I made a promise to myself when I began writing that I was going to keep the science in my science fiction. As a result I am going to have to pull up short on my hollow earth story as it is impossible for the Earth to be hollow! I actually did the math to figure out if centripetal force inside the Earth would hold you on the reverse surface and it would NOT! Then I read this great article about how the mass of the Earth could not support itself if it were hollow. So now I have to seriously rethink where this work is going and how I am going to reach the conclusion that I intended for the book without the Earth being hollow!