I was recently at a paranormal class about theories. The instructor talked about the M-theory, so I came home and tried to do research on this topic. This theory is about alternate dimensions and parallel worlds.
The instructor commented about that instead of getting photo's of ghosts or voices of ghosts that what if a parallel world or dimension had crossed into our world. And what we thought were ghosts were actually people in this other world.
The more I thought about this the more is does make sense as one theory to explain the sighting of ghosts. But I'm not 100% for sure on this.
On some of my research on the M-theory this is what I found on wikipedia. M-theory is a new limit ( the final, utmost, or furthest boundary or point as to extent) of string theory in which 11 dimensions of space time may be identified. M-theory is not yet complete; however it can be applied in many situations. The "M" in M-theory could stand for master, mathematical, mother, mystery, membrane, magick, or matrix.