Editing String theory (section)

=== Applications to nuclear physics ===
{{main|AdS/QCD correspondence}}

[[File:Meissner effect p1390048.jpg|thumb|left|alt=A magnet levitating over a superconducting material.|A [[magnet]] [[Meissner effect|levitating]] above a [[high-temperature superconductor]]. Today some physicists are working to understand high-temperature superconductivity using the AdS/CFT correspondence.<ref name="Merali 2011"/>]]

In addition to its applications to theoretical problems in quantum gravity, the AdS/CFT correspondence has been applied to a variety of problems in quantum field theory. One physical system that has been studied using the AdS/CFT correspondence is the [[quark–gluon plasma]], an exotic [[state of matter]] produced in [[particle accelerator]]s. This state of matter arises for brief instants when heavy [[ions]] such as [[gold]] or [[lead]] nuclei are collided at high energies. Such collisions cause the [[quarks]] that make up atomic nuclei to [[deconfinement|deconfine]] at temperatures of approximately two [[1,000,000,000,000|trillion]] [[kelvin]], conditions similar to those present at around {{math|10<sup>−11</sup>}} seconds after the [[Big Bang]].<ref>[[#Zwiebach|Zwiebach]], p. 559</ref>

The physics of the quark–gluon plasma is governed by a theory called [[quantum chromodynamics]], but this theory is mathematically intractable in problems involving the quark–gluon plasma.{{efn|More precisely, one cannot apply the methods of perturbative quantum field theory.}} In an article appearing in 2005, [[Đàm Thanh Sơn]] and his collaborators showed that the AdS/CFT correspondence could be used to understand some aspects of the quark-gluon plasma by describing it in the language of string theory.<ref name="Kovtun, Son, and Starinets 2001"/> By applying the AdS/CFT correspondence, Sơn and his collaborators were able to describe the quark-gluon plasma in terms of black holes in five-dimensional spacetime. The calculation showed that the ratio of two quantities associated with the quark-gluon plasma, the [[shear viscosity]] and volume density of entropy, should be approximately equal to a certain universal [[constant (mathematics)|constant]]. In 2008, the predicted value of this ratio for the quark-gluon plasma was confirmed at the [[Relativistic Heavy Ion Collider]] at [[Brookhaven National Laboratory]].<ref name="Merali 2011"/><ref name=Luzum/>