Black Holes or Firewalls: A Theory of Horizons

We present a quantum theory of black hole (and other) horizons, in which the standard assumptions of complementarity are preserved without contradicting information theoretic considerations. After the scrambling time, the quantum mechanical structure of a black hole becomes that of an eternal black hole at the microscopic level. In particular, the stretched horizon degrees of freedom and the states entangled with them can be mapped into the near-horizon modes in the two exterior regions of an eternal black hole, whose mass is taken to be that of the evolving black hole at each moment. Salient features arising from this picture include: (i) the number of degrees of freedom needed to describe a black hole is e^{A/2 l_P^2}, where A is the area of the horizon; (ii) black hole states having smooth horizons span only an e^{A/4 l_P^2}-dimensional subspace of the relevant e^{A/2 l_P^2}-dimensional Hilbert space; (iii) internal dynamics of the horizon is such that an infalling observer finds a smooth horizon with probability 1 if a state stays in this subspace. We identify the structure of local operators in the exterior and interior spacetime regions, and show that this structure avoids firewall arguments---the horizon can keep being smooth throughout the evolution. We discuss the fate of falling observers under various circumstances, especially when they manipulate degrees of freedom before entering the horizon, and find that an observer can never see a firewall by making a measurement on early Hawking radiation. We also consider the framework in an infalling reference frame, and argue that Minkowski-like vacua are not unique. In particular, the number of true Minkowski vacua is infinite, although the label discriminating these vacua cannot be accessed in usual non-gravitational quantum field theory. An application to de Sitter horizons is also discussed.Comment: 24 pages, 1 figure; minor revision

Low Energy Description of Quantum Gravity and Complementarity

We consider a framework in which low energy dynamics of quantum gravity is described preserving locality, and yet taking into account the effects that are not captured by the naive global spacetime picture, e.g. those associated with black hole complementarity. Our framework employs a "special relativistic" description of gravity; specifically, gravity is treated as a force measured by the observer tied to the coordinate system associated with a freely falling local Lorentz frame. We identify, in simple cases, regions of spacetime in which low energy local descriptions are applicable as viewed from the freely falling frame; in particular, we identify a surface called the gravitational observer horizon on which the local proper acceleration measured in the observer's coordinates becomes the cutoff (string) scale. This allows for separating between the "low-energy" local physics and "trans-Planckian" intrinsically quantum gravitational (stringy) physics, and allows for developing physical pictures of the origins of various effects. We explore the structure of the Hilbert space in which the proposed scheme is realized in a simple manner, and classify its elements according to certain horizons they possess. We also discuss implications of our framework on the firewall problem. We conjecture that the complementarity picture may persist due to properties of trans-Planckian physics.Comment: 18 pages, 1 figure; matches published versio

Hacia una política lingüística iberoamericana

El momento alcanzado por la cooperación iberoamericana, especialmente tras el reciente establecimiento de la Secretaría General Iberoamericana (SEGIB), es propicio para plantear las bases de una política lingüística iberoamericana. El elemento lingüístico es uno de los componentes constitutivos del propio sistema iberoamericano, y se percibe una convergencia cada vez mayor entre las iniciativas que toman forma en el campo de la cooperación lingüística y las manifestaciones y los programas de la cooperación iberoamericana. Por su creciente importancia, las cuestiones lingüísticas merecen, sin embargo, ir más allá; superar el trato indirecto y declarativo que se les viene concediendo en este ámbito multilateral, e incorporarlas de manera específica en el marco del sistema iberoamericano. La creación de la SEGIB abre nuevas posibilidades de desarrollar una política lingüística iberoamericana, o al menos de dar un nuevo impulso a la cooperación iberoamericana en materia de lenguas

A note on (no) firewalls: the entropy argument

An argument for firewalls based on entropy relations is refuted.United States. Dept. of Energy. Office of High Energy and Nuclear Physics (Contracts DE-FG02-05ER41360 and DE-AC02-05CH11231)National Science Foundation (U.S.) (Grants PHY-0855653 and DGE-1106400)Simons Foundation (Grant 230224

El Congreso Internacional de la Lengua Española de Cartagena de Indias: una crónica

En este ARI se realiza un balance del IV Congreso Internacional de la Lengua Española, que acaba de celebrarse en Cartagena de Indias (Colombia), y se comentan las perspectivas de la política internacional del español. Concluido el último Congreso Internacional de la Lengua Española (CILE), corresponde hacer un balance de la experiencia e interrogarse sobre sus repercusiones en el escenario iberoamericano. Este análisis repasa los principales rasgos del IV CILE –su impacto mediático, los protagonistas, los temas en debate– y adelanta algunas conclusiones provisionales sobre sus resultados en particular, sobre la evolución de los Congresos de la Lengua en general y, más ampliamente, sobre la orientación de la política internacional del español

Reconocimiento de palabras aisladas mediante redes neuronales sobre FPGA

Las redes neuronales artificiales (ANN) se han usado exitosamente para tareas de reconocimiento de voz. El nivel de paralelismo de las ANN es ampliamente significativo, tanto que no es explotado cuando su implementación se realiza en computadores de propósito general. Se busca diseñar un sistema de reconocimiento de palabras aisladas en un computador de propósito general y diseñar en VHDL la ANN del sistema de clasificación apta para la implementación sobre una FPGA, para aprovechar su paralelismo y comparar los resultados del desempeño, eficiencia y confiabilidad. Se presentan dos desarrollos, ambos con la misma red neuronal pero en un procesador de propósito general y un diseño en VHDL apto para su implementación en una FPGA. Ambos diseños se calificaron teniendo en cuenta su rendimiento tanto en acierto como en velocidad de procesamiento. El acierto se juzgó haciendo uso del método de validación leave one out y la velocidad se juzgó dependiendo del tiempo para procesar paquetes de palabras. El resultado final son diseños iguales, con aciertos similares pero con velocidades de procesamiento realmente diferentes.Artificial neural networks (ANN) have been used successfully in speech recognition tasks. The parallelism level of the ANN is widely significant, as much as is not exploded when its implementation has been made in general purpose processors. The main task is to design an isolated words recognition system in a general purpose computer and to design on VHDL the ANN of the classification system adequate to its implementation on a FPGA, to take advantage of its parallelism and to compare the performance, efficiency and reliability of both systems. In this document two developments are presented, both with the same neural network but in a general purpose processor and a design on VHDL skillful to its implementation on a FPGA. Both designs were qualified based on both performance skill and processing speed. The accuracy (skill) was judged by using the leave one out validation method and the speed were judged based on the time that take the processing of a word package. The final result are the same designs with similar accuracy but with a processing speed really different from each other