Little or no momentum is exchanged in the other two planes between the bodies. When this picture is evaluated in terms of mechanical stress, one finds that the bodies are not being pulled together by the gravitational field, but are instead pushed together by the pressure of their common field. In the figure below, a yoke and spring assembly illustrates the basic process of momentum flow and gravitational action. Springs 1 and 2 are under pressure, with x-momentum flowing from left to right. Springs 3 and 4, with x-momentum flowing from right to left, are under tension.
Gravity acts similarly.
Gravitation is still a bit mysterious, as it lacks a clear source of energy and medium for momentum exchange, in contrast to the Casimir Effect and well known electromagnetic interactions. Some theorists, notably Puthoff, suggest that the quantum fluctuations responsible for the Casimir Effect are responsible for gravity as well. Both employ the language and concepts of tensor dynamics to reveal a deeper structure in nature, one that is largely independent of the Page 3 detailed qualities of a source or system. Einstein's theory, for example, recreates the dynamics of a ball on a rubber sheet. The method is no less accurate for being applied to gravity, as the dynamics involved are perfectly analogous to one another.