"Who controls the past controls the future: who controls the present controls the past." George Orwell What is the one weapon you cannot, under any circumstances, allow your adversary to possess? No, not nuclear weapons — as dangerous as they are (and we might be close to finding out), you can deter them with nuclear weapons of your own and possibly even shoot them out of the sky. There is an even worse weapon, one for which you have no defense: The Time Machine.