Robert Sawyer: Calculating God

“Ah,” I said dubiously.

“But, even were that not true,” said Hollus, “there is another reason for all space-faring races to be comparably advanced.”

Something was tickling at the back of my mind, something I’d once seen Carl Sagan explain on TV: the Drake equation. It had several terms, including the rate of star formation, the fraction of stars that might have planets, and so on. By multiplying all the terms together, you were supposed to be able to guesstimate the number of intelligent civilizations that might currently exist in the Milky Way. I can’t remember all the terms, but I do remember the final one — because it chilled me when Sagan discussed it.

The final term was the lifetime of a technological civilization: the number of years between the development of radio broadcasting and the extinction of the race. Humans had first started broadcasting in earnest in the 1920s; if the Cold War had turned hot, our tenure as a technological species might have been as little as thirty years.

“You mean the lifetime of a civilization?” I said. “The span before it blows itself up?”

“That is one possibility, I suppose,” said Hollus. “Certainly, my own race had a difficult time learning to use nuclear power wisely.” The alien paused. “I am given to understand that many humans suffer from mental problems.”

I was startled by the apparent change of topic. “Umm, yes. I suppose that’s true.”

“As do many Forhilnors,” said Hollus. “It is another concern: as technology advances, the ability to destroy the entire race becomes more accessible. Eventually, it is in the hands not just of governments but also individuals — some of whom are unbalanced.”

That was a staggering thought. A new term in the Drake equation: f-sub-L, the fraction of members of your race who are loony.

The Hollus simulacrum moved a little closer to me. “But that is not the principal issue. I told you that my race, the Forhilnors, had made contact with one other technological race, the Wreeds, prior to meeting you; we actually first met them about sixty years ago — by going to Delta Pavonis and discovering them.”

I nodded.

“And I told you that my starship, the Merelcas, visited six other star systems, besides the Wreed home one, before arriving here. But what I did not tell you was that each of those six had, at one time, been home to an intelligent race of its own: the star you call Epsilon Indi, the star you call Tau Ceti, the star you call Mu Cassiopeae A, the star you call Eta Cassiopeae A, the star you call Sigma Draconis, and the star you call Groombridge 1618 all once had native intelligent life.”

“But they don’t anymore?”

“Correct.”

“What did you find?” I asked. “Bombed-out ruins?” My mind filled with visions of bizarre alien architecture, twisted and melted and charred by nuclear blasts.

“Never.”

“Then what?”

Hollus spread his two arms and bobbed his torso. “Abandoned cities, some immensely old — some so old, they had been deeply buried.”

“Abandoned?” I said. “You mean the inhabitants had gone somewhere else?”

The Forhilnor’s eyes touched in affirmation.

“Where?”

“That question still vexes.”

“Do you know anything else about the other races?”

“A great deal. They left many artifacts and records behind, and in some cases interred or fossilized bodies.”

“And?”

“And, at their ends, all were comparably advanced; none had built machines we could not understand. True, the variety of body plans was fascinating, although they all were — what is that phrase humans use? — ‘life as we know it.’ They were all carbon-based DNA lifeforms.”

“Really? Are you and the Wreeds also DNA-based?”

“Yes.”

“Fascinating.”

“Perhaps not,” said Hollus. “We believe that DNA is the only molecule capable of driving life; no other substance has its properties of self-replication, information storage, and compactibility. DNAs ability to compress into a very small space makes it possible for it to exist in the nucleuses of microscopic cells, even though when stretched out, each DNA molecule is more than a meter long.”

I nodded. “In the evolution course I used to teach, we considered whether anything other than DNA could do the job; we never came up with an alternative that was even remotely suitable. Did all the alien DNA use the same four bases: adenine and thymine, guanine and cytosine?”

“Are those these four?” said Hollus. Suddenly, his holoform projector made four chemical formulas float in the air between us in glowing green:

C5H5N5

C5H6N2O2

C5H5N5O

C4H5N3O

I peered at them; it’d been a while since I’d done any biochemistry. “Umm, yes. Yes, those are they.”

“Then, yes,” said Hollus. “Everywhere we have found DNA, it uses those four bases.”

“But we’ve shown in the lab that other bases could be used; we’ve even made artificial DNA that uses six bases, not four.”

“Doubtless extraordinary intervention was required to accomplish that,” said Hollus.

“I don’t know; I guess.” I thought about everything. “Six other worlds,” I said, trying to picture them in my mind.

Alien planets.

Dead planets.

“Six other worlds,” I said again. “All deserted.”

“Correct.”

I sought the right word. “That’s . . . frightening.”

Hollus did not dispute this. “In orbit around Sigma Draconis II,” he said, “we found what seemed to be a fleet of starships.”

“Do you suppose invaders had wiped out the indigenous life?”

“No,” said Hollus. “The starships were clearly built by the same race that had constructed the abandoned cities on the planet below.”

“They built starships?”

“Yes.”

“And they all left the planet?”

“Apparently.”

“But without using the starships, which were left behind?”

“Exactly.”

“That’s . . . mysterious.”

“It certainly is.”

“What about the fossil records on these planets? Do they have mass extinctions that coincide with ours?”

Hollus’s eyestalks moved. “That is difficult to say; if one could easily read fossil records without decades or centuries of searching, I never would have had to reveal myself to you. But as far as we have been able to tell, no, none of the abandoned worlds had mass extinctions at 440, 365, 225, 210, and 65 million years ago.”

“Were any of those civilizations contemporaneous?”

Hollus’s command of English was remarkable, but occasionally it did fail him. “Pardon?”

“Did any of them live at the same time as any of the others?”

“No. The oldest seems to have ended three billion years ago; the most recent, on the third planet of Groombridge 1618, about five thousand years ago. But . . .”

“Yes?”

“But, as I said, all the races seemed to be comparably advanced. Architectural styles varied widely, of course. But, to give you an example, our engineers dismantled one of the orbiting starships we found at Sigma Draconis II; it used different solutions to several problems from the ones we employ, but it was not fundamentally much better — perhaps a few decades beyond what we had developed. That is the way it was for all the races that had abandoned their worlds: they were all only slightly more advanced than the Wreeds or the Forhilnors — or Homo sapiens, for that matter.”

“And you think this happens to all races? They reach a point where they just leave their home planets?”

“Exactly,” said Hollus. “Or else something — perhaps God himself — comes along and takes them away.”