1,295 research outputs found

### Simple sufficient conditions for the generalized covariant entropy bound

The generalized covariant entropy bound is the conjecture that the entropy of
the matter present on any non-expanding null hypersurface L will not exceed the
difference between the areas, in Planck units, of the initial and final spatial
2-surfaces bounding L. The generalized Bekenstein bound is a special case which
states that the entropy of a weakly gravitating isolated matter system will not
exceed the product of its mass and its width. Here we show that both bounds can
be derived directly from the following phenomenological assumptions: that
entropy can be computed by integrating an entropy current which vanishes on the
initial boundary and whose gradient is bounded by the energy density. Though we
note that any local description of entropy has intrinsic limitations, we argue
that our assumptions apply in a wide regime. We closely follow the framework of
an earlier derivation, but our assumptions take a simpler form, making their
validity more transparent in some examples.Comment: 7 pages, revte

### Light-sheets and Bekenstein's bound

From the covariant bound on the entropy of partial light-sheets, we derive a
version of Bekenstein's bound: S/M \leq pi x/hbar, where S, M, and x are the
entropy, total mass, and width of any isolated, weakly gravitating system.
Because x can be measured along any spatial direction, the bound becomes
unexpectedly tight in thin systems. Our result completes the identification of
older entropy bounds as special cases of the covariant bound. Thus,
light-sheets exhibit a connection between information and geometry far more
general, but in no respect weaker, than that initially revealed by black hole
thermodynamics.Comment: 5 pages, 1 figure; v2: published version, improved discussion of weak
gravity condition, final paragraph adde

### The Holographic Principle for General Backgrounds

We aim to establish the holographic principle as a universal law, rather than
a property only of static systems and special space-times. Our covariant
formalism yields an upper bound on entropy which applies to both open and
closed surfaces, independently of shape or location. It reduces to the
Bekenstein bound whenever the latter is expected to hold, but complements it
with novel bounds when gravity dominates. In particular, it remains valid in
closed FRW cosmologies and in the interior of black holes. We give an explicit
construction for obtaining holographic screens in arbitrary space-times (which
need not have a boundary). This may aid the search for non-perturbative
definitions of quantum gravity in space-times other than AdS.Comment: 15 pages, 4 figures. Based on a talk given at Strings '99. Includes a
reply to recent criticism. For more details, examples, and references, see
hep-th/9905177 and hep-th/990602

### Flat space physics from holography

We point out that aspects of quantum mechanics can be derived from the
holographic principle, using only a perturbative limit of classical general
relativity. In flat space, the covariant entropy bound reduces to the
Bekenstein bound. The latter does not contain Newton's constant and cannot
operate via gravitational backreaction. Instead, it is protected by - and in
this sense, predicts - the Heisenberg uncertainty principle.Comment: 11 pages, 3 figures; v2: minor correction

### The nonlinear evolution of de Sitter space instabilities

We investigate the quantum evolution of large black holes that nucleate
spontaneously in de Sitter space. By numerical computation in the s-wave and
one-loop approximations, we verify claims that such black holes can initially
"anti-evaporate" instead of shrink. We show, however, that this is a transitory
effect. It is followed by an evaporating phase, which we are able to trace
until the black holes are small enough to be treated as Schwarzschild. Under
generic perturbations, the nucleated geometry is shown to decay into a ring of
de Sitter regions connected by evaporating black holes. This confirms that de
Sitter space is globally unstable and fragments into disconnected daughter
universes.Comment: 10 pages, 8 figures, to appear in PR

### Light Sheets and the Covariant Entropy Conjecture

We examine the holography bound suggested by Bousso in his covariant entropy
conjecture, and argue that it is violated because his notion of light sheet is
too generous. We suggest its replacement by a weaker bound.Comment: 5 pages, to appear in Classical and Quantum Gravit

### A covariant entropy bound conjecture on the dynamical horizon

As a compelling pattern for the holographic principle, our covariant entropy
bound conjecture is proposed for more general dynamical horizons. Then we apply
our conjecture to $\Lambda$CDM cosmological models, where we find it imposes a
novel upper bound $10^{-90}$ on the cosmological constant for our own universe
by taking into account the dominant entropy contribution from super-massive
black holes, which thus provides an alternative macroscopic perspective to
understand the longstanding cosmological constant problem. As an intriguing
implication of this conjecture, we also discuss the possible profound relation
between the present cosmological constant, the origin of mass, and the
anthropic principle.Comment: JHEP style, 9 pages, 1 figure, honorable mention award received from
Gravity Research Foundation for 2008 Essay Competitio

### (Anti-)Evaporation of Schwarzschild-de Sitter Black Holes

We study the quantum evolution of black holes immersed in a de Sitter
background space. For black holes whose size is comparable to that of the
cosmological horizon, this process differs significantly from the evaporation
of asymptotically flat black holes. Our model includes the one-loop effective
action in the s-wave and large N approximation. Black holes of the maximal mass
are in equilibrium. Unexpectedly, we find that nearly maximal quantum
Schwarzschild-de Sitter black holes anti-evaporate. However, there is a
different perturbative mode that leads to evaporation. We show that this mode
will always be excited when a pair of cosmological holes nucleates.Comment: 16 pages, LaTeX2e; submitted to Phys. Rev.

### A covariant entropy conjecture on cosmological dynamical horizon

We here propose a covariant entropy conjecture on cosmological dynamical
horizon. After the formulation of our conjecture, we test its validity in
adiabatically expanding universes with open, flat and closed spatial geometry,
where our conjecture can also be viewed as a cosmological version of the
generalized second law of thermodynamics in some sense.Comment: JHEP style, 9 pages, 1 figure, typos corrected, accepted for
publication in JHE

### Quantum Global Structure of de Sitter Space

I study the global structure of de Sitter space in the semi-classical and
one-loop approximations to quantum gravity. The creation and evaporation of
neutral black holes causes the fragmentation of de Sitter space into
disconnected daughter universes. If the black holes are stabilized by a charge,
I find that the decay leads to a necklace of de Sitter universes (`beads')
joined by near-extremal black hole throats. For sufficient charge, more and
more beads keep forming on the necklace, so that an unbounded number of
universes will be produced. In any case, future infinity will not be connected.
This may have implications for a holographic description of quantum gravity in
de Sitter space.Comment: 37 pages, LaTeX2e, 10 figures. v2: references adde

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