"First of all, you must understand that we are not particularly good tool users." Khorat held up one of his strange, clumsy-looking hands, so oddly at variance with his race's overall look of highly evolved gracefulness. "Not nearly as good as the Delkasu. Not even as good as you. Your single opposable thumb is a far more efficient arrangement."

"But," said Chloe, puzzled, "you colonized this system, and-" "Oh, yes, we can do anything you or even the Delkasu can do. It just takes us longer . . . especially in that particular case. Given our species' body ma.s.s, interplanetary colonization using reaction drives was a problem whose solution required thousands of years, not hundreds. Only the incentive of this system's potential wealth induced us to do it at all." "But," I argued, "surely your natural tool-using equipment didn't matter after you'd developed cybernetic technology to do it for you." A smile entered Khorat's voice. "I am reminded of your culture's folk saying about a certain avian life-form and its egg. You see, before we could reach the stage of robotic manipulators, we first had to painfully work our way through all the earlier levels of technology. By that time, our feet were set on a

pathway rather different from those of most tool-using races."

"With the help of the Medjavar." I knew I probably wasn't succeeding in keeping the sourness out of my voice.

"No doubt." Khorat was serene. "I am sure that this is the real reason we were as successful as we were; we were simply guiding the culture in the direction it was predisposed toward in any case. Also, unlike you or the Delkasu, we never experienced total war, with its pressure toward a certain kind of technological development, requiring a certain kind of mind-set.

"You already know some of the consequences. We never discovered the secret of interstellar travel, for example. And our entire material culture has a somehow anachronistic look in your eyes." ("Retro"

hadn't become part of the slang yet, so the translator didn't have it.) "At the same time, we advanced into fields of which you are barely aware, and which you would regard as branches of philosophy rather than science."

"Like the ultimate nature of time," Chloe stated levelly.

The Ekhemar didn't have eyebrows to raise, but that was the effect. "You are very perceptive. Yes . . .

that, and the kind of dimensional shifting whereby the flow of time can, within a strictly delimited locality, be reversed."So matters stood when the Delkasu arrived-the first Delkasu, a couple of your centuries before Sakandri incorporated them, and us, into his empire." Khorat began to look uncomfortable. "You may recall what I said about the Medjavar's att.i.tude toward the Delkasu. For the most part, the rest of the Ekhemasu shared it. But there were exceptions, especially in those early days. You see, one of our oldest and most primal terrors was that of meat-eating animals endowed with high intelligence and superior technology. Even after it became clear that the Delkasu did not think of us as a food source-and, indeed, were revolted by the concept of sentient meat-animals-the old fantasy still took a while to release its hold on us. One of those who never escaped its grip was a great scientist named Imhaermekh.

His loathing of the Delkasu caused him to pervert his genius into a monomaniacal quest for a way to expel them from our system. His researches led him deeper and deeper into the realms of dimensional physics, for he saw with extraordinary clarity that the only way historical inevitability can be fought is by changing history itself." Khorat subsided into a brooding silence. Chloe and I waited with all the patience we could muster, for even I had the sensitivity to recognize a being struggling to overcome agonizing embarra.s.sment.

Finally, Khorat spoke. "Like most individuals who want a thing badly enough, Imhaermekh finally achieved it. He never actually sent an Ekhemar back in time, but he succeeded in sending inanimate objects back into the recent past-they appeared seconds before the experiments. He had to be stopped." The artificial voice trailed off into silence again.

I like to flatter myself that I'm not a total clod. Still, as you may have noticed by now, my sensitivity has

limits.

"Well, Khorat," I began hesitantly, "what was the big deal? I mean, the Medjavar had already been suppressing dangerous technological innovations for thousands of years, right? So why was this any different?"

Khorat gave me a somber regard. "Influence, manipulation, concealment, suppression . . . yes, we are no strangers to these things. But only once in our entire history have we resorted to murder."

"Imhaermekh?" Chloe breathed.

"He had to be stopped," Khorat repeated, as much to himself as to us. Then he spoke more briskly. "The

saying that 'the end justifies the means' is, of course, nothing but self-serving rationalization. But when an end a.s.sumes an importance that is universal in scope, debate about means becomes irrelevant."Chloe spoke earnestly. "Khorat, I don't doubt your sincerity. But . . . but . . . time travel? The notion involves so many impossibilities I hardly know where to begin. First of all, it violates the conservation laws of physics."

"How so?"

"Suppose a, uh, time machine goes back to the year X. When it appears out of nowhere in that year, it's adding matter to the universe."

"But," Khorat explained, "the same amount was subtracted in the year in which it departed. The sum matter/energy total of the universe must, indeed, remain constant. But that total may balance out over time. The problem of 'extra matter' which worries you does not exist if the temporal dimension is taken into account."

"But," Chloe insisted doggedly, "even if that's true, what about relativity? Anything traveling backwards in time would be traveling faster than infinity!"

"Yeah," I put in. "Talk about swimming against the tide."

Khorat looked bewildered, and I belatedly recalled that his race, and their language, had developed on a planet with no moon, and hence no tides in its small landlocked seas. He pulled himself together, though.

"It is difficult to explain. You must understand that time travel depends on transposing one's vehicle to a dimension isolated from the time-flow of our own." I sensed that this was the translator software's inadequate best effort at expressing concepts for which English simply lacked the terminology. "Under these conditions, travel into the past is relatively easy. It involves simply separating oneself from the continuum. You are not so much traveling as standing still and letting the time-flow pa.s.s you by, leaving you farther and farther behind in the past." Khorat visibly struggled to express himself. "To borrow the terminology of s.p.a.ceflight, think of it as 'going into free fall.'

"However, while it is easy in terms of energy requirements, it is not fast. Most certainly it is not instantaneous. This is an image from your world's popular culture of which you must disabuse yourselves."

"How do you know about our world's popular culture?" I demanded sharply."I have made it my business to inform myself of it since it became obvious that the Tosava gevroth had found a buyer among your people. I soon discovered that time travel is a familiar fictional device . . .

and that your writers have many misconceptions about it.

"A significant amount of subjective time must be spent inside a field which allows large material

constructs to enter the dimensions of which I have spoken. And time inside that field pa.s.ses at the same rate as in the outside universe; there is no equivalent of 'relativistic time dilation.' The apparent length of the voyage is directly linked to how far back one wishes to go."

"Novak said something about going back to our early Industrial Revolution," Chloe mused. "About a hundred and fifty of our years. Her idea is to get forced-draft technological advancement started so early that by the time the Delkasu arrive we'll be in a position to deal with them as equals. She also mentioned the possibility of going back even farther than that, to periods about five hundred years in the past, or

even twenty-five hundred. But she said there were 'practical problems' with going back that far."

"There are indeed, in terms of sheer tediousness. Even her plan of going back a hundred and fifty years will involve a somewhat lengthy journey. Exactly how lengthy is difficult to know, as the amount of subjective time that pa.s.ses inside the field is dependent upon which dimension the ship has been shifted into. There are more than one, you see. As a general proposition, the more difficult they are to access, the shorter the time that must be spent in them. The information at Novak's disposal . . ." Khorat stopped

himself, clearly not wanting to pursue the subject. "But that is another matter. For now, suffice it to say that her objective is attainable."

"But . . ." Chloe sought to rally her thoughts. "All right: let's suppose you're right, and that time travel is

technically achievable, despite all the physical laws it seems to violate. That still leaves the philosophical objections to it. It destroys the whole concept of causality! If you go back and change the past in such a way as to foreclose the possibility of your own existence-shoot your own grandfather in his boyhood, say-then where did you come from in the first place?"

"Novak mentioned," I recalled, "a possibility that it might not change the future, but rather create a parallel time track-"

"She is wrong," Khorat interrupted me bluntly."Uh, Khorat, that is something our thinkers have speculated about. The idea that all possible outcomes of any given interaction are equally valid, mathematically speaking, and-"

"Then they are wrong," Khorat stated with even greater finality. "You must accept my word on this. As I said earlier, our civilization has explored the basic nature of reality more deeply than yours. The theory of many parallel time tracks is an ingenious intellectual construct. But in fact there is only the one linear reality, in which there is only the one actually realized outcome to each interaction."

"Well, then," declared Chloe, almost angrily, "we're back to the 'Grandfather Paradox' I mentioned earlier. If the universe that produced Novak never comes into existence, how can she have gone back and-?"

"That, too, is a fallacy. A time traveler really can murder his grandfather-a meat-eater's concept if ever there was one!-because his own existence is a product of a reality which preexists the one which his own time-meddling creates after he dimension-shifts back into phase with the normal universe and begins affecting it."

"I'm getting a headache," I complained.

Chloe ignored me. "But Khorat, a.s.suming that Novak carries out her plan, what happens to the reality we ourselves are living in? And when does whatever-it-is happen?"A transcendent somberness seemed to radiate from every detail of Khorat's expression and posture, until it filled the room. "I will attempt to answer those questions in reverse order. To repeat, subjective time spent in temporal transit pa.s.ses at the same rate as it does in the outside universe. Novak must return to Earth, prepare her ship-"

"You used the word 'ship' before," I interrupted.

"Yes. Time travel will only work in proximity to a spinning body of planetary ma.s.s. But for any number of reasons it is quite impractical on the actual surface of such a planet. Therefore, a 'time machine' must be a s.p.a.ce vehicle in orbit. But to continue: Novak must make her preparations, then make the actual temporal journey, and land on Earth in the year of her arrival. Whether or not her plans succeed is immaterial; her mere arrival would, in itself, be an event of such magnitude as to immediately begin

altering history. So at that moment, in terms of her own subjective existence and ours-""Blooey," I said, wondering how the translator would render that."I doubt if there will be any noise," said Khorat, confirming my opinion of his sense of humor. "I do not know, and cannot visualize, what will happen to us. But I can find no theoretical basis for a.s.suming our

continued existence. From our standpoint, I imagine our consciousness will simply stop."

After a while, Chloe felt a need to break the silence in the room. "Uh, Khorat, what you're saying has some disturbing theological implications. I mean, most of our religions a.s.sume that the consciousness-the 'soul,' as they put it-survives after death, either by entering into an afterlife or by being reincarnated into another life-form."

"Yes, we ourselves have devised religions with similar beliefs. I myself am an agnostic-which has always struck me as the rational position on the subject, whereas atheism is a particularly breathtaking form of arrogance. But in the eventuality we are contemplating, the question becomes almost moot."

"You're taking this very calmly, Khorat," I observed.

"If I give such an impression, it is because my own personal survival, and the survival of my familiar

world, is a trivial matter compared to the truly serious consequences of Novak's meddling in matters of which she has no understanding.""The truly serious consequences?" Chloe echoed faintly."Consider: in the world that Novak will create, time travel will belong to the realm of the possible. Even if she retains enough sanity to destroy the knowledge of how she did it, it will not matter in the long run, for the possibility will be common knowledge." Khorat studied us gravely. "One thing I have learned about your species in the course of my studies: if humans know for a certainty that a thing can be done, they will not rest until they have devised a way to do it. And there will be plenty of others with motives as strong as Novak's or Imhaermekh's for changing history-causes as compelling, and grievances as intense. So even if she succeeds in bringing about the kind of world she wants, she will have doomed that world in the long run. This will happen again . . . and again . . . and again. And beyond a certain point, theory suggests that the very fabric of ultimate reality will begin to fray, and unravel. The consequences are literally incalculable, for they lie beyond the capacity of any finite mind to grasp.

"Now, perhaps, you understand my seeming calmness in the face of the question of survival after death.

If our very universe is canceled out, then one must entertain the a.s.sumption that its G.o.d is canceled out as well."

Khorat's voice had dropped to a whisper that the translator could barely pick up. Then he fell silent, and this time I felt no urge to break the silence. And, being the least religious person you'd ever hope to meet, I wondered why I had to contain a shudder.

Chloe had more courage. "Khorat, what can be done?"

"Oh, it is already being done. We foresaw this possibility. And, contrary to our usual practice, we kept

the relevant data in duplicate. Indeed, our duplicate includes at least one crucial bit of knowledge that Novak does not possess.""What-?" I began."No. There will be time for detailed explanations later. The point is, we can-and must-take action to prevent this. And I must ask for your help.""Our help?" Chloe, visibly annoyed with herself, brought her voice back down from the squeak to which it had risen, and spoke in her customary husky contralto. "I can't imagine what help we can be, Khorat. But a.s.suming that there's any truth to what you've been saying, and you're trying to stop it from happening, then we have to help you. If there's anything useful we can do, we're under an ultimate moral imperative to do it."

"Yeah," I chimed in. In fact, I was a good deal less wholehearted about this than Chloe seemed to be. But she had made an unconditional commitment, and there was no way I could hold back and continue to live with her-or inside the same skin with myself.

Hey, I never claimed to be smart, did I?

CHAPTER FIFTEEN.

Even now, I still sometimes find myself wondering how far and how deep the excavations under the

Sanctuary went. G.o.d knows, Chloe and I never found out.