Is the Doctor a "ghost" or is the explanation more complicated than that?
Steven Moffat mentioned in an interview that one can, in theory, time travel and make your own ghost. Is that what's going on with the Doctor? Are we dealing with an alternate universe scenario perhaps? What are your theories Whovians?
Was the valley flooded intentionally in order to stop the alien warlord known as the Fisher King? How is he creating these "ghosts" and what's his end game? There are so many questions that need answering.
Don't miss Doctor Who Season 9 Episode 4 for all the answers.