In physics, a spin foam is a four-dimensional graph made out of two-dimensional faces that represents one of the configurations that must be summed to obtain Feynman's path integral (functional integration) describing the alternative formulation of quantum gravity known as loop gravity or loop quantum gravity. Physics (from the Greek, φυσικός (phusikos), natural, and φύσις (phusis), nature) is the science of nature in the broadest sense. ... This article is about a formulation of quantum mechanics. ... In physics, functional integration is integration over certain infinite-dimensional spaces. ... Quantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ... Loop quantum gravity (LQG), also known as loop gravity, quantum geometry and canonical quantum general relativity, is a proposed quantum theory of spacetime which attempts to blend together the seemingly incompatible theories of quantum mechanics and general relativity. ... This article needs to be cleaned up to conform to a higher standard of article quality. ...

In loop quantum gravity there are some results from a possible canonical quantization of general relativity. Any path integral formulation of the theory can be written in the form of a spin foam model, such as the Barrett-Crane model. Spin network is defined as a diagram (like Feynman diagram) which make a basis of connections between the elements of a differentiable manifold for the Hilbert spaces defined over them. Spin network provides a representation for computations of amplitudes between two different hypersurfaces of the manifold. Any evolution of spin network provides a spin foam over a manifold of one dimensional higher than the dimensions of the corresponding spin network. This article needs to be cleaned up to conform to a higher standard of article quality. ... In physics, quantization of a theory is the formulation of a classical theory in the formalism of quantum physics. ... Two-dimensional visualisation of space-time distortion. ... A spin network is a graph whose edges are associated with representations of a Lie group, G and vertices are associated with intertwiners of the edge reps adjacent to it. ... A Feynman diagram is a bookkeeping device for performing calculations in quantum field theory, invented by American physicist Richard Feynman. ... In mathematics, a manifold M is a type of space, characterised in one of two equivalent ways: near every point of the space, we have a coordinate system; or near every point, the environment is like that in Euclidean space of a given dimension. ... A spin network is a graph whose edges are associated with representations of a Lie group, G and vertices are associated with intertwiners of the edge reps adjacent to it. ... In mathematics, a manifold M is a type of space, characterized in one of two equivalent ways: near every point of the space, we have a coordinate system; or near every point, the environment is like that in Euclidean space of a given dimension. ... A spin network is a graph whose edges are associated with representations of a Lie group, G and vertices are associated with intertwiners of the edge reps adjacent to it. ...

A spin foam may be viewed as a history of evolution of a spin network. A spin network is a graph whose edges are associated with representations of a Lie group, G and vertices are associated with intertwiners of the edge reps adjacent to it. ...