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.
CHAPTER 5
Decryption Algorithm
Oh, speak again, bright angel…
The visiting scientists' quarters were now all occupied, indeed overcrowded, by selected luminaries of the SETI community. When the official delegations began arriving from Washington, they found no suitable accommodations at the Argus site and had to be billeted at motels in nearby Socorro. Kenneth der Heer, the President's Science Adviser, was the only exception. He had arrived the day after the discovery, in response to an urgent call from Eleanor Arroway. Officials from the National Science Foundation, the National Aeronautics and Space Administration, the Department of Defense, the President's Science Advisory Committee, the National Security Council, and the National Security Agency trickled in during the next few days. There were a few government employees whose precise institutional affiliations remained obscure.
The previous evening, some of them stood at the base of Telescope 101 and had Vega pointed out to them for the first time. Obligingly, its blue-white light flickered prettily.
“I mean, I've seen it before, but I never knew what it was called,” one of them remarked. Vega appeared brighter than the other stars in the sky, but in no other way noteworthy. It was merely one of the few thousand naked-eye stars.
The scientists were running a continuous research seminar on the nature, origin, and possible significance of the radio pulses. The project's public affairs office—larger than in most observatories because of widespread interest in the search for extraterrestrial intelligence—was assigned the task of filling in the lower-ranking officials. Every new arrival required an extensive personal briefing. Ellie, who was obliged to brief the senior officials, supervise the ongoing research, and respond to the entirely proper skeptical scrutiny being offered with some vigor by her colleagues, was exhausted. The luxury of a full night's sleep had eluded her since the discovery.
At first they had tried to keep the finding quiet. After all, they were not absolutely sure it was an extraterrestrial message. A premature or mistaken announcement would be a public relations disaster. But worse than that, it would interfere with the data analysis. If the press descended, the science would surely suffer. Washington as well as Argus was keen to keep the story quiet. But the scientists had told their families, the International Astronomical Union telegram had been sent all over the world, and still rudimentary astronomical data-basing systems in Europe, North America, and Japan were all carrying news of the discovery.
Although there had been a range of contingency plans for the public release of any findings, the actual circumstances had caught them largely unprepared. They drafted as innocuous a statement as they could and released it only when they had to. It caused, of course, a sensation.
They had asked the media's forbearance, but knew there would be only a brief period before the press would descend in force. They had tried to discourage reporters from visiting the site, explaining that there was no real information in the signals they were receiving, just tedious and repetitive prime numbers.
The press was impatient with the absence of hard news. “You can only do so many sidebars on “What is a prime number? ” one reporter explained to Ellie over the telephone.
Television camera crews in fixed-wing air taxis and chartered helicopters began making low passes over the facility, sometimes generating strong radio interference easily detected by the telescopes. Some reporters stalked the officials from Washington when they returned to their motels at night. A few of the more enterprising had attempted to enter the facility unobserved—by beach buggy, motorcycle, and in one case on horseback. She had been forced to inquire about bulk rates on cyclone fencing.
Immediately after der Heer arrived, he had received an early version of what was by now Ellie's standard briefing: the surprising intensity of the signal, its location in very much the same part of the sky as the star Vega, the nature of the pulses.
“I may be the President's Science Adviser,” he had said, “but I'm only a biologist. So please explain it to me slowly. I understand that if the radio source is twenty-six light-years away, then the message had to be sent twenty-six years ago. In the 1960s, some funny-looking people with pointy ears thought we'd want to know that they like prime numbers. But prime numbers aren't difficult. It's not like they're boasting. It's more like they're sending us remedial arithmetic. Maybe we should be insulted.”
“No, look at it this way,” she said, smiling. “This is a beacon. It's an announcement signal. It's designed to attract our attention. We get strange patterns of pulses from quasars and pulsars and radio galaxies and God- knows-what. But prime numbers are very specific, very artificial. No even number is prime, for example. It's hard to imagine some radiating plasma or exploding galaxy sending out a regular set of mathematical signals like this. The prime numbers are to attract our attention.”
“But what for?” he had asked, genuinely baffled.
“I don't know. But in this business you have to be very patient. Maybe in a while the prime numbers will turn
