Contact

CHAPTER 4 Prime Numbers

The cold black vacuum had been left behind. The pulses were now approaching an ordinary yellow dwarf star and had already begun spilling over the retinue of worlds in this obscure system.

They had fluttered by planets of hydrogen gas, penetrated into moons of ice, breached the organic clouds of a frigid world on which the precursors of life were stirring, and swept across a planet a billion years past its prime. Now the pulses were washing against a warm world, blue and whit, spinning against the backdrop of the stars.

There was life on this world, extravagant in its numbers and variety. There were jumping spiders at the chilly tops of the highest mountains and sulfur-eating worms in hot vents gushing up through ridges on the ocean floors. There were beings that could live only in concentrated sulfuric acid, and beings that were destroyed by concentrated sulfuric acid; organisms that were poisoned by oxygen, and organisms that could survive only in oxygen, that actually breathed the stuff.

A particular lifeform, with a modicum of intelligence, had recently spread across the planet. They had outposts on the ocean floors and in low-altitude orbit. They had swarmed to every nook and cranny of their small world. The boundary that marked the transition of night into day was sweeping westward, and following its motion millions of these beings ritually performed their morning ablutions. They donned great-coats and dhotis; drank brews of coffee, tea, or dandelion; drove bicycles, automobiles, or oxen; and briefly contemplated school assignments, prospects for spring planting, and the fate of the world.

The first pulses in the train of radio waves insinuated themselves through the atmosphere and clouds, struck the landscape and were partially reflected back to space. As the Earth turned beneath them, successive pulses arrived, engulfing not just this one planet but the entire system.

Very little of the energy was intercepted by any of the worlds. Most of it passed effortlessly onward—as the yellow star and its attendant worlds plunged, in an altogether different direction, into the inky dark.

Wearing a Dacron jacket displaying the word “Marauders” above a stylized felt volleyball, the duty officer, beginning the night shift, approached the control building. A klatch of radio astronomers was just leaving for dinner.

“How long have you guys been looking for little green men? It's more than five years, isn't it now, Willie?”

They chided him good-naturedly, but he could detect an edge to their banter.

“Give us a break, Willie,” another of them said. “The quasar luminosity program is going great guns. But it's gonna take forever if we only have two percent of the telescope time.”

“Sure, Jack, sure.”

“Willie, we're looking back toward the origin of the universe. There's a big stake in our program, too—and we know there's a universe out there; you don't know there's a single little green man.”

“Take it up with Dr. Arroway. I'm sure she'll be glad to hear your opinion, “he replied a little sourly.

The duty officer entered the control area. He made a quick survey of dozens of television screens monitoring the progress of the radio search. They had just finished examining the constellation Hercules.

They had peered into the heart of a great swarm of galaxies far beyond the Milky Way, the Hercules Cluster—a hundred million light-years away; they had tuned in on M-13, a swarm of 300,000 stars, give or take a few, gravitationally bound together, moving in orbit around the Milky Way Galaxy 26,000 light-years away; they had examined Ras Algethi, a double system, and Zeta and Lambda Herculis—some stars different from the Sun, some similar to it, all nearby. Most of the stars you can see with the naked eye are less that a few hundred light-years away. They had carefully monitored hundreds of little sectors of the sky within the constellation Hercules at a billion separate frequencies, and they had heard nothing. In previous years they had searched the constellations immediately west of Hercules—Serpens, Corona Borealis, Bootes, Canes Venatici… and there also they had heard nothing.

A few of the telescopes, the duty officer could see, were devoted to picking up some missed data in Hercules. The remainder were aiming, boresighted, at an adjacent patch of sky, the next constellation east of Hercules. To people in the eastern Mediterranean a few thousand years ago, it had resembled a stringed musical instrument and was associated with the Greek culture hero Orpheus. It was a constellation named Lyra, the Lyre.

The computers turned the telescopes to follow the stars in Lyra from starrise to starset, accumulated the radio photons, monitored the health of the telescopes, and processed the data in a format convenient for their human operators. Even one duty officer candies, a coffee machine, a sentence in elvish runes out of Tolkien by the Artificial Intelligence Laboratory at Stanford, and a bumper sticker reading BLACK HOLES ARE OUT OF SIGHT, Willie approached the command console. He nodded pleasantly to the afternoon duty officer, now collecting his notes and preparing to leave for dinner. Because the day's data were conveniently summarized in amber on the master display, there was no need for Willie to inquire about the progress of the preceding hours.

“As you can see, nothing much. There was a pointing glitch—at least that's what it looked like—in forty-nine,” he said, waving vaguely toward the window. “The quasar bunch freed up the one-tens and onetwenties about an hour ago. They seem to be getting very good data.”

“Yeah, I heard. They don't understand…”

His voice trailed off as an alarm light flashed decorously on the console in front of them. On a display marked “Intensity vs. Frequency” a sharp vertical spike was rising.

“Hey, look, it's a monochromatic signal.”

Another display, labeled “Intensity vs. Time,” showed a set of pulses moving left to right and then off the screen.

“Those are numbers,” Willie said faintly. “Somebody's broadcasting numbers.”

“It's probably some Air Force interference. I saw an AWACS, probably from Kirtland, about sixteen hundred hours. Maybe they're spoofing us for fun.”

There had been solemn agreements to safeguard at least some radio frequencies for astronomy. But precisely because these frequencies represented a clear channel, the military found them occasionally irresistible. If global war ever came, perhaps the radio astronomers would be the first to know, their windows to the cosmos overflowing with orders to battle-management and damage-assessment satellites in geosynchronous orbit, and with the transmission of coded launch commands to distant strategic outposts.

Even with no military traffic, in listening to a billion frequencies at once the astronomers had to expect some disruption. Lightning, automobile ignitions, direct broadcast satellites were all sources of radio interference.

But the computers had their number, knew their characteristics and systematically ignored them. To signals that were more ambiguous the computer would listen with greater care and make sure they matched no inventory of data it was programmed to understand. Every now and then an electronic intelligence aircraft on a training mission—sometimes with a radar dish coyly disguised as a flying saucer camped on its haunches—would fly by, and Argus would suddenly detect unmistakable signatures of intelligent life. But it would always turn out to be life of a peculiar and melancholy sort, intelligent to a degree, extraterrestrial just barely. A few moths before, an F-29E with state-of-the-art electronic countermeasures passed overhead at 80,000 feet and sounded the alarms on all 131 telescopes. To the unmilitary eyes of the astronomers, the radio signature had been complex enough to be a plausible first message from an extraterrestrial civilization.

But they found the westernmost radio telescope had received the signal a full minute before the easternmost, and it soon become clear that it was an object streaking through the thin envelop of air surrounding the Earth rather than a broadcast from some unimaginably different civilization in the depths of space. Almost certainly this one was the same thing.

The fingers of her right hand were inserted into five evenly spaced receptacles in a low box on her desk.

Since the invention of this device, she was able to save half an hour a week. But there hadn't really been a great deal to do with that extra half hour.

“And I was telling Mrs. Yarborough all about it. She's the one in the next bed, now that Mrs.

Wertheimer passed on. I don't mean to toot my own horn, but I take a lot of credit for what you've done.”

“Yes, Mother.”

She examined the gloss on her fingernails and decided that they needed another minute, maybe a minute-thirty.

“I was thinking about that time in fourth grade—remember? When it was pouring and you didn't want to go to school? You wanted me to write a note the next day saying you'd been out because you were sick. And I wouldn't do it. I said, “Ellie, apart from being beautiful, the most important thing in the world is an education. You can't do much about being beautiful, but you can do something about an education. Go to school. You never know what you might learn today. ” Isn't that right?”

“Yes, Mother.”

“But, I mean, isn't that what I told you then?”

“Yes, I remember, Mom.”

The gloss on her four fingers was perfect, but her thumb still had a dull matte appearance.

“So I got your galoshes and your raincoat—it was one of those yellow slickers, you looked cute as a button in it—and scooted you off to school. And that's the day you couldn't answer a question in Mr.

Weisbrod's mathematics class? And you got so furious you marched down to the college library and read up on it till you knew more about it than Mr. Weisbrod. He was impressed. He told me.”

“He told you? I didn't know that. When did you talk to Mr. Weisbrod?”

“It was a parent-teacher meeting. He said to me, “That girl of yours, she's a spunky one. ” Or words to that effect. “She got so mad at me, she became a real expert on it. ” “Expert. ” That's what he said. I know I told you about it.”

Her feet were propped up on a desk drawer as she reclined in the swivel chair; she was stabilized only by her fingers in the varnish machine. She felt the buzzer almost before she heard it, and abruptly sat up.

“Mom, I gotta go.”

“I'm sure I've told you this story before. You just never pay attention to what I'm saying. Mr.

Weisbrod, he was a nice man. You never could see his good side.”

“Mom, really, I've gotta go. We've caught some kind of bogey.”

“Bogey?”

“You know, Mom, something that might be a signal. We've talked about it.”

“There we are, both of us thinking the other one isn't listening. Like mother, like daughter.”

“Bye, Mom.”

“I'll let you go if you promise to call me right after.”

“Okay, Mom. I promise.”

Through the whole conversation, her mother's need and loneliness had elicited in Ellie a wish to end the conversation, to run away. She hated herself for that.

Briskly she entered the control area and approached the main console.

“Evening, Willie, Steve. Let's see the data. Good. Now where did you tuck away the amplitude plot? Good. Do you have the interferometric position? Okay. Now let's see if there's any nearby star in that field of view. Oh my, we're looking at Vega. That's a pretty near neighbor.”

Her fingers were punching away at a keyboard as she talked.

“Look, it's only twenty-six light-years away. It's been observed before, always with negative results. I looked at it myself in my first Arecibo survey. What's the absolute intensity? Holy Toledo. That's hundreds of janskys. You could practically pick that up on your FM radio.

“Okay. So we have a bogey very near to Vega in the plane of the sky It's at a frequency around 9. 2 gigahertz, not very monochromatic: The bandwidth is a few hundred hertz. It's linearly polarized and it's transmitting a set of moving pulses restricted to two different amplitudes.”

In response to her typed commands the screen now displayed the disposition of all the radio telescopes.

“It's being received by 116 individual telescopes. Clearly it's not a malfunction in one or two of them. Okay, now we should have plenty of time baseline. Is it moving with the stars? Or could it be some ELINT satellite or aircraft?”

“I can confirm sidereal motion, Dr. Arroway.”

“Okay, that's pretty convincing. It's not down here on Earth, and it probably isn't from an artificial satellite in a Molniya orbit, although we should check that. When you get a chance, Willie, call up NORAD and see what they say about the satellite possibility. If we can exclude satellites, that will leave two possibilities: It's a hoax, or somebody has finally gotten around to sending us a message. Steve, do a manual override. Check a few individual radio telescopes—the signal strength is certainly large enough—and see if there's any chance this is a hoax; you know, a practical joke by someone who wishes to teach us the error of our ways.”

“A handful of other scientists and technicians, alerted on their buzzers by the Argus computer, had gathered around the command console. There were half smiles on their faces. None of them was thinking seriously of a message from another world quite yet, but there was a sense of no-school-today, a break in the tedious routine to which they had become accustomed, and perhaps a faint air of expectation.

“If any of you can think of any other explanation besides extraterrestrial intelligence, I want to hear about it,” she said, acknowledging their presence.

“There's no way it could be Vega, Dr. Arroway. The system's only a few hundred million years old. Its planets are still in the process of forming. There isn't time for intelligent life to have developed there.

It has to be some background star. Or galaxy.”

“But then the transmitter power has to be ridiculously large,” responded a member of the quasar group who had returned to see what was happening. “We need to get going right away on a sensitive proper motion study, so we can see if the radio source moves with Vega.”

“Of course, you're right about the proper motion, Jack,” she said. “But there's another possibility.

Maybe they didn't grow up in the Vega system. Maybe they're just visiting.”

“That's no good either. The system is full of debris. It's a failed solar system or solar system still in its early stages of development. If they stay very long, their spacecraft'll be clobbered.”

“So they only arrived recently. Or they vaporize incoming meteorites. Or they take evasive action if there's a piece of debris on a collision trajectory. Or they're not in the ring plane but in polar orbit, so they minimize their encounters with the debris. There's a million possibilities. But you're absolutely right; we don't have to guess whether the source is in the Vega system. We can actually find out. How long will that proper motion study take? By the way, Steve, this isn't your shift. At least tell Consuela you're going to be late for dinner.”

Willie, who had been talking on the phone at an adjacent console, was displaying a wan smile.

“Well, I got through to a Major Braintree at NORAD. He swears up and down they have nothing that'll give this signal, especially not at nine gigahertz. 'Course, they tell us that every time we call. Anyway, he says they haven't detected any spacecraft at the right ascension and declination of Vega.”

“What about darks?”

By this time there were many “dark” satellites with low radar cross sections, designed to orbit Earth unannounced and undetected until an hour of need. Then they would serve as backups for launch detection or communications in a nuclear war, in case the first-line military satellites dedicated to these purposes were suddenly missing in action. Occasionally a dark would be detected by one of the major astronomical radar systems. All nations would deny that the object belonged to them, and breathless speculation would erupt that an extraterrestrial spacecraft had been detected in Earth orbit. As the Millennium approached, the UFO cults were thriving again.

“Interferometry now rules out a Molniya-type orbit, Dr. Arroway.”

“Better and better. Now let's take a closer look at those moving pulses. Assuming that this is binary arithmetic, has anybody converted it into base ten? Do we know what the sequence of numbers is?

Okay, here, we can do it in our heads… fifty-nine, sixty-one, sixty-seven… seventy-one… Aren't these all prime numbers?”

A little buzz of excitement circulated through the control room. Ellie's own face momentarily revealed a flutter of something deeply felt, but this was quickly replaced by a sobriety, a fear of being carried away, an apprehension about appearing foolish, unscientific.

“Okay, let's see if I can do another quick summary. I'll do it in the simplest language. Please check if I've missed anything. We have an extremely strong, not very monochromatic signal. Immediately outside the bandpass of this signal there are no other frequencies reporting anything besides noise. The signal is linearly polarized, as if it's being broadcast by a radio telescope. The signal is around nine gigahertz, near the minimum in the galactic radio noise background. It's the right kind of frequency for anyone who wants to be heard over a big distance. We've confirmed sidereal motion of the source, so it's moving as if it's up there among the stars and not from some local transmitter. NORAD tells us that they don't detect any satellites— ours or anybody else's—that match the position of this source. Interferometry excludes a source in Earth orbit anyway.

“Steve has now looked at the data outside the automated mode, and it doesn't seem to be a program that somebody with a warped sense of humor put into the computer. The region of the sky we're looking at includes Vega, which is an A-zero main sequence dwarf star. It's not exactly like the Sun, but it's only twenty-six light-years away, and it has the prototype stellar debris ring. There are no known planets, but there certainly could be planets we don't know anything about around Vega. We're setting up a proper motion study to see if the source is well behind our line of sight to Vega, and we should have an answer in— what? — a few weeks if we're restricted on our own, a few hours if we do some long-baseline interferometry.

“Finally, what's being sent seems to be a long sequence of prime numbers, integers that can't be divided by any other number except themselves and one. No astrophysical process is likely to generate prime numbers. So I'd say—we want to be cautious, of course—but I'd say that by every criterion we can lay our hands on, this looks like the real thing.

“But there's a problem with the idea that this is a message from guys who evolved on some planet around Vega, because they would have had to evolve very fast. The entire lifetime of the star is only about four hundred million years. It's an unlikely place for the nearest civilization. So the proper motion study is very important. But I sure would like to check out that hoax possibility some more.”

“Look,” said one of the quasar survey astronomers who had been hovering in the back. He inclined his jaw to the western horizon where a faint pink aura showed unmistakably where the Sun had set. “Vega is going to set in another couple of hours. It's probably already risen in Australia. Can't we call Sydney and get them looking at the same time that we're still seeing it?”

“Good idea. It's only middle afternoon there. And together we'll have enough baseline for the proper motion study. Give me that summary printout, and I'll telefax it to Australia from my office.”

With deliberate composure, Ellie left the assembled group crowded around the consoles and returned to her office. She closed the door very carefully behind her.

“Holy shit!” she whispered.

“Ian Broderick, please. Yes. This is Eleanor Arroway at Project Argus. It's something of an emergency.

Thanks, I'll hold on…. Hello, Ian? It's probably nothing, but we have a bogey here and wonder if you could just check it out for us. It's around nine gigahertz, with a few hundred hertz bandpass. I'm telefaxing the parameters now…. You have a feed good at nine gigahertz already on the dish? That's a bit of luck…. Yes, Vega is smack in the middle of the field of view. And we're getting what looks like prime number pulses….

Really. Okay, I'll hold on.”

She considered again how backward the world astronomical community still was. A joint computer data-basing system was still not on-line. Its value for asynchronous telenetting alone would…

“Listen, Ian, while the telescope finishes slewing, could you set up to look at an amplitude-time plot? Let's call the low-amplitude pulses dots and the high-amplitude pulses dashes. We're getting… Yes that's just the pattern we've been seeing for the last half hour…. Maybe. Well, it's the best candidate in five years, but I keep remembering how badly the Soviets got fooled with that Big Bird satellite incident around 74. Well, the way I understand it, it was a U. S. radar altimetry survey of the Soviet Union for cruise missile guidance…. Yes, a terrain mapper. And the Soviets were picking it up on omnidirectional antennas. They couldn't tell where in the sky the signal was coming from. Al they knew was they were getting the same sequence of pulses from the sky at about the same time every morning. Their people assured them it wasn't a military transmission, so naturally they thought it was extraterrestrial…. No, we've excluded a satellite transmission already.

“Ian, could we trouble you to follow it for as long as it's in your sky? I'll talk to you about VLBI later. I'm going to see if I can't get other radio observatories, distributed pretty evenly in longitude, to follow it until it reappears back here…. Yes, but I don't know if it's easy to make a direct phone call to China. I'm thinking of sending an IAU telegram…. Fine. Many thanks, Ian.”

Ellie paused in the doorway of the control room—they called it that with conscious irony, because it was the computers, in another room, that by and large did the controlling—to admire the small group of scientists who were talking with great animation, scrutinizing the data being displayed, and engaging in mild badinage on the nature of the signal. These were not stylish people, she thought. They were not conventionally good-looking. But there was something unmistakably attractive about them. They were excellent at what they did and, especially in the discovery process, were utterly absorbed in their work. As she approached, they fell silent and looked at her expectantly. The numerals were now being converted automatically from base 2 to base 10… 881, 883, 887, 907… each one confirmed as a prime number.

“Willie, get me a world map. And please get me Mark Auerbach in Cambridge, Mass. He'll probably be at home. Give him this message for an IAU telegram to all observatories, but especially to all large radio observatories. And see if he'll check our telephone number for the Beijing Radio Observatory.

Then get me the President's Science Adviser.”

“You're going to bypass the National Science Foundation?”

“After Auerbach, get me the President's Science Adviser.

In her mind she thought she could hear one joyous shout amidst a clamor of other voices.

By bicycle, small truck, perambulatory mailman, or telephone, the single paragraph was delivered to astronomical centers all over the world. In a few major radio observatories—in China, India, the Soviet Union, and Holland, for example—the message was delivered by teletype. As it chattered in, it was scanned by a security officer or some passing astronomer, torn off, and with a look of some curiosity carried into an adjacent office. It read:

ANOMALOUS INTERMITTENT RADIO SOURCE AT RIGHT ASCENSION 18h 34M, DECLINATION PLUS 38 DEGREES 41 MINUTES, DISCOVERED BY ARGUS SYSTEMATIC SKY SURVEY. FREQUENCY 9. 24176684 GIGAHERTZ, BANDPASS APPROXIMATELY 430 HERTZ. BIMODAL AMPLITUDES APPROXIMATELY 174 AND 179 JANSKYS. EVIDENCE AMPLITUDES ENCODE SEQUENCE OF PRIME NUMBERS. FULL LONGITUDE COVERAGE URGENTLY NEEDED.

PLEASE CALL COLLECT FOR FURTHER INFORMATION IN COORDINATING OBSERVATIONS.

E. ARROWAY, DIRECTOR, PROJECT ARGUS, SOCORRO, NEW MEXICO, U. S. A.