changing distance from Earth, records that can be compared to what would be expected for constant-G and variable-G models. So far, scientists have found no significant discrepancy from the standard gravitational theory with constant G.
Other techniques for determining lunar motions—and hence ascertaining the rotational history of Earth—involve measuring the occultation (covering up) of stars by the Moon, sifting through records of eclipses (for thousands of years), and examining the growth lines of certain types of fossils that reflect the ancient sequence of days and months. None of these methods are free of ambiguity. However, they have been useful in placing limits on the rate by which G could have varied.
In the early 1970s, Thomas Van Flandern, an expert on the lunar occultation of stars, applied his skills in an attempt to pin down the variability of G. Trained at Yale, he has long taken an iconoclastic approach to the study of the universe—arguing passionately against the standard Big Bang scenario. Using occultation data, he estimated that G has changed by about eight-billionths of a percent each year. This result sparked considerable controversy—to which he is no stranger. More recently, he has argued with NASA officials over his assertions that artificial structures could be seen in photographs of the Martian surface. Despite the controversial nature of his endeavors, Van Flandern has received a number of awards for his work—including one for a prize-winning essay in the Gravity Research Foundation competition.
Apart from long-term changes in terrestrial rotation, one of the curious notions arising from the possibility of a changing gravitational constant, according to at least some of the models, is the one that Earth has expanded over the eons. Today, such a hypothesis has little support in the geological community. If anything, most geologists