Please be seated," Rutherford told them as they entered. "Permit me to introduce Commander Jason Thanou, your mission leader." He was on his best behavior, giving Jason his Rangers rank and even pronouncing his surname correctly. ("Thane-oh," not "Than-ooh.") He then proceeded to introduce the new arrivals, which was redundant but which gave Jason a chance to study them.
Deirdre Sadaka-Ramirez wasn't quite as tall as he'd imagined from her face, which was probably just as well from the standpoint of blending into the Bronze Age population. She wasn't short, though, and her figure was a solidly constructed hourglass. The latter was obvious even in the no-nonsense jumpsuit she was wearing—maroon, which complemented her coloring. She gave Jason a brief smile of measured cordiality.
Doctor Nagel was very much as per expectations, aside from being somewhat stockier than his sharp features suggested. His consciously old-fashioned, expensively fusty clothing was the uniform of academia. Jason noted a tightening of his thin lips at Rutherford's use of the term "mission leader." As soon after the introductions as politeness permitted—or perhaps just slightly sooner than that—he turned to Rutherford, ignoring Jason.
"I say, Kyle, given my credentials in Aegean Bronze Age studies, surely it should be myself who—"
"No, Sidney. I remind you of the Articles of Agreement you signed with the Temporal Regulatory Authority."
"Well, er, yes, I seem to recall some legalistic boilerplate. But I naturally assumed that it didn't apply in my case."
"Revise your assumptions." Rutherford's brusqueness with a kindred spirit was almost shocking, until Jason recalled how the old bastard could be when it came to defending his administrative turf. "The Authority has exclusive jurisdiction of all extratemporal activities. That has been settled beyond dispute for a generation. And the Temporal Service is the Authority's enforcement arm. Every expedition into the past is required to be under the supervision of a Service representative whose legal powers are comparable to those of a ship's captain in the age of sail—and for much the same reasons. If you find you are unable in good conscience to abide by these terms, your only honorable course is to withdraw from the expedition." Rutherford took on a crafty look. "I daresay we could probably find a willing replacement from among the ranks of your colleagues."
Nagel's face darkened with emotion. "You mean that impudent puppy Boudreau! Or Markova, with her asinine, unacceptable theory that—" He got himself under control with a comically visible effort. "Of course not, Kyle. I have every intention of following the Authority's guidelines to the letter. I never meant to imply otherwise. And I have no doubt that Mr. Thanou's competence is of a high order."
"The Authority has the fullest confidence in him," said Rutherford pointedly.
"I'm sure we all do, regardless of . . . er, that is . . ." Nagel's we, addressed to Rutherford, had held a certain near-imperceptible intonation that Jason had learned to recognize. It meant "we Earthmen." But now Nagel trailed off to a miserable halt, having belatedly realized that making his meaning explicit might not be advisable. What brought him to that realization was a glare from Deirdre Sadaka-Ramirez—another outworlder—under which he now wilted.
Oh, yes, Jason sighed inwardly. This trip is going to be lots of fun.
"And now," said Rutherford after letting Nagel suffer for a few seconds, "I've asked Commander Thanou to give you the benefit of his extensive experience by answering any questions you may have about the theory and practice of time travel."
Deirdre Sadaka-Ramirez broke the awkward pause. "Actually, Commander, it might be better if you would simply run through the basics for us. I probably don't know enough about the subject to be able to frame questions."
At least she admits it, thought Jason. Nagel, now himself again, sat back with the superior smile of the overspecialized academic, secure in the certainty that his expertise in his particular field qualified him as an expert in every field.
"Surely, Ms. Sadaka-Ramirez," said Jason, giving her the look of undivided attention that he'd always found got the best results with women, "you must have some questions in your mind about it. Most people seem to, even though we've been doing it for a while now."
"Well, yes. I'm just afraid they'll seem foolish. I've read something of the history of time travel as a concept. It used to be a common fictional device, but one which was clearly understood to be impossible in the real world."
"So was beating the limiting velocity of light," Jason pointed out. "Until someone actually found a way around it. Around, not through. That's a crucial distinction."
"Understood," she nodded. "But time travel was regarded as a fundamental philosophical impossibility, because of the paradoxes it allowed for. As somebody once put it, if you could travel into the past, then what was to prevent you from killing your grandfather before he met your grandmother? In which case, you would never have been born . . . and so how could you have traveled back in time and killed him?"
"The 'Grandfather Paradox,' it was called," Jason nodded. "The classic response to it was: 'Why should I want to kill him? I think he's a wonderful old fellow.' " He held up a forestalling hand. "Yes, of course I'm being facetious. The possibility still exists, even if only for doing it by accident. And, in the entire scope of the future, there are bound to be people with good reasons for wanting to change history—killing Hitler while he was still just a bum in pre-World War I Vienna, for example, or similar cases in the early stages of the Transhuman movement. But please continue."
"The other problem was perhaps not as immediately obvious. If you could travel into the future and come back with, say, next week's racing results, it would mean information was being transmitted at more-than-infinite velocity, violating the relativistic lightspeed limit—which, as you've indicated, can't be violated, just evaded in certain mathematically limited ways. In fact, it would violate causality itself." She looked at Jason levelly and spoke in a challenging tone which was clearly habitual with her. "As far as I can see, those arguments are still as valid as they ever were. But they can't be, can they? After all, time travel is now so well established that it needs a bureaucracy to regulate it. So please help me with this."
"As a matter of fact," said Jason, "you haven't begun to exhaust the philosophical objections to time travel. Actually, I think you may have had the right idea the first time; I'll just start at the beginning, and hopefully the answers to your questions will become apparent." He turned to Nagel with a smile. "I apologize in advance if I seem to be patronizing you by lecturing you on what you may already know." Thus giving you a taste of being patronized, you pompous, conceited jackass! he loudly did not add. Without giving Rutherford a chance to summon up a warning glare, he started in.
"About seventy years ago, Weintraub made the crucial discovery that all matter possesses what he termed 'temporal energy potential,' an 'anchor' holding it in time. He confirmed this experimentally by manipulating it so as to displace objects in time. Those first experiments involved subatomic particles, and the displacement was of infinitesimal duration. Only with the most sensitive of measuring instruments was it possible to observe that the particles appeared a few microseconds before the experiment, remaining for a period measured in nanoseconds—the same period for which they vanished after the power was turned on—and then 'snapping back' to their proper time. Temporal energy potential is very stubborn stuff. It also exists only up to the constantly advancing 'present.' This, by the way, answers the second objection you raised, Ms. Sadaka-Ramirez. The future is, in an absolute sense, nonexistent until it happens. There can be no travel into it.
"At first Weintraub's discovery, however revolutionary in theoretical terms, had no practical application. Nobody, it seemed, had to worry about murdered grandfathers. But then, twenty years later, Fujiwara discovered an all-or-nothing process by which the temporal energy potential of objects could be cancelled entirely."
Rutherford, who had been doing an admirable job of holding his tongue, could no longer contain himself. "The mathematical underpinning of this process is one which—"
"—you don't want to hear about," Jason finished for him firmly. "Believe me, you really don't." Rutherford subsided unhappily, and Jason resumed. "All you need to know is that the process is controllable, so that matter can be sent back in time to a desired date in the past—and will remain in the past until its temporal energy potential is restored by use of a 'temporal retrieval device' or TRD, whereupon it 'snaps back' to the linear present."
"Uh . . . excuse me," Deirdre ventured. " 'Linear present' . . . ?"
"Sorry. That's a convenience label we use for the fact that time passes at the same rate for a temporally displaced object as it does in the 'present' from which the object was displaced. This became apparent in Weintraub's pioneering experiments, as I indicated earlier. And it proved to hold true for living beings as well, contrary to some earlier theoretical speculations that living matter constituted a 'reverse state of entropy' or something like that." Jason saw from his listeners' expressions that he was starting to lose them. Even Nagel's know-it-all look was wavering. "Let me put it this way. Suppose you were sent back in time from the Authority's displacer stage in Australia at 10:00 A.M. on June 1, and spent five days and one hour in the past before your TRD activated. You would then reappear on the stage at 11:00 A.M. on June 6. That's flat. Remember what I said before about the constantly advancing wave front between the past and the future that we call the 'present'? Well, you're wedded to it. You can't just pick a date and time you're going to return to. This is an immutable fact that the Service has to live with. It's fundamental to our operating procedures.
"Now, the displacement of matter back into the past requires a massive physical installation and a tremendous expenditure of energy. The actual energy requirement is tied to two factors: the mass being displaced, and how far back that mass is being sent. For this displacement, it's going to cost a lot to send even the three of us." From Rutherford's direction came a grunt of sad accord. "Furthermore, for objects of significant mass an initial energy surge is required—an 'oomph' if you will." Jason pretended not to notice Rutherford's wince of pain. "This sends the object in question back about three hundred years before the effect becomes controllable. Therefore you can't be sent to a time any more recent than that. Incidentally, this disposes of another theoretical difficulty with time travel; there is no possibility of going back and meeting your own younger self.
"Anyway, there is only one such installation. It's here on Earth—"
"Naturally," Nagel interjected.
Jason gritted his mental teeth. But Nagel, however insufferable, was right. Only on this planet was there a past—a human past, anyway—to be explored.
"—in Western Australia," Jason finished, proud of himself for his level tone of voice. "It had to be built in a relatively empty country, as far as possible from large population centers, because the energy requirements could only be met by an antimatter power plant. It's the only such power plant on the surface of Earth—or of any other inhabited planet—rather than in orbit like all the others. There are elaborate fail-safe systems in place, and the chances of an accident are considered vanishingly remote. But . . ." Jason let the thought trail off.
Nagel momentarily let his guard slip, and his expression showed that he'd never considered this issue. "Then why isn't this installation placed in space as well?"
"A reasonable question, Dr. Nagel." Jason decided he might as well be conciliatory, especially inasmuch as it really was a reasonable question. "In fact, for reasons which are too technical to go into just now, time travel will only work within, and in relation to, a substantial gravity field. If you think about it, this has to be the case. Otherwise . . . well, someone who traveled into the past would find himself watching Earth recede at roughly eighteen miles a second as it revolves around the Sun, and wishing he'd thought to wear a space suit." Actually, it was worse than that, given the Sun's orbital velocity around the center of the galaxy . . . and that was just for starters. But Jason decided to keep it simple. "Another fortunate consequence: it doesn't matter where the displacer is located on the surface of the planet producing the gravity field. The displacer stage can whisk you anywhere on Earth at the same time it's displacing you into the past. We won't have to make our way across the ancient world from Australia to Greece."
Nagel leaned forward, now openly intrigued. "But why hasn't this made all forms of public transportation on Earth obsolete? World-wide teleportation—"
"It doesn't work that way. Remember the three-hundred-year minimum trip into the past? You have to go at least that far back. And when your TRD activates and you regain your temporal energy potential, you snap back to exactly the same location you were displaced from, due to conservation-of-energy considerations. Anyway, even if it was possible to flick people around in the present, the expense would limit it to being a toy for the super rich."
Deirdre Sadaka-Ramirez spoke up. "You keep talking about this 'TRD.' . . ."
"Right—the temporal retrieval device. As I've explained, it takes a huge, expensive, energy-intensive installation we call the 'displacer' to cancel an object's temporal energy potential and send it into the past. But restoring that temporal energy potential so that the object returns to the linear present is almost unbelievably easy. For a human-sized object—with its clothing and as much mass as a human can conveniently carry—all it takes is a device that can be miniaturized to the size of a small pea, drawing an insignificant amount of energy. Good thing, too; this makes time travel practical."
"Yes, I can see that," she nodded her dark-auburn head. "I recall being told that we're going to have to have this device implanted. . . ." A cloud shadow seemed to cross her features. Nagel looked equally troubled. Jason understood their queasiness, which practically all of society shared. It was another hangover from the Transhuman madness.
"That's correct," he said quietly. "It's a very minor surgical operation, which will be performed after we get to Australia."
"Is that really necessary?" asked Nagel peevishly. "Can't we just carry the things?"
"Standard Temporal Service procedure dictates that—" Rutherford began. Jason motioned him to silence. He subsided huffily and let the younger man answer Nagel.
"Yes, I suppose so," Jason conceded. "You could carry an obviously advanced device which would take a lot of explaining in the past—and which you might lose. Or it could be miniaturized as I've said—in which case you'd almost certainly lose it. And if you lose it, you're stranded in the past permanently." Jason paused to let that sink in, then put on a reassuring smile. "Anyway, this doesn't involve any proscribed bionics. The TRD isn't neurally interfaced with your brain in any way."
"Then how do you activate the thing?" Nagel demanded.
"You don't. It activates automatically, at a predetermined moment, timed by atomic decay—and you're back on the displacer stage in Australia, in the linear present."
A look of alarm began to awake on Nagel's features. "But what if we should need to return to the present before that?"
"You can't," said Jason with finality. "This accounts for the provision in the Articles of Agreement you signed releasing the Temporal Regulatory Authority from liability." More "legalistic boilerplate" you couldn't be bothered with reading, he guessed. "If anything happens to you, you can't be rushed back to a modern hospital; you're stuck in the past for a fixed duration, with all that implies about medical care or the lack of it." Jason decided he'd better accentuate the positive. "This way, the Authority knows exactly when to expect you back, and can make sure the stage is clear at that time. Otherwise, you might find yourself occupying the same volume as another object." Jason didn't elaborate on that. His listeners' expressions showed he didn't need to.
"Yes," Deirdre said thoughtfully. "With only the one displacer stage in existence, I can see how 'traffic control' might be a problem. Bur what about our initial displacement into the past? There's not going to be anybody back then making sure our arrival location is clear."
"Yes!" exclaimed Nagel, to whom these problems had clearly never occurred. "And what about the air itself, in the space where we're going to occupy when we, uh, materialize?"
"Let me address those points in reverse order. We don't need to worry about the air, or any other matter in gaseous state; the energy release involved in the displacement suffices to shove it out of our way. And the displacement process involves a feedback feature which makes it impossible to send an object to time/space coordinates which are occupied by another solid object. If there's anything there, it will simply default to the nearest unoccupied location. Unfortunately, this does not work for the snapping-back process when the temporal energy potential is restored. Hence our concern with 'traffic control.' "
"All right," Deirdre nodded. "Understood. But isn't it a little unsettling to suddenly find yourself back in the present, without warning?"
"Oh, it won't be without warning," Jason assured her. "I'll let you know when to expect it."
"And how will you know?" Nagel inquired archly. "Do I gather you'll be wearing a wristwatch in the Bronze Age?"
"Scarcely, Dr. Nagel." Jason's voice was level and unapologetic. "In point of fact, I do have an actual, neurally interfaced computer implant."
For a moment, there was the kind of awkward silence that always prevails when people are too polite to pronounce a bigot word that has entered unbidden into their well-bred minds—in this case, cyborg.
"The Service enjoys a special, limited exemption from the Human Integrity Act," Jason explained, "as do certain law enforcement agencies like the Hesperian Colonial Rangers, from which I'm on temporary detached duty, in case you've wondered about this uniform. The implant has its uses for us. It enables us to carry around a lot of useful information. And I can use it to record whatever I see and hear—within limits, of course, since the storage capacity isn't infinite, but it's the only recording capability we'll have."
"That last feature is uniquely useful on this mission," Rutherford interjected. "In more recent eras, paper and ink would be locally obtainable; you would be able to take notes and conveniently bring them back with you. In the Bronze Age, that is not going to be the case." He took on a look of annoyance. "We really do need a new set of tenses for time travel, don't we?"
"Absolutely," Jason agreed, forestalling a digression. "But at any rate, another advantage of my implant is that I'll always know the actual time in the linear present."
Deirdre Sadaka-Ramirez spoke briskly, as though eager to move on to another subject. "Well, then, that's one thing we won't have to worry about. And this is all very interesting. But you still haven't answered my most basic question: how is it that we can travel back in time despite the paradoxes it seems to allow for? I suppose you're going to tell me the past can't be changed, but—"
"Oh, but the past can be changed," said Jason blandly. "We do it all the time."
They simply stared at him.
"In fact," he continued, enjoying the effect he was creating, "changing the past is the basis for our one, very unsatisfactory means of communicating with the present. You see, there is no such thing as a 'temporal radio' or anything like that."
"We're not totally ignorant, you know!" snapped Nagel.
"Of course not, Doctor," said Jason, in as soothing a tone as he could manage while snickering inwardly. "So you understand that time travelers are on their own. They can, however, leave a message—in some durable form, and well hidden—at a prearranged place and time. After that point in time rolls around in the linear present, the Authority sends somebody to that location to find it. And to answer your question before you even ask it: yes, we've thought of looking in such a location in advance. The message wasn't there. After the moment in the linear present when the plan called for the message to be deposited, the location was visited again . . . and the message was there."
There was an interval of uncomfortable silence.
"I was not aware of this . . . experiment," Nagel finally said.
"We don't go out of our way to publicize it," Rutherford admitted.
Deirdre Sadaka-Ramirez shook herself, and spoke almost defiantly. "Have you ever tried going to one of these locations before that 'point in the linear present' and staying there, watching, through that moment?"
Jason and Rutherford exchanged a look. Rutherford nodded.
"Naturally that's been thought of," Jason told her. "In fact, it's been done twice. In the first case, an expedition had been sent back to 1953 to clear up the details of Stalin's death. They were to leave a message at a particular location outside Moscow, Russia. A team was sent there to perform precisely the kind of observation you've suggested."
"And . . . ?" she breathed with a mixture of eagerness and apprehension.
"On the way from Australia, the team's aircar developed a malfunction. They were stuck in Calcutta until the moment was past. Then they went on to Moscow and found the message."
Deirdre Sadaka-Ramirez sat back, looking deflated and vaguely resentful.
"It was tried again when a team went back to 2021, a crucial time during the Chinese breakup. You can be sure every member of that team was required to be combat-trained! Anyway, that time the Authority made certain to have the observers in place at the message site outside the ruins of Beijing before the team even departed, and kept them there through the prearranged linear-present moment. The message never appeared."
"And what conclusions were drawn from that?" Deirdre asked eagerly.
"None. When the team returned—mostly in the form of corpses—the two survivors explained that they'd gotten caught up in a fire fight and had never been able to leave the message."
This time her look of resentment was not vague. Jason's smile only intensified it.
"I'm really not trying to be difficult." Well, maybe just a little, he mentally hedged. "I'm leading up to the real answer to your question about paradoxes. The past can be changed, yes—but only in small ways. Ways that don't create paradoxes. And don't ask me why. The incidence of alcoholism among physicists and philosophers has risen since they've started trying to figure it out. It seems to be related to the Observer Effect—Schrödinger's Cat, and all that. What it boils down to is that a time traveler can't change the observed world. Nobody ever had any reason to check those message sites before, so that's all right. But you can't go back and kill one of your own ancestors, simply because we know he didn't get killed."
"But," Nagel spluttered, "as a practical matter, what prevents you from killing him?"
"I have no idea, Dr. Nagel. But something will, if you try to. And the same goes for anything that will preclude the existence of your society. The past can be changed, but history can't."
Deirdre looked thoughtful. "You try to shoot Hitler in Vienna before World War I, and the gun will jam."
"That's one possibility. But the way these things more typically work, you'd find out later that you had shot some other bum by mistake."
Nagel, obviously uncomfortable with this entire discussion, made a blustering effort to assert control. "Shall we turn our attention to practicalities? One thing I do know—" a withering glare at Jason "—is that we are to be supplied with the local spoken language by direct neural induction."
"That is correct," Rutherford nodded. "It is one of the Authority's obligations, specified in the Articles of Agreement."
"Well and good. But how can this be possible for the era in question? Granted, my definitive study of the subject has established beyond reasonable question—not to be confused with the questions raised by upstarts like Boudreau and Markova!—that an early form of Greek was already being spoken on the mainland, while one or more languages of the Hittite-Luwian family still prevailed on Crete and the Cyclades islands, including Santorini. But even I do not pretend to be able to provide a pronouncing gazetteer for these languages!"
Rutherford, back in his element, smiled a smile that exceeded even his usual capacity for oozing complacency. "Please rest assured that this has been taken into account, Sidney. The very fact that this expedition is being dispatched should tell you that we know. . . ." He let the sentence hang.
"You know?" Nagel leaned forward with an avidity that seemed odd in one who claimed to know already. Perhaps, Jason thought, he wasn't quite as certain of his conclusions as he pretended. "But how . . . ? Oh, tell me—!"
"All in good time, Sidney." Rutherford wasn't really a sadist, Jason reflected, but he did love his little secrets. "This will come out in the briefings you will receive in Australia. For now, I've asked you all to meet here in Greece so that we can examine the landscapes in question first-hand. I realize, Sidney, that this will be somewhat redundant for you. I also caution you that those landscapes will be quite different in the seventeenth century B.C. For one thing, Greece was much more extensively forested then. Still, this type of familiarization is not without value. I have an itinerary planned for tomorrow. I suggest we all make an early night of it."
They took the hint and began filing out. As they departed, Deirdre Sadaka-Ramirez gave Jason a coolly appraising look, and a challenging smile lifted the corners of her full lips.
" 'A ship's captain in the age of sail,' eh? I hope you don't plan to flog us."
Jason returned her smile in kind. "Only when necessary."