As stated in his abstract, Dr. Overduin gave a non-technical overview about the relationship between gravity, spacetime, and inertia, which included points on Einstein's general relativity, and an attempted summary of 'Mach's principle'. Also, as stated in his abstract, he spoke on the topic of the Gravity Probe B project. What Dr. Overduin's abstract did not foretell was a somewhat humorous delay at the beginning of his talk that resulted from incompatibility between the University of Florida's mainly Microsoft hardware and Dr. Overduin's Linux based laptop. As a matter of fact, this presentation marked the first time ever that Dr. Overduin had to use Microsoft products.

The basic premise of the colloquium (minus highlighting trans-platform software incompatibilities) was that of removing all mass from the universe except one's self. The thought experiment then allows theorists (such as Dr. Overduin) to play around with the concept of whether or not spacetime is absolute.

As do most things scientific, this talk began with the examination of the giants of the past. In this case Copernicus, Kepler, Galileo, Descartes, Newton, and Leibniz all weighed in on whether or not they believed space and time ('spacetime' wasn't yet invented in the one-word sense) are relative or absolute. Newton, so the story goes, believed that he had proved absolute motion by spinning a full bucket of water, and noting the vortex that occurred in its center. Ernst Mach, in what would eventually help Einstein in his formulation of general relativity, argued with Newton on the premise of extending the diameter of the bucket without bound while holding the water's volume constant. Even specialists in the field do not agree on the full implications of 'Mach's Principle,' and as a result it has been officially given as many as 21 different forms. Some other topics of discussion included the similarities between the mathematics of electromagnetism and gravity, and some general background on general relativity.

Dr. Overduin is a theorist, and, correspondingly, the first half of his talk covered theory. Recently, though, he joined the Gravity Probe B (GPB) project, and that was the focus of the remainder of his talk. The aim of GPB is to measure the exact nature of the curve in spacetime produced by the mass of the earth, and to give experimental results that will agree theoretically with either general relativity or any number of other higher-dimensional gravity theories. The instrumentation in the GPB satellite is sensitive enough to detect angular deflections on the order of arcseconds, which approximately corresponds to the angular width of the head on a penny in Paris as seen from New York. The gyroscopes in the GPB (about the size of ping-pong balls) were so precisely made that, were they blown up to the size of the earth, the largest mountain would be about 8 feet tall. The results from GPB (analyzed in a double-blind manner between Harvard and Stanford) will be announced at the APS meeting in Jacksonville in April.

Dr. Overduin has a rather impressive resume, including some forty-plus published papers, and being one of the last assistants to Paul Dirac. Of course an impressive resume might intimidate a listener, however Dr. Overduin's colloquium was certainly well enough delivered that even an undergraduate (this author) could follow nearly all the material.

Dr. Overduin's Homepage: http://astro.uwaterloo.ca/~overduin/
GPB Homepage: http://einstein.stanford.edu/