Terrance Mann
Ok I've watched this movie a thousand times and it's one of my favorites. But something for the first time hit me when Shoeless Joe asks Terrance Mann if he would like to join them in the cornfield or whatever is beyond the cornfield. Is it possible that Terrance Mann himself was also a ghost? And that he was brought there to fulfill his dream of once playing at Ebbets field or something like that? Notice how he disappeared in the corn like the rest of the ghosts. Also it would explain why Ray wasn't asked to go with them, because he's not dead.
The only thing that would contradict this theory is that Ray showed Terrance the newspaper in the motel room showing that his father reported him missing. But then of course when Ray goes for his walk he is suddenly back in 1972. Any thoughts???