Theoretical and experimental research on general relativity with torsion is reviewed. An introductory section establishes definitions and notation, introduces tetrads, the anholonomic formulation and the Dirac equation in curved space with torsion. After that, gauge theories of gravitation are introduced, starting with local Poincaré gauge theory, in which the torsion arises as a translational gauge field strength, and other gauge approaches are described. Torsion that is derived from a potential, including a scalar, vector, and tensor potential is discussed, with emphasis on the antisymmetric tensor of the string theory kind. Teleparallel theories are described, conformal invariance is discussed and a brief section on the equation of motion is presented. Experiments that have searched for, or bounded, torsion are described and the possible physical manifestations are broken down into the broad areas of quantum effects, laboratory scale phenomena and large-scale tests. Finally, a discussion of the relationship between string theory and torsion is presented.

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Intensities of 10 22 W cm −2 have been reached and it is expected that this will be increased by two orders of magnitude in the near future. At these intensities the radiation reaction force is important, especially in calculating the terminal velocity of an electron. The following briefly describes some of the problems of the existing most well-known equations and describes an approach based on conservation of energy. The resulting equation is compared to the Landau Lifshitz and Ford O'Connell equations, and laboratory tests are proposed.

In gravitation with torsion of the string theory type, it is shown that the Dirac equation acquires a coupling of the form where is due to the torsion field. It is shown that this interaction produces a mechanism for spin flipping, and the cross section for this process is calculated. The results are applied to solar neutrinos.