1,729 research outputs found
Light-like Signals in General relativity and Cosmology
The modelling of light-like signals in General Relativity taking the form of
impulsive gravitational waves and light-like shells of matter is examined.
Systematic deductions from the Bianchi identities are made. These are based
upon Penrose's hierarchical classification of the geometry induced on the null
hypersurface history of the surface by its imbedding in the space-times to the
future and to the past of it. The signals are not confined to propagate in a
vacuum and thus their interaction with matter (a burst of radiation propagating
through a cosmic fluid, for example) is also studied. Results are accompanied
by illustrative examples using cosmological models, vacuum space-times, the de
sitter univers and Minkowskian space-time.Comment: 21 pages, latex, no figure
General relativity and cosmology derived from principle of maximum power or force
The field equations of general relativity are shown to derive from the
existence of a limit force or of a limit power in nature. The limits have the
value of c^4/4G and c^5/4G. The proof makes use of a result by Jacobson. All
known experimental data is consistent with the limits. Applied to the universe,
the limits predict its darkness at night and the observed scale factor. Some
experimental tests of the limits are proposed. The main counter-arguments and
paradoxes are discussed, such as the transformation under boosts, the force
felt at a black hole horizon, the mountain problem, and the contrast to
scalar--tensor theories of gravitation. The resolution of the paradoxes also
clarifies why the maximum force and the maximum power have remained hidden for
so long. The derivation of the field equations shows that the maximum force or
power plays the same role for general relativity as the maximum speed plays for
special relativity.Comment: 24 pages, 1 figure, LaTeX, published versio
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