I'm building a home for myself which is basically a collection of blocks floating in a black void. It all worked out better than expected, except that if I walk off one of the platforms I can just walk straight on out forever without falling. I wanted to post a picture of what I've built so you can see what I'm talking about but I guess I'm not allowed. Just imagine stone platforms floating in space.

Does anyone know how I can fix this? I need normal gravity in here.