I am a Christian, but I believe that ghosts are created by a device, or, as Joe Nickell said, that "they too are mental creations," meaning that we create ghosts.
Source:
Ghost - Wikipedia
en.wikipedia.org
Luke 24:39 proves the existence of ghosts in Christianity.
If the Word was God, with God being The Father, The Son, & The Holy Spirit (ghosts are spirits) and so many scientists around the world are Christian, why would they, the scientists, classify ghosts as part of the paranormal instead of classifying them as something real when The Bible clearly states in Luke 24:39 that ghosts are real?