Gravity is not a source of energy, it's an energy store. You need to put in energy to get back energy (at least the way i think you are proposing it here) Radi

Gravity is not a source of energy, it's an energy store. You need to put in energy to get back energy (at least the way i think you are proposing it here) Radioactive materials are also due to the sun, ours or others elsewhere in the universe. Earth does not produce them. Whatever heat our planet had in the beginning and continues to have, originated from the sun. No sun, no heat