CAMBRIDGE, 1:58 A.M.

by Gregory Benford

Gregory Markham returned to the Cavendish Laboratory at 9:13 P.M. Instead of going to his cluttered office, he descended into the basement. The corridors were poorly lit, and many laboratories yawned empty, stripped of equipment.

When he entered the large room reserved for the nuclear-resonance group, he nearly bumped into a tall, thin man standing just inside the door.

The man turned and smiled slightly. “You must be Markham,” he said, holding out his hand.

“Right. How did you know?”

“You’re the only one here who looks as though he might be an American.”

“Ah. I’ve been here six months, but apparently there’s something British that doesn’t rub off on visitors.”

“You’re better dressed than we are, for one thing.”

“You mean for a scientist I’m better dressed. Those tweeds of yours are quite fashionable.”

“We do a bit better in the government. It’s about all we seem to be doing well, these days,” the man said wryly.

“Oh, you must be Ian Peterson, then.”

“Didn’t I say that? Stupid of me. Yes, I rang you up two days ago. Sorry, I’m wandering around in a daze, I guess.”

“Crisis?”

“Of course, there’s always one these days. The Emergency Council has been in executive session since this morning. I was barely able to get the train down here in time.”

“Worried about North Africa?”

“That, yes. Looks as though it’s a full-scale dieback this time.”

“Damn. Is it all due to the drought?”

“Plus not having any food reserves. Disease is killing most of them now, though.”

Markham gestured into the laboratory. “Say, there’s Renfrew. Have you met?”

“No, I’ve only just arrived. He’s the heavyset one?” The two men stood on a raised platform overlooking a sprawl of scientific equipment. There were eight technicians working among the aisles. Roughing pumps chugged laboriously, and there were muffled conversations, but otherwise the laboratory was quiet

“I’d like a word before I meet Renfrew,” Peterson said. “I didn’t have much chance to sound you out on the telephone the other day.”

“I don’t have much of an opinion so far,” Markham said precisely.

“Nonetheless, you’re the fellow the Americans elected to send. You must know how they feel about this.”

“Strictly speaking, they didn’t ‘send’ anyone. I’m here with the Cavendish theory group, sabbatical leave. The National Science Foundation wired me last week to act as liaison.”

“Yes, you’re from the University of California at Irvine, right? A plasma physicist.”

“Most of my work has been in plasmas until the last few years. I wrote a paper on tachyons long ago, before they became fashionable. I suppose that’s why the NSF asked me to be here.”

Peterson lowered his voice. “There’s the rub, you see. I haven’t any technical background in this sort of thing. No one on the council has. We’ve got ecologists and systems people and that sort of thing, but… well, look, tell me, do you think this experiment might be of any real help?”

“Without being melodramatic,” Markham said slowly, “I believe it could save millions of lives.”

“If it works.”

“We know the technique works. It’s whether we can actually communicate with the past that we don’t know.”

“And this setup here—” Peterson swept his arm out across the laboratory bay—”can do that?”

“If we’re damned lucky. We know there were similar nuclear-resonance experiments in the Cavendish and a few other places in the States and the Soviet Union functioning as far back as the 1950’s. In principle they could pick up coherent signals induced by tachyons.”

“So we can send them telegrams?”

“Yes, but that’s all. It’s a highly restricted form of time travel, if you want to put it that way. This is the only way anyone’s figured how to send messages into the past. We can’t transmit objects or people.”

Peterson shook his head. “I did a degree in math, computers. But even I know there’s a paradox involved here somewhere. The old thing about shooting your grandfather, isn’t it? Someone on the council brought that up yesterday. We almost booted the whole idea out because of that, you know.”

“A good point. I made the same error in a paper back in 1970. It turns out there are paradoxes, and then, if you look at things the right way, paradoxes go away. Maybe I can explain—”

“Sorry, but I haven’t time for that now. The whole point, as I understand it, is to send these telegrams and tell somebody back in 1955 about our situation here.”

“Well, something like that. Warn them against chlorinated hydrocarbons, sketch in the effects on phytoplankton. Describe—”

“Hello, Greg! Glad to see you here.” Unnoticed, John Renfrew had mounted the catwalk from the bay below. He was a large, swarthy man with his white shirt partially untucked in his trousers. Lines of fatigue made his face seem ashen. Despite the chilly English spring, there were crescents of sweat in the cloth around his armpits. “And you’re Mr. Peterson, I expect,” Renfrew said with considerably less enthusiasm. “Come to see if I’ve been spending the council’s special appropriation wisely?”

“Something of the sort,” Peterson said distantly.

“I’m grateful for it, mind you that, and we’ll be showing you some results later on. But Professor Markham is here because I think the only way to really accomplish anything is to get the Americans to come in.”

“Since I’m not so essential,” Peterson said, “you might have scheduled this experiment at some more reasonable hour.”

“Couldn’t. Noise level in the day is too high, and anyway, the electric-power chaps won’t let us run in the peak usage times. We use a lot of high-tension devices to put out short bursts of tachyons, and they-”

“I’m sure,” Peterson said. “Could I please see the experiment?”

“Ah, yes, certainly.” Renfrew turned and led the way down the catwalk to the floor of the laboratory. The room was of bare stonework, outfitted with old-fashioned electrical connections and rather newer cables strewn through the aisles of apparatus. Some old, gray cabinets were of English manufacture, but most of the newer equipment was housed in brightly colored compartments from Maxwell Laboratories, Physics International, and other American firms. Peterson gathered these garish red-and-yellow units came from the council appropriation.

Renfrew led them to a complex array housed between the poles of a large magnet. “Superconducting setup, of course. We need the high field strength to get a nice sharp line during transmission.”

Peterson studied the maze of wires and meters. Cabinets housing rank upon rank of electronics towered over the men; he found the mass of it oppressive. He waited for Renfrew to begin, but when the man said nothing, Peterson pointed out a particular object and asked as to its function.

“Oh, I didn’t think you’d be wanting to know the technical side,” Renfrew said.

“Try me.”

“We’ve got a large nuclear source in there, see …” Renfrew pointed at the encased volume between the magnet poles. “We modulate the electric fields around the source—it’s cesium—in such a way that the nuclei give off tachyons. Particles that travel faster than light, you know. On the other side”—he pointed around the magnets, leading Peterson to a long cylindrical tank that protruded ten meters away from the magnets—”we draw out the tachyons and focus them into a beam. They’re a particular type of tachyon, ones that resonate only with cesium nuclei. Ordinary matter is transparent to tachyons, do you see?”

“Until they run into something,” Peterson said.

“No, no, that’s the point,” Renfrew said sharply. “Tachyons just don’t interact with most ordinary matter. They pass right through.”

“That’s why we can shoot them halfway across the galaxy without having them stopped,” Markham interjected.

“Except for cesium,” Renfrew said. “When one of our tachyons hits a cesium atom in a strong magnetic field—a situation that doesn’t occur naturally very often—it will be absorbed. The struck nucleus recoils then, with a very high momentum. It sends out shock waves in the lattice of the cesium sample.”

“That’s some other fellow’s cesium, I suppose?” Peterson said.

“One operating in 1955,” Renfrew said.

Markham added, “We hope.”

“We’re hoping the fellows doing the experiments back then will notice some large signals—they’ll perceive them as sound waves—carrying a message,” Renfrew said. “The whole point is that there must be enough tachyons striking that 1955 block of cesium metal to show up clearly. For that we have to concentrate a burst of tachyons and aim it just so—”

“Hold on,” Peterson said, putting up a hand. “Aim for what? Where is 1955?”

“Quite far away, as it works out,” Markham conceded. “Since 1955 the Earth has been going around the Sun, while our star itself is revolving about the hub of the galaxy. Add on to that the motion of our galaxy relative to the fixed rest frame of the center of mass of the universe—”

“You mean 1955 is in a different place, then?”

“Certainly. So we send out a broad beam that sweeps the volume we believe was occupied by the Earth at that particular time in the past,” Markham said.

“Sounds impossible.”

Markham shrugged. “It may be. The trick is that Renfrew here is creating tachyons with essentially infinite speed, so if we can hit the right spot in space, we can send a message back quite a long way. How far back we can go is related to the distance.”

“We’re aiming for a particular space-time point along the Earth’s geodesic,” Renfrew began.

“You’re traveling a bit too fast for me,” Peterson put in. “What were these results you were talking about?”

“We’ve been working with noise problems the last few months, that’s the main thing. The signal has to appear above the thermal background, so it’s accessible to the fellows back in the 1950’s, with their relatively crude equipment.”

Peterson shook his head. “I’m amazed you got the money for this.”

Renfrew’s face tightened. “Well, we did get it. Though it’s bloody well not enough.”

“You think you won’t be able to get through?” Markham said.

Renfrew turned to the American. “It’ll be a near thing. We need a lot more power to be sure. That’s where the Americans come in, if they will.”

“But you’ll try?” Peterson said.

“Right. The rig is set; we’ve been working on it all day.”

“When can we run?” Markham said.

“Now.”

It was 9:34 P.M.

José Basquan waited for the first threads of dawn to lighten the sky. Slowly he put his loose fishing gear in a mesh sack. He squatted at the threshold of a dark stone house, listening to the slowly gathering sounds of people arising through the village. He tried to ignore the gnawing, rumbling hunger in his belly.

He debated with himself for a moment and then decided a mouthful of wine would give him energy to begin. The cork came out with a dry pop, and he carefully trickled a pool of it into his mouth. It was sharp and rough; the fumes seemed to burn his nostrils, RODAS CABERNET. He read each letter to himself, moving his lips. José could still remember letters, but the words made no sense to him. Downslope from his house was a long, low wooden building with a sign atop it. To pass the time he slowly spelled the letters out to himself, as he had many times before. MITSUBISHI PACKING CORP.

There was no movement around the building, no lights were burning. There had been little work for months there, José knew, and some of the men who had learned that trade had moved away to another village in search of another job.

José heaved to his feet. If there was to be work for anyone, he had better get down to his boat. The bleak village of scattered one-story houses depended utterly upon the fishing fleet. There had been precious few hauls of fish in the last few weeks. The familiar casting areas yielded nothing. José and a few other men had found some shallow spots farther up the coast that occasionally gave a modest catch, but everyone knew those places were not dependable.

He walked slowly down the damp cobblestoned street. A drizzle began. He heard the high notes of excitement from the direction of the plank pier. There was also a low bass sound, like angry men yelling. José walked faster. A small hill hid the view of the ocean from him. He took a shortcut through a clump of stunted brown trees. A dead bird lay in his path, but he did not notice it. He rounded the brow of the hill.

The shouting grew louder. He squinted through the drizzle, and suddenly his eyes widened. Normally at dawn the Atlantic was dark and oily. Today it was a mottled red. A stench of rotting sea life rose from the narrow beach.

José did not have to go out in his skiff today to know he would find no fish. Something had happened. The ocean was dying.

November 16, 1991

Dear Alex:

I’m not going to make it down for Thanksgiving; there’s just too much to do here at Cal Tech. The last few weeks have been extremely exciting. I’m working with a couple of other people, and we really don’t want to break off our calculations, even for a holiday in Baja. I shall miss the prickly cactus and that delicious dry heat. Sorry, and maybe we can make it next time.

After breaking a promise like this, I really suppose I ought to tell you what’s stirred me up so. Probably a marine biologist like you won’t think all this is of such great concern—cosmology doesn’t count for much in the world of enzymes and titrated solutions and all that, I suppose—but to those of us working in the gravitational-theory group it looks as though there’s a genuine revolution around the corner. Or maybe it’s already arrived.

You must remember Malcolm Walmesley, the fellow who was best man at Jim and Hilary’s wedding? He’s tied into this, though somewhat indirectly. He and two others were the first to notice that quasars are clustered into two groups in our sky. This was way back in 1966, and you will get some idea of how difficult the observations are when I tell you that it has taken this long to follow up those first measurements in depth. It turns out the quasars are clumped together, representing a really large-scale clustering of matter in the universe.

This is related to a problem that’s been hanging around astrophysics for a long time. If there is a certain quantity of matter in the universe, then it is a closed geometry—like the surface of a sphere, you can move around on it, but you can’t escape. So people in our line of work have been wondering for some time if there is enough matter in our universe to close off the geometry. It would be nice to see if the geometry is closed by a direct experiment—say, by sending out a beam of light and seeing if it curves around and comes back eventually—but that experiment takes about twenty billion years to finish.

Just counting the luminous stars in the universe gives a small quantity of matter, not enough to close off space-time. But there’s undoubtedly a lot of unseen mass such as dust, dead stars, and black holes.

We’re now pretty sure that most galaxies have large black holes at their centers. That accounts for enough missing matter to close off our universe. What’s new is that the recent data on quasar distribution mean there are large fluctuations in matter density throughout our universe. If galaxies clump together somewhere in our universe, and their density gets high enough, their local space-time geometry could wrap around on itself, in the same way that our universe is closed.

We now have enough evidence to believe Tommy Gold’s old idea —that there are parts of our universe which have enough clustered galaxies to form their own closed geometry. They won’t look like much to us—just small areas with weak red light coming out of them. The shocker here is that these local density fluctuations qualify as independent universes. The time for forming a separate universe is independent of the size (it goes like square root of Gn, where G is the gravitational constant and n the density of the contracting region). Thus it’s independent of the size of the miniuniverse! A small universe will close itself off just as fast as a large one. This means all the various-sized universes have been around for the same amount of “time.” (Defining just what time is in this problem will drive you to drink, if you’re not a mathematician.)

The point here is that there may be closed-off universes inside our own. In fact, it would be a remarkable coincidence if our universe was the largest of all. We may be a local lump inside somebody else’s universe! Remember the old cartoon of a little fish being swallowed by a slightly larger one, in turn about to be swallowed by another bigger one, and so on ad infinitum? Well, we may be one of these fishes.

The last few weeks, I’ve been working on the problem of getting information about—or out of—these universes inside our own. Clearly, light can’t get out of one universe into the next. Neither can matter. The only possibility might be some type of particle that doesn’t fit into the constraints set by Einstein’s theory. There are several candidates like this, but Thorne (the grand old man around here) doesn’t want to get into that morass. Too messy, he says.

Some of us here think otherwise, which is why I’m working so hard on the problem. There’s a chance of a first-class discovery in this. We’ve had the devil of a time pursuing things, with the food strike and the big fire in L.A. And I scarcely think anyone will give much of a damn, with the world in its present state. But that’s what the academic life is for.

I’m going to try to get through to La Jolla sometime soon, and maybe we can see each other then. Sorry about Baja.

Sincerely,

Charles

At 10:22 P.M. John Renfrew began tapping slowly on a 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 said.

“Simple Morse,” Markham said.

“I see, to maximize the chances of it’s 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 juggled, a scattered random field. “How can there be that much noise in a chilled cesium sample?” Markham asked.

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

“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?” Peterson said.

“Bloody hell, I didn’t say that. There’s just something wrong now. 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, 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 looking 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. Markham rubbed a thumbnail against his lower lip and studied the yellow noise spectrum on the green oscilloscope screen. After a moment he said, “Have you got a correlator you could use on this rig?”

Renfrew stopped for a moment and thought. “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 away without saying anything. Markham climbed the stairway and said, “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. It will probably take an hour or so.”

“That bad?”

“Seems so. There’s a large diatom bloom off the South American coast, Atlantic side.”

“Bloom?”

“Biologist’s word. It means the thyloplankton are coming to terms with the chlorinated hydrocarbons we’ve been using in fertilizer. Apparently marine animals can’t get along with this new diatom. They’re dying off, and the whole food chain might be threatened.”

“I see. Can we do anything about it?”

“I don’t know. We’ve been trying some methods in the Indian Ocean, anticipating something like this might happen. I don’t know if we can shift resources to the lower Atlantic that fast.”

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

“Yes, it’s a pub in Jesus Green.”

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

“It’s, let’s see, ten-forty-five. Yes, that’s a good idea. See you near midnight.”

The Physical Review D, Vol. 2, No. 2, 263-265, 15 July 1970

“The Tachyonic Antitelephone”

G. A. Markham, D. L. Book, and W. A. Newcomb

Lawrence Radiation Laboratory, University of California,

Livermore, California

(Received 23 June 1969)

The problem of detecting faster-than-light particles is reconsidered in relation to Tolman’s paradox. It is shown that some of the experiments already under way or contemplated must either yield negative results or give rise to causal contradictions.

Hypothetical faster-than-light particles (tachyons) have recently received considerable attention, both theoretically1-3 and experimentally.4-6 Still, there are difficult questions of causality associated with faster-than-light signals. We hope to show that these have not been adequately resolved. In particular, it appears that at least some current attempts to produce and detect tachyons are foredoomed to failure on fundamental grounds.

In 1917 Tolman 7 presented an argument (Tolman’s paradox) showing that if faster-than-light signals can be propagated, then communication with the past is possible. That is, they would comprise an “antitelephone.”

Recently Bilaniuk, Deshpande, and Sudarshan 1 have attempted to answer this argument with a “reinterpretation principle.” They note that a tachyon of negative energy —E leaving point 1 at time t_1 and arriving at point 2 at an earlier time t_2 may be reinterpreted as a tachyon of energy +E traveling from 2 to 1. Thus the earlier of the two events can always be viewed as an emission and the later as an absorption. They point out that the end of the tachyon’s world line that appears “earlier” depends on the reference frame of the observer. That is, emission of a tachyon may be viewed as absorption by another observer. As we shall see, this statement is not sufficient of itself to refute Tolman’s paradox.

Note that Tolman’s paradox deals only with faster-than-light communication. It does not rule out tachyons, which for some reason may not be used as a signaling system. There is no paradox associated with an unmodulated tachyon beam. Current theories deal mainly with noninteracting tachyons. The moment interactions are introduced, Tolman’s paradox must be faced… .

James Whyteborn was late for work. He hastily shook out his jacket and hung it in the dark narrow cloakroom. He put on his white smock and fumbled with the buttons. His head was blurred and it ached, either from the cheap Algerian red of the night before or simple fatigue. He hated this job; maybe that had something to do with it.

He pushed open the heavy door into the preparation room. The chill air made Whyteborn shiver, and the foreman gave him a significant look. He hurried to his post. Well, hell. He wouldn’t have been late if he hadn’t had to take the damned bus from Croydon through Caterham, and then run into that jam at the railway crossing. Nothing ever seemed to work right these days.

He took out his working case, the chemical analyzers and needles and the rest. He was reasonably sure that he understood most of the checks he was to make, but the government seemed to add a new test every time he turned around. Whyteborn got his kit in order and went to the first fine of carcasses. He looked aside as he approached, wanting to delay the moment until the last. It didn’t seem to matter whether it was pork or beef or lamb, the sight of a carcass hanging from a hook, partially chopped to pieces and still bleeding, made him ill. If he wasn’t a vegetarian, maybe it would be easier.

He did the first row all right, drawing out the samples and making the color-coded checks required. He ignored the gobs of yellow fat that dangled in the air, the stringy meat interlaced with blue and brown streaks.

By the second row he had begun to feel the dull buzzing pain behind his eyes again, and his attention wavered. Whyteborn checked his watch; still quite a long time till tea break.

He came to a line of pigs neatly strutted and cleaned. There was a special set of tests for these, recently started by the government inspectors. Something to do with the protein supplements given the hogs, ground-up cod and whitefish marrow, something like that.

He inserted a needle, took a sample, and tested it in the analyzer. The color indicator came out neutral. Whyteborn felt his headache getting worse. He shuffled on to the next body and repeated the process. This result was somewhat worse, but Whyteborn knew he probably wasn’t doing the test right. It seemed likely this meat would come out all right if he was careful about his procedures. He looked down the long row of silently hanging hog carcasses and felt the room spin around him. God, it was really bad this morning. He shouldn’t have drunk the wine. He should have called in sick.

He put away his kit. That was enough for this line. The tests came out neutral or maybe a little better, and anyway, what did it matter, the tests weren’t that good in any case, and Whyteborn wasn’t about to eat any of this rubbish. Christ, only the rich could buy this stuff now.

He coughed and his head felt worse. He decided to take his tea break early. What a piss-up of a day this was.

The Whim was gloomy, even considering the energy shortage. Ian Peterson pushed his way through a crowd near the front door and stood for a moment trying to get his bearings. A yellowed poster announced that some menu items were discontinued—temporarily, of course. The Whim was surprisingly crowded; then Peterson remembered that most experimental work at Cambridge was done at night, due to its low priority. The university crowd had apparently adapted well; some of them even seemed to be in good spirits.

He made his way across the crowded eating section, through blue curls of pipe smoke layered in the air. Someone called his name, and 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. Thought I might have the tongue, though it’s incredibly expensive.”

Peterson studied the menu. “Lot of salads, aren’t there? There doesn’t seem to be anything worth eating these days.”

“Anything with meat in it is just impossible.”

“Yes, except the cheaper cuts. I don’t see how you can eat tongue, knowing it came out of some animal’s mouth.”

“Have an egg instead, then?”

Peterson 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.”

When the waitress had brought Peterson’s ale and Markham’s Mackeson stout, Peterson suddenly noticed an odd sour tang in the air. “Is that what I think? They allow that in here?”

Markham looked around and sniffed the air. “Marihuana, 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.”

“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.

“Score to you. Despite all the rhetoric, I’m sure that’s why it was legalized. I’ll bet the rate of use goes up pretty soon, too.”

“The news that bad?”

“Worse, if anything.”

“How much does the bloom cover?”

“Apparently almost all the south Atlantic. The large fishing areas are gone. As far as patrols can tell, there is nothing left alive inside. And the perimeter is growing.”

“We’d better get Renfrew’s experiment on the air, then.”

“That’s what I don’t understand. 1 may be a nonspecialist, but how in hell do you get around that grandfather paradox bit? How can we possibly change the past?”

“Quite honestly, no one knows for certain. Renfrew’s is the first experiment done with tachyons that deliberately tries to reach the past. All the ideas he’s working under depend on new advances in cosmology and relativity and particle physics. No one has been able to put all these ideas together in a coherent philosophical package.”

“Then how the hell can you say this might work?”

“There are good theoretical reasons to think it might. The trick is that you can change the past so long as the physical circumstances of the experiment aren’t also altered in the process.”

Peterson shook his head. “Don’t follow.”

“Look, we want to get word that use of fertilizer-sensitive grains won’t work in the long run, that the oceans are so damned vulnerable, more so than anything else. That whole countries will begin to go down the drain by the 1980’s. We can send that information—the laws of physics and causality will let us—as long as we don’t solve the problem so well that the Renfrew experiment never gets performed. That is, unless we do something that cuts off the message itself. So we can make things better. At least, there isn’t any reason in the theory why we can’t.”

“That’s what you’re asking the government to support?”

“The council did, didn’t it?”

“Only on advice. Do you think the National Science Foundation will come in with some money for Renfrew?”

Markham shrugged. The waitress arrived with their food, and both men began to eat quickly. “If Renfrew’s personality has anything to do with it, I think we can write off the whole affair.”

“Yes, I’m rather amazed that he’s so hostile,” Peterson said. “Any idea why?”

“Sure. He’s had to scrounge and fight like billy-hell to get this thing together. I think he’s getting paranoid about it. Yet he’s doing just what should be done. He’s checking important implications of a new cosmological theory that uses tachyons as an essential part. It took half a century for Weber to test for Einstein’s gravitational waves, you remember. Well, Renfrew is speeding up the process a bit for tachyons.”

“He’s already found them, hasn’t he?”

“Yes, but to use them—there’s the rub.”

“That settles it, then. The council secretary wanted me to return to London immediately, but I won’t. I’ll stay a few more hours to see if this thing comes out. Shouldn’t we be getting back over to the laboratory?”

Markham took a long pull at his stout. “I suppose so,” he sighed. “What time is it?”

“Morning already. One-oh-eight.”

The stars were out as Markham and Peterson made their way back to the Cavendish. Their walk took them through the Euclidean perfection of Kings College, through an ivy arch, and down a small, cobbled lane. They went along the backs, Markham rather relishing the experience as only Americans do at Cambridge, and then passed through the Great Court of Trinity. The air was heavy and damp, giving their footsteps an odd hollow ring.

As they entered the nuclear-resonance laboratory, Renfrew looked up and waved energetically. “Where’ve you been? We’ve got everything set up.”

“Sorry, I was delayed,” Peterson said.

Renfrew nodded to two technicians and beckoned them down the stairs. “I have a Scott correlator rigged in, as you asked,” he said to Markham. “But our noise problem is just as bad.”

“I expected so,” Markham said. When Renfrew seemed surprised, he went on, “I’ve been doing some calculations and a bit of reading since I left. I think there may be an explanation for the anomalous noise level. It’s not thermally generated at all, if I’m right. Instead, the noise comes from tachyons. Your cesium sample isn’t transmitting tachyons, it’s receiving them. There’s a tachyon background we’ve neglected.”

“A background?” Renfrew said. “From what?”

“Let’s see. Try the correlator.”

Renfrew made a few adjustments and stepped back from the oscilloscope. “That should do it.”

“Do what?” Peterson put in.

“This is a lock-in coherence analyzer,” Markham said. “Which means it can cull out the genuine noise in the cesium sample—soundwave noise, that is—and bring any signals up out of the random background.”

“Which is just what it’s doing,” Renfrew said quietly. He stared intently at the oscilloscope face. A complex wave form wavered across the scale.

“It seems to be a series of pulses strung out at regular intervals,” Renfrew said. “But the signal decays in time.” He pointed at the fluid line that faded into the noise level as it neared the right hand of the screen.

“Quite regular, yes,” Markham said. “Here’s one peak, then a pause, then two peaks together, then nothing again, then four nearly on top of each other, then nothing… . Strange.”

“What do you think it is?” Peterson asked.

“Not ordinary background, that’s clear,” Renfrew answered.

“It’s coherent, can’t be natural,” Markham said.

Renfrew: “No. More like…”

“A code,” Markham finished.

It was 1:56 A.M.

“Let’s take some of this down,” Markham said. He began writing on a clipboard. “Is this a real-time display?”

“No, I just rigged it to take a sample of the noise for a hundred-microsecond interval.” Renfrew reached for the oscilloscope dials. “Would you like another interval?”

“Wait until I copy this.”

Peterson said, “Why don’t you just photograph it?”

Renfrew looked at him significantly. “We have no film. There’s a shortage, and priority doesn’t go to laboratories these days, you know.”

“Anyone here know Morse?” Markham interrupted.

Renfrew shook his head. Peterson said, “I probably still remember some.”

Markham handed him the clipboard. “Try that. Meanwhile, let’s have another interval analyzed.”

Renfrew made an adjustment, and another pattern appeared on the scope, this time covering only half the time period before it was submerged in the noise level. Markham began copying its features.

“Odd,” Peterson said. “It decodes to ‘Nd Meat I’—that’s all.”

“At least it’s English,” Markham said. “Try this.”

Renfrew wrinkled his brow. “What’s happening?”

“Someone is sending us time telegrams, I’d say,” Markham said. “Telegrams to one-fifty-eight A.M., Cambridge. They’re having trouble getting through the noise level.”

“Word from the future,” Renfrew said slowly. “They must know we set up this attempt to signal back to the 1950’s. So they’re trying to reach us, too. Makes sense, doesn’t it?”

“Trouble is,” Markham said, “can you transmit through that noise?”

Renfrew thought a moment. “I don’t believe so. This is the best equipment I could muster. I might be able to pick up a factor of two in sensitivity with a few modifications, but I doubt it. And there’s no point in going to lower temperatures, if the noise level is this high.”

Peterson held up the clipboard, “‘AMSNU QUEALSEUD POH3E4C.’ Gibberish.”

“I was afraid of that, too,” Markham said.

“What are you talking about?” Renfrew said sharply.

“All that background noise doesn’t arise naturally, or at least, that’s my guess. It’s formed by overlaying a lot of different coherent signals, from many different sources. Every once in a while this particular space-time point we’re at gets a burst of a coherent signal somewhat larger than the rest. That’s what we’ve been decoding. But the noise level is so high, not much can get through before it’s swallowed up again. Apparently focusing is difficult. If our technology is strained right now, I doubt we’ll get very much more.”

Renfrew began pacing back and forth with sudden energy. He waved at the laboratory technicians who had left their posts and gathered around the three men. “Keep an eye on,” he called, and motioned them away. When he turned back, Peterson could see clearly the lines of fatigue in the man’s face. “Look, if you’re right, why are there so many signals coming in?”

“And why does this second message come out nonsense?” Peterson added.

Markham gestured at the oscilloscope screen. “Try another one, John. I’ll bet you find that quite a few of the signals that get above noise level are incomprehensible.”

Renfrew moved to the oscilloscope, and when he had a new trace, Peterson began copying it. Markham went on, “There’s going to be gibberish simply because either the senders don’t use Morse or the senders don’t speak our language.”

“You mean from the far future, then?” Peterson said.

“No, not necessarily. Though that’s possible.” Markham made a tent of his fingers and smiled into it in what was clearly his favorite academic gesture. “John, I know you’ve been busy with this experiment and haven’t had time to keep up with theoretical developments. But the very existence of tachyons and the rest of the so-called ‘new relativity’ leads to far-reaching, almost incredible conclusions.”

“I don’t have time for much reading,” Renfrew said with a note of dismissal.

“Leisure of the theory class,” Markham said laconically. “Not that there are that many technical journals left—I’ve gotten most of this from Thorne’s group at Cal Tech. The astrophysical data pretty well show now that there are quite a few ‘nested universes’ inside our own. They look like infrared emission readings to us. The light we are getting is from the era before the space-time geometry closed off in those areas.”

“This one says ‘DI4KLT O RYE3’—it appears you are right,” Peterson said.

“Um. Well, perhaps. We should do quite a few more before we conclude anything,” Renfrew conceded. “But what’s this about astrophysics? I’ve not paid much attention to that. Those fellows seem to speculate in ideas like stockbrokers.”

Markham smiled and nodded. “Granted, they often take a grain of truth and blow it up into a kind of intellectual puffed rice … but this time they may have a point. Charles Wickham sent me some calculations that look convincing. The reason it ties in with your work, John, is that tachyons are the only thing that can even theoretically escape from a closed space-time geometry.”

“Why’s that?” Peterson said.

“Well, they violate the tenets of the old relativity theory, Einstein’s. That’s a clue in itself. But let’s not go into that. The only point I want to make is that we are getting tachyon noise. It’s unlikely that natural effects will give much tachyon noise—Christ, we’re measuring a hundred times the expected value. I think we’re getting the signals emitted by other civilizations, signals that have escaped from the nested universes inside our own.”

“Well, I suppose that makes sense,” Peterson said. “Other societies might try to use tachyons too. After all—and I still don’t understand why faster-than-light particles can let you communicate back in time-”

“It’s simple,” Renfrew interjected, “comes right out of special relativity. The-”

“We’ll skip it,” Peterson said firmly. “Aliens sending tachyon signals makes sense, though I can’t see that it’s any use to us.”

“Here’s another,” Renfrew said, handing a sheet to Peterson. “Decode it.”

Peterson wrote for a moment and then read out, “‘CE RN 4 KJ QOEC.’ “

“At first I thought it might be something about CERN, the European nuclear agency,” Markham said, “but the rest is just random.”

Renfrew compressed his lips. There was a long silence. Between the magnet coils, the liquid nitrogen bath that immersed the nuclear sample gave off a pale fog. There came an occasional snap as ice formed on its jacket.

Abruptly Renfrew stood up. “Not much bloody chance of CERN being in the picture, is there?” He turned to Peterson. “Our brilliant crisis managers shut it down three years ago.”

Peterson studied him coldly. “The fact remains, Dr. Renfrew, that you have failed to live up to your promises. You cannot contact the past.”

Markham: “But look, all we have is an idea about why it doesn’t work. We have to see if this is galactic-scale background. We can check again, see if there is some angular dependence to the incoming noise. It might be avoidable someway.”

Peterson pointed at Renfrew. “You yourself said you couldn’t improve sensitivity much more.”

“I can’t, but-”

“The Emergency Council hasn’t got funds or time for pursuing your hobbies. There’s no point in studying theoretical questions like this tachyon business if we’re all heading slam-bang for the rapids ahead,” Peterson said.

Renfrew had begun pacing again, but he suddenly turned on Peterson and said savagely, “Yes, no use at all, is it? Research is nothing to you buggering power-mad bastards. Climbing all over each other to direct the latest disaster.”

Markham raised his hand and began, “Now, John—”

“Sure enough, we’re headed for the rapids, but if so, what’s the point of everybody trying to pilot the boat, eh? That doesn’t stop you council sons-of-bitches from—”

Peterson sprang to his feet. “From trying to stop runaway technology, yes!”

“That’s all your type thinks about, isn’t it? Bad technology got you into this, so you’re going to get out using solely your wits, is it? Only the Americans can get us out of this bloody mare’s nest now. Only they’ve kept up any kind of respectable science and engineering–-”

The cold seeps into his bones. José Basquan sits on the doorstep of his house and watches the cobblestoned streets. He has been waiting for two days. They have all been waiting, the entire village, for the promised truckload of food from the government regional storehouse. The truck is late. Some say it will not come.

The children in the streets do not play anymore. They stare dully ahead, unable to focus properly. Few people pass by his house. José watches a woman shuffle by, her belly distended. She is carrying a basket, but there is nothing in it. He has heard the tales of dysentery, the word of the radio about cholera. His fingers toy with the cut on his wrist. It has not closed completely, though it is three days old. José knows it will not heal unless he gets food. He should get up and search for something, but the villagers have already scavenged the countryside around. There is no place left to go. He sits and watches the street and waits for the truck.

(AP) United Airlines Flight 347, London to Washington, D.C., encountered turbulence on its approach to Dulles Airport and crashed in the early hours of the morning. The plane went down in a wooded area and burned upon impact. Witnesses said the plane appeared to explode as it struck the trees. Early reports mention no survivors. This latest in a series of airline disasters has …

Peterson awakes slowly. There is a murmur of movement around him, but he is lethargic, his limbs slack. He studies the latticework of glass and metal standing beside his bed for a long moment and then decides he must sit up and continue writing the telegram. He struggles up and finds his pen. He begins to write, but the noise in the ward is distracting. Patients lie on temporary pallets, some of them moaning and others staring unmoving at the ceiling. Peterson concludes that the food poisoning must be more widespread than he thought. The nurses move quickly through the ward, stepping primly over the patients in the aisles, and ignore the chorus of pleadings that come from all sides.

Peterson shuts the scene out of his mind. He continues writing.

. . . though I sent my report several days ago, I expected at that time that it would be considerably reinforced at the National Science Foundation by the in-person appearance of Dr. Markham. Only yesterday did I learn that he died when his return flight to Washington went down. Dr. Markham told me before he left that he thought the rash of airline crashes was not pure accident, that defective manufacturing in the airplanes themselves was responsible, and I fear that had I not urged him to go in person, he would not have flown at all. It was only because of Dr. Markham that I realized the potential significance of the Cavendish tachyon experiments. I have some personal difficulties with Dr. Renfrew, but I was persuaded by Dr. Markham to overlook these in the light of the gathering crisis.

I will not describe to you the chaos and near starvation that prevail all around me today. I imagine similar scenes must be going on in many other of the Western nations. I hesitate to think what the rest of the world is like.

I have telephoned my office to send you the copies of Dr. Markham’s notes that I retained. As you study them, you will undoubtedly conclude that the entire matter of communicating with the 1950’s or 1960’s, which gives us enough lead time to measurably affect the present day, is technically very difficult. But if only a small bit of information can get through, we must make the effort.

The technical argument speaks for itself. I am unqualified to add anything further about that. But there is something about the Renfrew experiment that has only today occurred to me, and I feel I should bring it up.

We received a few scattered bits of signals that momentarily peaked above the tachyon noise level. It seems to me that the existence of these signals is in itself of momentous importance. They are evidence that someone in the future still speaks English and can send tachyon signals. We have no way of knowing how far in the future that time might be. A pessimist might say that the fact that people in the future want to communicate with us is in itself a bad sign. What disasters lie ahead, that others would reach back into the past and try to alter events?

I take the other view. That men can still send tachyon signals from the future is a sign that there are solutions to these crises. Our ecosystems may not be fatally unstable. Perhaps something can be done.

I urge immediate action on my report of …

Rain spattering in his face awakens him. The cold numbs his legs, but he is too weak to stand. There is no one in the street now, only a huddled form lying in a doorway down the hill. The form has not moved for a day now. José rests his head in his hands, rocking from side to side. He knows the truck is going to come. If he can sit here in the cold stone doorway long enough, the truck will come.

A brown organic bloom begins to spread off the coast of Spain. Fishermen report it, but at first their descriptions are not understood by local officials, and word does not reach the oceanographic community until the bloom is several hundred kilometers in diameter. A stench begins to rise from the sea. Fish are dying in unparalleled numbers; the bloom becomes redder as it spreads. Similarities to the South American bloom multiply. Biologists soon agree that the phenomena are related: Manodrin, a chlorinated hydrocarbon used in insecticides, has opened a new life niche among the microscopic algae. A new variety of diatom has evolved; it uses an enzyme that breaks down Manodrin. The diatom silica also excretes a breakdown product that interrupts transmission of nerve impulses in animals. Dendritic connections fail. In Lisbon birds fall from the sky and die within minutes. The beaches are dark with rotting sea life. The bloom spreads.

John Renfrew works late, alone, though he is weak from dysentery. Most of his technicians have not appeared for work since the breakdown of the food-supply network. It is rumored that many people are fleeing to the countryside. Every sound Renfrew makes echoes hollowly in the Cavendish. He is the only man left in the building. The heat was long ago turned off. Electrical power is low but still functioning. The campus itself seems nearly entirely abandoned; for the last few days he has seen only a few figures in the distance. The trains have stopped. He has not heard the distant rumble of an airplane for many days.

The tachyon noise level remains constant. Occasionally he can resolve a few brief snatches of coded signals, but never as much as a complete sentence. Most of the messages are clearly not Morse. Some are complex wave forms, others almost pure sine waves.

Nothing Renfrew can do reduces the noise level. He cannibalizes electronics gear from other untended experiments in the Cavendish, but there is little improvement. The dysentery becomes worse. He feels his brow and realizes he has a fever. He hears strange, distant sounds like voices, but when he goes to investigate, there is no one else in the building. There is only the gritty scraping of his own shoes on the stone floor.

He drinks great quantities of water, but nothing stops the dysentery. His throat burns. As he works, the laboratory shifts in and out of focus, as though under water.

He tries to think calmly and cleanly about what Markham said in the train station, about Kerr black holes and the riddle of cosmology. Even Einstein’s theory carried acausal loops in it, Markham said, matter swallowed into the net of space-time and spitting out elsewhere in the differential geometry, elsewhen. Elsewhen. And now tachyons and worlds sliding into other worlds, G times n, tensor geometries folding inward, blindly, following the squiggles and jots of Riemann and Littenberg.

There is an ache behind his eyes. Renfrew shivers as the cold seeps into him. He reads the latest fragment, “ENZYME INHIBITED B.” That is all.

He scans the other bits of signal, hoping for something that makes sense. They all mean something to someone, but who? Where? When? His apparatus opens up communication with all the rest of the universe, instantly. Men could talk to great cultures that span the stars. A telegram from Andromeda would take no longer than one from London. Even other, enclosed universes are accessible. There may be macrouniverses, larger than our own, all sending tachyon messages that leak out of the space-time curvature and sleet through this laboratory, through Renfrew, through everything.

He shakes his head. Incredible. Unless there is some unsuspected natural source of tachyons, the random yellow jitter on his oscilloscope is a wealth of information. But all the form and structure is eroded into noise by overlapping too many messages. Because everyone is talking at once, no one can hear.

But no, Renfrew thinks to himself, rocking back and forth to keep warm. No, they aren’t all talking at once. All times are represented, all places, each split nanosecond, all things smeared together in a vast ocean of noise.

The universes are all connected, he sees, as behind him the pumps cough, the electronics gear gives an occasional ping. Tachyons of 10-13 centimeters size flash across whole universes, 10^28 centimeters of cooling matter, in less time than Renfrew’s eye takes to absorb a photon of the pale, watery light. The tachyons zip by, carrying word of alien thoughts. All size scales, all distances, are wound in upon each other. Singularities suck up the stuff of creation, event horizons ripple, worlds coil into worlds.

Renfrew shakes himself. Christ, the fever. It claws at him, runs glowing smoke fingers through his mind.

Again he tries his equipment. The oscilloscope gives a complex wave, but the decoding makes no sense. Perhaps there is no message, never was. Causality weighs its leadened hand on events. But where were cause and effect in such an infinite matrix of worlds? Where the past, which the future? No beginning or end, only an endless series of nested universes.

He smiles to himself with flinty irony. Attempting to sidestep causality, he is caught again in its snare. The grandfather paradox remains; an infinite series of grandfathers will live out their lives safe from Renfrew. The noise wins, the noise prevents his tinkering.

The only thing left was to forget the past, let it lie in musty pages, on gravestones. Renfrew sees he must turn to the future. There is someone up there, in the times ahead, still sending.

ENZYME INHIBITED B. Someone is calling.

Hello, 7:11 A.M., 1995. Hello, ENZYME INHIBITED B.

Whispers flit across the tachyon spectrum, embedding soft words of tomorrow in the cesium. Someone is there. Someone brings hope. The infinite goddamn universe has not beaten him yet.

The room is cold; Renfrew huddles by his instruments. He is trying a modification of the signal correlator when suddenly the lights flicker and wink out. All power is gone. Utter blackness rushes in.

Renfrew takes a long time to feel his way out of the basement laboratory and into sunlight. It is a bleak, gray morning, but he does not notice this; it is enough to see light at all. As he stands outside the Cavendish, he can hear no sound whatever from the entire town of Cambridge. The breeze carries a sour tang.

He feels a curious heady lightness. He does not know what lies ahead. Perhaps Peterson has gotten through to the Americans. If there is no causality, then nothing is known, the past and future are equal riddles. Renfrew takes a few hesitant steps across a geometrically flattened green and feels a surge of something he cannot name. He moves more firmly. With resolution, puffing slightly, he sets out to walk into the countryside.

Nested universes collapse inward on nested universes, onionskin within onionskin. They hum in the infrared. Tachyons sputter from their cores.

The galaxy is a swarm of colored dots, turning with majestic slowness in the great night.

The bloom laps at the Dover coast. Surf foams pink on the beaches.

Ian Peterson’s cable reaches Washington.

Gregory Benford writes:

Theorem: Time travel is impossible.

Proof: If a time machine exists, it can be used to make paradoxes. Cause and effect will be reversed. This means logical contradictions can exist in the operating of the universe. This is unacceptable.

So goes the logic, and quite neat it is. I am a theoretical physicist, and the argument looks compelling to me. In fact, I wrote a paper on the subject in 1970, with David Book and William Newcomb.

In the late 1960’s, much dust was being raised about a hypothetical particle, the tachyon, which could travel faster than light. Now, faster-than-light travel (FTL) is a mainstay of science fiction. One might think that a scientist who was also a writer of fiction would leap at the possibility of FTL. After all, tachyons seemed to promise a reasonable explanation for those galaxy-spanning ships so beloved in SF. But I didn’t cheer the advent of tachyons; instead, I attacked it.

The reason lies in the theorem announced above. Einstein’s Special Theory of Relativity can be used to show that if FTL particles exist, they can be employed in a transmitter; and the signals emitted by this tachyonic telephone could be sent back in time. So FTL implies time travel, paradoxes, and all the elaborate games that SF writers have played with the idea since H. G. Wells.

David Book, William Newcomb, and I worked out a simple proof based on Einstein’s theory, especially designed to overcome an argument that certain particle theorists had constructed. These theorists wanted to avoid the time-paradox problem, and thought they had. Book, Newcomb, and I showed that if tachyons could be detected in an experiment at all, they implied communication through time. And if somehow tachyons couldn’t be detected, but existed anyway … what was the use of doing experiments to find them?

Since those days, tachyons have fared rather badly. The experiments designed to detect them failed to find anything, and despite a spate of tachyon theories, no one has gotten around the time-paradox problem.

But still… sometimes I wonder. Suppose time paradoxes are not totally disallowed in our universe, but are merely highly unusual? In a certain sense, paradoxical events can occur within the boundaries of the General Theory of Relativity. In the last few years we’ve gotten quite accustomed to black holes and white holes, places where matter may “tunnel through” space itself, to reappear in distant galaxies.

I don’t think the tachyon ferment is totally resolved, and indeed it may never be. Its very difficult to show that something doesn’t exist.

All these thoughts led me to think about the time-travel stories so beloved in SF, and whether they seemed probable. Even if time travel was possible, would it really come about that way? So I tried to deal with the problem in a fashion that felt right to me—that seemed dramatically interesting and had some reasonable scientific underpinning. (Not correct, just reasonable!) All time-travel stories are dreams, really, and this one is no different. If the real thing comes along someday, it will undoubtedly be unlike anything I’ve guessed … I hope.

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