THE "DARK SIDE" OF GRAVITATIONAL EXPERIMENTS

Abstract

Theoretical speculations about the quantum nature of the gravitational interaction have motivated many recent experiments. But perhaps the most profound and puzzling questions that these investigations address surround the observed cosmic acceleration, or Dark Energy. This mysterious substance comprises roughly 2/3 of the energy density of the universe. Current gravitational experiments may soon have the sensitivity to detect subtle clues that will reveal the mechanism behind the cosmic acceleration. On the laboratory scale, short-range tests of the Newtonian inverse-square law (ISL) provide the most sensitive measurements of gravity at the Dark Energy length scale, λ d = (ħc/ρ d )1/4 ≈ 85 μm, where ρ d ≈ 3.8 keV / cm 3 is the observed Dark Energy density. This length scale may also have fundamental significance that could be related to the "size" of the graviton. At the University of Washington, we are conducting the world's most sensitive, short-range test of the Newtonian ISL.