84 research outputs found
Black Holes: Classical Properties, Thermodynamics and Heuristic Quantization
I discuss the no hair principle, the recently found hairy solutions, generic
properties of nonvacuum spherical static black holes, and the new no scalar
hair theorems. I go into the generic phenomenon of superradiance, first uniform
linear motion superradiance, then Kerr black hole superradiance, and finally
general rotational superradiance and its possible applications in the
laboratory. I show that the horizon area of a nearly stationary black hole can
be regarded as an adiabatic invariant. This invariance suggests that quantum
horizon area is quantized in multiples of a basic unit. Consideration of the
quantum version of the Christodoulou reversible processes provides support for
this idea. Horizon area quantization dictates a definite discrete black hole
mass spectrum, so that Hawking's semiclassical spectrum is predicted to be
replaced by a spectrum of nearly uniformly spaced lines whose envelope is
roughly Planckian. Line natural broadening seems not enough to wash out the
lines. To check on the possibility of line splitting, I present a simple
algebra involving, among other operators, the black hole observables. Under
simple assumptions it also leads to the uniformly spaced area spectrum.Comment: LaTeX, 44 pages, 4 eps figs. and conf_cg.sty included. Lectures
delivered at the IX Brazilian School on Cosmology and Gravitation, Rio de
Janeiro 7-8/98. Updated references and positioning on page correcte
Black hole hair: twenty--five years after
Originally regarded as forbidden, black hole ``hair'' are fields associated
with a stationary black hole apart from the gravitational and electromagnetic
ones. Several stable stationary black hole solutions with gauge or Skyrme field
hair are known today within general relativity. We formulate here a ``no
scalar--hair'' conjecture, and adduce some new theorems that almost establish
it by ruling out - for all but a small parameter range - scalar field hair of
spherical black holes in general relativity, whether the field be
self--interacting, coupled to an Abelian gauge field, or nonminimally coupled
to gravity.Comment: 6 pages, Latex, Invited talk at the Second Sakharov Conference in
Physics, Moscow, May 20-24, 1996; briefer version to appear in the
proceeding
Disturbing the Black Hole
I describe some examples in support of the conjecture that the horizon area
of a near equilibrium black hole is an adiabatic invariant. These include a
Schwarzschild black hole perturbed by quasistatic scalar fields (which may be
minimally or nonminimally coupled to curvature), a Kerr black under the
influence of scalar radiation at the superradiance treshold, and a
Reissner--Nordstr\"om black hole absorbing a charge marginally. These clarify
somewhat the conditions under which the conjecture would be true. The desired
``adiabatic theorem'' provides an important motivation for a scheme for black
hole quantization.Comment: 15 pages, LaTeX with crckapb style, to appear in ``The Black Hole
Trail'', eds. B. Bhawal and B. Iyer (Kluwer, Dordrecht 1998
Optimizing entropy bounds for macroscopic systems
The universal bound on specific entropy was originally inferred from black
hole thermodynamics. We here show from classical thermodynamics alone that for
a system at fixed volume or fixed pressure, the ratio of entropy to
nonrelativistic energy has a unique maximum . A simple
argument from quantum dynamics allows one to set a model--independent upper
bound on which is usually much tighter than the universal
bound. We illustrate with two examples.Comment: 13 pages, 2 figures, LaTe
Limitations on quantum information from black hole physics
After reviewing the relation of entropy to information, I derive the entropy
bound as applied to bounded weakly gravitating systems, and review the bound's
applications to cosmology as well as its extensions to higher dimensions. I
then discuss why black holes behave as 1-D objects when emitting entropy, which
suggests that a black hole swallows information at a rate restricted by the
one-channel information capacity. I discuss fundamental limitations on the
information borne by signal pulses in curved spacetime, from which I verify the
mentioned bound on the rate of information disposal by a black hole.Comment: LaTeX, 14 pages. Lecture delivered at XXV International School of
Theoretical Physics, Ustron, Poland, Sep. 10-16, 2001 (proceedings edited by
M. Biesiada to appear in Acta Physica Polonica B). It is an abridged
streamlined version of one of my Erice (2001) lectures, gr-qc/010704
Preparing the State of a Black Hole
Measurements of the mass or angular momentum of a black hole are onerous,
particularly if they have to be frequently repeated, as when one is required to
transform a black hole to prescribed parameters. Irradiating a black hole of
the Kerr-Newman family with scalar or electromagnetic waves provides a way to
drive it to prescribed values of its mass, charge and angular momentum without
the need to repeatedly measure mass or angular momentum throughout the process.
I describe the mechanism, which is based on Zel'dovich-Misner superradiance and
its analog for charged black holes. It represents a possible step in the
development of preparation procedures for quantum black holes.Comment: Essay in honor of Mario Novello's sixtieth birthday. LaTeX 209, 12
pages, no figure
Holographic Bound from Second Law
The holographic bound that the entropy (log of number of quantum states) of a
system is bounded from above by a quarter of the area of a circumscribing
surface measured in Planck areas is widely regarded a desideratum of any
fundamental theory, but some exceptions occur. By suitable black hole gedanken
experiments I show that the bound follows from the generalized second law for
two broad classes of isolated systems: generic weakly gravitating systems
composed of many elementary particles, and quiescent, nonrotating strongly
gravitating configurations well above Planck mass. These justify an early claim
by Susskind.Comment: Invited talk at Marcel Grossman IX meeting in Rome, July 2000;
improved version of Phys. Lett. B 481, 339 (2000). 7 pages, LaTeX with
included mprocl.st
An alternative to the dark matter paradigm: relativistic MOND gravitation
MOND, invented by Milgrom, is a phenomenological scheme whose basic premise
is that the visible matter distribution in a galaxy or cluster of galaxies
alone determines its dynamics. MOND fits many observations surprisingly well.
Could it be that there is no dark matter in these systems and we witness rather
a violation of Newton's universal gravity law ? If so, Einstein's general
relativity would also be violated. For long conceptual problems have prevented
construction of a consistent relativistic substitute which does not obviously
run afoul of the facts. Here I sketch TeVeS, a tensor-vector-scalar field
theory which seems to fit the bill: it has no obvious conceptual problems and
has a MOND and Newtonian limits under the proper circumstances. It also passes
the elementary solar system tests of gravity theory.Comment: 18 pages, invited talk at the 28th Johns Hopkins Workshop on Current
Problems in Particle Theory, June 2004, Johns Hopkins University, Baltimore.
Corrections to Sec.7 for error pointed out by D. Giannios. To appear online
in JHEP Proceedings of Scienc
Do We Understand Black Hole Entropy ?
I review various proposals for the nature of black hole entropy and for the
mechanism behind the operation of the generalized second law. I stress the
merits of entanglement entropy {\tenit qua\/} black hole entropy, and point out
that, from an operational viewpoint, entanglement entropy is perfectly finite.
Problems with this identification such as the multispecies problem and the
trivialization of the information puzzle are mentioned. This last leads me to
associate black hole entropy rather with the multiplicity of density operators
which describe a black hole according to exterior observers. I relate this
identification to Sorkin's proof of the generalized second law. I discuss in
some depth Frolov and Page's proof of the same law, finding it relevant only
for scattering of microsystems by a black hole. Assuming that the law is
generally valid I make evident the existence of the universal bound on entropy
regardless of issues of acceleration buoyancy, and discuss the question of why
macroscopic objects cannot emerge in the Hawking radiance.Comment: plain TeX, 18 pages, Plenary talk at Seventh Marcel Grossman meeting
at Stanford University, gr-qc/9409015, revised to include a figur
Relativistic gravitation theory for the MOND paradigm
The modified newtonian dynamics (MOND) paradigm of Milgrom can boast of a
number of successful predictions regarding galactic dynamics; these are made
without the assumption that dark matter plays a significant role. MOND requires
gravitation to depart from Newtonian theory in the extragalactic regime where
dynamical accelerations are small. So far relativistic gravitation theories
proposed to underpin MOND have either clashed with the post-Newtonian tests of
general relativity, or failed to provide significant gravitational lensing, or
violated hallowed principles by exhibiting superluminal scalar waves or an
\textit{a priori} vector field. We develop a relativistic MOND inspired theory
which resolves these problems. In it gravitation is mediated by metric, a
scalar field and a 4-vector field, all three dynamical. For a simple choice of
its free function, the theory has a Newtonian limit for nonrelativistic
dynamics with significant acceleration, but a MOND limit when accelerations are
small. We calculate the and PPN coefficients showing them to
agree with solar system measurements. The gravitational light deflection by
nonrelativistic systems is governed by the same potential responsible for
dynamics of particles. To the extent that MOND successfully describes dynamics
of a system, the new theory's predictions for lensing by that system's visible
matter will agree as well with observations as general relativity's predictions
made with a dynamically successful dark halo model. Cosmological models based
on the theory are quite similar to those based on general relativity; they
predict slow evolution of the scalar field. For a range of initial conditions,
this last result makes it easy to rule out superluminal propagation of metric,
scalar and vector waves.Comment: ReVTeX and 3 eps figures; 34 pages; postpublication replacement with
some corrections to Secs.IV.A+C, V and Appendix D (incorporates erratum Phys.
Rev. D71, 069901(E) (2005)
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