Half the city was in ruins, swept and raked by the stabbing rays that probed down from the upper reaches of the atmosphere, blasted by hydrogen and atomic bombs that shook the very bedrock of the planet and shattered great, sky-high towers of white masonry into drifting dust. Twisted wreckage fell into the city from the battle area, great cruisers reduced to grotesque metal heaps, bent and burned and battered out of all semblance to a ship, scorched and crushed and flattened by the energy unloosed in the height of battle.
"They have new weapons," said the Engineer. "New weapons and better screens. We can hold them off a little longer. How much longer I do not know.”
In the laboratory, located in the base of one of the tallest of the skyscrapers in the great white city, the Engineers and the Earthlings had watched the battle for long hours. Had seen the first impact of the fleets, had watched the first dogfight out at the edge of atmosphere, had witnessed the Hellhounds slowly drive the defenders back until the invaders were within effective bombardment distance of the city itself.
"They have a screen stripper," said the Engineer, "that is far more effective than anything we have ever seen. It is taking too much of our ships' energy to hold up their screens under this new weapon.”
In the telescopic screen a brilliant blue-white flash filled all the vision-plate as a bomb smashed into one of the few remaining towers. The tower erupted with a flash of blinding light and disappeared, with merely the ragged stump of masonry bearing mute testimony to its once sky-soaring height.
"Isn't there anyone who can help us?" asked Kingsley. "Surely there is someone to whom we might appeal.”
"There is no one," said the Engineer. "We are alone. For thousands of light years there are no other great races to be found. For millions of years the Hellhounds and the Engineers have fought, and it has always been those two and just those two alone. Thus it is now. Before, we have driven them off.
Many times have we destroyed them almost to the point of annihilation that we might hold their cosmic ambitions under proper check. Now it seems they will be the victors.”
"No other race," said Gary, musing, "for thousands of light years.”
He stared moodily at the screen, saw a piece of twisted wreckage that had at one time been a ship crash into the stump of broken tower and hang there, like a bloody, smoke-blackened offering tossed on the altar of war.
"But there is," he said. "There is at least one great race very near to us.”
"There is?" asked Caroline. "Where?”
"On the other universe," said Gary. "A race that is fully as great, as capable as the Engineers. A race that should be glad to help us in this fight.”
"Great suffering snakes," yelped Herb, "why didn't we think of that before?”
"I do not understand," said the Engineer. "I agree they are a great race and very close to us. Much too close, in fact. But they might as well be a billion light years away. They can do us no good. How would you get them here?”
"Yes," rumbled Kingsley, "how would you get them here?”
Gary turned to the Engineer. "You have talked to them," he said. "Have you any idea of what kind of people they might be?”
"A great people," said the Engineer. "Greater than we in certain sciences.
They are the ones who notified us of the danger of the approaching universes. They knew they were nearing our universe when we didn't even know there was another universe other than our own. Such very clever people.”
"Talk to them again," said Gary. "Give them the information that will enable them to make a miniature universe… one of Caroline's hyperspheres.”
"But," said the Engineer, "that would do no good.”
"It would," said Gary, grimly, "if they could use the laws of space to form a blister on the surface of their universe. If they could go out to the very edge of their space-time frame and create a little bubble of space — a bubble that would pinch off, independent of the parent universe and exist independently in the five-dimension inter-space.”
Gary heard the rasp of Kingsley's breath in his helmet phones.
"They could cross to our universe," rumbled the scientist. "They could navigate through the inter-space with complete immunity.”
Gary nodded inside his helmet. "Exactly," he said.
"Why, Gary," whispered Caroline, "what a thought!”
"Boy," said Herb, "I can hardly wait to see them Hellhounds when we sic those fellows on them.”
"Maybe," said Tommy, "they won't come.”
"I will talk to them," said the Engineer.
He left the room and they followed him through a mighty corridor to another room filled with elaborate machinery.
The Engineer strode to a control panel and worked with dials and studs.
Intense blue power surged through long tubes and flashed in dizzy whirls through coils of glass.
Tubes boomed into sudden brilliance and the deep hum of power surged into the room.
They could hear the probing fingers of the Engineer's thoughts, thrusting out, calling to those other people in another universe. The power of thought being hurled through the very warp and weave of twisted time and space.
Then came another probing thought, a string of thoughts that were impossible to understand, hazed and blurred and all distorted. But apparently perfectly clear to the Engineer, who stood motionless under the inverted cone of glass that shimmered with blue fire of power.
Two entities talking to one another and the queer, challenging unknown of five-dimensional inter-space separating them!
The power ebbed and the blue fire sank to a glimmer in the tubes.
The Engineer turned around and faced the Earthlings.
"They will come," he said, "but only on one condition.”
Suddenly a shiver went through Gary. Condition! That was something he hadn't thought about — that these other things might exact terms, might want concessions, might seek to wring front another universe some measure of profit for a service done.
He had always thought of them as benevolent beings, entities like the Engineers, living a life of service, establishing themselves as guardians of their universe. But that was it. Would they go out of their way to save another universe? Or would they fight only for their own? Was there such a thing as selflessness and universal brotherhood? Or must the universes, in time to come, be forever at one another's throats, as in ancient times nations had torn at one another in savage anger, in more recent times planets had warred for their selfish interests?
"What condition?" asked Kingsley.
"That we or they find out something concerning the nature of the inter-space and of the energy which will be generated when the universes rub," said the Engineer. "They are willing to come and fight for us, but they are not willing to deliberately invite disaster to themselves. No one knows what the inter-space is like. No one knows what laws of science it may hold. There may be laws that are utterly foreign to both our universes, laws that would defy our every bit of knowledge. They are afraid that the budding of a smaller universe from the surface of their own might serve to generate the energy they know will result when two four-dimensional frames draw close to one another.”
"Now, wait," said Gary. "There is something I didn't consider when I proposed this thing. It just occurred to me now. When you said the word 'condition,' it came to my mind that they might want concessions or promises. I was wrong, interpreted the thought wrong. But the idea is still there. We don't know what these things in the other universe might be. We don't know what they look like or what their philosophy is or what they can do. If we allowed them to come here, we'd be giving them a key to this universe. Just opening the door for them. They might be all right and they might not. They might take over the universe.”
"There's something to that," said Tommy. "We should have thought of it before.”
"I do not believe it," said the Engineer. "I have some reason to believe they would not be a menace to us.”
"What reason?" rumbled Kingsley.
"They notified us of the danger," said the Engineer.
"They wanted help," said Tommy.
"We have been of little help to them," said the Engineer.
"What difference does it make?" asked Herb. "Unless we can do something about this energy, we're going to be goners, anyhow. And that goes for the other universe as well. If they could save themselves by ruining us, maybe they'd do it, but it's a cinch that if we puff out they go along with us.”
"That's right," agreed Kingsley. "It would be to their interest to help us beat off the Hellhounds on the chance that we might find something to save the universes. They wouldn't be very likely to turn on us until somebody had figured out something about this energy.”
"And we can't control something we don't understand," said Caroline. "We have to find out what that energy is, what it's like, what form it is apt to take, something about it, so we will know how to handle it.”
"How much more time have we to find some way to save us from the big explosion?" asked Gary.
"Very little time," said the Engineer. "Very little time. We are perilously close to the danger point. Shortly the two space-time frames of the two universes will start reacting upon one another, creating the lines of force and stress that will set up the energy fields in the inter-space.”
"And you say there is another race that can tell us about this inter-space?”
"One other race I know of," said the Engineer. "There may be others, but I know only of this one. And it is hard to reach. Perhaps impossible to reach.”
"Listen," said Gary, "it is our only chance. We might as well fail in reaching them as waiting here for the energy to come and wipe us out. Let a couple of us try. The others may find something else before it is too late.
Caroline's hyperspheres might take care of the energy, but we can't be sure. And we have to be sure. The universe depends upon us being sure. We can't just shoot in the dark.
We have to know.”
"And if we find out," said Herb, "those guys over in the other universe can come over and help us hold the Hellhounds off while we rig up the stuff we have to have.”
"I'm afraid," said Kingsley, "we have to take the chance.”
"Chance," said the Engineer. "It's a whole lot more than chance. The place I have in mind may not even exist.”
"May not even exist?" asked Caroline and there was an edge of terror in her words.
"It is far away," said the Engineer. "Not far in space — perhaps even close to us in space. But far away in time.”
"In time?" asked Tommy. "Some great civilization of the past?”
"No," said the Engineer. "A civilization of the future. A civilization which may never exist. One that may never come to be.”
"How do you know about it, then?" flared Gary.
"I followed its world line," said the Engineer. "And yet not its actual world line, but the world line that was to come. I traced it into the realm of probability. I followed it ahead in time, saw it as it is not yet, as it may never be. I saw the shadow of its probability.”
Gary's head reeled. What talk was this? Following of probable world lines.
Tracing the course of an empire before it had occurred! Seeing a place that might not ever exist. Talking of sending someone to a place that might never be!
But Caroline was talking now, her cool voice smooth and calm, but with a trace of excitement tinging the tenor of her words.
"You mean you used a geodesic tracer to follow the world line into probability. That you established the fact that in some future time a certain world may exist under such conditions as you saw. That barring unforeseen circumstances it will exist as you saw it, but that you cannot be certain it ever will exist, for the world line you traced could not take into account that factor of accident which might destroy the world or divert it from the path you charted, the path that it logically would have to take.”
"That is correct," said the Engineer. "Except for one thing. And that is that the world will exist as I saw it in some measure. For all probabilities must exist to some extent. But its existence might be so tenuous that we could never reach it… that for us, in hard, solid fact, it would have no real existence. In other words, we could not set foot upon it. For every real thing there are infinite probabilities, all existing, drawing some shadow of existence from the mere fact that they are probable or have been probable or will be probable. The stress and condition of circumstance selects one of these probabilities, makes it an actuality. But the others have an existence, just the same. An existence, perhaps, that we could not perceive.”
"But you did see this shadow of probability?" rumbled Kingsley.
"Yes," said the Engineer, "I saw it very plainly. So plainly that I am tempted to believe it may be an actuality in time to come. But of that I cannot be sure. As I said, it may not exist, may never exist — at least to an extent where we could reach it — where it would have any bearing on our lives.”
"There is a chance, though, that we could reach it?" asked Gary.
"There is a chance," said the Engineer.
"Then," said Herb, impatiently, "what are we waiting for?”
"But," said Gary, "if the universe is destroyed, if we should fail and the universe be destroyed, would that probability still be there? Wouldn't the fact that you saw it prove that we will find some way to save the universe?”
"It proves nothing," said the Engineer. "Even were the universe destroyed, the probability would still exist, for the world could have been.
Destruction of the universe would be a factor of accident which would eliminate actuality and force all lines of probability to remain mere probability.”
"You mean," breathed Caroline, "that we could go to a world which exists only as a probable world line and get information there to save the universe — that even after the universe is destroyed, if we fail and it is destroyed, the information which might have saved it still could be found, but too late, of course, to be of any use to us, on that probable world?”
"Yes," said the Engineer, "but there would be no one to find it then. The solution would be there, never used, at a time when it would be too late to use it. It is so hard to explain this thought as it should be explained.”
"Maybe it's all right," said Herb, "but I crave action. When do we start for this place that might not be there when we get where we headed for?”
"I will show you," said the Engineer.
They followed him through a maze of laboratory rooms until they came to one which boasted only one piece of equipment, a huge polished bowl set in the floor, blazing with reflected light from the single lamp that shone in the ceiling above it.
The Engineer indicated the bowl. "Watch," he told them.
He walked to a board on the opposite wall and swiftly set up an equation on a calculating machine. The machine whirred and clicked and chuckled and the Engineer depressed a series of studs in the control board. The inside of the bowl clouded and seemed to take on motion, like a gigantic whirlpool of flowing nothingness. Faster and faster became the impression of motion.
Gary found himself unable to pull his eyes away from the wonder of the bowl — as if the very motion were hypnotic.
Then the swirl of motion began to take form, misty, tenuous form, as if they were viewing a strange solar system from a vast distance. The solar system faded from view as the vision in the bowl narrowed down to one planet. Other planets flowed out of the picture and the one grew larger and larger, a ball swinging slowly in space.
Then it filled all the bowl and Gary could see seas and cities and mountains and vast deserts. But the mountains were not high, more like weathered hills than mountains, and the seas were shallow. Deserts covered most of the spinning globe and the cities were in ruins.
There was something tantalizingly familiar about that spinning ball, something that struck a chord of memory, something about the solar system — as if he had seen it once before.
And then it struck him like an open hand across his mouth.
"The Earth!" he cried. "That is the Earth!”
"Yes," said the Engineer, "that is your planet, but you see it as it will be many millions of years from now. It is an old, old planet.”
"Or as it may never be," whispered Caroline.
"You are right," said the Engineer. "Or as it may never be.”