James Overduin's Web Page

Towson University

My Department

Latest papers:

·         Cosmocoffee

·         NASA ADS

Science news:

·         NASA Watch

·         New Scientist

Favorite blogs:

·         Antimatter

·         Bad Astronomy

·         John Baez

·         Cosmic Variance

·         Dark & Otherwise

·         Growing Pains

·         Insoluble Pancake

·         Not Even Wrong

·         Resonaances

·         Science Capital

·         Skulls in the Stars

·         Starts with a Bang

·         Swans On Tea

·         Ned Wright

·         xcd

Organizations:

·         AAPT

·         AAS

·         AIP

·         CADC

·         Hyperspace

Background

Welcome to my internet home. I joined the Department of Physics, Astronomy and Geosciences at Towson University as a full-time faculty member in August 2009. Prior to that I spent 5 years (2003-8) as a Visiting Scientist with the Gravity Probe B (GP-B) and the Satellite Test of the Equivalence Principle (STEP) experiments at Stanford University. Earlier, I worked as a JSPS (Japan Society for the Promotion of Science) Postdoctoral Fellow at Waseda University in Tokyo, Japan (2001-3) and an Alexander von Humboldt Fellow at the University of Bonn in Germany (2000-1). I obtained my PhD from the University of Victoria (1998) and my MSc from the University of Waterloo (1992) with a thesis based on research carried out at the Space Sciences Laboratory at the University of California, Berkeley (1991). My BSc (1989) is from Waterloo. To date I have published two books and over 50 research articles.

Research

 

I am especially interested in the interface between the fields of gravitation, cosmology and high-energy physics. There is discovery potential here, not just because so much remains to be explained, but because many of the leading explanations are becoming testable, either now or in the forseeable future.

For students: The interplay between theory and observation provides many opportunities for student involvement, whether at the level of senior undergraduate term projects or something deeper. These fields have a reputation for being difficult, and progress does often require a certain comfort with mathematics. But the questions waiting to be answered could not be simpler. What causes mass and inertia? Why is gravity always attractive, never repulsive (like electromagnetism)? Is gravity the same thing as curved spacetime (the continuum picture of General Relativity theory) or is it better described like all the other forces, as the exchange of virtual particles (the quantum field theory picture)? Or are these pictures complementary, like the wave and particle pictures of light? If so, why are they so hard to reconcile? Are extra dimensions required? If so, why don't we see or experience them in everyday life? If you are fascinated by questions like these, and willing to develop the mathematical skills to study them, come and talk to me!

Gravitation and High-Energy Physics

 

Gravity Probe B measuring the warp and twist of spacetime near the earth [from the GPB website;
adapted from J. Overduin & H.-J. Fahr, "Spacetime, matter and the vacuum", Naturwissenschaften 88 (2001) 229]

Our best current theory of gravity, Einstein's General Relativity, is incompatible with the Standard Model of particle physics that successfully describes the other three forces of nature (the electromagnetic, weak and strong nuclear forces). This impasse has been called by Nobel Prizewinner Steven Weinberg the "one veritable crisis" remaining in theoretical physics. Progress in such situations usually depends on a combination of new theoretical ideas and experimental strategies that probe at "weak spots" where existing limits and predictions are unsure. In the case of gravity, two such spots involve spin and the universality of free fall, also known as the Equivalence Principle. A review article I co-authored with Paul Wesson on a class of extended theories of gravity known as Kaluza-Klein theories ranks 22nd among the "top-cited articles of all time" on the gravitation and cosmology arXiv with over 400 citations to date. I am especially interested in the prospects for testing such theories with controlled space experiments like Gravity Probe B (GP-B) and the Satellite Test of the Equivalence Principle (STEP). Some other publications:

 

 

I've written an online resource on this subject called "SPACETIME: from the Greeks to Gravity Probe B". This website received over 500 "diggs" at digg.com and the animations used in it (co-designed with Bob Kahn) won a bronze medal at the 29th annual Telly Awards (2008). For students: I have openings for several ongoing projects in this area. One involves setting limits on possible violations of the equivalence principle by solar-system bodies using astronomical data on objects near stable Lagrange points, such as the Trojan asteroids. This would best fit students with proficiency in astronomy and classical mechanics. The second involves characterizing the properties of possible test materials to be used in modern-day versions of Galileo's Pisa experiment. This would be most appropriate for students with interests in engineering and modern physics. The third project uses computer codes to check properties of solutions of Einstein’s field equations in more than four spacetime dimensions, and attempts to constrain higher-dimensional and other extensions of general relativity with experimental data. This project would suit those with demonstrated interest in mathematical physics and experience with Mathematica.

Cosmology and Astroparticle Physics

 

The densities of dark energy and dark matter determine whether we live in a flat (k=0), closed (k=+1) or open
(k=-1) universe [From J.M. Overduin & P.S. Wesson, Dark Sky, Dark Matter (Institute of Physics Press, 2003)]

The cosmic background radiation that bathes our galaxy at all wavelengths carries a wealth of information, not just about the visible universe, but also about the unseen dark matter and energy which are believed to comprise 95% of the universe by weight. Dark energy is particularly puzzling. Its existence appears to be forced on us by observation, but makes little sense in the context of modern quantum field theory (this is known for historical reasons as the "cosmological-constant problem"). One way to reconcile the two points of view is to allow dark-energy density to evolve with time. My PhD thesis on this topic was completed just months before dark energy was detected by observational cosmologists. The short version (co-authored with Fred Cooperstock) is an arXiv topcite 100+ article with over 200 citations to date. Some other work:

 

 

 

Dark matter is thought to make up about 25% of the universe by density, as against 70% for dark energy. But most of the leading candidates for dark matter are not perfectly dark. In theory, they are unstable to annihilation or radiative decay and therefore contribute to the cosmic background radiation at some wavelength. The night sky thus serves as nature’s own dark-matter detector. My work in this area has recently been summarized in a book (co-authored with Paul Wesson) titled The Light/Dark Universe (World Scientific, 2008). For students: the research described in this book is ongoing, with multiple opportunities for student involvement. Those with a historical or philosophical bent might be drawn to the deep questions surrounding Olbers' Paradox (or why the sky is dark at night---not as trivial as it may seem). Those whose interests lie in core subjects such as electromagnetism, radiation transport and scattering theory will be challenged to calculate exactly how much light should (or should not) be reaching the Earth in various wavebands (the role of dust absorption is of particular interest). Practically inclined students might use data on the intensity of the night sky from detectors to draw inferences about everything from the properties of stars and galaxies to the age of the universe. For students interested in modern physics, I have a number of ongoing projects regarding the contributions to the background light from decays and annihilations of as-yet undetected particles and fields such as "warm" dark-matter particles, super-heavy "cold" relics from the big bang, and objects predicted by contemporary high-energy unified-field theories. I am also investigating theoretical mechanisms for dark energy based on the phenomenon of tunneling in quantum mechanics. These topics would be accessible to students with some upper-year background in astronomy, electromagnetism and/or quantum mechanics.

Other Topics

 

How might vision have evolved around a red dwarf star like Gliese 876? [Image ©Lynette Cook; reproduced by
permission in J.M. Overduin, "Eyesight and the solar Wien peak", American Journal of Physics 71 (2003) 216-219]

I’ve worked on other topics including the evolution of eyesight around the sun (see illustration at right), prospects for observing quantum spacetime foam in laser interferometers, and the lives of scientists such as Wolfgang Priester (an early proponent of dark energy) and Leopold Halpern (the last assistant to both Schrodinger and Dirac, who developed a generalization of General Relativity incorporating particle spin). I’m currently collaborating with a Russian-speaking colleague to produce a translation of some seminal papers from the 1950s by the fascinating physicist Yu. B. Rumer. For students: you are welcome to contact me anytime with questions or ideas for projects in theoretical, mathematical, philosophical, historical or almost any other kind of physics or astronomy you wish to pursue. I look forward to hearing from you!

 

Last Updated: Feb. 2, 2013