The Direction of Gravity

How much do we really know about gravity? Though our knowledge is sufficient to send people to the Moon, there is a large and fundamental gap in our empirical data; and there are basic questions about gravity that are rarely even asked, and so remain unanswered. The gap concerns the falling of test objects near the centers of larger gravitating bodies. Newton's theory of gravity and Einstein's theory, General Relativity, though giving essentially the same answers, describe the problem quite differently. A discussion of this difference--which emphasizes the role of clock rates in Einstein's theory--evokes a question concerning the most basic characteristic of any theory of gravity: Is the motion due to gravity primarily downward or upward; i.e., inward or outward? Have our accepted theories of gravity determined this direction correctly? The answer to this question may seem obvious. We will find, however, that we don't really know. And most importantly, it is emphasized that we can get an unequivocal answer by performing a relatively simple laboratory experiment.