Gravitation, Cosmology, and Cosmic-Ray Physics (1986) / Chapter Skim
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9. Gravitational Theory: Opportunities
9. Gravitational Theory: Opportunities
Pages 72-79
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From page 72... ...
The research problems discussed here are selected from the menu of topics that theorists currently consider important. CLASSICAL GRAVITATION, SINGULARITIES, ASYMPTOTIC STRUCTURE Although we now seem to have a decent understanding of the basic physics of the General Theory of Relativity in the nonquantum regime, outstanding problems of great significance remain.
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From page 73... ...
QUANTUM GRAVITY The unification of gravitation physics with quantum physics or the construction of a completely new theory incorporating both is one of the greatest challenges in theoretical physics. The challenge confronts us not so much because of the possibility of immediate experimental test (simple order-of-magnitude estimates indicate that laboratory tests of a quantum theory of gravity are not likely within the decade covered by this report)
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From page 74... ...
Perhaps the most important is the problem of the cosmological constant, or energy density, of the vacuum state. Calculation of quantum corrections to typical field theories suggests a cosmological constant of the order of unity on the Planck scale; observation tells us it is 10~2° times smaller.
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From page 75... ...
A partial list of them includes the canonical approach, covariant perturbation theory, Euclidean quantum gravity, quantum field theory in curved space-time, geometrical quantization, twister theory, discrete gravity, curvaturesquared theories, nonlinear quantum mechanics, spin networks, induced gravity, asymptotic quantization, quantum cosmology, supergravity theories, Kaluza-Klein theories, and superstring theories. One could perhaps even attempt to assess their prospects viewed from some present perspective.
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From page 76... ...
The ordered field interacts with the hole's rotation-induced gravitomagnetic field to produce ~102°-V potentials that accelerate relativistic particles out the poles, forming jets. This model exemplifies the complexity and variety of physics possible for black holes in an astrophysical setting and the importance of more detailed observations.
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From page 77... ...
An example is the problem of the black-hole binary, in which one follows the orbital decay and final coalescence of two black holes in a binary system with energy loss by gravitational waves. As possibly the strongest gravitywave source in the universe, this mechanism holds great promise for testing relativity in the regime of highly dynamical strong fields, if the wave forms can be detected and measured.
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From page 78... ...
At present all these seem far too weak to measure, but the possibility exists that some such effect will turn up that is within experimental reach. So far, no actually or potentially observable phenomena in high-energy physics have been tied to gravity, but modern Grand Unified Theories are importantly influenced by virtual processes that transpire at the grand unification mass scale, which may be only 2 to 4 orders of magnitude below the Planck mass scale of quantum gravity.
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From page 79... ...
Modern ideas from algebraic geometry have significantly influenced and contributed to the progress of the twister program and to the study of complex spaces at asymptotic null infinity. One can also expect this close relationship with mathematics to grow as mathematical tools become even more important in the exploration of theoretical ideas.
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