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Loop quantum gravity
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<p>Loop quantum gravity (LQG) is a theory of <a href="/facts/Quantum_gravity/t7whBMNE">quantum gravity</a> that incorporates matter of the <a href="/facts/Standard_Model/LhVGf9ow">Standard Model</a> into the framework established for the intrinsic quantum gravity case. It is an attempt to develop a quantum theory of gravity based directly on <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a>'s geometric formulation rather than the treatment of gravity as a mysterious mechanism (force). As a theory, LQG postulates that the structure of <a href="/facts/Spacetime/uRIN1x4b">space and time</a> is composed of finite loops woven into an extremely fine fabric or network. These networks of loops are called <a href="/facts/Spin_network/EEE1kUfI">spin networks</a>. The evolution of a spin network, or <a href="/facts/Spin_foam/Lau32tx6">spin foam</a>, has a scale on the order of a <a href="/facts/Planck_length/4o04JYdD">Planck length</a>, approximately 10−35 meters, and smaller scales are meaningless. Consequently, not just matter, but space itself, prefers an atomic structure. </p><p>The areas of research, which involve about 30 research groups worldwide, 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 <a href="/facts/Spin_foam/Lau32tx6">spin foam</a> theory. The most well-developed theory that has been advanced as a direct result of loop quantum gravity is called <a href="/facts/Loop_quantum_cosmology/yxfgqNe6">loop quantum cosmology</a> (LQC). LQC advances the study of the early universe, incorporating the concept of the <a href="/facts/Big_Bang/I5T1vTnv">Big Bang</a> into the broader theory of the <a href="/facts/Big_Bounce/kGXNX90A">Big Bounce</a>, which envisions the Big Bang as the beginning of a <a href="/facts/Metric_expansion_of_space/f6Uvt79B">period of expansion</a>, that follows a period of contraction, which has been described as the <a href="/facts/Big_Crunch/bCewhu87">Big Crunch</a>. </p>