Theory of everything

A hypothetical physical theory that would describe all fundamental particles and forces within a single framework, including gravity and quantum phenomena.

Standard Model: The quantum field theory describing known elementary particles and three fundamental interactions, excluding gravity. It already unifies electromagnetic and weak interactions and describes the other known particles.
String theory: A theoretical framework in which fundamental entities are one-dimensional strings whose vibrational states appear as particles. Its spectrum can include a graviton, offering a route to quantum gravity and unification.
Effective field theory: A theory that describes phenomena within a specified energy range without claiming validity at all scales. Unlike a theory of everything, it can be scientifically useful while remaining explicitly limited in scope.
Planck scale: The regime near the Planck length and energy, where quantum effects of gravity are expected to become significant. Directly probing this regime is beyond the energies achievable in current experiments.
Electroweak interaction: The unified description of electromagnetic and weak interactions that applies at sufficiently high energies. Its experimental confirmation shows that distinct forces can emerge from one underlying framework.
General relativity: Einstein’s theory of gravity, describing it as the curvature of spacetime caused by matter and energy. Any complete framework must recover its tested account of gravity at large scales.
Loop quantum gravity: An approach to quantum gravity that quantizes spacetime geometry without requiring a unified account of all forces. It seeks quantum gravity but does not, by itself, unify the Standard Model interactions.
Reductionism: The methodological view that complex phenomena can be explained through simpler components and their interactions. The ambition to derive all fundamental physics is a strong form of explanatory reduction.
Cosmic inflation: A proposed brief period of accelerated expansion in the early universe. Its underlying physics is unknown and may provide evidence about fundamental fields and high-energy theories.
Proton decay: A hypothetical transformation of a proton into lighter particles, forbidden in the Standard Model but predicted by some unification theories. Its observation would support certain grand unified models; searches have found no decay.

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