Despite more than 200 years of experiments, the best laboratory determinations of the force of gravity have yielded no better than a ballpark figure. Adding to the haziness, metrologists have scarcely probed the force's strength at distances of 1 millimeter or less. There, gravity may vary drastically from Newton's law, possibly signaling the presence of unseen extra dimensions, some theories suggest (SN: 2/19/00, p. 122: Hunting for Higher Dimensions).
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