If the sign of a successful scientific theory is that you get more out of it than you put in, then the most successful of all must be Einstein’s general theory of relativity. Starting from a few simple principles and earthy thought experiments, such as what would happen if you got stuck in a falling elevator, general relativity predicts everything we know about gravity and much we never suspected. In the latest example, John Swain of Northeastern University suggests that it might be possible to build a gravitational transformer that transfers kinetic energy just as an electrical transformer transfers electrical energy.
The idea is based on the uncanny resemblance between the equations of general relativity and those of electricity and magnetism. The gravitational attraction that makes apples fall is analogous to an electric field, with mass playing the role of electric charge. And just as the motion of electric charges gives rise to a magnetic field, so the motion of mass gives rise to a “gravitomagnetic” field. Earth’s spin, for instance, tugs on satellites in an effect known as frame dragging.
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