Q1. What is superconductivity and how is it used in gravity measurements?
A： Superconductivity is the phenomenon by which the electrical resistance of a material drops to zero below a certain critical temperature, accompanied by perfect diamagnetism. A superconducting gravimeter exploits this effect: a superconducting sphere is levitated inside a Dewar (cryogenic vessel) without resistance, and any disturbance below the surface or change in surrounding mass causes the sphere to shift. Coils around the sphere automatically record the displacement. The instrument can resolve gravity changes finer than 10⁻¹¹ m/s², detecting extremely small environmental variations.