"Try to think of the vast areas of so-called empty void between the galaxies," Ortine went on patiently. "Try to consider that these areas are no more empty than the areas between the stars visible to you in your telescopes. My universe might be called the other side of the universe--if you can think of the universe as a coin." "I understand--a little," Justin told him. "Now tell me--why are you here? And why do you want _me_?" Ortine flicked ashes on the floor, which immediately absorbed them. He said, "I have been sent here to prevent your planet from destroying itself and probably forcing your sun into nova. "For while your sun is not a great star it lies in an area correspondent to one of the most congested and thickly settled areas of my universe. It is not supposed to go into the nova stage for some billions of your years. Should it happen in the near future--as it will if my mission is unsuccessful--something like catastrophe will result on the opposite side of the coin." "How can you be sure it will happen?" Justin asked quietly. "Because, thanks to certain differences of structure between our universe and yours, we can follow the whole stream of your time," Ortine replied matter-of-factly. "Your past, of course, is not dead--you have already seen proof of that here on Belvoir--nor is your future yet unborn. In short, the past still exists, the future does exist." "In that case," said Justin, "Why don't you give up and go home?" "Because"--Ortine's sincerity was self evident--"neither your past nor your future is immutable. Needless to say, we do not believe in altering history on any world unless it must be done to avert needless disaster. It is my mission to alter both Earth's past and its future by effecting the course of the key events of your history." "It sounds like rather a large order," said Justin. "It is," Ortine replied simply. "While our time-span is far different from yours--I suppose I have existed for several thousand of your years--it is the first such assignment in my memory or that of my mentors." "Then you cannot follow your own past and future," said Justin. "Unfortunately not." Ortine looked unhappy. "No species has ever been able to do that reliably. We are all trapped within the span of our own time. But yours is so infinitesimal to us that we are able to read it easily--just as your scientists can read and to some extent predict the lives of fruit-flies." "Not a very happy simile," Justin put in. "My apologies," said Ortine. "In the matter of size between us there are no such discrepancies. It is wholly a matter of temporal maladjustment. And it is my theory that the shortness of your life-span is responsible for the self-inflicted doom that threatens not only your world and your sun but a number of ours." "You might have something there," said Justin. "But what in hell do you want us to do about it? Live forever?"