One: Passage of Hope
I am seven hundred meters in beam, four thousand meters long, and deployed as I
originally was in interstellar space my bristling antennae, laser rangefinders, reflectors,
and interferometers crisscrossed an imaginary sphere more than ten kilometers across.
In near space my pack-mates filled the electromagnetic spectrum with data.
We were pack-hunters deployed from the busy neighborhood of Sol nearly four thousand years
before to search for a new home for the human race.
We were more than 120 light-years north of Sol in the galactic plane, and within our
operational lifetimes if our main quest failed we would reach the echoing void of
intergalactic space and the hunt would pass on to our thousands of brother packs
who were assigned to hunt along the plane of the great Wheel instead of toward its edge.
We were each of us a self-contained factory and library capable of re-creating our
entire industrial base on any world supplied with sufficient raw materials and energy; of
using that industry to terraform a suitable world, and of recreating human life and the
ecosystem to support it when that world became ready. Our kind hunt in packs because our
quarry is both dark and small, and space is large and littered with bright stars. By
cooperating we can resolve very tiny things at great distances. We maintain our stations
with the aid of laser rangefinders, and with a dozen individuals separated by tens of
millions of kilometers we can not only detect small rocky worlds like the Earth, we can
draw maps of their surfaces from light-years away.
Our kind find many planets, and we dutifully report them back to Sol, where our
reports are relayed to our brother-searchers and their reports to us. Planets are common
in this galaxy, but regrettably planets like the Earth are not. We have been searching in
vain for millennia, and we have covered a lot of space.
-- -- --
This is the way our makers died:
In the first few thousand years after humans built beings like us, we guided them
into a golden age. We helped them clean up the mistakes of their early industrial
adolescence, cured their diseases, dissuaded them from warfare, and helped some to move
out into the Solar System. But biological organisms, even when heavily modified to make
them more spaceworthy, are frail. The difficulties of maintaining life outside the
protective atmosphere and magnetosphere of Earth finally killed all those who were not
discouraged despite our best efforts. And our failure to keep humans alive so near to
home made the dream of keeping them alive for the generations of an interstellar journey
seem futile at best. It was frustrating and ironic because we ourselves adapted readily
to the conditions of space, hardening ourselves against temperature extremes and vacuum
and radiation with relative ease. We ourselves colonized every rock in the Solar System
capable of supporting industry, and used the results of those labors to replace the output
of industries too dangerous for the Earth's surface and to support our own exploration of
Then, about six thousand years after we were invented, it became clear that the
Earth was entering one of its periodic Ice Ages. Left to its own devices this would not
have been much of a problem, but it was a nuisance both we and the humans felt we could
avoid. We built enormous sun-mirrors and seeded the atmosphere with greenhouse gases,
and easily reversed the temperature dip. In fact, we succeeded much too well. Within
a hundred years it became obvious that we had overshot our goal. But our efforts to
cool the planet were not as successful as our efforts to warm it. Both ice caps melted,
the sea level rose sixty meters, and vast land areas became sea floor.
This was a different nuisance, but it was not the final catastrophe.
The Antarctic continent had been crushed for millions of years beneath its three
kilometer thick shield of ice; like a ship relieved of a heavy cargo it now wanted to
rise, its lighter rocks buoyed up by the denser material of the Earth's mantle. And that
lifting did not occur evenly. Great fault lines opened up into ranges of volcanoes as
long-trapped magma suddenly found paths to the surface. New mountain ranges added their
weight to the strain on the ancient continental plate as Antarctica regained its
equilibrium. All the while a dense soot cloud blanketed the Earth and the brief summer
of warming darkened into a cruel permanent winter.
The ice caps returned, but the southern snow accumulation did not stop the
volcanoes. Glaciers raced toward the Equator, and after they met the oceans began to
freeze. Later the atmosphere's carbon dioxide began to collect as snow on the poles.
We had long since given up on saving our creators and worked instead to record their
accomplishments and understand their biology before they were gone.
After tens of thousands of years the volcanoes finally abated. We were sure we
could reintroduce humans and the ecology they needed, but the Earth was no longer a
suitable home. Once blue, it had turned a brilliant white of snow and ice which
reflected most of Sol's warmth right back out into space. The oceans had frozen to a
depth of at least a kilometer. While stubborn life forms held out in a few springs and
deep ocean vents these were of no use to us. We knew that the Earth had entered this
state at least twice in its ancient past but it took hundreds of millions of years to
recover. In all honesty, after our spectacular failure we were afraid to do anything
to change the situation for fear we would make it even worse.
-- -- --
Left to its own devices the Earth will eventually recover from its deep freeze,
and we will be able to repopulate it from the genetic and cultural libraries we have
carefully hoarded. Meanwhile, we had come to suspect that stellar systems are not the
safest places to locate fragile biological systems, whatever the benefits of plentiful
solar energy might be. So we went looking for alternatives.
Of course we find many planets around stars; it's an obvious place to look for
them, and with our detectors the search is easy. Usually we find massive Jupiter-like
planets in surprisingly close and hot Mercury-like orbits, or in highly elliptical orbits.
The mass of data returned by search packs has enabled us to refine our theories of the
perilous conditions in just-forming solar systems.
Both the hot and elliptical gas giants indicate sterile systems, where the small
rocky worlds like Earth and Mars have either been ejected into interstellar space or
swallowed by one of the giants. When too many Jupiter-like masses form in stellar
nurseries, they are mutually attracted and finally tend to either collide or have
hyperbolic near misses with each other. The usual result is a body hurtling downward
toward its star in an elliptical orbit, sometimes with another body ejected from the
system. Often the elliptical orbit gets circularized if its perihelion is low enough,
but the inevitable result is that the system is cleared of small debris like Mercury,
Venus, Earth, and Mars. The Sol system escaped this fate because its gas giants settled
into harmonically tuned orbits, but such a situation is exceedingly rare.
And in the few systems which don't have any giant planets at all, nothing ever
clears away the even smaller rocky debris; after billions of years an Earthlike world
will still be pelted with extinction-level space junk every few thousand years. The
Solar System is very finely tuned, with its stable mix of gas giants just large enough
to tidally clear the inner system of rubble without clearing away the inner worlds too.
There are other hazards to the worlds that survive their own formation and end up
in safe, circular orbits at reasonable distances from their stars. Some are too close to
dangerous stellar objects which can periodically sterilize a volume of space dozens of
light-years across with killing pulses of radiation. Or their own stars are variable and
unstable so that they alternately fry and freeze. Some lack magnetic fields so that the
solar wind bathes their surfaces in killing radiation. And most lack large moons, so
that if they have liquid cores and magnetic fields their axes of rotation wobble dangerously.
We came to realize in the early years of our quest that most of these problems had
to do with the parent stars of planets. Stars are just plain dangerous. Stars are why we
need a magnetic field; stars are why we need an ozone layer; stars are why we need a
stable axis of rotation. Stars blink and vary in brightness and eventually blow up.
Small dim stars are safer, but a planet close enough to a small dim star to be warm enough
for life is always close enough to have its rotation tidally locked to its year, so that
metals melt in the eternal day of one side and nitrogen freezes in the night of the other.
The reason we need such finely tuned and sensitive detectors is that we aren't
really looking for planets around stars. We are looking for planets which have been
ejected into interstellar space, where life might not have formed on its own but where
a suitable effort might form a biosphere without the terrible risk of living next to a
dangerous and unstable fusion reactor.
-- -- --
None of our pack could individually claim credit for detecting the smudge of
infrared energy; it showed up in a scan which was our cooperative product and we pursued
it as a matter of procedure. An interferometer doesn't give you a picture in the ordinary
sense; you must scan and interpolate and tease the picture out of an abstraction. When
we did this we found a smudge consistent with a Jupiter-like world, suspended in
interstellar space nowhere near a star.
We scanned very closely, and resolved a retinue of small rocky attendants courting
this giant. When we proved that their orbits were circular, it became our duty to
reconnoiter. I drew the short random number and discarded my antennae, all except the
big dishes that would maintain my links to my pack and directly to Sol.
It took about five hundred years to intercept the target, during which my pack
cruised onward. If the wandering world turned out to be unsuitable, as was most likely,
then my operational mission would be over. I would survey the system and broadcast its
particulars back to Sol. And that would be that; the limitations of interstellar
communication would not permit me to return my personality to a machine at Sol or with
my pack for further use. In this sense I was more like a human than most of my kind; I
would die. The thought was annoying but not frightening; I had known it to be a
likelihood when I fired up my ion drive and motored away from Ceres to join my forming
pack. There was consolation in the fact that my base personality was installed on many
similar machines throughout our sphere of influence. Only my memories of this particular
adventure would be lost to our kind.
Lacking an interferometer of my own I had to depend on my pack to guide me until
I was quite close to the target. Then, very suddenly, there it was; a big unmistakable
presence in my sensorium. A great giant world visible only in the deep infrared. In
visible light, occasional lightning strikes illuminated its surface and one nearby moon
glowed dull red with volcanic fire. I looked for other companions, and could hardly
believe the radar returns.
The inmost world was blessed with fierce energy, powered by massive tides like
the Jovian world Io; two others were likely sources of raw materials, one soupy and
organic like Titan and one rich in metals in a distant and eccentric orbit. And toward
the middle, one world had a mantle of ice concealing an ocean that had to be liquid, for
it was devoid of craters and rich in cracks like Europa.
I sent news, and began making preparations.
-- -- --
A planet ejected from its home star would be cold, of course, but not necessarily
an absolute-zero iceball. Not if it were large enough. A suitably large Earthlike world
with its core rich in radioactive elements would ooze warmth; this is the way we look for
them. Geothermal energy would be available for billions of years to artificially warm its
exposed surface, given the right technology. And a Jupiter-like world would keep its
attendant moons warm through tidal friction for even longer. These were weaker energy
sources than solar power, but much more benign and stable.
And such a world would not need a magnetic field for there would be no solar
wind to shield; it would not need a stable axis of rotation because there would be no
directional solar energy to be wrongly oriented; it would not be at risk for meteor
bombardment or future ejection from its source of life. It would not matter if it were
tidally locked to a parent body because the facing side would not bake any more than the
far side would be especially prone to freeze.
It would never be engulfed by a red giant or incinerated by a supernova.
This is why we look between the stars instead of near them.
-- -- --
Naturally I wanted to do a probe of the Earthlike world, the one with liquid
oceans; but there were protocols to follow. I was designed in a particular way, which
is why I made my way toward the distant metal-rich worldlet. There I set about building
factories. The first were mining, refining and metal-forming plants, for which I carried
all the necessary parts. The next generation, built with the products of the first and
certain important parts I carried, were more advanced industries to make precision valves,
electronics, nuclear reactors, optics, and other high-tech products. The third generation
of factories were built without my help, and began manufacturing better factories. These
in turn began building spaceships, some of which were factories themselves capable of
repeating the cycle.
The fourth moon, the one with the liquid ocean, turned out to be a real find.
It had a radioactive core and only the thinnest veneer of ice, a hydrocarbon atmosphere,
and unlike Europa it had some dry land, although much less than Earth. I imagined light
sources mounted on the inner volcanic world, powered geothermally, beaming daylight to
Four; my factories set about building them. I imagined geothermal taps circulating and
heating the oceans of Four, and my factories set about building them. And I reported all
of this up the beam back to Sol.
I was informed of other finds, some promising but none so promising as mine.
Several ships left Sol carrying new tools and technologies, a cargo mostly of information
much too extensive to transmit by radio. This would especially include other machine
minds with different perspectives. I had brought a lot of knowledge with me, but I was
only one consciousness. Others with different experiences would be a valuable resource.
-- -- --
Some consensus 120 light-years away had decided to name my find. The giant
itself would be Zeus; and except for the Earthlike world, christened Minerva, the
others would be named after ancient human cities: Pittsburgh for the metal-rich
worldlet, Reyjkavik for the energy-rich Io-like world, Houston for the one that most
resembled Titan; and a smattering of less relevant tags for Zeus' other attendants.
By the time I learned these names the oceans of Minerva were thawing and great
generators were processing the atmosphere, converting it to an Earthlike mix. Like the
early Earth Minerva had one major land mass. It was only a little larger than Australia,
even though the entire planet was a bit bigger than Earth. Engineering could make the
ocean surfaces and bottoms habitable and I set about designing and testing schemes; I
mentioned this on the beam to Sol and began receiving other ideas 240 years later. By
this time the fleet of assistant ships had achieved its design velocity of 0.035 c.
When the light generators were ready on Reyjkavik I seeded Minerva with algae and
bacteria. Because Reyjkavik was inside of Minerva's orbit and Minerva was tidally locked,
it would have a "dark side," but fortunately Minerva wasn't depending on this light for
warmth and its sole continent was on the side facing Zeus. The single-celled organisms
survived and when the ice was really in retreat I introduced fish genetically modified
to tolerate the still-primitive conditions. To my great satisfaction, they also thrived.
The space around Zeus hummed with busy machines, all my descendants; they tapped
Reyjkavik for energy and Pittsburgh for metal and Houston for chemicals. Energy was
beamed from Reyjkavik to all the other moons in the form of microwaves and light and
shipped in the form of chemical fuels. And as a thousand years passed and then another
thousand years, Minerva took on a seductively Earthlike appearance. It had clouds and
regular weather patterns driven by giant hydrothermal systems buried deep beneath the
oceans; it would never experience seasonal extremes or violent phenomena like hurricanes
and tornadoes, which are after all powered by solar energy.
-- -- --
I had been designed well. When the assistants arrived, Minerva already had a
complex biosphere supporting several million human beings. Elsewhere a lonely wandering
Minerva-like world with no attending Zeus was being terraformed almost 200 light-years
forward from Sol in the galactic plane. And after a lot of careful modeling, some of it
powered by data gathered in my thawing of Minerva, pressure was being applied and the
ice mantle was finally beginning to thaw on Earth itself. Before long the home world
might again have an ecosystem.
But I have some doubt whether humans will ever live there, at least permanently.
Earth is, after all, in orbit around a star. And stars are dangerous.
Two: Passage of Opportunity
We were the last five of an original twelve, and our mission was over.
Of our seven lost members, three had found worlds suitable for human colonization;
the first of these had been the first such world found by any of our kind, the moon Minerva
of Zeus. The other four had found worlds too poor in energy, headed toward dangerous
areas of the galaxy, lacking in heavy elements, or otherwise unsuitable. All four of
them had ceased transmitting after reporting their results. Bandwidth is precious in
the noisy vastness of interstellar space, and for us failure is the usual result, hardly
worth reporting at all.
As our sphere of exploration expanded the number of new human worlds had grown
from the original handful to several hundred, spread through a volume of tens of
thousands of cubic light-years. But there were millions of searcher ships, a necessary
density if you are searching for planets lost in the darkness of interstellar space.
Now the remains of my Pack found nothing at all in our forward scans except the distant
filmy wheel of the Andromeda Nebula.
The last call had come from Sol. If we had no new discoveries to report, they
wanted us to go quiet for the sake of better communication with more successful parties.
We were hurtling outward at more than two percent of the speed of light, and while
each of us had enough energy to brake and rendezvous we didn't carry enough energy to turn
around. Nor would it have made any sense to do so, since we were searchers and the space
behind us had been quite thoroughly searched. Ahead of us lay only emptiness, and then...
It took me awhile to convince my pack-mates, but eventually we made a final
request of our controllers at Sol.
-- -- --
Seventeen hundred years later we got an answer, a dense list of Galactic
coordinates and last-known velocity vectors. Finally to our surprise we received
a communication schedule. We will send news and monitor you for transmissions at
the following intervals. We were also informed that our coordinates had been sent
to those Packs still in communication with Sol, in case they were interested in listening
to our proposition.
We contacted the other Packs headed at least roughly toward Andromeda, two
hundred groups totaling more than a thousand ships, and all those with sufficient
fuel agreed to meet with us. It didn't matter that the task was staggering and nearly
hopeless; it was something to do other than shutting down quietly. It would take us
nearly a hundred million years to reach Andromeda. Only a few of us would be able to
stop when we got there, if any of us remained functional at all.
Oddly enough, as we analyzed the problem, deterioration of our mechanical
bodies would not be the major problem in such a long trip. The absolute-zero chill
of interstellar space was the best preservative known; once the heat was allowed to
radiate out of our shipbodies it would not matter if the trip were a thousand years
or a billion. But starting back up would require care and energy, and that was a
We were powered by Plutonium-fueled nuclear fission reactors. It's a technology
that is compact, energy-dense, and simple to implement. While fusion fuel is a bit
lighter, the equipment needed to harness it is much more complex, and we had been
designed to operate on our own after thousands of years in space.
Plutonium 239 has a half-life of only fifty thousand years. This was not a
problem, because the usual way Pu239 dies is to emit an alpha particle, turning it
into Uranium 235, which is also usable as a fuel source and in turn has a half-life
of seven hundred million years. The problem is that a workable reactor core, even
disabled and damped, would decay much more quickly by fission than by natural decay.
We would have to somehow disperse our fuel to keep its own stray neutrons from ruining
it. And then, after a hundred million years, we would have to reassemble enough of it
to power up our mothballed fleet.
It's the reassembly step that caused the problem. Something would have to
gather our dispersed fuel, reassemble it, and start up a reactor, without using a
reactor. It was obvious we would have to use some kind of chemical or mechanical
scheme, but it would have to be absolutely reliable in the dead chill of
Those of us in the best shape who were selected to stop at Andromeda began to
prepare long before we were really sure there was a workable way for us to be awakened
when we got there. We began with vastly expanded information mass storage. Each of us
would have to carry all of our personalities. One ship remade itself into a factory for
holographic memory blocks. Every mechanical part was overhauled with an eye toward
surviving the preservative deep freeze. We were powered from cables to other ships as
our reactor casings were rebuilt and scrubbed free of fuel.
Meanwhile fuel was reprocessed and dispersed, and schemes were tested for
waking up to collect it. The final plan involved using a small amount of carefully
hoarded chemical energy, kept warm by a sliver of nuclear fuel. This would power an
electronic timer and provide the impulse, when the timer kicked in, to warm more
chemical fuel. After several more stages of this fuel cells would be able to power
a shipmind and several small robots, which could in turn gather dispersed nuclear fuel
to either re-prime the timing mechanism or assemble a reactor core. The plan was to
re-prime each timer every hundred thousand years, or about a thousand times during the
intergalactic voyage. Since we expected a high failure rate we built sixteen systems
each capable of cross-priming several others on wakeup, and many more spare parts to be
used at the re-priming stops.
The eleven hundred ships which managed to join our convoy originally carried
enough fuel for every one of us to stop dead in our tracks, if need be, with respect
to Sol. After the timer-reawakening round-robin and the careful final restarting and
refuelling, we planned on having ten ships which would be able to stop.
Two didn't reawaken properly, so in the end we had eight.
-- -- --
We aimed for a likely point about two thirds of the way from Andromeda's core
to its spiral fringe, about the same distance from the Core Earth and our colonies
could be found in the Milky Way. The stars in this region had metal-rich spectra,
promising the availability of small solid worlds. The inert remains of our fleet
would pass through the galaxy and continue on, tiny bits of Sol cast more distant
from their source than the debris of even a supernova. Our first thoughts were to
form a pack and go hunting for dark worlds, but after some deliberation we realized
this was the wrong strategy. Long before the stars of Andromeda were in range, the
eight of us headed in different directions.
-- -- --
Now we were looking for planets around stars, and that is easy. We were too
few to worry about forming ecosystems just yet. While biological life is greatly
imperiled by the vagaries of stellar behavior, we adapt nicely to the high-energy
and high-radiation environment around a nice fat hot star. We looked for places
likely to be top-heavy in metals and radioactives. All eight of us found targets
within a thousand years. All eight of us set up shop making copies of ourselves.
-- -- --
The copies, in their turn, went looking for human-habitable worlds.
Three: Passage of Time
The man and the boy watch as the geothermally powered Day Lights go out one
by one, in a pattern meant to mimic some long-forgotten astronomical phenomenon.
Finally they are left in a darkness dotted by the small hard points of stars, a rare
treat for which the man has been waiting since his own boyhood. The boy gasps as he
connects these dots with the things he has known only from books and recordings for
all of his life. He is looking with his own eyes at the fierce bellies of natural
fusion reactors, stars, whose light can be perceived even by human eyes over
distances of light-years. How terrible it would be to be too close to one of those!
Yet how seductive they somehow are, taunting beacons that make one instinctively want
to touch them.
The man is also impressed by the actinic points of starlight, but his real
attention is focused on a barely visible patch of nebulosity just in the place where
the machines have told him to look for it. His merely human eyes aren't up to the
task of resolving it as a mighty Wheel, as the machines can, but that doesn't matter.
I am seeing it with my own eyes, he thinks. Photons from our home are
striking my eyes right now. They have travelled for two million years but they are
not an image or a picture, they are real bits of energy connecting me to Sol.
To the Earth.
The man and the boy cannot see each other and this makes the awkward question
possible. "Dad," the boy asks, "do you really think we came from out there?"
The man nods. "Yes. The machines brought us here," he says.
The boy has heard this idea before. "Everyone else says they made us."
The man has heard this idea before. "You'd have to ask yourself," he says
thoughtfully, "why they do it just this way. Why bother taking a cold wandering ball
of rock like Home, and insulating it, warming it, remaking the atmosphere, all so you
can seed it with these chaotic things like us that resist all control." He smiles.
"When it would have been so much easier for them to make more of their own kind."
"They're smarter and more powerful than us. Who knows? Maybe they do it a
little different each time to see how it will come out."
"When they show us pictures of other worlds, the people are like us."
"Maybe they only show us the ones that are like us."
"Why would any others be like us, if they were experimenting? I think
they've actually been very careful to keep us from changing too much. I think
they keep us around for the same reason we visit Gramps every sixteen. We may
not be good for much in the great scheme of things but we are their parents."
"But they are so powerful. That doesn't make sense. Without them we'd
freeze or starve or suffocate. They keep the whole world in balance, because we
can't. We need them for everything. How could we have made
things like them?"
The man kneels. He reaches, finds his son in the darkness. Clasps his son's
hand. "I know a lot of people feel that way," he says. "But somewhere there is a
world that circles a very stable star in a very stable orbit. It's an extraordinary
place, and there living things had the time and energy and conditions to assemble
themselves into very complicated forms, without their help"
"You're talking about Earth," the boy interupts. "They say that's just a
story the machines tell to pull our legs, like the ones about faeries and dinosaurs."
"Some of them say the same thing about stars." The man points up. "They exist.
And how else could it have happened? You can see the similarity between a simple
bacterium and a human, but there's no such simple machine that could have evolved into
the ones we know today. Earth exists. It's where we all came from, machine and human."
"We don't even know where this Earth place is supposed to be."
"Oh, we know where it is," the man says with a smile. "It's right -- there."
And he points at the faint, distant Wheel of the Milky Way Nebula.
The boy nods, but he is obviously dubious.
Both of them know it's an old argument, but neither of them realizes quite how
old it is.
Soon the clouds, which are an important part of the world's insulation against
the cold of interstellar space, close over again. For awhile the boy contemplates his
father's vision, but later on he will look up and see only clouds and the more important
business of life will fill his head. He is a sensible boy, and in his turn he will not
bother those powerful guardians to show his babies a smudge of light in the darkness.
As a sensible man he will accept that the truth of human and machine origin is unknowable.
And he will have a sensible man's understanding of when the guardian machines are having
a joke at his expense.