Imagine there is a hollow sphere charged with positive charge, distributed evenly. Then a proton is placed in the cavity. Would the proton levitate stably in the middle of the cavity? By Earnshaw Theorem, any configuration of system with fixed field strength which obey inverse square law will not enable us to have stable levitation. (Since there are no local maxima or minima). But, in the above case, if the proton doesn't stay stably in the middle, where can it go? It is repelled in every direction isn't it? Does the system above do not obey some of the assumption required by Earnshaws Theorem? Thanks in advanced.