Timescape

CHAPTER NINE

“WELL, WHERE THE HELL IS HE?” RENFREW EXPLODED. He paced up and down his office, five steps each way.

Gregory Markham sat quietly, watching Renfrew. He had meditated for half an hour this morning and felt relaxed and centered. He looked beyond Renfrew, out the big windows the Cav sported as the prime luxury item in its construction. The broad fields beyond lay flat and still, impossibly green in the first rush of summer. Cyclists glided silently along the Coton footpath, bundles perched on their rear decks. The morning air was already warm and lay like a weight. Blue shrouded the distant spires of Cambridge and ringed the yellow sun that squatted over the town. This was the blissful fraction of the day when there seemed an infinite span of time before you, Markham thought, as though anything could be accomplished in the sea of hushed minutes that stretched ahead.

Renfrew was still pacing. Markham stirred himself to say, “What time did he say he’d be here?”

“Ten, damn it. He set out hours ago. I had to call his office about something and I asked if he was still there. They told me he’d left very early in the morning, before the rush hour. So where is he?”

“It’s only ten past,” Markham pointed out reasonably.

“Yes, but hell, I can’t get started until he gets here. I’ve got the technicians standing by. We’re all set. He’s wasting everybody’s time. He doesn’t care for this experiment and he’s making it hard on us.”

“You got the funding, didn’t you? And that equipment from Brookhaven.”

“Limited funds. Enough to keep going, but only just. We’ll need more. They’re strangling us. You know arid I know that this may be the only chance of pulling us out of the hole. What do they do?—make me run the experiment on a shoestring and then that sod doesn’t even care enough to show up on time to watch it.”

“He’s an administrator, not a scientist. Sure, the funding policy does seem short-sighted. But look, the NSF won’t send anything more without more pressure. They’re probably using it for something else. You can’t expect Peterson to work miracles.”

Renfrew stopped his pacing and stared at him. “I suppose I have made it rather obvious that I don’t like him. I hope Peterson himself isn’t aware of it or it might turn him against the experiment.”

Markham shrugged. “I’m sure he knows. It’s clear to anyone you two have different personality types, and Peterson’s no fool. Look, I can talk to him, if you want—I will, in fact. As to you turning him off the experiment—tripe. He must be used to being disliked. I don’t suppose it bothers him at all. No, I think you can count on his support. But only partial support. He’s trying to cover all his bets and that means spreading support pretty thin.”

Renfrew sat down in his swivel chair. “Sorry if I’m a bit tense this morning, Greg.” He ran thick fingers through his hair. “I’ve been working evenings as well as days—may as well use the light—and I’m probably tired. But mainly I’m frustrated. I keep getting noise and it scrambles up the signals.”

A sudden flurry of subdued activity in the lab caught their attention. The technicians who had been casually chatting a minute before were now looking purposeful and prepared. Peterson was threading his way across the lab floor. He came to the door of Renfrew’s office and nodded curtly to the two men.

“Sorry I’m late, Dr. Renfrew,” he said, offering no explanation. “Shall we start on it right away?”

As Peterson turned towards the lab again, Markham noticed with mild surprise the caked mud on his elegant shoes, as though he had been walking in ploughed fields.

It was 10:47 a.m. Renfrew began tapping slowly on the signal key. Markham and Peterson stood behind him. Technicians monitored other output from the experiment and made adjustments.

“It’s this easy to send a message?” Peterson asked.

“Simple Morse,” Markham said.

“I see, to maximize the chances of its being decoded.”

“Damn!” Renfrew suddenly stood up. “Noise level has increased again.”

Markham leaned over and looked at the oscilloscope face. The trace danced and jiggled, a scattered random field. “How can there be that much noise in a chilled indium sample?” Markham asked.

“Christ, I don’t know. We’ve had trouble like this all along.”

“It can’t be thermal.”

“Transmission is impossible with this going on?” Peterson put in.

“Of course,” Renfrew said irritably. “Broadens the tachyon resonance line and muddles up the signal.”

“Then the experiment can’t work?”

“Bloody hell, I didn’t say that. There’s just a holdup. I’m sure I can find the problem.”

A technician called down from the platform above. “Mr. Peterson? Telephone call, says it’s urgent.”

“Oh, all right.” Peterson hastened up the metal stairway and was gone. Renfrew conferred with some technicians, checked readings himself, and fretted away several minutes. Markham stood peering at the oscilloscope trace.

“Any idea what it could be?” he called to Renfrew.

“Heat leak, possibly. Maybe the sample isn’t well insulated from shocks, either.”

“You mean people walking around the room, that sort of thing?”

Renfrew shrugged and went on with his work. Greg rubbed a thumbnail against his lower lip and studied the yellow noise spectrum on the green oscilloscope screen. After a moment he asked, “Have you got a correlator you could use on this rig?”

Renfrew stopped for a moment, thinking. “No, none here. We have no use for one.”

“I’d like to see if there is any structure we could bring out of that noise.”

“Well, I suppose we could do that. Take a while to scrounge up something suitable.”

Peterson appeared overhead. “Sorry, I’m going to have to go to a secured telephone. Something’s come up.” Renfrew turned without saying anything. Markham climbed the stairway.

“I think there will be a delay in the experiment, anyway”

“Ah, good. I don’t want to return to London just yet, without seeing it through. But I’ll have to talk to some people on a confidential telephone line. There’s one in Cambridge. It will probably take an hour or so.”

“Things are that bad?”

“Seems so. That large diatom bloom off the South American coast, Atlantic side, appears to be expanding out of control.”

“Bloom?”

“Biologist’s word. It means the phytoplankton are coming to terms with the chlorinated hydrocarbons we’ve been using in fertilizer. But there’s something more to this one. The technical people are scrambling to find out how this case differs from the earlier, smaller effects on the ocean food chain.”

“I see. Can we do anything about it?”

“I don’t know. The Americans have some controlled experiments in the Indian Ocean, but I gather progress is slow.”

“Well, I won’t keep you from the telephone. I’ve got something to work on, an idea about John’s experiment. Say, do you know the Whim?”

“Yes, it’s in Trinity Street. Near Bowes & Bowes.”

“I’ll probably need a drink and some food in an hour or so. Why don’t we meet there?”

“Good idea. See you round midday.”

The Whim was packed with undergraduates. Ian Peterson pushed his way through a crowd near the door and stood for a moment trying to get his bearings. The students near him were passing jugs of beer over each other’s heads and some spilled on him. Peterson took out a handkerchief and wiped it off with distaste. The students had not noticed. It was the end of the academic year and they were in boisterous spirits. A few were already drunk. They were talking loudly in dog Latin, a parody of some official function they had just attended.

“Eduardus, dona mihi plus beerus!” shouted one.

“Beerus? O Deus, quid dicit? Ecce sanguinus barbarus!” another declaimed.

“Mea culpa, mea maxima culpa!” the first speaker responded in mock contrition. “But what’s beer in bloody Latin?”

Several voices answered. “Alum!” “Vinum barbaricum!” “Imbibius hopius!” There were shouts of laughter. They thought they were being very witty. One of them, hiccuping, slid gently to the floor and passed out. The second speaker raised his arm above him and solemnly intoned. “Requiescat in pace. Et lux perpetua something or other.”

Peterson moved clear of them. His eyes were becoming accustomed to the comparative gloom after the brightness of Trinity. On the wall a yellowed poster announced that some menu items were discontinued—temporarily, of course. In the center of the pub a large coal range popped and hissed. An harassed cook presided over it, shifting pans from smaller rings to larger ones and back. Whenever he lifted a pan from one of the rings, a glow of light from inside the range momentarily lit his hands and perspiring face, so he abruptly loomed like an earnest, orange ghost. Students at tables around the stove called encouragement to him.

Peterson made his way across the crowded eating section, through blue curls of pipe smoke layering the air. The acrid tang of marijuana reached him, mingled with the odors of tobacco, cooking oil, beer and sweat. Someone called his name. He peered around until he saw Markham in a side booth.

“It’s chancy finding anyone here, isn’t it?” Peterson said as he sat down.

“I was just ordering. Lots of salads, aren’t there? And plates full of crappy carbohydrates. There doesn’t seem to be much worth eating these days.”

Peterson studied the menu. “I think I may have the tongue, though it’s incredibly expensive. Any kind of meat is just impossible.”

“Yes, isn’t it.” He grimaced. “I don’t see how you can eat tongue, knowing it came out of some animal’s mouth.”

“Have an egg, instead?”

Markham laughed. “I suppose there’s no way to turn. But I think I’ll splurge and have the sausages. That should do up my budget pretty nicely.”

The waiter brought Peterson’s ale and Markham’s Mackeson stout. Peterson took a big swallow.

“They allow marijuana here, then?”

Markham looked around arid sniffed the air. “Dope? Sure. All the mild euphorics are legal here, aren’t they?”

“They have been for a year or two. But I thought by social convention, if there’s any of that left, one didn’t smoke it in public places.”

“This is a university town. I expect the students were smoking it in public long before it was legalized. Anyway, if the government wants to distract people from the news, there’s no point in requiring them to do it only at home,” Markham said mildly.

“Ummm,” Peterson murmured.

Markham stopped his Mackeson stout short of his mouth and looked at him. “You’re being noncommittal. I guessed right, then? The government had that in mind?”

“Let’s say it was brought up.”

“What’s the Liberal government going to do about these drugs that increase human intelligence, then?”

“Since I moved up to the Council I haven’t had a great deal of contact with those problems.”

“There’s a rumor the Chinese are way ahead on them.”

“Oh? Well, I can scotch that one. The Council had an intelligence report on precisely that point last month.”

“They gather intelligence on their own members?”

“The Chinese are formal members, but—well, look, the problems of the last few years have been technical. Peking has enough on its hands without meddling into subjects where they have no research capability.”

“I thought they were doing well.”

Peterson shrugged. “As well as anyone can with a billion souls to care for. They’re less concerned with foreign matters these days. They’re trying to slice up precisely equal portions of an ever-diminishing pie.”

“Pure communism at last.”

“Not so pure. Equal slices keeps down unrest due to inequality. They’re reviving terraced farming, even though it’s labor-intensive, to get food production up. The opiate of the masses in China is groceries. Always has been. They’re stopping use of energy-intensive chemicals in farming, too. I think they’re afraid of side effects.”

“Such as the South American bloom?”

“Dead on.” Peterson grimaced. “Who could’ve foreseen—?”

From the crowd there came a sudden, rattling cry. A woman surged up from a nearby table, clutching at her throat. She was trying to say something. Another woman with her asked, “Elinor, what is it? Your throat? Something caught?”

The woman gasped, a rasping cough. She clutched at a chair. Heads turned. Her hands went to her belly and her face pinched with a rush of pain. “I—it hurts so—” Abruptly she vomited over the table. She jerked forward, hands clutching at herself. A stream of bile spattered over the plates of food. Nearby patrons, frozen until this moment, frantically spilled from chairs and backed away. The woman tried to cry out and instead vomited again. Glasses smashed to the floor; the crowd moved back. “He—elp!” the woman cried. A convulsion shook her. She tried to stand and vomited over herself. She turned to her companion, who had retreated to the next table. She looked down at herself, eyes glazed, and pressed her palms to her belly. Hesitantly she stepped back from the table. She slipped suddenly and crashed to the floor.

Peterson had been shocked into immobility, as had Markham. As she fell he leaped to his feet and dashed forward. The crowd muttered and did not move. He leaned over the woman. Her scarf was tangled about her neck. It was twisted and sour with puke. He yanked at it, using both hands. The fabric ripped. The woman gasped. Peterson fanned the air around her, creating a breeze. She sucked in air. Her eyes fluttered. She stared up at him. “It… it hurts… so…”

Peterson scowled up at the surrounding crowd. “Call a doctor, will you? Bloody hell!”

The ambulance had departed. The Whim staff were busy mopping up. Most of the patrons were gone, driven off by the stench. Peterson came back from the ambulance, where he had followed, making sure the attendants had a sample of her food.

“What did they say it was?” Markham asked.

“No idea. I gave them the sausage she’d been eating. The medic said something about food poisoning, but those weren’t any poisoning symptoms I’ve ever heard about.”

“All we’ve been hearing about impurities—”

“Maybe.” Peterson dismissed the idea with a wave of his hand. “Could be anything, these days.”

Markham sipped meditatively on his stout. A waiter approached bearing their food. “Tongue for you, sir,” he said to Peterson, placing a platter. “And sausage here.”

Both men stared at their meals. “I think…” Markham began slowly.

“I agree,” Peterson followed up briskly. “I believe we’ll be skipping these. Could you fetch me a salad?”

The waiter looked dubiously at the plates. “You ordered this.”

“So we did. Surely you don’t expect us to choke it down after what’s just happened, do you? In a restaurant like this?”

“Well, I dunno, the manager, he says—”

“Tell your manager to watch his raw materials or I’ll bloody well have this place closed down. Follow me?”

“Christ, no reason to—”

“Just tell him that. And bring my friend here another stout.”

When the waiter had backed away, obviously unwilling to confront either Peterson or the manager, Markham murmured, “Great. How’d you know I’d prefer another stout?”

“Intuition,” he said with weary camaraderie.

They had both had more drinks when Peterson said, “Look, it’s Sir Martin who’s really the technical type on the British delegation. I’m a nonspecialist, as they call it. What I want to know is, how in hell do you get around this grandfather paradox bit? That fellow Davies explained about the discovery of tachyons right enough, and I accept that they can travel into our past, but I still can’t see how one can logically change the past.”

Markham sighed. “Until tachyons were discovered, everybody thought communication with the past was impossible. The incredible thing is that the physics of time communication had been worked out earlier, almost by accident, as far back as the 1940s. Two physicists named John Wheeler and Richard Feynmann worked out the correct description of light itself, and showed that there were two waves launched whenever you tried to make a radio wave, say.”

“Two?”

“Right. One of them we receive on our radio sets. The other travels backward in time—the ‘advanced wave,’ as Wheeler and Feynmann called it.”

“But we don’t receive any message before it’s sent.”

Markham nodded. “True—but the advanced wave is there, in the mathematics. There’s no way around it. The equations of physics are all time-symmetric. That’s one of the riddles of modern physics. How is it that we perceive time passing, and yet all the equations of physics say that time can run either way, forward or backward?”

“The equations are wrong, then?”

“No, they’re not. They can predict anything we can measure—but only as long as we use the ‘retarded wave,’ as Wheeler and Feynmann called it. That’s the one that you hear through your radio set.”

“Well, look, surely there’s a way to change the equation round until you get only the retarded part.”

“No, there isn’t. If you do that to the equations, there’s no way to keep the retarded wave the same. You must have the advanced wave.”

“All right, where are those backward-in-time radio shows? How come I can’t tune into the news from the next century?”

“Wheeler and Feynmann showed that it can’t get here.”

“Can’t get into this year? I mean, into our present time?”

“Right. See, the advanced wave can interact with the whole universe—it’s moving back, into our past, so it eventually hits all the matter that’s ever born. Thing is, the advanced wave strikes all that matter before the signal was sent.”

“Yes, surely.” Peterson reflected on the fact that he was now, for the sake of argument, accepting the “advanced wave” he would have rejected only a few moments before.

“So the wave hits all that matter, and the electrons inside it jiggle around in anticipation of what the radio station will send.”

“Effect preceding a cause?”

“Exactly. Seems contrary to experience, doesn’t it?”

“Definitely.”

“But the vibration of those electrons in the whole rest of the universe has to be taken into account. They in turn send out both advanced and retarded waves. It’s like dropping two rocks into a pond. They both send out waves. But the two waves don’t just add up in a simple way.”

“They don’t? Why not?”

“They interfere with each other. They make a crisscross network of local peaks and troughs. Where the peaks and troughs from the separate patterns coincide, they reinforce each other. But where the peaks of the first stone meet the troughs of the second, they cancel. The water doesn’t move.”

“Oh. All right, then.”

“What Wheeler and Feynmann showed was that the rest of the universe, when it’s hit by an advanced wave, acts like a whole lot of rocks dropped into that pond. The advanced wave goes back in time, makes all these other waves. They interfere with each other and the result is zero. Nothing.”

“Ah. In the end the advanced wave cancels itself out.”

Suddenly music blared over the Whim’s stereo: “An’ de Devil, he do de dance whump whump with Joan de Arc—”

Peterson shouted, “Turn that down, will you?”

The music faded. He leaned forward. “Very well. You’ve shown me why the advanced wave doesn’t work. Time communication is impossible.”

Markham grinned. “Every theory has a hidden assumption. The trouble with the Wheeler and Feynmann model was that all those jiggling electrons in the universe in the past might not send back just the right waives. For radio signals, they do. For tachyons they don’t. Wheeler and Feynmann didn’t know about tachyons; they weren’t even thought of until the middle ‘60s. Tachyons aren’t absorbed the right way. They don’t interact with matter the way radio waves do.”

“Why not?”

“There different kinds of particles. Some guys named Feinberg and Sudarshan imagined tachyons decades ago, but nobody could find them. Seemed too unlikely. They have imaginary mass, for one thing.”

“Imaginary mass?”

“Yes, but don’t take it too seriously.”

“Seems a serious difficulty.”

“Not really. The mass of these particles isn’t what we’d call an observable. That means we can’t bring a tachyon to rest, since it must always travel faster than light. So, if we can’t bring it to a stop in our lab, we can’t measure its mass at rest. The only definition of mass is what you can put on the scales and weigh—which you can’t do, if it’s moving. With tachyons, all you can measure is momentum—that is, impact.”

“You have a complaint about the food, sir? I am the manager.”

Peterson looked up to find a tall man in a conservative gray suit standing over their table, hands clasped behind him military style. “Yes, I did. Mostly I preferred not to eat it, in view of what it did to that lady a short while ago.”

“I do not know what the lady was eating, sir, but I should think your—”

“Well, I do, you see. It was certainly close enough to what my friend here ordered to make him uncomfortable.”

The manager bridled slightly at Peterson’s manner. He was sweating slightly and had a harried look. “I fail to see why a similar type of food should—”

“I can see it quite plainly. A pity you can’t.”

“I am afraid we shall have to charge you for—”

“Have you read the recent Home Office directives on imported meats? I had a hand in writing them.” Peterson gave the manager the full benefit of his assessing gaze. “I would say you probably get much of your imported meat from a local supplier, correct?”

“Well, of course, but—”

“Then you presumably know that there is a severe restriction on how long it can be kept before use?”

“Yes, I’m sure…” the manager began, but then hesitated when he saw the look on Peterson’s face. “Well, actually I haven’t read much of those lately because—”

“I think I would take more care in future.”

“I am not sure the lady actually ate any imported meat whatever—”

“I would look into it, if I were you.”

Abruptly the man lost some of his military bearing. Peterson looked at him with assurance.

“Well, I think we can forget the misunderstanding, sir, in light of—”

“Indeed.” Peterson nodded, dismissing him. He turned back to Markham. “You still haven’t got round the grandfather thing. If tachyons can carry a message back to the past, how do you avoid paradoxes?” Peterson did not mention that he had gone through a discussion with Paul Davies at King’s about this, but understood none of it. He was by no means assured that the ideas made any sense.

Markham grimaced. “It’s not easy to explain. The key was suspected decades ago, but nobody worked it out into a concrete physical theory. There’s even a sentence in the original Wheeler-Feynmann paper—’It is only required that the description should be logically self-consistent.’ By that they meant that our sense of the’ flow of time, always going in one direction, is a bias. The equations of physics don’t share our prejudice—they’re time-symmetric. The only standard we can impose on an experiment is whether it’s logically consistent.”

“But it’s certainly illogical that you can be alive even after you’ve knocked off your own grandfather. Killed him before he produced your father, I mean.”

“The problem is, we’re used to thinking of these things as though there was some sort of switch involved, that only had two settings. I mean, that your grandfather is either dead or he isn’t.”

“Well, that’s certainly true.”

Markham shook his head. “Not really. What if he’s wounded, but recovers? Then if he gets out of the hospital in time, he can meet your grandmother. It depends on your aim.”

“I don’t see—”

“Think about sending messages, instead of shotgunning grandfathers. Everybody assumes the receiver—back there in the past—can be attached to a switch, say. If a signal from the future comes in, the switch is programmed to turn off the transmitter—before the signal was sent. There’s the paradox.”

“Right.” Peterson leaned forward, finding himself engrossed despite his doubts. There was something he liked about the way scientists had of setting up problems as neat little thought experiments, making a clean and sure world. Social issues were always messier and less satisfying. Perhaps that was why they were seldom solved.

“Trouble is, there’s no switch that has two settings—on and off—with nothing in between.”

“Come now. What about the toggle I flip to turn on the lights?”

“Okay, so you flip it. There’s a time when that switch is hanging in between, neither off nor on.”

“I can make that a very short time.”

“Sure, but you can’t reduce it to zero. And also, there’s a certain impulse you have to give that switch to make it jump from off to on. In fact, it’s possible to hit the switch just hard enough to make it go halfway—try it. That must’ve happened to you sometime. The switch sticks, balanced halfway between.”

“All right, granted,” Peterson said impatiently. “But what’s the connection to tachyons? I mean, what’s new about all this?”

“What’s new is thinking of these events—sending and receiving—as related in a chain, a loop. Say, we send back an instruction saying, ‘Turn off the transmitter.’ Think of the switch moving over to ‘off.’ This event is like a wave moving from the past to the future. The transmitter is changing from ‘on’ to ‘off.’ Now, that—well, let’s call it a wave of information— moves forward in time. So the original signal doesn’t get sent”

“Right. Paradox.”

Markham smiled and held up a finger. He was enjoying this. “But wait! Think of all these times being in a kind of loop. Cause and effect mean nothing in this loop. There are only events. Now as the switch moves towards ‘off,’ information propagates forward into the future. Think of it as the transmitter getting weaker and weaker as that switch nears the ‘off’ position. Then the tachyon beam that transmitter is sending out gets weaker.”

“Ah!” Peterson suddenly saw it. “So the receiver in turn gets a weaker signal from the future. The switch isn’t hit so hard because the backward-in-time signal is weaker. So it doesn’t move so quickly toward the ‘off’ mark.”

“That’s it. The closer it gets to ‘off,’ the slower it goes. There’s an information wave traveling forward into the future, and—like a reflection—the tachyon beam comes back into the past.”

“What does the experiment do then?”

“Well., say the switch gets near ‘off,’ and then the tachyon beam gets weak. The switch doesn’t make it all the way to ‘off’ and—like that toggle controlling the lights—it starts to fall back toward ‘on.’ But the nearer it gets to ‘on,’ the stronger the transmitter gets in the future.”

“So the tachyon beam gets stronger,” Peterson finished for him. “That in turn drives the switch away from ‘on’ and back towards ‘off.’ The switch is hung up in the middle.”

Markham leaned back and drained his stout. His tan, weakened by the dim Cambridge winter, crinkled with the lines of his wry smile. “It flutters around there in the middle.”

“No paradox.”

“Well…” Markham shrugged imperceptibly. “No logical contradictions, yes. But we still don’t actually know what that intermediate, hung-up state means. It does avoid the paradoxes, though. There’s a lot of quantum-mechanical formalism you can apply to it, but I’m not sure what a genuine experiment will give.”

“Why not?”

Markham shrugged again. “No experiments. Renfrew hasn’t had the time to do them, or the money.”

Peterson ignored the implied criticism; or was that his imagination? It was obvious that work in these fields had been cut back for years now. Markham was simply stating a fact. He had to remember that a scientist might be more prone simply to state things as they were, without calculating a statement’s impact. To change the subject Peterson asked, “Won’t that stuck-in-the-middle effect prevent your sending information back to 1963?”

“Look, the point here is that our distinctions between cause and effect are an illusion. This little experiment we’ve been discussing is a causal loop—no beginning, no end. That’s what Wheeler and Feynmann meant by requiring only that our description be logically consistent. Logic rules in physics, not the myth of cause and effect. Imposing an order to events is our point of view. A quaintly human view, I suppose. The laws of physics don’t care. That’s the new concept of time we have now—as a set of completely interrelated events, linked self-consistently. We think we’re moving along in time, but that’s just a bias.”

“But we know things happen now, not in the past or future.”

“When is ‘now’? Saying that ‘now’ is ‘this instant’ is going around in circles. Every instant is ‘now’ when it ‘happens.’ The point is, how do you measure the rate of moving from one instant to the next? And the answer is, you can’t. What’s the rate of the passage of time?”

“Well, it’s—” Peterson stopped, thinking.

“How can time move? The rate is one second of movement per second! There’s no conceivable coordinate system in physics from which we can measure time passing. So there isn’t any. Time is frozen, as far as the universe is concerned.”

“Then…” Peterson raised a finger to cover his confusion, frowning. The manager appeared as though out of nowhere.

“Yes sir?” the man said with extreme politeness.

“Ah, another round.”

“Yes sir.” He hustled off to fill the order himself. Peterson took a small pleasure in this little play. To get such a response with a minimum display of power was an old game with him, but still satisfying.

“But you still believe,” Peterson said, turning back to Markham, “that Renfrew’s experiment makes sense? All this talk of loops and not being able to close switches…”

“Sure it’ll work.” Markham accepted a glass dark with the thick stout. The manager placed Peterson’s ale carefully before him and began, “Sir, I want to apol—”

Peterson waved him into silence, impatient to hear Markham. “Perfectly all right,” he said quickly.

Markham eyed the manager’s retreating back. “Very effective. Do they teach that in the best schools?”

Peterson smiled. “Of course. There’s lecture, then field trips to representative restaurants. You have to get the wrist action just right.”

Markham saluted with the stout. After this silent toast he said, “Oh yes, Renfrew. What Wheeler and Feynmann didn’t notice was that if you send a message back which has nothing to do with shutting off the transmitter, there’s no problem. Say I want to place a bet on a horse race. I’ve resolved that I’ll send the results of the race back in time to a friend. I do. In the past, my friend places a bet and makes money. That doesn’t change the outcome of the race. Afterward, my friend gives me some of the winnings. His handing over the money won’t stop me from sending the information—in fact, I can easily arrange it so I only get the money after I’ve sent the message.”

“No paradox.”

“Right. So you can change the past, but only if you don’t try to make a paradox. If you try, the experiment hangs up in that stuck-in-between state.”

Peterson frowned. “But what’s it like? I mean, what does the world seem like if you can change it round?”

Markham said lightly, “Nobody knows. Nobody’s ever tried it before.”

“There were no tachyon transmitters until now.”

“And no reason to try to reach the past, either.”

“Let me get this straight. How’s Renfrew going to avoid creating a paradox? If he gives them a lot of information, they’ll solve the problem and there’ll be no reason for him to send the message.”

“That’s the trick. Avoid the paradox, or you’ll get a stuck switch. So Renfrew will send a piece of the vital information—enough to get research started, but not enough to solve the problem utterly.”

“But what’ll it be like for us? The world will change round us?”

Markham chewed at his lower lip. “I think so. We’ll be in a different state. The problem will be reduced, the oceans not so badly off.”

“But what is this state? I mean, us sitting here? We know the oceans are in trouble.”

“Do we? How do we know this isn’t the result of the experiment we’re about to do? That is, if Renfrew hadn’t existed and thought of this idea, maybe we’d be worse off. The problem with causal loops is that our notion of time doesn’t accept them. But think of that stuck switch again.”

Peterson shook his head as though to clear it. “It’s hard to think about.”

“Like tying time in knots,” Markham conceded. “What I’ve given you is an interpretation of the mathematics. We know tachyons are real; what we don’t know is what they imply.”

Petersen looked around at the Whim, now mostly deserted. “Strange, to think of this as being an outcome of what we haven’t done yet. All looped together, like a hooked rug.” He blinked, thinking of the past, when he had eaten here. “That coal stove—how long have they had that?”

“Years, I suppose. Seems like a sort of trademark. Keeps the place warm in winter, and it’s cheaper than gas or electricity Besides, they can cook at any time of day, not just the power hours. And it gives the customers something to watch while they’re waiting for their orders.”

“Yes, coal’s the long-term fuel for old England,” Peterson murmured, apparently more to himself than Markham. “Bulky though.”

“When were you a student here?”

“In the ’70s. I haven’t been back very often.”

“Have things changed much?”

Peterson smiled reminiscently. “I dare say my rooms haven’t changed much. Picturesque view of the river and all my clothes get moldy from the damp…” He shook off his mood. “I’ll have to be getting back to London soon.”

They elbowed through the students to the door and out into the street. The June sunshine was dazzling after the pub’s dark interior. They stood for a moment, blinking, on the narrow sidewalk. Pedestrians stepped off into the street to walk past them and cyclists swerved around the pedestrians with a trilling of bells. They turned left and strolled back towards King’s Parade. On the corner opposite the church, they paused to look in the windows of Bowes & Bowes bookstore.

“Do you mind if I go in for a minute?” Peterson asked. “There’s something I want to look for.”

“Sure. I’ll come in, too. I’m a bookstore freak; never pass one by.”

Bowes & Bowes was almost as crowded as the Whim had been earlier, but the voices here were subdued. They edged cautiously between the knots of students in black gowns and pyramids of book’s on display. Peterson pointed out one on a less conspicuous table towards the back of the store.

“Have you seen this?” he asked, picking up a copy and handing it to Markham.

“Holdren’s book? No, I haven’t read it yet, though I talked to him about it. Is it good?” Markham looked at the title, stamped in red on a black cover—The Geography of Calamity: Geopolitics of Human Dieback by John Holdren. In the bottom right corner was a small reproduction of a medieval engraving of a grinning skeleton with a scythe. He thumbed through it, paused, began to read. “Look at this,” he said, holding the book out to Peterson. Peterson ran his eyes over the chart and nodded.

Markham whistled softly. “Is it accurate?”

“Oh, yes. Underestimated, if anything.”

Peterson moved towards the back of the store. A girl was perched on a high stool adding a column of figures into an auto-accountant. Her fair hair hung forward, hiding her face. Peterson studied her covertly while leafing through some of the books in front of him. Nice legs. Fashionably dressed in some frilly peasant style he disliked. A blue Liberty scarf artfully arranged at her neck. Slim now, but not for many more years, probably. She looked about nineteen. As though aware of his gaze, she looked up straight at him. He continued to stare at her. Yes, nineteen and very pretty and very aware of it, too. She slid from her stool and, clutching papers defensively to her chest, came over to him.

“May I help you?”

“I don’t know,” he said with a slight smile. “Maybe. I’ll let you know if you can.”

She took this as a flirtatious overture and responded with a routine which probably, he reflected, was a knock-out with the local boys. She turned away from him and looked back over her shoulder, saying huskily, “Let me know then.” She gave him a long look from under her lashes, then grinned cheekily and flaunted her ways towards the front of the store. He was amused. At first, he had really thought that she intended her coquettish routine seriously, which would have been ludicrous if she hadn’t been so pretty Her grin showed that she was playacting. Peterson felt suddenly in very good spirits and almost immediately noticed the book he had been looking for.

He picked it up and went to look for Markham. The girl was with two others, her back to him. Her companions were laughing and staring. They obviously told her he was watching them, because she turned to look at him. She really was exceptionally pretty. He made a sudden decision. Markham was browsing through the science fiction selection.

“I have a couple of errands,” Peterson said. “Why don’t you go on ahead and tell Renfrew I’ll be there in half an hour?”

“Okay, fine,” Markham said. Peterson watched him as he strode out the door, moving athletically, and disappeared into the alley behind the building known as Schools.

Peterson looked for the girl again. She was serving someone else, a student. He watched as she went through another routine, leaning forward more than was necessary to write a receipt, quite enough to enable the student to look down the front of her blouse. Then she straightened up and looked quite offhand as she gave him his book in a white paper bag. The student went out, with a disconcerted look on his face. Peterson caught her eye and lifted the book in his hand. She slammed the cash register shut and came over to him.

“Yes?” she asked. “Have you made up your mind?”

“I think so. I’ll take this book. And maybe you could help me with something else. You live in Cambridge, do you?”

“Yes. You don’t?”

“No, I’m from London. I’m on the Council.” He despised himself immediately. Like shooting a rabbit with a cannon. No artistry at all. Anyway, he had all her attention now, so he might as well take advantage of it. “I wondered if you could recommend any good restaurants around here to me?”

“Well, there’s the Blue Boar. And there’s a French one in Grantchester that’s supposed to be good, Le Marquis. And a new Italian one, II Pavone.”

“Have you eaten at any of them?”

“Well, no…” She blushed slightly and he knew she regretted appearing at a disadvantage. He was well aware that she had named the three most expensive restaurants. His own favorite had not been mentioned; it was less showy and less expensive, but the food was excellent.

“If you could choose, which one would you go to?”

“Oh, Le Marquis. It looks a lovely place.”

“The next time I’m up from London, if you’re not doing anything, I would count it as a great favor if you would have dinner there with me.” He smiled intimately at her. “It gets pretty dull, traveling alone, eating alone.”

“Really?” she gasped. “Oh, I mean…” She struggled furiously to repress her triumphant excitement. “Yes, I’d like that very much.”

“Fine. If I could have your telephone number…”

She hesitated and Peterson guessed she had no telephone. “Or if you’d rather, I can simply stop by this shop early on.”

“Oh yes, that would be best,” she said, seizing on this graceful out.

“I’ll look forward to it.”

They walked forward to the front desk, where he paid for his book. When he left Bowes & Bowes, he turned the corner towards Market Square. Through the side windows of the bookstore he could see her in consultation with her two friends. Well, that was easy, he thought. Good God, I don’t even know her name.

He crossed the square and walked through Petty Cury with its bustling throng of shoppers, coming out opposite Christ’s. Through its open gate the green lawn in its quad was visible and behind that, the vivid colors of a herbaceous border against the gray wall of the Master’s Lodge. In the gateway the porter sat reading a paper. A knot of students stood studying some lists on the bulletin board. Peterson kept on going and turned into Hobson’s Alley. He finally found the place he was looking for: Foster and Jagg, coal merchants.