One limitation to such an attack, Professor Teller points out, is the boomerang effect of these gases on the attacker himself. The radioactive gases would eventually drift over his own country, too. He adds, however, that since these gases have different rates of decay—some faster, some slower—the attacker is in a position to choose those radioactive products best suited to his attack. “With the proper choice he could ensure that his victim would be seriously damaged by them, and that they would have decayed by the time they reached his own country.” “It is not even impossible to imagine,” in the words of Professor Teller, “that the effects of an atomic war fought with greatly perfected weapons and pushed by utmost determination will endanger the survival of man.... This specific possibility of destruction may help us realize more clearly the probable consequences of an atomic war for our civilization and the possible consequences for the whole human race.” On this point Professor Szilard is much more specific. “Let us assume,” he said at a University of Chicago Round Table, “that we make a radioactive element which will live for five years and that we just let it go into the air. During the following years it will gradually settle out and cover the whole earth with dust. I have asked myself, ‘How many neutrons or how much heavy hydrogen do we have to detonate to kill everybody on earth by this particular method?’ I come up with about fifty tons of neutrons as being plenty to kill everybody, which means about 400 tons of heavy hydrogen” (deuterium). Now, obviously Professor Szilard was stating the extreme case. He merely called attention to the scientific fact that man now has at his disposal, or soon will have, means that not only could wipe out all life on earth, but could also make the earth itself unfit for life for many generations to come, if not forever. Here we have indeed what is probably the greatest example of irony in man’s history. The very process in the sun that made life possible on earth, and is responsible for its being maintained here, can now be used by man to wipe out that very life and to ruin the earth for good. It is inconceivable that any leaders of men today, or in the near future, would resort to such an extreme measure. But the fact remains that such a measure is possible. And it is by no means unthinkable that a Hitler, faced with certain defeat, would not choose to die in a great Götterdämmerung in which he would pull down the whole of humanity with him to destruction. And who can be bold enough to guarantee that another Hitler might not arise sometime, somewhere, possibly in a rejuvenated Germany making another bid for world domination or total annihilation?