Precision Tests of Contemporary Ideas in Gravitational/Particle Physics

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This award supports the University of Washington Eot-Wash Group to develop novel, highly-sensitive torsion-balance instruments to search for the ultra-weak forces allowed by modern ideas in theoretical physics; especially attempts to unify gravity with the other three fundamental forces. This unification is faced with two deep problems: the extreme weakness of gravity compared to the other known forces, and the enormous observed disparity between the cosmological constant and the quantum-mechanical predictions of the vacuum-energy density. Theoretical ideas for overcoming these problems often predict new gravitational phenomena that can be tested with improved instruments. In particular, (1) Newton's inverse-square law will be tested down to length scales substantially smaller than the diameter of a human hair to probe for "large" extra dimensions and to test a possible explanation for the observed smallness of the cosmological constant. These tests should be able to probe new gravitational-strength interactions with length scales down to 25 micrometers; (2) Einstein's Weak Equivalence Principle will be tested with a sensitivity 50 times better than previously published results. This will test a key postulate of Einstein's relativistic theory of gravity and will close a loophole in the ongoing Lunar-Laser-Ranging test of the Strong Equivalence Principle. It also probes speculations about the source of the mysterious "dark energy" that appears to comprise two thirds of the total mass-energy of the Universe; (3) A special torsion pendulum containing almost a mole of polarized electrons will be used for several novel experiments of unprecedented sensitivity including a search for CPT-violating fields frozen into the universe, a search for macroscopic CP-violating interactions, a search for macroscopic, velocity-dependent, P-violating interactions, and a search for the exotic spin-spin interactions predicted by current ideas about "ghost condensate" gravity; (4) A new torsion-balance instrument will be commissioned and used to search for the force produced by axion-like particles.The Eot-Wash Group has applied the techniques of experimental gravitation to address a broad variety of basic questions of interest to the gravitational, elementary-particle and cosmology communities. This research has required and produced technical innovations that have found applications in other areas such as gravity-wave detection. The Group's results are widely disseminated through publications and by colloquia, invited talks, lab tours and public lectures, and have been featured in magazine and newspaper articles in this country and in Europe. The variety of scientific issues addressed by the Eot-Wash Group and the many experimental challenges involved provide an excellent education in experimental physics for graduate students and postdoctoral fellows, as well as unusually attractive opportunities for undergraduate research projects. This award will provide support for graduate students, postdoctoral researchers and several undergraduate projects.