Contact - Carl Sagan [37]
"Here, you see? This is the repeating message. We're now into the first repetition. Every bit of information, every dot and dash-if you want to think of them that way-is identical to what it was in the last block of data. Now we analyze the total number of buts. It's a number in the tens of billions. Okay, bingo! It's the product of three prime numbers."
Although Drumlin and Valerian were both beaming, it seemed to Ellie they were experiencing quite different emotions.
"So what? What do some more prime numbers mean?" a visitor from Washington asked.
"It means-maybe-that we're being sent a picture. You see, this message is made of a large number of bits of information. Suppose that large number is the product of three smaller numbers; it's a number times a number times a number. So there's three dimensions to the message. I'd guess either it's a single static three-dimensional picture like a stationary hologram, or it's a two-dimensional picture that changes with time-a movie. Let's assume it's a movie. If it's a hologram, it'll take us longer to display anyway. We've got an ideal decryption algorithm for this one."
On the screen, they made out an indistinct moving pattern composed of perfect whites and perfect blacks.
"Willie, put in some gray interpolation program, would you? Anything reasonable. And try rotating it about ninety degrees counterclockwise."
"Dr. Arroway, there seems to be an auxiliary sideband channel. Maybe it's the audio to go with the movie."
"Punch it up."
The only other practical application of prime numbers she could think of was public-key cryptography, now widely used in commercial and national security contexts. One application was to make a message clear to dummies; the other was to keep a message hidden from the tolerably intelligent.
Ellie scanned the faces before her. Kitz looked uncomfortable. Perhaps he was anticipation some alien invader or, worse, the design drawings of a weapon too secret for her staff to be trusted with. Willie looked very earnest and was swallowing over and over again. A picture is different from mere numbers. The possibility of a visual message was clearly rousing unexamined fears and fantasies in the hearts of many of the onlookers. Der Heer had a wonderful expression on his face; for the moment he seemed much less the official, the bureaucrat, the presidential adviser, and much more the scientist.
The picture, still unintelligible, was joined by a deep rumbling glissando of sounds, sliding first up and then down the audio spectrum until it gravitated to rest somewhere around the octave below middle C. Slowly the group became aware of faint but swelling music. The picture rotated, rectified, and focused.
Ellie found herself staring at a black-and-white grainy image of… a massive reviewing stand adorned with an immense art deco eagle. Clutched in the eagle's concrete talons…
"Hoax! It's a hoax!" There were cries of astonishment, incredulity, laughter, mild hysteria.
"Don't you see? You've been hoodwinked," Drumlin was saying to her almost conversationally. He was smiling. "It's an elaborate practical joke. You've been wasting the time of everybody here."
Clutched in the eagle's concrete talons, she could now see clearly, was a swastika. The camera zoomed in above the eagle to find the smiling face of Adolf Hitler, waving to a rhythmically chanting crowd. His uniform, devoid of military decorations, conveyed a modest simplicity. The deep baritone voice of an announcer, scratchy but unmistakably speaking German, filled the room. Der Heer moved toward her.
"Do you know German?" she whispered. "What's it saying?"
"The Fuehrer," he translated slowly, "welcomes the world to the German Fatherland for the opening