New Frontiers in Experimental Gravitation

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The University of Washington Eot-Wash Group will develop specialized instruments with unprecedented sensitivity for the ultra-weak forces suggested by some modern explanations for the apparent accelerated expansion of the Universe and by theoretical attempts to unify gravity with the other three fundamental forces. In particular, we will enhance the sensitivity to violations of the weak equivalence principle by a factor of about 10. This will test a key postulate of Einstein's laws of gravity, provide a laboratory test of the gravitational property of galactic dark matter, close a loophole in the ongoing Lunar-Laser-Ranging test of the strong equivalence principle, probe speculations about the source of the mysterious "dark energy" that apparently comprises two thirds of the total mass-energy of the Universe, set stringent constraints on Lorentz-symmetry-violation in gravity, and probe any idea that predicts ultra-feeble "fifth" forces. Additionally we will test Newton's inverse-square law down to length scales substantially smaller than the diameter of a human hair. This will probe for "large" extra dimensions, test a possible explanation for the observed smallness of the cosmological constant and rule out a large class of "chameleon" theories that were proposed to hide the many long-range interactions generated by string theories. These tests should be able to probe new gravitational-strength interactions with length scales down to 20 micrometers. We will search for new short-range spin-spin forces arising from exotic bosons using an electron-spin polarized pendulum/attractor instrument with 10-fold rotational symmetry.Because open questions about gravity are central to the gravitational, elementary-particle and cosmology communities and fascinate the scientifically literate community as well, (could anti-matter fall differently from matter? could the extra dimensions predicted by string theories have detectable effects? could dark matter have unusual long-range fields? is gravity truly the weakest force or could there be a whole regime of ultra-weak forces?) the Eot-Wash Group's work continues to have an unusually broad impact. Their results are widely disseminated through publications, invited talks and colloquia, invited review articles, lab tours, meetings with undergraduates at other universities and colleges, public lectures, and have been featured in magazine and newspaper articles in this country and in Europe. Group members have created a chapter on gravity and feature in a video documentary for the Annenberg Course "Physics for the 21st Century". The group's work has been featured in articles in Nature and The Economist and in an episode of "Through the Wormhole with Morgan Freeman". The broad range of scientific issues addressed by the Eot-Wash Group and the many technical challenges involved provide an excellent education in experimental physics and in high-tech instrumentation for graduate students and postdoctoral fellows, as well as unusually attractive opportunities for undergraduate research projects.