Homepage of James Overduin

"To abdicate an interest in science is to walk with open eyes toward slavery" (Jacob Bronowski)		James received his MSc in Physics from the University of Waterloo and his PhD in Physics and Astronomy from the University of Victoria. He has published approximately 50 articles in refereed journals and conference proceedings, most of which can be found in the SPIRES-HEP archive ("find a overduin") or the NASA ADS (check both the "Astronomy" and "Physics" boxes). Two of these articles are Topcite 100+ papers in the SPIRES-HEP archive: one (with Fred Cooperstock) on cosmology with decaying dark-energy density and another (with Paul Wesson) on higher-dimensional general relativity. The latter is currently ranked #29 on the list of Top Cited Articles of All Time in the gr-qc archive (2006 edition). James was the lead author of Dark Sky, Dark Matter (Institute of Physics Press, 2003), a textbook on Olbers' paradox, background radiation and the astro-particle physics of dark matter and dark energy. He is presently a visiting scientist with Stanford University's Gravity Probe B experiment, where he is working on an online resource called "Spacetime: from the Greeks to Gravity Probe B." His address:
Gravity Probe B, Hansen Experimental Physics Labs Stanford University, Stanford CA 94305-4085 Email:

Image by James Overduin, Pancho Eekels and Bob Kahn 2005 [adapted from James Overduin & Hans-Jörg Fahr, Naturwissenschaften 88 (2001) 229]

Gravity Probe B and the Nature of Spacetime

Does spacetime exist absolutely, or is it pushed and pulled by the presence and motion of matter in it? This question, which goes back to thinkers such as Ernst Mach and others, is being tested experimentally by Gravity Probe B. According to Einstein's theory of general relativity, the mass of the Earth creates a bowl-like "depression" in the spacetime around it (as represented somewhat inadequately by only two spatial dimensions in the figure at right), while its spin causes a smaller sideways "twist" in spacetime --- as if you were to lower a rapidly spinning bowling ball into a large container of viscous mud. These changes in the spacetime around the Earth can be tracked with the aid of ultra-precise gyroscopes in low-Earth orbit, like those aboard the Gravity Probe B spacecraft. If Einstein was right, then the spin axes of these gyroscopes should slowly "fall into" the depression over time (the geodetic effect) and also twist ever so slightly around in direction of the Earth's rotation (the frame-dragging effect). No such effects are predicted in Newtonian gravity, where the direction of gyroscopic spin axes remains fixed with respect to "absolute space." Other theories, such as higher-dimensional extensions of general relativity, predict values somewhere between those of Einstein and Newton; see for example Liu and Overduin, Astrophys. J. 538 (2000) 386 (preprint version here). Gravity Probe B completed the science data collection phase of its mission in August 2005, with nearly one year's worth of data taken. That data is now in the process of being analyzed, and a final announcement about the results is expected in 2008.