Most of us have probably never seen a ghost face to faceless and there may be people who claim there is no such thing! But even they must admit that witches fly on broomsticks and carry black cats, who are really ghosts in disguise! And you can be sure that even those who laugh at ghost stories won't hang around graveyards at midnight, or walk too close to a haunted house.

For science has taught us many things about the world we see around us. But what do we know about the unseen world around us?