Hartlefest & 15th Pacific Coast Gravity Meeting

Simon Ross, UCSB

A one-day meeting in celebration of Jim Hartle's 60th birthday was held at the ITP at UCSB on the 25th of February. It was followed by the 15th Pacific Coast Gravity Meeting, which took place on the 26th and 27th. Hartlefest had a relaxed schedule, with four invited speakers representing a few of the areas Jim has been interested in. Most people attended both meetings, making this one of the larger PCGMs, with a packed schedule of fifty-one speakers, and large audiences.

At Hartlefest, Gary Horowitz led off with a discussion of the answers string theory gives to some questions in quantum gravity, and went on to review the recent conjecture by Maldacena relating gauge theory and string theory. He was followed by Karel Kuchar, who supplemented his talk on the quantization of diffeomorphism-invariant systems with some anecdotes about Jim and some fashion tips. Kip Thorne talked about the effect of tides on the calculation of gravitational waveforms from binary systems, and about daring ideas to beat the standard quantum limit in gravity wave detectors by not measuring the positions of the test masses. The closing speaker was Murray Gell-Mann, who gave a non-technical talk on generalized quantum mechanics and how the familiar classical world could emerge as an approximate description.

Following the talks, there was a reception and then a buffet dinner at the ITP. Once all this food and wine had worked their magic, some brave people got up to honor Jim in a variety of entertaining ways. Gary Horowitz and a group of assistants led the audience in singing the relativity hymn (see http://cosmic.physics.ucsb.edu/hymn.html ). Matt Fisher presented a version of `The Cat in the Hat' written with his family in honor of the contributions of Jim and others to the ITP. A large number of people shared their memories of Jim, and everyone had a good time. The scientific part of Hartlefest is on-line at http://www.itp.ucsb.edu/online/hartle_c99/. To encourage a relaxed atmosphere, the after-dinner remarks were not recorded.

The Pacific Coast Gravity Meetings are a popular regional institution. They provide an opportunity to get together with colleagues, catch up on gossip, and hopefully learn some interesting new physics. The organization is very informal, to encourage participation by the widest possible range of people. Anyone who wants to speak can, and all speakers get the same amount of time. In the same spirit, I will attempt to briefly review all the sessions here, although there is clearly a risk that no information will survive the compression.

The meeting opened with a session of talks on cosmology. Daniel Suson, Warner Miller and Kent Harrison focussed on classical aspects of the early universe. David Salopek argued that Hamilton-Jacobi methods are useful for both classical and quantum studies. Richard Woodard made the striking proposal that the incorporation of quantum back-reaction provides a natural mechanism for ending inflation. Later in the meeting, Beverly Berger and Jim Isenberg presented results of numerical studies of cosmological singularities.

With LIGO nearing completion, it was no surprise that there were a number of talks related to production and detection of gravitational waves. Scott Hughes, John Whelan and Lior Burko discussed different approaches to calculating the effect of radiation reaction on the sources. Richard Price explained the close limit in rotating black hole mergers, in which a perturbed Kerr black hole is used as an approximate description. In a later talk, Alcides Garat argued that there is no conformally flat slicing of Kerr, which complicates the study of these perturbations. William Krivan and Zeferino Andrade discussed the tail in the waveform, which comes from quasi-normal ringing of the resulting object. Patricia Purdue showed tidal effects are gauge invariant, filling in some of the picture Kip Thorne had sketched on the previous day. Lee Lindblom reviewed the r-mode instability of rapidly rotating neutron stars, and discussed detection prospects.

On the detection side, Teviet Creighton considered a surprising noise source: the gravitational attraction between the test masses and wind. Massimo Tinto addressed data analysis and unequal arm lengths in a space-based interferometer. Jolien Creighton and Gabriela Gonzalez discussed ways of dealing with noise in the detectors. Shane Larson gave a talk on using gravity wave signals to limit the mass of the graviton.

There were also talks on more general numerical work. Carsten Gundlach and David Garfinkle used the self-similar critical solution to explain scaling properties observed in numerical studies of gravitational collapse. James Bardeen, James York and Luisa Buchman described the program of constructing a hyperbolic system out of general relativity. Buchman described some numerical results obtained by implementing one of these systems.

The talks on quantum gravity covered a wide range of approaches and issues. Herbert Hamber discussed using a homemade supercomputer built from PCs to obtain results in a Regge theory approach. Jorge Pullin gave a thorough review of the history and recent progress in the quantum geometry program. Bryce DeWitt and Charles Torre described some techniques in the superspace formulation. Alejandro Corichi argued that reconstructing a physical geometry from a point in the phase space may be non-trivial. Sharmanthie Fernando and David Kastor talked about states where the metric must be an operator-valued function. Jennie Traschen demonstrated agreement between a Born-Infeld field theory and a spacetime picture of a string-threebrane system. Kirill Krasnov argued that quantum gravity can be represented as a constrained version of the topological BF theory, which might provide an interesting formal approach to the path integral.

The effects of quantizing fields on a classical background continue to be an active subject for research. Bill Hiscock re-examined the disruption of the chronology horizon in Misner space. Paul Anderson and Brett Taylor discussed backreaction effects in extremal and nearly extremal black holes. Ted Jacobson discussed the effects of changing the dispersion relation for the quantum fields. Michele Vallisneri attributed the Unruh effect to the failure of classical special relativistic ideas in curved backgrounds.

Mathematical aspects of classical gravity were discussed at several points in the meeting. Kristin Schleich proved a theorem relating black hole topology to the topology of scri in asymptotically anti-de Sitter spacetimes. Don Witt talked about the uniqueness of locally static solutions with a cosmological constant. Robert Mann showed that in 1+1 gravity, the two-body problem can be exactly solved. Arthur Fischer talked about general relativity as an unconstrained dynamical system. Frank Estabrook and Andre Wehner offered classical alternatives to general relativity motivated by symmetries. Micheal Martin emphasized the similarity between the contracted Christoffel symbols and a gauge field. Tevian Dray discussed the potential of octonionic fermions to explain the features of the standard model. William Pezzaglia proposed a new approach to spinning particles involving polygeometric spaces. Leonard Abrams and Homer Ellis proposed alternatives to the Schwarzschild solution.

At the end of the meeting, the Bell prize for the best student talk was awarded to Teviet Creighton of Caltech for his talk on "Atmospheric gravity gradients: a low-frequency noise limit for LIGO". Some information about PCGM is available at:


Next year's PCGM will be at Los Alamos National Lab, organized by Warner Miller.

Jorge Pullin