Probing Fundamental Physics with Gravitational Experiments

University Of Washington, Seattle WA

Investigators

Abstract

In modern physics nature is described by two theories. One is the "Standard Model", which describes all material properties with quantum particles; the other is "General Relativity", Einstein's theory that describes gravitation. Most physicists think that there must be a connection between these two theories, but to date there is no experimental signature for such a connection. Furthermore, the discoveries of dark matter and dark energy suggest that gravitation phenomena exist that lie outside of General Relativity. The group at the University of Washington specializes in measuring ultra-feeble forces to search for unprecedentedly small deviations from gravity as described by General Relativity. While observing any deviations from General Relativity would be a revolutionary scientific discovery, it may also have consequences for future technical applications of GPS or next-generation precision clocks. Technology and technical expertise developed by this group has applications ranging from industrial metrology to earthquake prediction. Modern ideas for unifying gravity and particle physics, as well as the observations of dark energy and dark matter, suggest that General Relativity is not a complete theory and that new ultra-feeble forces of nature may remain undiscovered. The table-top experiments of the University of Washington gravity laboratory (Eot-Wash Group) provide a unique opportunity to probe for new physics at the intersection of general relativity, cosmology, and particle physics. The group leads the field of ultra-weak force detection through technical expertise, innovation, and by responding to the most relevant timely and timeless physics questions. Specifically, the group will: 1) Continue to test the equivalence principle (EP): It is almost certain that any connection between General Relativity and the Standard Model violates the EP. The group's torsion balance experiments provide the most precise EP-tests over ranges between microns and 100 km. The group has upgraded the flagship rotating torsion-balance instrument with a fused silica torsion fiber and will carry out a new EP measurement. 2) Dark matter's only known interaction appears to be gravitational. Following recent theoretical suggestions that dark matter may be bosonic with particle masses as low as 10exp(-22) eV/c2, the group will search dark matter evidence by re-analyzing archival datasets and by collecting new ultra-sensitive silica-fiber-based measurements. 3) Test Newton's Inverse-Square Law at short distances: The Eot-Wash group has measured and tested gravity at distances below 50 microns. The group will begin another measurement cycle with upgrades to its existing instrument. 4) Advance the frontier of low-frequency ultra-small-force technology: Innovative and challenging technology development has enabled the group's success. With a vision towards the future, the group will continue pursuing development of cryogenic instruments, optical readout, and silica fibers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.