Jorv’s boyish face had been working, and now he said, “Don’t take away my big dinosaurs, Ame! I’ve been running a different set of assumptions through the computer, and I can get bipeds up to twenty feet tall and quadrupeds twice that scale.”
“Bone is bone, and histology is histology,” Ame said tolerantly, “but if you want to postulate more efficient absorptive surfaces than human beings have, and a food intake of a quarter ton a day, and radiators to get rid of body heat, you’re welcome to your big dinosaurs.”
It was the usual sort of professional banter, but Bram could all but see Smeth’s suspicious mind working to make something more of it. Poor Smeth, he thought. The case was hopeless, but it wasn’t up to him to tell Smeth that!
“So these … dinosaurs disappeared at the approximate time of the core explosion?” Jun Davd mused. “Hmmm … allowing time for some undefined process to spread to Earth’s latitude in the galaxy at the quite reasonable rate of about one and one-half percent of the speed of light?”
“Not just the dinosaurs, Jun Davd,” Jorv said. “They disappeared completely—every last one of them—but many other land animals and most marine species disappeared at the same time. If the record that we’ve been given is correct.”
“And about one hundred fifty-five million years before that mass extinction,” Ame put in, “there was another major extinction in which half of all animal families were wiped out. And one hundred and fifty-five million is almost an exact multiple of twenty-six million.”
“What’s the significance of twenty-six million?” Jun Davd asked.
Ame and Jorv fell over themselves to be the one to tell him. Ame won out. “The geological record we got from Original Man—and you must realize it’s only a summary, without the detail we’d like—shows that there seem to be major species die-offs at intervals that work out to an average of about twenty-six million years.”
Jorv amended: “In two cases, there seems to have been a follow-up extinction of species at an interval somewhere between thirteen and fifteen million years.”
“That’s what worries me,” Ame said. “There were two cycles of extinction that followed the dinosaur disappearances that don’t appear to have affected the precursors of Homo sapiens, but add another thirteen million years to that and you get a value pretty close to the time when Original Man’s Message was cut off.”
“Jao,” Jun Davd said, turning around. “What sort of correlation can we get on that major date of one hundred and fifty-five million years prior to the last core explosion?”
Jao’s fingers flew over his board. “It’s hard to say, Jun Davd. We got one scenario that could have put another core explosion about there. You know, the one where we factored in the expanding molecular ring at the center. But we don’t know enough yet.”
Jun Davd turned back to Ame. “There’s not enough to go on,” he said. “We have one striking correlation of a core explosion with one of your two major extinctions and one more possible correspondence. But there’s been no more explosion since the dinosaurs disappeared and no periodic phenomenon that subdivides the major events into twenty-six-million-year cycles.”
“How about this?” Jao said. “Imagine something that sweeps the galaxy like the spokes of a wheel. Imagine eight spokes. Four major spokes, like the arms of a cross. And in between, four minor spokes, also arranged roughly as a cross. As Man’s sun orbits the galactic center, it encounters a spoke approximately every twenty-six million years.”
“Why eight spokes?” Jun Davd inquired.
“You have to start somewhere. Eight has a nice symmetry. Besides, it works out in lots of ways. You’ll see in a minute.”
“What do you mean?” Ame asked, leaning forward.
“Look,” Jao said. He did something to his console, and the tremendous scene behind the holo wall vanished, to be replaced by the rough scrawls Jao was tracing on his touch pad with one meaty forefinger.
“Hey, wait a minute!” Smeth protested.
“The universe won’t go away,” Jao said. “I’ll bring it back in a minute. I want everyone to see this.”
A bold vertical line in screaming orange grew in the illusory void behind the wall. “We start with a two-spoke model,” Jao said. “Two opposing arms, like a lot of cosmic phenomena. Like galactic gas jets, for example. Now we add another pair of arms at right angles.”
He slashed another orange line across the first. It wasn’t quite horizontal—apparently by design, because as everyone watched, the second pair of arms, responding to whatever crude instructions he had punched into his board, slowly turned until the adjustment was made.
“You see, there’s some repulsive force holding them equidistant from the two previous arms,” Jao said. “Like magnetism. Now we subdivide one more time.”
Two more crude slashes turned the cross into an asterisk. This time the finger-painted lines weren’t as thick, and they were a paler orange. They were also slightly out of position, but after a moment the second cross rotated with respect to the first until all the angles were equal.
“These are the baby arms,” Jao said. “They’re not full-grown yet. They’re weaker. That’s why I drew them skinny.”
Jorv, with growing excitement, said, “What did you mean when you said it works out?”
“For starts, when you multiply these twenty-six-million-year events of yours by eight, you get a figure of two hundred and eight million years. Which is a pretty good match for the length of time it takes Man’s sun to make one complete orbit around the galactic center.”
“Very suggestive,” Jun Davd said. “Eight events per solar orbit. Of course, you’re assuming either that the spokes are stationary, or the sun is stationary, or the spokes are rotating at twice the sun’s speed at the radius of the sun’s orbit.”
“Like I said, you have to start somewhere,” Jao said. “I like figures that come out even. So you begin with a nice regular series—two, four, eight. And multiples of orbital speed—which incidentally would put the end of a full-grown spoke somewhere at the rim of the galaxy.”
“Why not a ten-spoke model?” Smeth interrupted, with a sidelong glance at Ame. “You’d get a multiple of two hundred and sixty million years, which is closer to the two-hundred-and-fifty-million-year galactic year that some of us prefer!”
Jao shrugged. “Suit yourself. You could make that work, too, with a little fiddling with the relative velocities. You can work out the figures if you like. But an eight-spoke model’s more elegant.”
“I take it there’s more,” Jun Davd prompted.
Jao brightened. “Yah. Watch this.”
His thick fingers busied themselves on the board, and a bright yellow dot appeared about halfway out on one of the orange spokes. It began tracing a slow circle around the center of the geometric figure. A moment later the eight-armed figure began to revolve, too, at a somewhat faster rate, with the arms continually overtaking the dot.
“Now, let’s label the arms so we can keep track of them,” Jao said.
Letters popped up, alphabetizing the arms. Jao did not stop the process quickly enough, and a second round of letters began to subtend the first.
“That’s okay, leave it,” Jao said. “If I were laying this out flat, I’d be going past eight into the next cycle, anyway.”
Ame and Jorv were intent on the garish sketch hanging in the space before them. Bram could see Ame’s lips moving as she counted to herself.
“Now we take those forty-five-degree angles and subdivide them again,” Jao said.
Eight more lines grew within the spoked figure. These were dotted lines, even paler and more tentative than the lines of the second cross. Not all of them were full-length. Several of them still fell short of the yellow dot’s circular orbit.