Ok, im sure similar questions have been asked but here it goes. You start digging a hole with the intention of digging straight through the planet. Your hole will be straight but will only go through the mantle, missing the core and outer core, so you have avoided the weightlessness of the earth's core. So what happens? you keep digging down and you get closer the surface on the other side of the world. Do you at some point fall back? when do you become upside down?