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 gravitational 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. Furthermore, using instruments developed for gravity measurement, the group will look for signatures of dark matter. Technology and technical expertise developed by this group has applications ranging from industrial metrology to earthquake prediction to preparing the country’s STEM workforce. Modern ideas for unifying gravity and particle physics, as well as the observation of dark energy and dark matter, suggest that some aspects of gravity remain undiscovered. The table-top experiments of the University of Washington gravity laboratory (Eöt-Wash Group) provide a unique opportunity to search for new physics at the intersection of General Relativity, cosmology, and particle physics. The group is a leader in the field of ultra-weak force detection through technical expertise and innovation and by responding to the most relevant timely and timeless physics questions. Specifically, the group will: 1) 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 balances provided the most precise laboratory EP-tests. With highly increased sensitivity through fused silica torsion fibers, a novel gravity gradient measurement, an improved pendulum and better instrument control, new EP measurements will be carried out that will be up to 15 times more sensitive than the group’s previous measurements in constraining B-L couplings. Furthermore, the EP-test’s generality and relevance to cosmology will be enhanced by probing the EP involving hydrogen-rich test masses. 2) Test Newton's Inverse-Square Law (ISL) at short distances: The group will use its expertise in measuring gravity at short distances to build a new instrument and carry out measurements to test gravity at distances as short as 20 µm. 3) Search for ultra-light dark matter using torsion balances. 4) Advance the frontier of low-frequency ultra-small-force technology: Innovative and challenging technology development has enabled the group’s success. The group will further improve angle measurement and develop interferometric and capacitive distance gauges. 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.