"But where did they come from?" That was the simplest way to pose her graduate thesis. Everyone had a basic knowledge of what a ghost was, despite the non-believer aspect. Although the where was what she really wanted to know, along with her two lab partners of course.
Before she met Jack and Vlad she thought she was the only one serious enough about this "para-science". Everyone else in her class seemed to only be there for the thrill of it, she was there for science.
Her lab mates worked together to come up with the theory that ghosts did not in fact come from our world, but a parallel one. Now if only they could prove it.
It took research, field studies and even more research but eventually they came to the conclusion that there were natural portals that connected to two dimensions, but they seemed to operate in the purest form of random Maddie had ever encountered. The lack of order and regularity was not helpful.
And then Jack had the most brilliant idea, "why not just make a machine that can bust through to the other side?"
Why not indeed.