Digging Earth To Reach The other Side. It Takes only 42 minutes

Iwe've barely scratched Earth's surface. The deepest hole humans have drilled is only about 12.3 km, while Earth’s radius is about 6,371 km. The short answer is: a hidden civilization-sized world is extraordinarily unlikely, but the deep Earth absolutely contains things we haven't directly explored. Here's the beautiful part of the physics. In a simplified Earth model where density is treated as uniform, gravity inside Earth increases linearly with distance from the center. That makes the motion approximately simple harmonic motion. The theoretical journey from one surface to the opposite surface is roughly: 42 minutes And back to where you started: 84 minutes That's remarkably fast. A real Earth with its actual density structure changes the result, but the basic idea remains fascinating.