I can't prove anything, but I know what has occurred in my family life. But there was a time that many things were not known to exist. Giant squid for one example. They were known to exist for centuries but no one ever had physical evidence. With technology, they have verified their existance. Could we just be in the 18th century of understanding ghosts? At one time we thought the moon was made of green cheese, now we know it isn't. Just because we don't understand things, should not discount them as a possible fact.

Spirits/ghosts have been seen for thousands of years. They have been discussed long before we knew the Earth was round and the Universe didn't revolve around our planet.

Sure, for the outsider, I can't expect you to understand what my family had seen/experienced. However, I can tell you that with every fiber of my body, I know what I've experienced. You either accept my experience or you don't.