  We know that the generally accepted theories of gravity and quantum mechanics
are fundamentally incompatible. Thus, when we try to combine these theories, we
must beware of physical pitfalls. Modern theories of quantum gravity are trying
to overcome these problems. Any ideas must confront the present agreement with
general relativity, but yet be free to wonder about not understood phenomena,
such as the dark matter problem and the anomalous spacecraft data which we
announce here. This all has led some ``intrepid" theorists to consider a new
gravitational regime, that of antimatter. Even more ``daring" experimentalists
are attempting, or considering attempting, the measurement of the gravitational
force on antimatter, including low-energy antiprotons and, perhaps most
enticing, antihydrogen.
