CWRU Physics Faculty
Professor of Physics and Astronomy
B.S., Univ. of Michigan (1987)
Ph.D., Princeton (1993)
John Ruhl's Site
The Cosmic Microwave Background Radiation (CMB) carries an enormous amount of information about the universe at a redshift z = 1,000, a few hundred thousand years after the big bang. We can also use the CMB as a "backlight" to learn more about the lower redshift universe. Studies of the CMB can answer many fundamental questions about the nature of the universe.
The CMB is almost uniform in its brightness across the sky; its brightness at frequencies from roughly 0.5 mm to 10 cm is very close to that of a 2.7 K Planck blackbody. However, there are small variations in the brightness, at the level of tens of microKelvin. It is also slightly polarized. By studying these temperature variations and the polarization, we have learned many interesting things (including the global curvature of spacetime in the universe, the amount of normal matter, and the amount and nature of the dark matter and "dark energy" in the universe), and will learn even more in the future.
We are currently working on two projects to explore the properties of the CMB. SPIDER is a balloon-borne instrument that will measure the polarization on large angular scales; in addition to learning more about the reionization epoch of the universe (near z=10), the ultimate goal of SPIDER is to detect the unique pattern of polarization that would be imprinted by gravity waves created during Inflation, when the universe was only 10-34 (or so!) seconds old.
Our other main project is the South Pole Telescope, which is a 10m diameter telescope located at the South Pole. We are currently observing with a camera that is optimized to look for clusters of galaxies via the Sunyaev-Zeldovich effect (using the CMB as a "backlight"), and to characterize the temperature variations of the CMB on very small angular scales (down to 1 arcminute). These observations tell us about the history of structure formation in the universe, and hopefully more about the nature of Dark Energy.
We are also working to build a new polarization-sensitive camera for the SPT, which will measure CMB polarization on very small angular scales. We hope to detect the effect of neutrino mass on structure formation with these measurements, as well as look for the gravitational waves from Inflation.