Inhomogeneous spacetimes as a dark energy model

Tolman-Bondi inhomogeneous spacetimes are used as a cosmological model for type Ia supernova data. It is found that with certain parameter choices the model fits the data as well as the standard $\Lambda$CDM cosmology does.Comment: 9 pages, 6 figures, Added Reference

The motion of galaxy clusters in inhomogeneous cosmologies

Lemaitre-Tolman-Bondi inhomogeneous spacetimes can be used as a cosmological model to account for the type Ia supernova data. However, such models also give rise to large velocities of galaxy clusters with respect to the cosmic microwave background. Those velocities can be measured using the kinematic Sunyaev-Zeldovich effect. This paper presents a calculation of galaxy cluster velocities as a function of redshift for such a model.Comment: 7 pages, 2 figure

How extreme are extreme black holes?

We examine the properties of nearly extremal black holes produced by gravitational collapse. It is shown that an observer who crosses the black hole horizon at late times rapidly encounters a singularity.Comment: 10 pages, 3 figure

Matters of Gravity, The Newsletter of the Topical Group on Gravitation of the American Physical Society, Volume 35, Winter 2010

GGR News: - GGR Program at the APS meeting in Washington D.C., by David Garfinkle - we hear that..., by David Garfinkle Research Briefs: - Supernovae modelling, by Ian Hawke Conference Reports: - ADM-50, by Richard WoodardComment: 11 pages, late

The fine structure of Gowdy spacetimes

The approach to the singularity in Gowdy spacetimes consists of velocity term dominated behavior, except at a set of isolated points. At and near these points, spiky features grow. This paper reviews what is known about these spikes.Comment: contribution to A Spacetime Safari: Essays in honor of Vincent Moncrie

On "the'' electric field of a uniformly accelerating charge

The problem of the electric field of a uniformly accelerating charge is a longstanding one that has led to several issues. We resolve these issues using techniques from linguistics, cognitive psychology, and the mathematics of partial differential equations

Black hole entropy as a consequence of excision

Black hole entropy is shown to be a consequence of restricting our description of physics to the exterior of black holes. This precludes the need for a statistical mechanical description of this entropy in terms of microstates

Matters of Gravity, The Newsletter of the Division of Gravitational Physics of the American Physical Society, Volume 50, December 2017

DGRAV News: We hear that .... APS April Meeting Town Hall Meeting Conference Reports: Hawking Conference Benasque workshop 2017 QIQG 3 Obituary: Remembering Cecile De Witt-Morett

Numerical Relativity Beyond Astrophysics

Though the main applications of computer simulations in relativity are to astrophysical systems such as black holes and neutron stars, nonetheless there are important applications of numerical methods to the investigation of general relativity as a fundamental theory of the nature of space and time. This paper gives an overview of some of these applications. In particular we cover (i) investigations of the properties of spacetime singularities such as those that occur in the interior of black holes and in big bang cosmology. (ii) investigations of critical behavior at the threshold of black hole formation in gravitational collapse. (iii) investigations inspired by string theory, in particular analogs of black holes in more than 4 spacetime dimensions and gravitational collapse in spacetimes with a negative cosmological constant.Comment: Review paper submitted to Reports on Progress in Physic

Matters of Gravity, The Newsletter of the Division of Gravitational Physics of the American Physical Society, Volume 47, June 2016

DGRAV News: DGRAV we hear that.... Research Briefs: GW150914 Obituaries: Remembering Felix Pirani Remembering David Finkelstein Steve, the physicist Remembering Sergio Dain Editorial: Gravitational physics in the modern universit