One theory explains ALL of it. "Ghosts" AND "Phantom objects" . Ghosts are simply LIVING PEOPLE we are seeing via natural "glitches' or "Portals" in another TIME. This explains their clothing and other props, like eyeglasses and walking sticks, etc.---that have no "spirit" element. Inanimate objects like "Ghost Cars", or "Ghost Trains", etc. are ALSO objects in another time.
We are likely looking at natural "time Overlaps" or Einstein -Rosen Bridges that connect one TIME (or place) to another ----momentarily at least, forming a LOCAL overlap or" window" into the past.--------It is even better than the "Spirit Theory": as it IS Scientific, AND we do not have to "invent" beings like "Spirits".
Two of the best Physicists of the age say such "bridges/Wormholes" are possible, so this is the best theory and explains ALL aspects of the observations (Spirit theory cannot explain clothing OR Phantom objects)
That Time overlaps or shifts CAN apparently exist in low energy, natural situations strongly suggest that STUDY of alleged "Ghosts" may lead to an understanding in Physics that might lead to practical Time travel Technology