why do ghosts float on non existant floors or look at at an empty wall then dissapears?

Answer 1

Ghost only remember what it was like when they were living. So if you change anything or something changes naturally, it can give them the appearance to float and look at "empty walls".

Answer 2

Because most ghosts are simply on "autopilot"...think of a CD on repeat...for some reason they're stuck doing one action the exact same way they did it when they were alive. While it might look as though they're walking into a wall now in their lifetime, they would have been walking into another room. As for the nonexistent floors, many houses settle as they age, so the floors that might have been right under their feet 100 years ago, are now two or three inches lower. In the same vein, looking at an empty wall might actually be them looking AT something that was there in their lifetime, a friend, a lover, a mirror, a portrait...damn near anything.

Answer 3

I would think that the ghosts your speaking of are either "recordings" of life, therefore only a image of a person looking at something no longer there, or spirits existing in our time but only seeing what haunts them, i.e. the past.