"Why have we never detected radio signals from the advanced societies which must sure be out there in space? Karl had many theories, but in the end he settled on the simplest. It's not original, and I'm sure you've heard it before."
"We ourselves broadcast radio signals for only about a hundred years, roughly spanning the twentieth century. By the end of that time, we'd switched to cable and optical and satellite systems, concentration all their power where it was needed, and not spilling most of it wastefully to the stars. This may well be true of all civilizations with a technology comparable to ours. They only pollute the universe with
indiscriminate radio noise for a century or two — a very brief fraction of their entire history."
"So even if there are millions of advanced societies in this Galaxy, there may be barely a handful just where we were three hundred years ago — still splashing out radio waves in all directions. And the laws of probability make it most unlikely that any of these early electronic cultures will be within detection range; the nearest may be thousands of light-years away."
"But before we abandon the search, we should explore all the possibilities — and there's one that had never been investigated, because until now there was little we could do about it. For three centuries, we've been studying radio waves in the centimeter and meter bands. But we have almost completely
ignored the very long waves — tens and hundreds of kilometers in length."
"Now of course there were several good reasons for this neglect. In the first case, it's impossible to study these waves on Earth — they don't get through the ionosphere, and so never reach the surface. You have to go into space to observe them."
"But for the very longest waves, it's no good merely going up to orbit, or to the other side of the Moon, where CYCLOPS was built. You have to go halfway out to the limits of the Solar System."
"For the Sun has an ionosphere, just like the Earth's — except that it's billions of times larger. It absorbs all waves more than ten or twenty kilometers in length. If we want to detect these, we have to go out to Saturn."
"Such waves have been observed, but only on a few occasions. About forty years ago, a Solar Survey mission picked them up; it wasn't looking for radio waves at all, but was measuring magnetic fields
between Jupiter and Saturn. It observed pulsations that must have been due to a radio burst at around
fifteen kilohertz, corresponding to a wavelength of twenty kilometers. At first it was thought that they came from Jupiter, which is still full of electromagnetic surprises, but that source was eventually ruled out, and the origin is still a mystery."
"There have been half a dozen observations since then, all of them by instruments that were
measuring something else. No one's looked for these waves directly; you'll see why in a moment."
"The most impressive example was detected ten years ago, in ‘66, by a team doing a survey of
Iapetus. They obtained quite a long recording, rather sharply tuned at nine kilohertz —that's thirty-three kilometers wavelength. I thought you might like to hear it..."
Duncan consulted a slip of paper and carefully tapped out a long sequence of numbers and letters on
the Minisec. Into the anechoic stillness of that strange room, Karl spoke from the grave, in a brisk,
businesslike voice.
"This is the complete recording, demodulated and speeded up sixty-four times, so that two hours is compressed into two minutes. Starting now."
Across twenty years of time, a childhood memory suddenly came back to Duncan. He recalled
listening out into the Titanian night for that scream from the edge of space, wondering if it was indeed the voice of some monstrous beast, yet not really believing his own conjecture, even before Karl had
demolished it. Now that fantasy returned, more powerful than ever.
This sound — or rather, infrasound, for the original modulation was far below the range of human
hearing — was like the slow beating of a giant heart, or the tolling of a bell so huge that a cathedral could be placed inside it, rather than the reverse. Or perhaps the waves of the sea, rolling forever in unvarying rhythm against some desolate shore, on a world so old that though Time still existed, Change was dead...
The recording, as it always did, set Duncan's skin crawling and sent shivers down his spine. And it
brought back yet another memory — the image of that mightiest of all Earth's creatures, leaping in power and glory into the sky above Golden Reef. Could there be beasts among the stars, to whom men would be
as insignificant as the lice upon the whale?
It was a relief when the playback came to an end, and Karl's surprisingly unemotional voice
commented: "Note the remarkably constant frequency — the original period is 132 seconds, not varying by more than point one percent. This implies a fairly high Q — say..."