Tau Zero

“Not the way he behaves,” Reymont said. “Or smells.”

“Be polite, Constable, or I’ll charge you myself.” Lindgren drew breath. “You don’t seem to make allowance for huma

“Yes, madame, I do,” Reymont said. “I do not expect them to behave so as to make matters worse.”

“There is some truth in that,” Lindgren conceded.

Nilsson squirmed and looked sulky. “I was trying to spare them disappointment at the end of this flight,” he muttered.

“Are you absolutely certain you weren’t indulging your ego?” Lindgren sighed. “Never mind. Your standpoint is legitimate.”

“No, it isn’t,” Reymont contradicted. “He gets his 1 per cent by counting every star. But obviously we aren’t going to bother with red dwarfs — the vast majority — or blue giants or anything outside a fairly narrow spectral range. Which reduces the field of search by a whopping factor.”

“Make the factor ten,” Nilsson said. “I don’t really believe that, but let’s postulate we have a 10 per cent probability of finding Nova Terra at any one of the Sol-type stars we try. That nevertheless requires us to hunt among five to get our even chance. Ten years? More like twenty, all things considered. The youngest among us will be getting past his youth. The loss of so many reproductive opportunities means a corresponding loss of heredity; and our gene pool is minimal to start with. If we wait several decades to beget children, we can’t beget enough. Few will be grown to self-sufficiency by the time their parents start becoming helpless with advancing age. And in any case, the human stock will die out in three or four generations. I know something about genetic drift, you see.”

His expression grew smug. “I didn’t wish to hurt feelings,” he said. “My desire was to help, by showing your concept of a bold pioneer community, planting humankind afresh in a new galaxy … showing that for the infantile fantasy which it is.”

“Have you an alternative?” Lindgren inquired.

A tic began in Nilsson’s face. “Nothing but realism,” he said. “Acceptance of the fact that we will never leave this ship. Adjustment of our behavior to that fact.”

“Is it the reason you’ve been soldiering on the job?” Reymont demanded.

“I dislike your term, sir, but it is true there is no point in building equipment for long-range navigation. We are not going anywhere that makes any difference. I ca

“You understand, I suppose,” Reymont said, “that for maybe half the people aboard, the logical thing to do once they’ve decided you’re right, is to commit suicide.”

“Possibly.” Nilsson shrugged.

“Do you hate life so much yourself?” Lindgren asked.

Nilsson half got up and fell down again. He gobbled. Reymont surprised both his listeners by turning soft-ma

“I didn’t fetch you here only to get your gloom-peddling stopped. I’d rather know why you haven’t been thinking how to improve our chances.”

“How can they be?”

“That’s what I want to learn from you. You’re the observational expert. As I recall, you were in charge of programs back home which located something like fifty planetary systems. You actually identified individual planets, and typed them, across light-years. Why can’t you do the same for us?”

Nilsson pounced. “Ridiculous! I see that I must explain the topic in kindergarten terms. Will you bear with me, First Officer? Pay attention, Constable.

“Granted, an extremely large space-borne instrument can pick out an object the size of Jupiter at a distance of several parsecs. This is provided the object gets good illumination without becoming lost in the glare of its sun. Granted, by mathematical analysis of perturbation data gathered over a period of years, some idea can be obtained about companion planets which are too small to photograph. Ambiguities in the equations can, to a degree, be resolved by close interferometric study of flare-type phenomena on the star; planets do exert a minor influence upon those cycles.

“But” — his finger prodded Reymont’s chest — “you do not realize how uncertain those results are.

Journalists delighted in trumpeting that another Earthlike world had been discovered. The fact always was, however, that this was one possible interpretation of our data. Only one among numerous possible size and orbit distributions. And subject to a gross probable error. And this, mind you, with the largest, finest instruments which could be constructed. Instruments such as we do not have with us here, nor have room for if we could somehow build them.

“No, even at home, me sole way to get detailed information about extrasolar planets was to send a probe and later a ma

“I implore you, Constable, to learn a little science, a little logic, and a bare touch of realism. Eh?” Nilsson ended with a crow of triumph.

“Professor—” Lindgren tried.

Reymont smiled crookedly. “Don’t worry, madame,” he said. “No fight will come of it. His words don’t diminish me.”

He inspected the other man. “Believe it or not,” he went on, “I knew what you’ve told us. I also knew you are, or were, an able fellow. You made i

“Will you be so good as to condescend to suggest a procedure?” Nilsson sneered.

“I’m no scientist, nor much of a technician,” Reymont said. “Still, a few things look obvious to me. Let’s suppose we have entered our target galaxy. We’ve shed the ultra-low tau we needed to get there, but we have one yet of … oh, whatever is convenient. Ten to the minus third, maybe? Well, that gives you a terrifically long baseline and cosmic-time period to make your observations. In the course of weeks or months, ship’s time, you can collect more data on a given star than you had on any of Sol’s neighbors. I should think you could find ways to use relativity effects to give you information that wasn’t available at home. And naturally, you can observe a large number of Sol-type stars simultaneously. So you’re bound to find some you can prove — prove with exact figures that leave no reasonable doubt — have planets with masses and orbits about like Earth’s.”

“Assuming that, the question of atmosphere, biosphere, will remain. We need a short-range look.”

“Yes, yes. Must we stop to take it, though? Suppose, instead, we lay out a course which brings us hard by the most promising suns, in sequence, while we continue to travel near light-speed. In cosmic time, we’ll have hours or days to check whatever planet interests us. Spectroscopic, thermoscopic, photographic, magnetic, write your own list of clues. We can get a fair idea of conditions on the surface. Biological conditions too. We could look for items like thermodynamic disequilibrium, chlorophyl-reflection spectra, polarization by microbe populations based on L-amino acids … yes, I imagine we can get an excellent notion of whether that planet is suitable. At low tau, we can examine any number in a small stretch of our own time. We’ll have to use automation and electronics, in fact; we ourselves couldn’t work fast enough. Then, when we’ve identified the right world, we can return to it. That will take a couple of years, agreed. But they’ll be endurable years. We’ll know, with high probability, that we have a home waiting for us.”