i can't knoew for sure if there are ghosts but i do believe that some people have a wild imagination that has been triggered by something logic that can be explained,
some people in here claim that they have seen ghost but there are several almost too many things that can cause hallucinations.
toxic air like wet paint or unventilated rooms can be a source,
a shortage of rest can also cause halucinations and even when you are in bed you can see things floating in the air, i had that myself once, i was sleeping but still slightly awake which caused me to see my own dreams while i could still see my room.
certain medicins can also cause this especially when they are strong or when you just started using them.
the neighbour of my granddad claimed to be visited multiple times by an angel who asked her to write a book about the ending of the world, (it's practically an old religious story about spirits who live on forever and worlds that end and start over and over to refresh it actualy but i don't want to spoil her fun)
anyway what i'm saying is that it's hard to proof if there are gods, angels, spirits and ghosts or not since the people who tell these stories usualy had certain circumstances which might have caused these halucinations.