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Lockstep: A Possible Galactic Empire

Karl Schroeder, Analog Science Fiction and Fact, May 2014

Traveling to the stars is a grand aspiration. But is it the right problem to solve?

In January 2012, DARPA and NASA announced a grant to establish the 100 Year Starship Foundation. The grand aim of the Foundation is to develop the technologies, systems, economic plans, and sociology that might get us to the stars. It's a fantastic endeavor, which has already caught the imaginations of some of the best thinkers of the age. I think it’s a great and worthy endeavor, and I hope they’re successful.

When I was seven years old, I watched Neil Armstrong set foot on the Moon, so I grew up on the vision too. Or – well, no, that’s not entirely true. I grew up on stories of easy, nearly-instant star travel, mostly Andre Norton’s tales of galactic civilizations: I grew up on the dreams of space opera. In space opera, we don’t just have star travel; we have aliens walking our streets, we have Free Traders, Scouts, and the uniformed Patrol carrying blasters at their hips. We have extinct Forerunner civilizations that have scattered their ruins and mysterious artifacts across the galaxy. And our heroes and heroines can board a starship, travel to exotic and far-distant worlds, have adventures, and return before dinner – or at least, before New Year’s.

That is not quite the same vision that the 100 Year Starship Foundation is pursuing. You see, back in the early twentieth century – just at the time that science fiction writers were beginning to write about those mysterious alien worlds and empires spanning multiple star systems – Einstein showed that nothing could travel faster than light. This little problem would henceforth hang over the head of any science fiction reader who dreamed about the grand vision of space opera.

A universe in which you can board a star-ship, sail to a planet light-years away in a matter of days, and then return to find no one back home aged any more than you … that wouldn’t be our universe. Despite the theorizing of generations of physicists (most recently Alcubierre), FTL travel remains pure speculation.

I think the grand epic mythology of space opera was early twentieth-century science fiction’s greatest gift to humanity. It was a vision of hope, of endless growth and discovery made possible by our technological civilization. That vision has inspired generations of young people to take up careers in science and engineering, and try their hand at actually improving the world they live in. I’m pretty sure it inspired most of the people working on the 100 Year Starship project. I think covertly (or, quite openly) many of them still hope that, even if they don’t succeed in building the space opera future, that somebody, perhaps standing on the shoulders of their work, will. And they think that the big problem to solve in order to make that future possible is the problem of star travel.

After all, the enabler for space opera is faster than light travel; or, if not FTL, at least, star travel of some kind. And when you frame the problem this way, it’s a hard problem. You’ll probably need one hundred years to crack it, if it can be cracked at all. A lot of people are working very hard to solve this problem.

But is it the problem we need to solve? We want the space-opera future of unlimited galactic travel to exotic planets. That’s what we want. Is there a way to frame that goal that doesn’t require faster than light travel?

I’ve been thinking about this for a while. In 2002 I took a stab at solving the problem with my novel Permanence. That book was based on the premise that brown dwarf stars were far more common than had been suspected. If there were dozens of brown dwarfs for every lit star, then they could serve as way stations, and even destinations in their own right. The stars might be as far away as ever, but exotic and colonizable planets might be closer than we’d thought.

It turns out that brown dwarfs are not that common. Permanence didn’t quite solve the problem of how to have a space-opera future in the universe we’ve got. I always felt I was on the right track, though: the question we want to answer is not how to travel faster than light, but how to create the kind of future that faster-than-light travel would give us. In other words, FTL would give us a particular kind of civilization; but what else could give us that civilization?

(Less than) interstellar travel

In late 2011, I stumbled across an astronomy preprint on Arxiv.org, called “Nomads of the Galaxy,” by Louis E. Strigari, Matteo Barnabé, Philip J. Marshall, and Roger D. Blandford – and I thought I might have what I needed. The paper is simple and direct: the authors estimate that there are one hundred thousand free-floating “nomad” planets for every star in the galaxy. This estimate is based on microlensing studies; basically, we keep seeing stars blink as something tiny passes in front of them, and it’s become clear that the vast majority of those little eclipses are not caused by planets bound to the star in question. They’re full-scale worlds that were ejected from the stars that gave them birth, and now they wander rootless and invisible through the galaxy. We’d never know they were there if they didn’t occasionally pass in front of something else.

At about the same time, several other astrobiology papers were suggesting that some nomad planets, if they existed, could provide life-sustaining conditions, usually deep underground. Superearth planets in particular could retain habitable conditions under a thick blanket of atmosphere for billions of years, without needing energy from a nearby sun. Even an Earth-sized planet, frozen over at the surface, might nurture a Europan-style subsurface ocean, kept alive by the residual heat of the world’s formation. This, along with the Strigari et al. paper, implied there could be dozens, even hundreds of potential targets for human colonization between our world and the nearest star.

The size distribution of these planets almost certainly follows a power law, meaning that the smallest worlds will be by far the most common, and Earth-sized or larger worlds pretty rare. Still, out of a population of one hundred thousand, there might be dozens that could provide sustenance to earthly life without terraforming. It was a dazzling idea – but not quite good enough to invent a whole civilization around it.

Aside from the rarity of truly habitable worlds, there was the little problem that no matter how many of these worlds there might be in our vicinity, they’re still separated from one another by vast distances. A thumbnail calculation suggested that there’s about 1/10 of a lightyear between them. The first human-built object to reach interstellar space and until recently the fastest artificial object ever made, the Voyager 1 space probe, would take 1,700 years to travel between two of these nomad worlds.

So, in a sense this puts us back to Square One: how to solve the problem of distance.

Lockstep time

Solving the problem of distance, though, is not the same as solving the problem of speed. Speed (or velocity), distance and duration are related, but not identical issues. A space-faring civilization with the resources of an entire solar system at its disposal can probably solve the problem of speed. We can probably eventually build gigantic starships that travel at some respectable fraction of lightspeed – if we all pull together. In the space opera universe, though, families, companies, religious splinter groups, and criminal organizations buy or build their own starships. Anybody can travel between the worlds. Because I’m a storyteller, that was the particular future I wanted to enable.

What was needed was a truly crazy idea – something completely possible and utterly ridiculous, that would solve the problem. The truly ridiculous but possible solution I’d like to propose is something I call locksteps.

Locksteps don’t involve faster than light technology because they don’t have to. In my novel of the same name, no ship travels at more than a couple of percent lightspeed. The lockstep empire’s seventy thousand worlds are separated by huge distances, but the entire civilization is less than two light years across. I assumed that the capital planet, Destrier, is in the center of this rough sphere of worlds. In that case, ships heading out from Destrier at 1.5% of the speed of light could reach a substantial fraction of the worlds in only thirty years.

We haven’t built the engines that could power a ship to such velocities, but we know how they would work. The simplest design for a lockstep-quality drive is something called a Fission Fragment Rocket (FFR). Its power source is a small dense cloud of uranium powder held together by magnetic fields and allowed to reach a near-critical chain reaction. In this state the cloud throws off shattered bits of uranium atom at high velocities, and you just deflect these out of the back of the engine using magnetic fields. The FFR is so simple, in fact, that you can imagine little colonies on the smallest and poorest lockstep worlds building their own.

Thirty years between planets is still nothing like the hours or days pictured in your average SF movie. This is not our space opera future. So, here’s the ridiculous part: what if those thirty years could be made to seem like a single night, both to the travelers and to the people back home and at the destination?

Some ideas are impossible and loony. Some (like faster than light travel) seem reasonable but are impossible. And some, like the lock-step empire, are loony and (just) possible.

In Canada we have these tiny wildflowers that grow during our brief Arctic summer. They’re the most fragile things imaginable, and they winter over in negative-fifty-degree temperatures, under blasting winds and air as dry as any desert on Earth. They’ve thrived in conditions like this for millions of years because they don’t try to fight the cold. They work with it.

It wouldn’t be enough for a human civilization to cower under the ice of a few frozen-over Earth-sized nomads. A true interstellar empire – one that actually prospered between the stars – would have to have the same attitude toward resources as Arctic life. It would have to gather and use energy and material in those brief periods when it could, and it would have to be able to hibernate the rest of the time. So, imagine colonies on far-flung nomad worlds, whose citizens spend most of their time in a difficult-but-not-impossible state of artificial hibernation, while their machines patiently gather the energy and resources needed for a brief flowering of activity. The longer you can hibernate, the more time your machines have to harvest and build, and the more extravagant a lifestyle you can have during those times when you’re awake. The Arctic summer is extravagant; why shouldn’t the interstellar one be as well?

This is the idea of lockstep time: use hibernation to solve the problems of distance and duration, rather than trying to solve the problem of speed. It’s not just travelers moving between the worlds that spend trip-time in cold-sleep: the worlds themselves, both origin and destination, do the same. Do this ridiculous thing, and the problem of speed goes away.

Turns, frequencies, and jubilee

The decisive element that turns these far-flung worlds into a true interstellar empire is synchronization. If you and your neighboring planets adopt the same hibernation frequency – for instance, a ratio of hibernation-time/awake-time, expressed in months, of 360/1 – then hundreds or even thousands of planets are literally one night’s sleep away. You’ll have to wait a month to come back, but when you do, only a month will have passed back home as well; there’s no relativistic “twin problem” in the lockstep worlds.

From here, the logic of the locksteps becomes pretty direct. Those worlds that synchronize their turns experience the same passing of time. The longer you sleep, the more worlds are “next door.” And those worlds that operate on different frequencies are separated from you by a barrier more fundamental than distance.

A lockstep is my name for a group of colonies – be they individual space stations, clusters of buildings dug into the depths of comets, planet-bound cities or whole worlds – that sleep and wake on the same frequency, ratio, and schedule. Lockstep 360/1, for instance, collectively sleeps for thirty years at a time (except for its robotic sentries, resource harvesters, and factories). When its worlds wake, they all wake simultaneously and are awake for a month. Travelers who set out thirty years ago, if they are not still in transit, have been at their destination for perhaps years. They’ve been hibernating too, waiting for this moment. Now they wake and disembark, and at the end of the month new travelers set out, entering cold sleep at the same time as the rest of the lockstep. In this way, simultaneous time is experienced throughout the entire region, regardless of its size.

Far-flung destinations may require more than one hop to reach. Some ships will cruise for centuries before reaching the more remote worlds. This, however, is no different from travel in the age of sailing ships, when some ports of call were weeks away, and some many months. Global empire was possible under those conditions in the 1800s; it will be possible between the stars in a similar mode.

The longer you sleep, the smaller this problem becomes. A lockstep that slept for a million years at a time could experience a galaxy’s worth of planets as right next door. Of course, those planets would change unrecognizably between turns, so you might not want to go that far. But, a frequency of thirty years … that’s within the lifespan of trees, and certainly rivers, hills, and the buildings on them would not normally crumble overnight. And on frozen-over worlds like Pluto and the Kuiper planets, the landscape really won’t change over the lifespans of people, even if those lives are stretched out over hundreds of thousands of years.

The price you’ll pay is that time on worlds like Earth will seem to accelerate. A version of the twin paradox does exist in the lockstep worlds: if you leave your twin on Earth to join 360/1, they will have died of old age less than three months (turns) after you arrive. Stepping into lockstep time means leaving Earth, and all other realtime worlds, behind. There is no going back. If you pay this price, however, you get in return more worlds to explore than any realtimer could dream of. Those poor souls from Earth may in their lifetimes travel to other worlds – eight or ten of them. You can experience thousands.

Strangely, the most inaccessible places may be right next door. If your neighbors are lock-steps that operate on a different frequency, then you’ll rarely if ever see them. Two cities might exist side by side, whose inhabitants never meet because they live at different frequencies. Those frequencies might never match up exactly, but most will go in and out of phase: locksteps 360/1 and 372/1, for instance, will both wake simultaneously once every 960 years. I call the simultaneous waking of two or more locksteps a jubilee.

Jubilee is a special time among the lock-steps. Then, diverse cultures come together – parallel worlds that seldom meet catch a glimpse of one another. The rest of the time, the dormant fortresses and cities of locksteps of different frequency are as mysterious to one another as they are to those who live their lives in realtime.

If you think about it, having multiple lock steps can be beneficial. No matter how meager its resources, you can carpet a planet with lockstep cities because only one lockstep will normally be awake at any one time. If it’s a rich planet – a habitable Earth-like world, for instance – it could sustain a population of tens of billions with minimal impact to the biosphere, because only a fraction of that population would be drawing on its ecosystem services during a given period.

Scale

One obvious objection is that if you are actually able to stay awake all the time, you can harvest resources and manufacture much faster. Isn’t it obviously to your advantage to do so? For instance take two planets, one where the colonists hibernate for a decade and then awake for one month at the end of that time; and another where they are awake all the time. Surely the second world will be 120 times as productive as the first?

Firstly, we’re assuming that there is no limiting factor among all the resources that will slow World Two’s productivity rate (fundamental scarcity of some critical element or of energy etc.). We’re also assuming that World One doesn’t have a machine economy that is always awake even when its human population sleeps. This is an important idea for lock-steps: the tiniest of comets might not have enough energy or accessible elements to sustain a human colony, but if a population of energy-sipping robots slowly but constantly mines and manufactures for decades at a time, they may be able to produce enough, in a few years, to enable the brief awakening of a sizeable city.

Even so, let’s assume that World Two (our always-awake world) can mine and build and harvest as fast as it wants. It has an advantage in those areas. But does this advantage hold for trade as well?

If it’s using simple FFR rockets, World Two can exchange trade goods with its neighbors on a sixty-year round-trip schedule. For it, the benefits of one trade exchange are diluted across an entire human lifetime (give or take). For World One, which collectively sleeps for a decade at a time, one trade exchange is diluted across only six months of subjective time. World Two may mine and manufacture 120 times faster than World One, but it also uses those resources 120 times as quickly, while in absolute terms both worlds trade at the same rate. If you look at the lives of people living on these worlds, the difference is dramatic: across the lifetime of an individual, they experience the same productivity. They may appear radically different from an outside observer, but from within, these worlds feel the same.

World One, however, benefits from an enormous advantage in trade – again, looked at from within. A citizen of World One who sleeps for ten years at a time doesn’t experience those ten years, only the brief summers that follow. Chained together, those summers make a life similar to that of World Two’s citizens – except for the constant flood of trade goods that World One (subjectively) experiences.

Actually, the difference is even more dramatic, because while World Two may increase its productivity by spreading out across its (flat) landscape, World One can increase its trade capacity eight times faster by increasing the (three-dimensional) volume of space in which it trades. The longer World One sleeps, the more worlds its ships can reach during … let’s call it a turn. Double the geographical hinterland of World Two’s planet-bound economy, and you increase its economic power by roughly four times. Double the distance in three-dimensional space that World One’s ships can travel during a turn, however, and you multiply its potential trading partners by eight.

For hibernating worlds, trade scales faster than the exploitation of local resources.

Hibernation vs. FTL

The most important word in science fiction is if … if Einstein was wrong, or if Alcubiere was right, and somebody discovered a miraculous technology to travel faster than light … if it took less than the energy of an entire galaxy to use it once … the ifs pile up pretty fast when we’re talking about FTL. There are little issues like navigation, and what happens when an FTL ship encounters a large immovable object like, say, the Earth. The time-honored science fiction technique known as “hand-waving” usually comes into play to deal with issues like this.

In order to imagine an FTL civilization, we have to pile on the ifs and hand-wave like crazy. By contrast, what do we have to do to imagine locksteps? We have to imagine near-perfect hibernation technology.

Humans can’t hibernate. So far, attempts to develop hibernation technology for unmodified human beings have failed. There are promising avenues and hints of avenues to explore. Right now, cold-sleep is impossible.

But, in contrast to FTL, we know of no reason why hibernation would be impossible, provided we allow some biological alterations to human physiology. It’s a bit of a transhumanist cheat to redesign the human genome to give us an inbuilt hibernation reflex – but not much of one. In Lockstep, I’ve imagined a combination of extremely meticulous and careful external mechanisms – devices that monitor you down to the cellular level and do repair on individual cells if necessary – and genetic alteration. Nanotech in the body coordinates with the hibernation chambers I call cicada beds to allow humans to slip into cold sleep, and even be frozen solid to await resurrection after the thirty-year sleep. That reawakening could actually take months, as the machinery carefully repairs cumulative damage, tones your muscles for you, and so on. It doesn’t matter to the sleeper.

There are actually lots of ways to do it. If you believe in the possibility of uploading or backing-up the human brain, then the lock-step citizens could have their neural patterns stored while the physical body is recycled; then, when waking is required, a new body is printed and the mind inserted back into it. I don’t like this idea, though; it’s almost as hand-wavy as FTL. The cicada beds are pretty conservative by comparison. But maybe there are other techniques, like some sort of quantum-level flash-freezing, or insanely powerful magnetic fields that lock every atom in the body in place. For Lockstep I invented the denners, genetically and cybernetically altered animals similar to cats that can take over the role of the cicada bed, making it possible for humans to hibernate anywhere at any time. Biological as well as mechanistic solutions are possible; and you can set a lockstep frequency to account for any amount of recovery time that might be needed between sleeps. Maybe a month is too brief a period to be awake, and maybe thirty years is too long to sleep. Doesn’t matter – these times can be adjusted according to what’s actually possible.

The point is that the more you look at FTL, the less likely it seems, while the more you look at hibernation, the more avenues to it open up. I take this as a hint about where to spend my mental energies.

Redefining our way to the stars

It’s true that the locksteps are a bit of a cheat. They exemplify the idea that there are few problems that can’t be solved by redefining them. In this case, the problem was never the impossibility of faster-than-light travel; it was the difficulty of imagining how to have a space opera, Star Wars-type future in the universe we’ve been given. And unlike FTL, this is a solvable problem.

People have thought of lots of other solutions, too. Uploading and virtual universes can give us countless worlds to explore. The locksteps are for people who want those worlds to be real, physical places. The price is that they’ll almost all be frozen iceballs; and, of course, that you’ll be leaving your own era behind forever if you join a lockstep.

All of which makes me wonder: what have I missed? Is there an even better solution that will give us the space opera future science fiction promised us? Are there other clever redefinitions even better than locksteps?

One thing that’s clear is that we’re not done learning. Maybe FTL will turn out to be possible; but even if not, discoveries like the one hundred thousand free-floating planets per star will continue to come. Even if we can’t do FTL, we may discover technologies that make it unnecessary – clever reality-hacks that give us the future we wanted, just by another route.

The point is that we needn’t abandon reality for fantasy. Aspirational, exciting futures are still possible, provided we use a little imagination and stay open to the possibilities of the real. I’m a bit of a curmudgeon in this regard. I think that a fantastic future that is nonetheless possible is infinitely more worthy of our attention than a fantastic future that’s just a fantasy. Call me crazy, but there it is. There’s more than one way to go. Who needs FTL, when you’ve got all the time in the world?

Linked from 25/2/2019 Journal