum mechanics]] at very high energies using the usual framework of quantum field theory. At lesser energy levels it is usually ignored, while for energies approaching or exceeding the Planck scale, a new theory of [[quantum gravity]] is required. Other approaches to this problem include [[string theory]] and [[M-theory]], [[loop quantum gravity]], [[noncommutative geometry]], [[scale relativity]], [[causal sets|causal set theory]] and [[P-adic quantum mechanics]].<ref>Number Theory as the Ultimate Physical Theory, Igor V. Volovich, [http://empslocal.ex.ac.uk/~mwatkins/zeta/volovich1.pdf empslocal.ex.ac.uk/~mwatkins/zeta/volovich1.pdf], [http://10.1134/S2070046610010061 10.1134/S2070046610010061]</ref> |
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==Cosmology== |
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{{anchor|Planck epoch}} |
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In [[Big Bang cosmology]], the '''Planck epoch''' or '''Planck era''' refers to the earliest stage of the [[Big Bang]], before the [[cosmic time|time passed]] was equal to the [[Planck time]], approximately 10<sup>−43</sup> seconds. |
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There is no currently available physical theory to describe such short times, and it is not clear in what sense the concept of [[time]] is meaningful |
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for values smaller than the Planck time. It is generally assumed that [[quantum gravity|quantum effects of gravity]] dominate physical interactions at this time scale. At this scale, the [[grand unification|unified force]] of the [[Standard Model]] is assumed to be [[Theory of everything|unified with gravitation]]. Inconceivably [[Planck temperature|hot]] and [[Planck density|dense]], the state of the Planck epoch was succeded by the [[Grand unification epoch]], where gravitation is separated from the unified force of the Standard Model, in turn followed by the [[Inflationary epoch]], which ended after about 10<sup>−32</sup> seconds (i.e. ten billion times the Planck time).<ref name="KolbTurner1994">{{cite book|author1=Edward W. Kolb|author2=Michael S. Turner|title=The Early Universe|url=http://books.google.com/?id=l6Z8W33JWGQC&pg=PA447|accessdate=10 April 2010|year=1994|publisher=Basic Books|isbn=978-0-201-62674-2|page=447}}</ref> |
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Expressing [[fundamental constant]]s in terms of the Planck scale may lead to insights into [[cosmology]].<ref>{{cite journal|author=P.A.M. Dirac|year=1938 |title=A New Basis for Cosmology |journal=[[Proceedings of the Royal Society A]] |volume=165 |issue=921 |pages=199–208 |doi=10.1098/rspa.1938.0053 |bibcode = 1938RSPSA.165..199D }}</ref> After the measurement of the [[cosmological constant]] in 1998, estimated at 10<sup>−122</sup> in Planck units, it was noted that this is suggestively close to the reciprocal of the [[Age of the Universe]] squared.<ref> J.D. Barrow and F.J. Tipler, ''The Anthropic Cosmological'' Principle, Oxford UP, Oxford (1986), chapter 6.9.</ref> Barrow and Shaw (2011) proposed a modified theory in which Λ is a field evolving in such a way that its value remains Λ ~ ''T''<sup>-2</sup> throughout the history of the universe.<ref>John D. Barrow, Douglas J. Shaw, "The Value of the Cosmological Constant", ''General Relativity and Gravitation 43, 2555-2560 (2011) |
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DOI: 10.1007/s10714-011-1199-1, arXiv:1105.3105.</ref> |
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==Other uses== |
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{{refimprove section}} |
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The term '''Planck scale''' can also refer to a [[length scale]] or time scale. |
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{| class="wikitable" style="text-align:left" |
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! Quantity !! SI equivalent |
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| [[Planck time]] || 5.39121 × 10<sup>−44</sup> s |
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| [[Planck mass]] || 2.17645 × 10<sup>−8</sup> kg |
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| [[Planck length]] (''ℓ''<sub>P</sub>) || {{val|1.616252|e=-35|u=m}} |
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The [[Planck length]] is related to [[Planck energy]] by the [[uncertainty principle]]. At this scale, the concepts of size and distance break down, as [[quantum indeterminacy]] becomes virtually absolute. Because the [[Schwarzschild radius]] of a [[black hole]] is roughly equal to the [[Compton wavelength]] at the Planck scale, a photon with sufficient energy to probe this realm would yield no information whatsoever. Any photon energetic enough to precisely measure a Planck-sized object could actually ''create'' a particle of that dimension, but it would be massive enough to immediately become a black hole (a.k.a. [[Planck particle]]), thus completely distorting that region of space, and swallowing the photon. This is the most extreme example possible of the uncertainty principle, and explains why only a [[quantum gravity]] theory reconciling [[general relativity]] with [[quantum mechanics]] will allow us to understand the dynamics of [[space-time]] at this scale. Planck scale dynamics are important for cosmology because if we trace the evolution of the cosmos back to the very beginning, at some very early stage the universe should have been so hot that processes involving energies as high as the Planck energy (corresponding to distances as short as the Planck length) may have occurred. This period is therefore called the Planck era or [[Planck epoch]]. |
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==See also== |
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* [[Planck epoch]] |
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* [[Planck particle]] |
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* [[Quantum gravity]] |
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* [[Max Planck]] |
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==References== |
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{{reflist}} |
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==External links== |
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* [http://www.phys.unsw.edu.au/einsteinlight/jw/module6_Planck.htm The Planck scale: relativity meets quantum mechanics meets gravity] from 'Einstein Light' at UNSW |
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* [http://csep10.phys.utk.edu/astr162/lect/cosmology/planck.html The Planck Era] from U of Tennessee Astrophysics pages |
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* [http://math.ucr.edu/home/baez/planck/ Higher-Dimensional Algebra and Planck-Scale Physics] by [[John C. Baez]] |
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* [http://arxiv.org/abs/1001.1205 Six easy roads to the Planck scale] |
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* {{cite book|title=The Planck Epoch|url=http://www.universeadventure.org/eras/era1-plankepoch.htm}} |
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* {{cite book|title=Evolution of the Universe through the Planck Epoch|url=http://www.springerlink.com/content/r977119j22h24071/}} |
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* [http://csep10.phys.utk.edu/astr162/lect/cosmology/planck.html The Planck Era] from U of Tennessee Astrophysics pages |
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* [http://zebu.uoregon.edu/~imamura/209/apr5/planck.html The Planck Era] from U of Oregon Cosmology pages |
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* [http://www.astronomycafe.net/anthol/planck.html The Planck Era] by Sten Odenwald from Astronomy Cafe |
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* [http://abyss.uoregon.edu/~js/ast123/lectures/lec17.html The Plank Epoch] by professor James Schombert 39O |
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* [http://www.site.uottawa.ca:4321/astronomy/index.html#Planckera The Planck Era - definition] from U of Ottawa's Astronomy Knowledge Base |
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{{quantum gravity}} |
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{{DEFAULTSORT:Planck Scale}} |
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[[Category:Astrophysics]] |
[[Category:Astrophysics]] |
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[[Category:Particle physics]] |
[[Category:Particle physics]] |
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