The apparent path of an object is different for observers in different reference frames. A ball dropped from the top of the mast on a moving ship lands at the base of the mast. An observer on the ship sees the path as straight down while one on the dock sees the path as a diagonal. How many paths are possible for the ball ? Do the paths sum?, are some combinations of paths destructive? This concept of different paths for different observers struck me as being related to the double slit experiment, for the path of the ball dropped from the top of the mast only becomes real when it is observed. The boat is slit A the dock is slit B.