Searches for Composition-Dependent Effects
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As we discussed in Chapters 1 and 2, composition-dependent effects are those (apparently) gravitational effects which depend on the chemical composition of the test masses. A simple example would be a difference in the accelerations of two dissimilar objects dropped from the same height, an experiment Galileo is reputed to have carried out. We noted in Chapter 1 that any such difference could be ascribed to the presence of a new force rather than to gravity, but for most experimental purposes we can describe the relevant experiments without reference to any specific theoretical picture. (Theory is important, however, when comparing the sensitivities of different experiments, since such comparisons necessarily involve assumptions about the relative sizes and charges of different sources and detectors. This, in turn, introduces model-dependent assumptions about the form on the non-Newtonian force.) Interest in such experiments has greatly increased in recent years, and a number of imaginative techniques have been developed to search for such composition-dependent effects. In anticipation of the ensuing discussion, we summarize some of the main conclusions that have emerged to date.
KeywordsEquivalence Principle Gravity Gradient Test Mass Torsion Balance Newtonian Gravity
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