I had a friend that was a sound engineer and he thought ghosts were an electromagnetic phenomenon. He thought the electromagnetic properties of the brain were somehow “impressed” on a certain area with the right conditions and “played back” when conditions were right.
CC
I had a philosophy professor in college that also explored parapsychology. He believed that just as some people seem to display precognitive abilities, some people may be postcognitive and get a sense of events after they occurred, i.e. a visitor to a civil war battlefield may report seeing a ghost of a union or rebel soldier in 2023, but it's not the soldier's ghost that wandered forward in time, but rather, the mind's eye of the 2023 visitor that has wandered backwards (or maybe just a re-enactor that missed his tour bus ;)