James Overduin's Web
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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. Gravitation and High-Energy Physics
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 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
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 |
