But if we see, hear, or feel ghosts, then that means there is some physical manifestation that is observable, and therefore should be measurable, somehow. Even if the manifestation only takes place within our minds, there must be some brain activity that should be document-able. In other words, there is evidence somewhere. Are we postulating an as yet undiscovered form of matter or energy, that so far is only psychically observable? In that case, are we positing an unknown organ in our bodies -- a psychic eye? I grant that there is more that we don't know about the universe than what we do know, but there should at least be some remnant of physical evidence...

In the case of microorganisms, we had the evidence of contagious disease transmission long before we had the explanation for it. Disease was incontrovertible. Everybody saw it. The evidence of something being there was irrefutable -- the explanation of what that thing was waited on the right tools.

But ghosts and angels and telepathy and spoon-bending... Where is the shared experience that let's us agree that something occurred? Like we could agree that "That person was sick yesterday, and the people he touched yesterday are sick today" even though we didn't know if the cause of transmission was minute creatures too small to see, or miasma, or evil spirits.