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Fall 2008
Physics & Astronomy Colloquium
Room 411, Thornton Hall (unless otherwise noted)
4:05 PM (refreshments at 3:50)
[Talks in Thornton 429 begin at 4:00; refreshments at 3:45]

Brandon BrownBrandon Brown
Department of Physics,
University of San Francisco
September 29, 2008
4PM, Thornton 411
How do organisms sense the Earth's magnetic field?
Behavioral research has discovered a growing list of animals that can sense
the Earth's magnetic filed. Organisms with significant migratory patterns or
light-impaired environments are the most typical examples. In many cases,
the sensitivity is exquisite enough to distinguish field variations of a
microtesla in magnitude and a few degrees in vertical inclination. This talk
will review examples of behavioral experiments from several systems,
including crustaceans, reptiles, and mammals. It will also describe the two
predominant theoretical mechanisms by which a creature could sense magnetic
fields. One model relies on deposits of magnetic materials influencing
neurons, while the other, the "radical pair" hypothesis, requires
non-trivial quantum mechanical effects within an organism's visual system.
At present, significant questions plague each model, and experiments suggest
multiple mechanisms may be in play. This colloquium will present the first
steps, and the remaining challenges, in developing a new option for the

Department of Physics and Astronomy
San Francisco State University
1600 Holloway
San Francisco, CA 94132-4163
Phone: 415-338-1659
Fax: 415-338-2178