Even when all the known physical and psychological factors have been eliminated as explanations, it's possible that ghost sightings may be caused by forces that we just don't yet understand. Robert Schoch, associate professor of natural science at Boston University, has been doing research on the relationship between brain waves and geomagnetic waves. Schoch cited the phenomenon of "crisis apparitions" -- when family members see the "ghost" of a faraway relative at the exact moment that person died. "Some people will dismiss this as coincidence," Schoch said. "But there have been, in my assessment, very good statistical studies of such things that take it out of the realm of coincidence."
According to Schoch's hypothesis, such apparitions aren't ghosts at all, in the sense of otherworldly spirits. Instead, the phenomenon may be a kind of extrasensory perception that we can't yet measure. Schoch's research concerns whether brain waves of certain emotional states may be transferred between people over long distances on low-frequency wavelengths -- the same wavelengths that are detected in the Earth's geomagnetic field.
"One study looked at crisis apparitions and geomagnetic patterns on the surface of the Earth," Schoch said. "It turns out that the incidents of crisis apparitions correlate with geomagnetic flux."
Schoch said it can be professionally risky, in the academic community, to advance any theories that include parapsychology phenomena like ESP or ghost sightings. But he still believes there is value in exploring these topics. "When you get rid of all the bogus crap, which is 95 percent plus of it, there is a residuum left where it seems to be something real."