7,372 research outputs found
The Library of Babel
We show that heavy pure states of gravity can appear to be mixed states to
almost all probes. Our arguments are made for Schwarzschild black
holes using the field theory dual to string theory in such spacetimes. Our
results follow from applying information theoretic notions to field theory
operators capable of describing very heavy states in gravity. For certain
supersymmetric states of the theory, our account is exact: the microstates are
described in gravity by a spacetime ``foam'', the precise details of which are
invisible to almost all probes.Comment: 7 pages, 1 figure, Essay receiving honorable mention in the 2005
Gravity Research Foundation essay competitio
What we don't know about time
String theory has transformed our understanding of geometry, topology and
spacetime. Thus, for this special issue of Foundations of Physics commemorating
"Forty Years of String Theory", it seems appropriate to step back and ask what
we do not understand. As I will discuss, time remains the least understood
concept in physical theory. While we have made significant progress in
understanding space, our understanding of time has not progressed much beyond
the level of a century ago when Einstein introduced the idea of space-time as a
combined entity. Thus, I will raise a series of open questions about time, and
will review some of the progress that has been made as a roadmap for the
future.Comment: 15 pages; Essay for a special issue of Foundations of Physics
commemorating "Forty years of string theory
Quantum geometry and gravitational entropy
Most quantum states have wavefunctions that are widely spread over the
accessible Hilbert space and hence do not have a good description in terms of a
single classical geometry. In order to understand when geometric descriptions
are possible, we exploit the AdS/CFT correspondence in the half-BPS sector of
asymptotically AdS_5 x S^5 universes. In this sector we devise a
"coarse-grained metric operator" whose eigenstates are well described by a
single spacetime topology and geometry. We show that such half-BPS universes
have a non-vanishing entropy if and only if the metric is singular, and that
the entropy arises from coarse-graining the geometry. Finally, we use our
entropy formula to find the most entropic spacetimes with fixed asymptotic
moments beyond the global charges.Comment: 29 pages, 2 figures; references adde
Information Recovery From Black Holes
We argue that if black hole entropy arises from a finite number of underlying
quantum states, then any particular such state can be identified from infinity.
The finite density of states implies a discrete energy spectrum, and, in
general, such spectra are non-degenerate except as determined by symmetries.
Therefore, knowledge of the precise energy, and of other commuting conserved
charges, determines the quantum state. In a gravitating theory, all conserved
charges including the energy are given by boundary terms that can be measured
at infinity. Thus, within any theory of quantum gravity, no information can be
lost in black holes with a finite number of states. However, identifying the
state of a black hole from infinity requires measurements with Planck scale
precision. Hence observers with insufficient resolution will experience
information loss.Comment: First prize in the Gravity Research Foundation Essay Competition, 8
pages, Late
On the existence of supergravity duals to D1--D5 CFT states
We define a metric operator in the 1/2-BPS sector of the D1-D5 CFT, the
eigenstates of which have a good semi-classical supergravity dual; the
non-eigenstates cannot be mapped to semi-classical gravity duals. We also
analyse how the data defining a CFT state manifests itself in the gravity side,
and show that it is arranged into a set of multipoles. Interestingly, we find
that quantum mechanical interference in the CFT can have observable
manifestations in the semi-classical gravity dual. We also point out that the
multipoles associated to the normal statistical ensemble fluctuate wildly,
indicating that the mixed thermal state should not be associated to a
semi-classical geometry.Comment: 22 pages, 2 figures. v2 : references added, typos correcte
Gauge Dependence in the AdS/CFT Correspondence
We consider the AdS space formulation of the classical dynamics deriving from
the Stueckelberg Lagrangian. The on-shell action is shown to be free of
infrared singularities as the vector boson mass tends to zero. In this limit
the model becomes Maxwell theory formulated in an arbitrary covariant gauge.
Then we use the AdS/CFT correspondence to compute the two-point correlation
functions on the boundary. It is shown that the gauge dependence concentrates
on the contact terms.Comment: 13 pages, REVTEX, misprints in the abstract corrected. Minor changes.
Version to be publishe
Constraints Faced by Stakeholders under Agriculture Technology Management Agency (ATMA)
Agriculture Technology Management Agency (ATMA) is a registered society in India with key stakeholders enmeshed with various agricultural activities for sustainable agricultural development in the state, with focus at district level. It is a hotbed for integrating research, extension and marketing activities and decentralizing day-to-day management of the public Agricultural Technology Development and Dissemination System. The present study was carried out in Andhra Pradesh state to explore the constraints faced by the extension functionaries at each level of decentralized management. Moreover, constraints perceived by the farmers with the support of ATMA in realizing their needs were also studied
Typicality versus thermality: An analytic distinction
In systems with a large degeneracy of states such as black holes, one expects
that the average value of probe correlation functions will be well approximated
by the thermal ensemble. To understand how correlation functions in individual
microstates differ from the canonical ensemble average and from each other, we
study the variances in correlators. Using general statistical considerations,
we show that the variance between microstates will be exponentially suppressed
in the entropy. However, by exploiting the analytic properties of correlation
functions we argue that these variances are amplified in imaginary time,
thereby distinguishing pure states from the thermal density matrix. We
demonstrate our general results in specific examples and argue that our results
apply to the microstates of black holes.Comment: 22 pages + appendices, 3 eps figure
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