Editing Theory of everything (section)

===Conventional sequence of theories===
A theory of everything would unify all the [[fundamental interaction]]s of nature: [[gravitation]], the [[strong interaction]], the [[weak interaction]], and [[electromagnetism]]. Because the weak interaction can transform [[elementary particles]] from one kind into another, the theory of everything should also predict all the different kinds of particles possible. The usual assumed path of theories is given in the following graph, where each unification step leads one level up on the graph.

{{tree chart/start}}
{{tree chart| | | | |TOE| | TOE=Theory of everything }}
{{tree chart| | | | | |!| | }}
{{tree chart| | | | |QG| | QG=[[Quantum gravity]] }}
{{tree chart| | | | | |!| | }}
{{tree chart| |REL|-|^|-|GUT| | REL=[[General Relativity|Space Curvature]] | GUT=Electronuclear force ([[Grand Unified Theory]]) }}
{{tree chart| | |!| | | | | |!| | }}
{{tree chart| |SMC| | | |SMP| SMC=[[Lambda-CDM model|Standard model of cosmology]] | SMP=[[Standard model of particle physics]]}}
{{tree chart| | | | | | | | |!| | }}
{{tree chart| | | | |QCD|-|^|-|-|EWT| | QCD=[[Strong interaction]]<br />[[Special unitary group|SU(3)]] | EWT=[[Electroweak interaction]]<br />[[Special unitary group|SU(2)]] x [[Unitary group|U(1)]]<sub>[[hypercharge|Y]]</sub> }}
{{tree chart| | | | | | | | | | | | |!| | }}
{{tree chart| | | | | | | | |WNF|-|^|-|EMF||WNF=[[Weak interaction]]<br />[[Special unitary group|SU(2)]]|EMF=[[Electromagnetism]]<br />[[Unitary group|U(1)]]<sub>EM</sub>}}
{{tree chart| | | | | | | | | | | | | | | |!| | | | | | }}
{{tree chart| | | | | | | | | | | |EF|-|^|-|MF| |EF=[[Electricity]]|MF=[[Magnetism]] }}
{{tree chart/end}}

In this graph, electroweak unification occurs at around 100 GeV, grand unification is predicted to occur at 10<sup>16</sup> GeV, and unification of the GUT force with gravity is expected at the [[Planck energy]], roughly 10<sup>19</sup> GeV.

Several [[Grand Unified Theory|Grand Unified Theories]] (GUTs) have been proposed to unify electromagnetism and the weak and strong forces. Grand unification would imply the existence of an electronuclear force; it is expected to set in at energies of the order of 10<sup>16</sup> GeV, far greater than could be reached by any currently feasible [[particle accelerator]]. Although the simplest grand unified theories have been experimentally ruled out, the idea of a grand unified theory, especially when linked with [[supersymmetry]], remains a favorite candidate in the theoretical physics community. Supersymmetric grand unified theories seem plausible not only for their theoretical "beauty", but because they naturally produce large quantities of dark matter, and because the inflationary force may be related to grand unified theory physics (although it does not seem to form an inevitable part of the theory). Yet grand unified theories are clearly not the final answer; both the current standard model and all proposed GUTs are [[quantum field theory|quantum field theories]] which require the problematic technique of [[renormalization]] to yield sensible answers. This is usually regarded as a sign that these are only [[effective field theory|effective field theories]], omitting crucial phenomena relevant only at very high energies.<ref name="Carlip" />

The final step in the graph requires resolving the separation between quantum mechanics and gravitation, often equated with general relativity. Numerous researchers concentrate their efforts on this specific step; nevertheless, no accepted theory of [[quantum gravity]], and thus no accepted theory of everything, has emerged with observational evidence. It is usually assumed that the theory of everything will also solve the remaining problems of grand unified theories.

In addition to explaining the forces listed in the graph, a theory of everything may also explain the status of at least two candidate forces suggested by modern [[physical cosmology|cosmology]]: an [[inflation (cosmology)|inflationary force]] and [[dark energy]]. Furthermore, cosmological experiments also suggest the existence of [[dark matter]], supposedly composed of fundamental particles outside the scheme of the standard model. However, the existence of these forces and particles has not been proven.