So... what are ghosts?
Are they the remnants of the departed, such as imprinted memories, are they individuals bleeding through from an alternate universe or dimension, perhaps a projection from our own psyche. Maybe aliens if you believe that they could be arsed to travel a thousand light years just to fuck with us, what a great sense of humour if they did.
I've seen and experienced various things one might attribute to ghosts, strange mists with no explanation, randomly occurring scents that come and go too fast and strong to be explained away with confidence, scratches, the odd "orb", unusual sounds etc.
I'm not skeptical of the existence of the phenomena, i am skeptical of the idea that it's dead people, or demons etc.
I've looked into psychology and physics for a rational explanation and have yet to find anything conclusive. It's promising but requires more data. So all we can do is pose the question and consider the possibilities, so... what are ghosts?