I think you'll need to provide a bit more information about the game for us to intelligently answer your question. Beyond offering you a good physics library or engine, you haven't told up much else other than you're using core geometric shapes.

Is it a massive battle between the cubes and spheres again? They are always fighting. It's the cubes trying to get into the sphere's territory is the problem.

Sorry my friend, but we'll need much more information to understand what it is that you want to know. More information so we can help please.