Editing Loop quantum gravity (section)

{{Short description|Theory of quantum gravity, merging quantum mechanics and general relativity}}
{{Technical|date=September 2024}}
{{Use dmy dates|date=July 2020}}
{{How-to|date=May 2019}}
{{Beyond the Standard Model|expanded=[[Quantum gravity]]}}

'''Loop quantum gravity''' ('''LQG''') is a theory of [[quantum gravity]] that incorporates matter of the [[Standard Model]] into the framework established for the intrinsic quantum gravity case. It is an attempt to develop a quantum theory of gravity based directly on [[Albert Einstein]]'s geometric formulation rather than the treatment of gravity as a mysterious mechanism (force). As a theory, LQG postulates that the structure of [[Spacetime|space and time]] is composed of finite loops woven into an extremely fine fabric or network. These networks of loops are called [[spin network]]s. The evolution of a spin network, or [[spin foam]], has a scale on the order of a [[Planck length]], approximately 10<sup>−35</sup> meters, and smaller scales are meaningless. Consequently, not just matter, but space itself, prefers an atomic structure.

The areas of research, which involve about 30 research groups worldwide,{{sfn|Rovelli|2008}} share the basic physical assumptions and the mathematical description of quantum space. Research has evolved in two directions: the more traditional canonical loop quantum gravity, and the newer covariant loop quantum gravity, called [[spin foam]] theory. The most well-developed theory that has been advanced as a direct result of loop quantum gravity is called [[loop quantum cosmology]] (LQC). LQC advances the study of the early universe, incorporating the concept of the [[Big Bang]] into the broader theory of the [[Big Bounce]], which envisions the Big Bang as the beginning of a [[Metric expansion of space|period of expansion]], that follows a period of contraction, which has been described as the [[Big Crunch]].