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100 Years of Relativity Space-Time Structure: Einstein and Beyond ...

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Was <strong>Einstein</strong> Right? 20910 -810 -9EötvösRennerFree-fallη10 -1010 -11PrincetonBoulderFifth-forcesearchesEöt-Wash10 -12MoscowLLREöt-Wash10 -13η= a 1 -a 2(a 1+a 2)/210 -14 YEAR OF EXPERIMENT19801970196019401920190019902000Fig. 1. Selected tests <strong>of</strong> the Weak Equivalence Principle, showing bounds on the fractionaldifference in acceleration <strong>of</strong> different materials or bodies. “Free-fall” <strong>and</strong> Eöt-Washexperiments, along with numerous others between 1986 <strong>and</strong> 1990, were originally performedto search for a fifth force. The dark line <strong>and</strong> the shading below it show evolvingbounds on WEP for the Earth <strong>and</strong> the Moon from Lunar laser ranging (LLR).Universities <strong>of</strong> Washington, Seattle, <strong>and</strong> California, San Diego, plans touse enhanced laser <strong>and</strong> telescope technology, together with a good, highaltitudesite in New Mexico, to improve the Lunar laser-ranging bound byas much as an order <strong>of</strong> magnitude 10 .High-precision WEP experiments, can test superstring inspired models<strong>of</strong> scalar-tensor gravity, or theories with varying fundamental constants inwhich weak violations <strong>of</strong> WEP can occur via non-metric couplings. Theproject MICROSCOPE, designed to test WEP to a part in 10 15 has beenapproved by the French space agency CNES for a possible 2008 launch. A

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