arXiv subjects

Jorge Pullin

Publications and source records attributed to Jorge Pullin.

At least 91 records · Page 5Linked to original sources

arXiv2008

Modern space-time and undecidability

The picture of space-time that Minkowski created in 1907 has been followed by two important developments in physics not contained in the original picture: general relativity and quantum mechanics. We will argue that the use of concepts of those theories to construct space-time implies conceptual modifications in quantum mechanics. In particular one can construct a viable picture of quantum mechanics without a reduction process that has outcomes equivalent to a picture with a reduction process. One therefore has two theories that are entirely equivalent experimentally but profoundly different in the description of reality they give. This introduces a fundamental level of undecidability in physics of a kind that has not been present before. We discuss some of the implications.

gr-qc↗

arXiv2007

Loop quantization of spherically symmetric midi-superspaces : the interior problem

We continue the study of spherically symmetric vacuum space-times in loop quantum gravity by treating the interior of a black hole. We start from a midi-superspace approach, but a simple gauge fixing leads to a Kantowski--Sachs form for the variables. We show that one can solve the quantum theory exactly in the (periodic) connection representation, including the inner product. The evolution can be solved exactly by de-parameterizing the theory and can be easily interpreted as a semi-classical evolution plus quantum corrections. A relational evolution can also be introduced in a precise manner, suggesting what may happen in situations where it is not possible to de-parameterize. We show that the singularity is replaced by a bounce at which quantum effects are important and that the extent of the region at the bounce where one departs from classical general relativity depends on the initial data.

gr-qc↗

arXiv2007

Relational physics with real rods and clocks and the measurement problem of quantum mechanics

The use of real clocks and measuring rods in quantum mechanics implies a natural loss of unitarity in the description of the theory. We briefly review this point and then discuss the implications it has for the measurement problem in quantum mechanics. The intrinsic loss of coherence allows to circumvent some of the usual objections to the measurement process as due to environmental decoherence.

quant-ph↗

arXiv2007

Uniform discretizations: a new approach for the quantization of totally constrained systems

We discuss in detail the uniform discretization approach to the quantization of totally constrained theories. This approach allows to construct the continuum theory of interest as a well defined, controlled, limit of well behaved discrete theories. We work out several finite dimensional examples that exhibit behaviors expected to be of importance in the quantization of gravity. We also work out the case of BF theory. At the time of quantization, one can take two points of view. The technique can be used to define, upon taking the continuum limit, the space of physical states of the continuum constrained theory of interest. In particular we show in models that it agrees with the group averaging procedure when the latter exists. The technique can also be used to compute, at the discrete level, conditional probabilities and the introduction of a relational time. Upon taking the continuum limit one can show that one reproduces results obtained by the use of evolving constants, and therefore recover all physical predictions of the continuum theory. This second point of view can also be used as a paradigm to deal with cases where the continuum limit does not exist. There one would have discrete theories that at least at certain scales reproduce the semiclassical properties of the theory of interest. In this way the approach can be viewed as a generalization of the Dirac quantization procedure that can handle situations where the latter fails.

gr-qc↗

arXiv2007

Fundamental spatiotemporal decoherence: a key to solving the conceptual problems of black holes, cosmology and quantum mechanics

Unitarity is a pillar of quantum theory. Nevertheless, it is also a source of several of its conceptual problems. We note that in a world where measurements are relational, as is the case in gravitation, quantum mechanics exhibits a fundamental level of loss of coherence. This can be the key to solving, among others, the puzzles posed by the black hole information paradox, the formation of inhomogeneities in cosmology and the measurement problem in quantum mechanics.

gr-qc↗

arXiv2006

Instability of charged and rotating naked singularities

We provide evidence that ``super-extremal'' black hole space-times (either with charge larger than mass or angular momentum larger than mass), which contain naked singularities, are unstable under linearized perturbations. This is given by an infinite family of exact unstable solutions in the charged non rotating case, and by a set of (unstable) numerical solutions in the rotating case. These results may be relevant to the expectation that these space-times cannot be the endpoint of physical gravitational collapse.

gr-qc↗

arXiv2006

Uniform discretizations: a quantization procedure for totally constrained systems including gravity

We present a new method for the quantization of totally constrained systems including general relativity. The method consists in constructing discretized theories that have a well defined and controlled continuum limit. The discrete theories are constraint-free and can be readily quantized. This provides a framework where one can introduce a relational notion of time and that nevertheless approximates in a well defined fashion the theory of interest. The method is equivalent to the group averaging procedure for many systems where the latter makes sense and provides a generalization otherwise. In the continuum limit it can be shown to contain, under certain assumptions, the ``master constraint'' of the ``Phoenix project''. It also provides a correspondence principle with the classical theory that does not require to consider the semiclassical limit.

gr-qc↗

arXiv2006

Consistent discretization and canonical classical and quantum Regge calculus

We apply the ``consistent discretization'' technique to the Regge action for (Euclidean and Lorentzian) general relativity in arbitrary number of dimensions. The result is a well defined canonical theory that is free of constraints and where the dynamics is implemented as a canonical transformation. This provides a framework for the discussion of topology change in canonical quantum gravity. In the Lorentzian case, the framework appears to be naturally free of the ``spikes'' that plague traditional formulations. It also provides a well defined recipe for determining the measure of the path integral.

gr-qc↗

arXiv2006

Fundamental decoherence from quantum gravity: a pedagogical review

We present a discussion of the fundamental loss of unitarity that appears in quantum mechanics due to the use of a physical apparatus to measure time. This induces a decoherence effect that is independent of any interaction with the environment and appears in addition to any usual environmental decoherence. The discussion is framed self consistently and aimed to general physicists. We derive the modified Schroedinger equation that arises in quantum mechanics with real clocks and discuss the theoretical and potential experimental implications of this process of decoherence.

gr-qc↗

arXiv2006

Matters of Gravity, The Newsletter of The Topical Group in Gravitation of the American Physical Society, Volume 27, Spring 2006

GGR News: GGR program at the APS April meeting in Dallas We hear that..., 100 years ago, by Jorge Pullin Research Briefs: What's new in LIGO, by David Shoemaker LISA Pathfinder, by Paul McNamara Recent progress in binary black hole simulations, by Thomas Baumgarte Conference reports: Workshop on Emergence of Spacetime, by Olaf Dreyer Quantum gravity subprogram at the Isaac Newton Institute, by Jorma Louko Global problems in Math Relativity at the Newton Institute, by Jim Isenberg Loops '05, by Thomas Thiemann Numrel 2005, by Scott Hawley and Richard Matzner Apples With Apples Workshop in Argentina, by Sascha Husa

gr-qc↗

arXiv2005

Consistent discretizations as a road to quantum gravity

We present a brief description of the ``consistent discretization'' approach to classical and quantum general relativity. We exhibit a classical simple example to illustrate the approach and summarize current classical and quantum applications. We also discuss the implications for the construction of a well defined quantum theory and in particular how to construct a quantum continuum limit.

gr-qc↗

arXiv2005

Arbitrary black-string deformations in the black string-black hole transitions

We study the possible black string-black hole transition by analyzing the structure of the apparent horizon for a large family of time-symmetric initial data. We observe that, as judged by the apparent horizon, it is possible to generate arbitrarily deformed black strings at a moment of time symmetry. A similar study for hyperspherical black holes reveals that although arbitrarily deformed hyperspherical black holes can be constructed, the proper distance between the north and south poles along the extra direction has an upper limit.

hep-th↗

arXiv2005

Matters of Gravity, the newsletter of the Topical Group in Gravitation of APS

GGR News: The WYP speakers program, by Richard Price We hear that..., by Jorge Pullin 100 Years ago, by Jorge Pullin Research Briefs: What's new in LIGO, by David Shoemaker Recent developments in the information loss paradox, by Eanna Flanagan Gravity Probe B mission ends, by Bob Kahn Conference reports: 6th Edoardo Amaldi Meeting, by Matthew Benacquista Workshop on Numerical Relativity, BIRS, by Carsten Gundlach 8th Capra Meeting on Radiation Reaction, by Leor Barack Theory and experiment in quantum gravity, by Elizabeth Winstanley

gr-qc↗

arXiv2005

Fundamental gravitational limitations to quantum computing

Lloyd has considered the ultimate limitations physics places on quantum computers. He concludes in particular that for an ``ultimate laptop'' (a computer of one liter of volume and one kilogram of mass) the maximum number of operations per second is bounded by $10^{51}$. The limit is derived considering ordinary quantum mechanics. Here we consider additional limits that are placed by quantum gravity ideas, namely the use of a relational notion of time and fundamental gravitational limits that exist on time measurements. We then particularize for the case of an ultimate laptop and show that the maximum number of operations is further constrained to $10^{47}$ per second.

quant-ph↗

arXiv2005

Classical and quantum general relativity: a new paradigm

We argue that recent developments in discretizations of classical and quantum gravity imply a new paradigm for doing research in these areas. The paradigm consists in discretizing the theory in such a way that the resulting discrete theory has no constraints. This solves many of the hard conceptual problems of quantum gravity. It also appears as a useful tool in some numerical simulations of interest in classical relativity. We outline some of the salient aspects and results of this new framework.

gr-qc↗

arXiv2005

Consistent discretizations: the Gowdy spacetimes

We apply the consistent discretization scheme to general relativity particularized to the Gowdy space-times. This is the first time the framework has been applied in detail in a non-linear generally-covariant gravitational situation with local degrees of freedom. We show that the scheme can be correctly used to numerically evolve the space-times. We show that the resulting numerical schemes are convergent and preserve approximately the constraints as expected.

gr-qc↗

arXiv2005

Discrete space-time

We review recent efforts to construct gravitational theories on discrete space-times, usually referred to as the ``consistent discretization'' approach. The resulting theories are free of constraints at the canonical level and therefore allow to tackle many problems that cannot be currently addressed in continuum quantum gravity. In particular the theories imply a natural method for resolving the big bang (and other types) of singularities and predict a fundamental mechanism for decoherence of quantum states that might be relevant to the black hole information paradox. At a classical level, the theories may provide an attractive new path for the exploration of issues in numerical relativity. Finally, the theories can make direct contact with several kinematical results of continuum loop quantum gravity. We review in broad terms several of these results and present in detail as an illustration the classical treatment with this technique of the simple yet conceptually challenging model of two oscillators with constant energy sum.

gr-qc↗

arXiv2005

Matters of Gravity, the newsletter of the Topical Group on Gravitation of the Americal Physical Society

GGR News: Message from the Chair, by Jim Isenberg Einstein@Home, by Bernard Schutz We hear that..., by Jorge Pullin 100 Years ago, by Jorge Pullin Research Briefs: What's new in LIGO, by David Shoemaker Frame-dragging in the news in 2004, by Cliff Will Cosmic (super)strings and LIGO, by Xavier Siemens Conference reports: The first gulf coast gravity conference, by Richard Price Imagining the future, by Shane Larson VI Mexican School, by Alejandro Corichi

gr-qc↗