Contact - Carl Sagan [24]
She realized with a start that she had arrived at the Rockefeller Center station. As she quickly stepped out through an accumulation of daily newspapers abandoned on the floor of the subway car, a headline of the News-Post had caught her eye: GUERRILLAS CAPTURE JOBURG RADIO. If we like them, they're freedom fighters, she thought. If we don't like them, they're terrorists. In the unlikely case we can't make up our minks, they're temporarily only guerrillas. On an adjacent scrap of newspaper was a large photo of a florid, confident man with the headline: HOW THE WORLD WILL END. EXCERPTS FROM THE REV. BILLY JO RANKIN'S NEW BOOK. EXCLUSIVELY THIS WEEK IN THE NEWS-POST. She had taken the headlines in at a glance and tried promptly to forget them. Moving through the bustling crowds to the meeting hotel, she hoped she was in time to hear Fujita's paper on homomorphic radio telescope design.
* * *
Superposed on the whine of the tires was a periodic thump at the joins of swathes of pavement, which had been resurfaced by different New Mexico road crews in different epochs. What if an interstellar message were being received by Project Argus, but very slowly-one bit of information every hour, say, or every week, or every decade? What if there were very old, very patient murmurs of some transmitting civilization, which had no way of knowing that we get tired of pattern recognition after seconds or minutes? Suppose they lived for tens of thousands of years. And taaaaalked verrrry slooooowwwwly. Argus would never know. Could such long-lived creatures exist? Would there have been enough time in the history of the universe for creatures who reproduced very slowly to evolve to high intelligence? Wouldn't the statistical breakdown of chemical bonds, the deterioration of their bodies according to the Second Law of Thermodynamics, force them to reproduce about as often as human beings do? And to have lifespans like ours? Or might they reside on some old and frigid world, where even molecular collisions occur in extreme slow motion, maybe only a frame a day. She idly imagined a radio transmitter of recognizable and familiar design sitting on a 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 faster 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