It has long been theorized that UFOs are able to attain such incredible speed and maneuvering by causing a repulsive force on the earth's geomagnetic field. Magnetohydrodynamics proves that a vehicle can use magnetism to propel itself without any external man-made assistance (such as in bullet trains). Two questions then: What is the feasibility of the hypothesis that UFOs exert a repulsive force on the geomagnetic field as a form of propulsion? Is there any way an observer would be able to detect this? Thank you very much in advance for your time.