I'm open to the idea of there being more to the universe than what we know, but ghosts as we "know" it definitely not. If ghosts as we "know" it were real there would have been proof since 2000...too much handheld tech is out there for there not to be proof.
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It depends though, what we view as ghosts is not real....that's a simple fact as we would have seen them. Any other possibilities of new life or spiritual forms are open to speculation...but it's just as arrogant to say ghosts could possibly be real as to say they aren't as with our tech we would have seen something.