I've had a look at the paper : there are at least two objections to it : The first appeals to an idea popularity not considered as Leibnitzian, although the truth on the matter is more complex : the idea of ether , namely , for space , or space-time to have reality , it must have "matrix style" unique and absolute coordinates for every point . The spheres are distinguished by possessing different coordinates . The second , affirms a mode of 'esse est percipi' , namely, a universe cannot be 'real' without at least one 'real observer' .Such an observer will distinguish the spheres . Even ignoring the above objections , to the extent that they can be real without any observer or coordinates , they are either distinct , or are the same object . (in the same way members of the same equivalence class in a group are the same in a factor group ) . That object would be something along the lines of 'the potentiality of a sphere to be to the left and/or to the right of an observer' .
The identity of indiscernibles can be formulated as simple principle of second order logic applicable to every mathematical object : ?F(Fx ? Fy) ? x=y. No one would dispute it's truth with regards to real numbers, for example . To apply it to reality , one needs an extra piece of info/assumption : that is, the doctrine of the pythagoreans, that the universe is mathematical at the deepest level : "Number rules the universe" -Pythagoras