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This web page location: RelativityClassical PhysicsUnified Field Theory, positrons, quantum electrodynamics, relativity theory, spectral linesSince 1915 the theory of relativity has undergone much development and expansion by Einstein and by the British astronomers James Hopwood Jeans, Arthur Stanley Eddington, and Edward Arthur Milne, the Dutch astronomer Willem de Sitter, and the German American mathematician Hermann Weyl. Much of their work has been devoted to an effort to extend the theory of relativity to include electromagnetic phenomena (see Unified Field Theory). Although some progress has been made in this area, these efforts have been marked thus far by less success. No complete development of this application of the theory has yet been generally accepted. See Elementary Particles. The astronomers mentioned above also devoted much effort to developing the cosmological consequences of the theory of relativity. Within the framework of the axioms laid down by Einstein, many lines of development are possible. Space, for example, is curved, and its exact degree of curvature in the neighborhood of heavy bodies is known, but its curvature in empty space is not certain. Moreover, scientists disagree on whether it is a closed curve (such as a sphere) or an open curve (such as a cylinder or a bowl with sides of infinite height). The theory of relativity leads to the possibility that the universe is expanding; this is the most likely theoretical explanation of the experimentally observed fact that the spectral lines of all distant nebulae are shifted to the red; on the other hand the expandinguniverse theory also supplies other possible explanations. The latter theory makes it reasonable to assume that the past history of the universe is finite, but it also leads to alternative possibilities. See Cosmology. Much of the later work on relativity was devoted to creating a workable relativistic quantum mechanics. A relativistic electron theory was developed in 1928 by the British mathematician and physicist Paul Dirac, and subsequently a satisfactory quantized field theory, called quantum electrodynamics, was evolved, unifying the concepts of relativity and quantum theory in relation of the interaction between electrons, positrons, and electromagnetic radiation. In recent years, the work of the British physicist Stephen Hawking has been devoted to an attempted full integration of quantum mechanics with relativity theory. Article key phrases: 

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