If we consider a box( in our quantum world ) with three balls having total mass 'M= m1 + m2 +m3' . After changing their positions, now, calculating the mass will give another value which is not equal to 'M' but 'M*=m*1 +m*2 + m*3)', which implies our mass is not conserved. then how could energy be conserved (E= mc2) ??!