The individual orbs looked a lot like black-and-white photographs of Jupiter, except that they didn't have neat latitudinal bands of cloud.

Rather, the clouds — or whatever it was that formed the visible surface markings — seemed to swirl in simple convection cells from equator to pole, the kind of pattern one might expect if the spheres had next to no rotation. In the intervening space between the world-sized spheres was a diaphanous fog of gas or particles that formed a translucent haze; doubtless this fog had been responsible for most of the twinkling effect they'd observed.

The whole thing — spheres and surrounding fog — looked like assorted steel ball bearings rolling around in a pile of black silk stockings.

How do they — barked Jag, and Keith immediately knew what he was going to say. How could world-sized objects be packed so closely together?

There were perhaps ten diameters between the closest of the objects, and fifteen or so between the ones that were least tightly packed.

Keith couldn't imagine any pattern of stable orbits that would keep them from collapsing together under their own gravitational attraction.

If this was a natural grouping, it seemed unlikely that it could be an old one. Throwing some light on the subject had only made the mystery deeper.

On Earth, cells contain mitochondria for converting food to energy, undulopodia (thrashing tails including those that propel sperm), and, in plants, plastids for storing chlorophyll.

The ancestors of these organelles were originally independent free-swimming creatures. They came together in symbiosis with a host being whose DNA is now walled off in the nucleus; to this day, some organelles still contain vestigial DNA of their own.

On Flatland, diverse ancestors also learned to work together, but on a much grander scale. An Ib was actually a combination of seven large life-forms — indeed, "Ib" is short for "integrated bioentity."

The seven parts are the pod, the watermelon-shaped creature containing the supersaturated solution in which the crystals of the principal brain grow; the pump, the digestive/respiratory structure that surrounds the pod like a blue sweatshirt tied around a green pot belly, with tubular arms hanging down for feeding and excreting; the twin wheels, fleshy hoops coated with quartz; the frame, a saddle-shaped gray construct that provides axles for the wheels and anchor points for the other elements; the bundle, sixteen copper-colored ropes that normally form a heap in front of the pump but can snake out as needed; and the web, a sensor net that covers the pump, pod, and upper frame. The web has an eye and a bioluminescent dot wherever two or more of its strands intersect. Although they have no speech organs, Ibs hear as well as terrestrial dogs do, and they accept with good humor spoken names bestowed by members of other races. Starplex's ExOps manager was Rhombus; Snowflake was senior geologist; Vendi (short for Venn Diagram) was a hyperdrive engineer; and Boxcar — well, Boxcar was the biochemist with whom Rissa was collaborating on the most important project in history.

In 1972, Earth's Club of Rome began preaching the limits of growth.

But with all of space now at humanity's fingertips, there were no more constraints. To hell with the textbook 2.3 children. If you wanted 2*10^3 kids, there was room enough for all of them — and for you, too.

The argument that individuals had to die in order to allow the race to advance no longer applied.

Boxcar and Rissa were trying to increase the lifespans of the Commonwealth races. The problem was daunting; so much of how life worked still remained mysterious. Rissa doubted that the riddle of aging would be solved in her lifetime, although within a century someone would likely find the key. The irony was not lost on her: Clarissa Cervantes, senescence researcher, probably belonged to the final human generation that would know death.

The average human lifespan was a hundred Earth years; Waldahudin lived to be about forty-five (the fact that they were self-sufficient after only six years didn't quite compensate for the shortness of their span; some humans thought the knowledge that they were the shortest-lived of the Commonwealth sentients was what made them so disagreeable); dolphins were good for eighty years with proper health care; and, barring accidents, an Ib would live for precisely 641 Earth years.

Rissa and Boxcar thought they knew why Ibs lived so much longer than the other races. Human, dolphin, and Waldahud cells all have a Hayflick limit: they proper!y reproduce only a finite number of times.

Ironically, Waldahud cells had the highest limit — about ninety-three' times — but their cells, like the creatures composed of them, had the shortest life cycle. Human and dolphin cells could divide about fifty times: But the organelle clusters — there was no overall membrane to mike them a single cell — that made up the body of an Ib could reproduce indefinitely. What eventually kills most Ibs is a mental short circuit: when the crystals of the central brain, which form matrices at a constant rate, reach their maximum information capacity, the overflow causes the basic routines governing respiration and digestion to become garbled.

Since she didn't seem to be needed on the bridge, Rissa had gone down to her lab to join Boxcar. She was sitting in a chair; Boxcar was positioned next to her. They watched the data scrolling up the monitor plate rising from the desk in front of them. The Hayflick limit had to be governed by cellular timers of some sort. Since it was observed in cells from both Earth and Rehbollo, they'd hoped comparison genome mapping would help. Attempts to correlate across genetic platforms the mechanisms for timing body growth, puberty, and sexual functions had all been successful. But, maddeningly, the cause of the Hayflick limit remained elusive. Maybe this latest test — maybe this statistical analysis of inverted telomerase RNA codohs — maybe — Lights winked on Boxcar's sensor web.

"It saddens me to note that the answer is not there," said the translated voice, British, as all Ib voices were, and female, as half of them were arbitrarily assigned.

Rissa let out a heavy sigh. Boxcar was right; another dead end.

"I intend no offense with this comment," said Boxcar, "but I'm sure you know that my race has never believed in gods. And yet when I encounter a problem like this — problem that seems, well, designed to thwart solution — it does make one think that the information is being deliberately withheld from us, that our creator does not want us to live forever."

Rissa made a small laugh. "You may be right. A common theme among human religions is the belief that gods jealously guard their powers.

And yet why build an infinite universe, but put life on only a handful of orlds.

"Begging your generous pardon for pointing out the obvious," said Boxcar, "but the universe is only infinite in that it has no borders.

It does however contain a finite amount of matter. Still, what is it that your god is said to have commanded? Be frui tful and multiply?"

Rissa laughed. "Filling the universe would take an awful lot of multiplying."

"I thought that was an activity you humans enjoyed."

She grunted, thinking of her husband. "Some more than others."

"Forgive me if I'm being ' ' ,, intrusive, said Boxcar, "but PHANTOM prefaced the translation of your last sentence with a glyph indicating that you spoke it ironically. It is doubtless me who is to blame, but I seem to be missing a layer of your meaning."

Rissa looked at the Ib — a faceless, six-hundred-kilogram wheelchair.

Pointless to discuss such matters with her — with it, a sexless gestalt that knew nothing of love or marriage, a creature to whom an entire human lifespan was a brief interlude. How could it understand the stages a marriage went through — the stages a man went through.