cliff of methane ice, feebly illuminated by a distant red dwarf sun, while far below waves of an ammonia ocean beat relentlessly against the shore—incidentally generating a white noise indistinguishable from that of the surf at Cozumel.
The opposite was possible as well: the fast talkers, manic little creatures perhaps, moving with quick and jerky motions, who transmitted a complete radio message—the equivalent of hundreds of pages of English test—in a nanosecond. Of course, if you had a very narrow bandpass to your receiver, so you were listening only to a tiny range of frequencies, you were forced to accept the long time-constant. You would never be able to detect a rapid modulation. It was a simple consequence of the Fourier Integral Theorem, and closely related to the Heisenberg Uncertainty Principle. So, for example, if you had a bandpass of a kilohertz, you couldn't make out a signal that was modulated at fasted than a millisecond. It would be kind of a sonic blur. The Argus bandpasses were narrower than a hertz, so to be detected the transmitters must be modulating very slowly, slower than one bit of information a second. Still slower modulations—longer than hours, say—could be detected easily, provided you were willing to point a telescope at the source for that length of time, provided you were exceptionally patient. There were so many pieces of the sky to look at, so many hundreds of billions of stars to search out. You couldn't spend all your time on only a few of them.
She was troubled that in their haste to do a full sky survey in less than a human lifetime, to listen to all of the sky at a billion frequencies, they had abandoned both the frantic talkers and the laconic plodders.
But surely, she thought, they would know better than we what modulation frequencies were acceptable. They would have had previous experience with interstellar communication and newly emerging civilizations. If there was a broad range of likely pulse rates that the receiving civilization would adopt, the transmitting civilization would utilize such a range. Modulate at microseconds, modulate at hours. What would it cost them? They would, almost all of them, have superior engineering and enormous power resources by Earth standards. If they wanted to communicate with us, they would make it easy for us. They would send signals at many different frequencies. They would use many different modulation timescales.
They would know how backward we are, and would have pity.
So why had we received no signal? Could Dave possibly be right? No extraterrestrial civilizations anywhere? All those billions of worlds going to waste, lifeless, barren? Intelligent beings growing up only in this obscure corner of an incomprehensibly vast universe? No matter how valiantly she tried, Ellie couldn't make herself take such a possibility seriously. It dovetailed perfectly with human fears and pretentions, with unproved doctrines about life-after-death, with such pseudosciences as astrology. It was the modern incarnation of the geocentric solipsism, the conceit that had captured our ancestors, the notion that we were the center of the universe. Drumlin's argument was suspect on these grounds alone. We wanted to believe it too badly.
Wait a minute, she thought. We haven't even examined the northern skies once with the Argus system. In another seven or eight years, if we've still heard nothing, that'll be the time to start worrying.
This is the first moment in human history when it's possible to search for the inhabitants of other worlds. If we fail, we've calibrated something of the rarity and preciousness of life on our planet—a fact, if it is one, very much worth knowing. And if we succeed, we'll have changed the history of our species, broken the shackles of provincialism. With the stakes this high, you have to be willing to take some small professional risks, she told herself. She pulled off the side of the road and did a shallow racing turn, changed gears twice, and accelerated back toward the Argus facility. The rabbits, still lining the roadside, but now pinked by dawn, craned their necks to follow her departure.
CHAPTER 4
Prime Numbers
Are there no Moravians in the Moon, that not a missionary has yet visited this poor pagan planet of ours to civilize civilization and Christianize Christendom?
Silence alone is great; all else is weakness.
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
