Loop quantum gravity (LQG) is a theory that describes the quantum properties of gravity. It is also a theory of quantum space and quantum time, because, as discovered with general relativity, the geometry of spacetime is a manifestation of gravity. LQG is an attempt to merge and adapt standard quantum mechanics and standard general relativity. The main output of the theory is a physical picture of space where space is granular. The granularity is a direct consequence of the quantization. It has the same nature of the granularity of the photons in the quantum theory of electromagnetism or the discrete levels of the energy of the atoms. But here it is space itself which is discrete.
More precisely, space can be viewed as an extremely fine fabric or network "woven" of finite loops. These networks of loops are called spin networks. The evolution of a spin network over time, is called a spin foam. The predicted size of this structure is the Planck length, which is approximately meters. According to the theory, there is no meaning to distance at scales smaller than the Planck scale. Therefore LQG predicts that not just matter, but also space itself, has an atomic structure.
Today LQG is a vast area of research, developed in several directions, which involves about 50 research groups world wide. They all share the basic physical assumptions and the mathematical description of quantum space. The full development of the theory is pursued in two directions: the more traditional canonical loop quantum gravity and the younger covariant loop quantum gravity, or spin foam theory.
Several research directions study the physical consequences of the theory. Among these, the most developed is the application of LQG to cosmology, called Loop quantum cosmology (LQC). LQC applies LQG ideas to the study of the early universe and the physics of the Big Bang. Its most spectacular consequence is that the evolution of the universe can be continued beyond the Big Bang. The Big Bang appears thus to be replaced by a sort of cosmic Big Bounce.
Read more about Loop Quantum Gravity: History, Key Concepts, Problems and Comparisons With Alternative Approaches
Other articles related to "loop quantum gravity, quantum gravity, quantum, loop quantum":
... The theory of LQG is one possible solution to the problem of quantum gravity, as is string theory ... Contrary to this, LQG is based only on quantum theory and general relativity and its scope is limited to understanding the quantum aspects of the gravitational interaction ... and time and provide a tentative but detailed physical and mathematical picture of quantum spacetime ...
... There have been recent claims that loop quantum gravity may be able to reproduce features resembling the Standard Model ... Utilization of quantum computing concepts made it possible to demonstrate that the particles are able to survive quantum fluctuations ... Fotini Markopolou, and Lee Smolin suggested that in any of a class of quantum gravity theories similar to loop quantum gravity in which spacetime comes in discrete chunks, excitations of ...
... When investigating the effects the theory of loop quantum gravity would have on cosmology, a loop quantum cosmology model has evolved that provides a possible mechanism for cosmological inflation ... Loop quantum gravity assumes a quantized spacetime ...
... His ideas have attracted interest in the field of loop quantum gravity, as they may represent a way of incorporating the Standard Model into loop quantum gravity ... This would make loop quantum gravity a candidate theory of everything ...
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