Eighth Midwest gravity meeting

Richard Hammond, North Dakota

The Eighth Midwest Relativity Meeting was held September 24--25 at North Dakota State University in Fargo. The transparencies are electronically published on the MWRM8 website http://www.phys.ndsu.nodak.edu/mrm8.html

The meeting was kicked off with a bang by Beverly Berger's characterization of singularities for generic matter. In her work she assumed the existence of only one Killing vector, and discussed the outlook for the case of no symmetries. Bob Wald presented an intriguing discussion of the Path Integral in quantum gravity, and after emphasizing our incomplete understanding of both the wave function and the path integral, compared it with the parameterized Schödinger quantum mechanics, in the context of tunneling, and showed there was a critical parameter for tunneling. Rich Hammond demonstrated how a cosmological term gradient breaks the principle of equivalence and gave an upper bound for its gradient based on laboratory results.

Jean Krisch discussed cosmology in D+1 dimensions, and showed that as D increased the Planck temperature decreased. Jim Wheeler explained his conformal theory of gravity in 4+4 dimensions, while Terry Bradfield used a ``compensating'' field to obtain conformal invariance. Mike Martin examined gauge fields in the context of a classical unified theory of gravity and electromagnetism.

Gabor Kunstatter made his debut at MWRMs with a discussion on the entropy of black holes (why is it so large?) in gravitation with a scalar field. Brett Taylor showed how a scalar field can make the black hole temperature zero, and Leopoldo Zayas discussed procedures for obtaining black hole entropy using string theory methods.

Bill Hiscock gave an overview of the OMEGA project, which, if chosen, will be one of NASA's new smaller missions which will orbit an interferometer around earth-moon. He emphasized that there are six known white dwarf binaries that OMEGA should detect. Shane Larson calculated the noise in the interferometer without resorting to the usual long wavelength approximation. Ted Quinn calculated the force on a scalar particle in curved space including the radiation reaction force. Ken Olum explained fast travel in terms of negative mass, or Casimir-type energy. We all know the picture with Einstein standing in front of the blackboard with `` $R_{i\kappa}=0?''$. Dwight Vincent gave a fascinating account of this picture, from its photo-shoot in 1931 at the Mt. Wilson Observatory, to modern commercialization of it. Discussions focused on the meaning of the question mark, and what physics was actually being questioned.

Charro Gruver derived the material action for gravitation with torsion, and showed how to obtain the correct conservation law for angular momentum plus spin. Bill Pezzaglia derived equations of motion for particles with spin in the presence of torsion by generalizing the Lagrangian to include an area term.

Robert Mann presented an interesting exact solution for the N-body problem in two dimensional gravity with a scalar field, and showed, for example, that when the Hamiltonian becomes large with respect to 3mc2 the relativistic effects are fully evident. Thomas Baumgarte defined a new conformal 3-metric to modify the ADM formalism, and discussed geodesic slicing vs. harmonic slicing with regard to numerical solutions.

Ed Glass gave an illuminating discussion of the Vaiyda metric, and showed that a generalization leads to both a null fluid and string fluid. Ivan Booth discussed boundary terms and Steve Harris discussed the future causal boundary and multiply warped spacetimes. Mike Ashley discussed the properties of the a-boundary as a topological object. Homer Ellis explained space-time-time, and `dark hole' solutions with singularities. Ian Redmount examined quantum field theory states in Robertson Walker cosmology and claimed that particles can only be well defined in an open universe. This created a lively discussion with Wald pointing out that his results are probably not valid for massless particles (such as photons). The discussion continued when Berger, Mann, and John Friedmann joined the fray.

Marc Paleth reported on the Wigner function and the relation between its peaks and regions of high correlation. Another lively discussion followed when Zayas questioned the $\hbar\rightarrow0$ limit. Andreas Zoupas explained how environmental de-coherence arises from the master equation and the reduced equation. James Geddes gave a detailed account of the measure in the path integral from the point of view of a collection of subsets.

Excitement grew as meeting neared its end with John Friedmann's fascinating discussion of how, in a window between 109 and 1010, perturbations in a rotating neutron star can grow. Finally, Abraham Ungar used the law of Einstein velocity addition to generalize the laws of motion, and suggested tests for his theory.

Jorge Pullin