Thegrand unification energy, or theGUT scale, is the energy level above which, it is believed, theelectromagnetic force,weak force, andstrong force become equal in strength and unify to one force governed by asimple Lie group. The exact value of the grand unification energy (if grand unification is indeed realized in nature) depends on the precise physics present at shorter distance scales not yet explored by experiments. If one assumes theDesert andsupersymmetry, it is at around 1025eV or GeV (≈ 1.6megajoules).
SomeGrand Unified Theories (GUTs) can predict the grand unification energy but, usually, with large uncertainties due to model dependent details such as the choice of thegauge group, theHiggs sector, the matter content or further free parameters. Furthermore, at the moment it seems fair to state that there is no agreedminimal GUT.
The unification of theelectroweak force and thestrong force with thegravitational force in a so-called "Theory of Everything" requires an even higher energy level which is generally assumed to be close to thePlanck scale of GeV. In theory, at such short distances, gravity becomes comparable in strength to the other three forces of nature known to date. This statement is modified if there exist additional dimensions of space at intermediate scales. In this case, the strength of gravitational interactions increases faster at smaller distances and the energy scale at which all known forces of nature unify can be considerably lower. This effect is exploited in models oflarge extra dimensions.
The most powerfulcollider to date, theLarge Hadron Collider (LHC), is designed to reach about 104 GeV in proton–proton collisions. The scale 1016 GeV is only a feworders of magnitude below thePlanck energy of 1019 GeV, and thus not within reach of man-made earth bound colliders.[1]
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