What is possible? Everything. It just depends on what level we are able to effectively manipulate the universe. Suppose for a moment that the universe is comprised of 'bits' at the very smallest possible scales. We do not currently have direct (root) access to these bits, so we must manipulate them from within the system. Because our universe is NP-complete, given enough control over these universal bits, anything that is thinkable is possible. Will we ever be able to control these bits? It remains to be seen, but I should think so eventually.