I create a large mountain out of an extremely dense material and hollow out a cavern beneath it. What kind of material would be best and how tall would the mountain need to be for its gravity to counter earths gravity? I want to create a low gravity chamber.
Neutronium would be nice but thats hard to come by. How about lead or spent uranium? Maybe not uranium. Even spent radioisotopes have some residual radiation don't they? Something dense anyway. Gold would be nice but I doubt there is enough on earth. Maybe after Planetary Resources freights a few asteroids of the stuff back to Earth it will be more affordable. Anyway, what would work and what would be financially feasible?