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arxiv: hep-th/9905177 · v3 · submitted 1999-05-24 · ✦ hep-th · astro-ph· gr-qc

A Covariant Entropy Conjecture

classification ✦ hep-th astro-phgr-qc
keywords boundconjectureentropyadmittedareabecausebekensteinblack
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We conjecture the following entropy bound to be valid in all space-times admitted by Einstein's equation: Let A be the area of any two-dimensional surface. Let L be a hypersurface generated by surface-orthogonal null geodesics with non-positive expansion. Let S be the entropy on L. Then S does not exceed A/4. We present evidence that the bound can be saturated, but not exceeded, in cosmological solutions and in the interior of black holes. For systems with limited self-gravity it reduces to Bekenstein's bound. Because the conjecture is manifestly time reversal invariant, its origin cannot be thermodynamic, but must be statistical. Thus it places a fundamental limit on the number of degrees of freedom in nature.

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