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Stepping Stones Across the Cosmos

by J. N. Nielsen

Nick Nielsen thinks big. In fact, today’s essay, which ranges over vast stretches of time and space and places human civilization in a continually expanding context, reminds me of nothing so much as the Olaf Stapledon of Starmaker. As with Stapledon, the questions are deeply philosophical: If we find a way to travel arbitrarily close to the speed of light, thus creating a civilization Carl Sagan once envisioned — one spread not only over space but over aeons — how will we cohere as a species? And what forms will our migrations take after the first pioneers have left our niche in the cosmos behind? For more of Nielsen’s work, see his blogs Grand Strategy: The View from Oregon and Grand Strategy Annex.


In my previous Centauri Dreams post, Cosmic Loneliness and Interstellar Travel, I argued that our cosmic loneliness is the reason we seek peer species and peer civilizations in the universe, that interstellar travel is a more practicable way to explore the universe for intelligent life than SETI/METI communication, and that such travel will eventually result as a consequence of the development of a 1G starship (a spacecraft that can accelerate or decelerate at a rate equal to terrestrial gravity). In my Centauri Dreams post prior to that, SETI, METI, and Existential Risk, I argued that SETI efforts will find technological civilizations if they are out there, and, by the same token, we will be found whether we want to be found or not, but we ought not to shrink from this possibility because the potential risk is at the same time a civilizational opportunity.

In this present post I would like to explore what kind of large-scale spacefaring civilization would emerge from the positions I have taken in the previous posts, specifically, the idea that we would be found by advanced civilizations if there were any, but we haven’t been found. I would like for these three Centauri Dreams posts to be understood as one long argument (as Darwin said of his Origins), and the argument is this: if it makes more sense to travel than to communicate, and if there is no sign of travel to Earth by extraterrestrial civilizations, then we are alone, or very nearly alone, in the cosmos. We may not be absolutely alone in the universe, but we are likely to be sufficiently alone that we can embark upon the initial stages of building a spacefaring civilization without the likelihood of finding any peer civilization in our initial voyages.

On the basis of physics as we understand it today, the spacefaring civilization we are capable of building will be subject to the constraints of a relativistic universe (except in the case of a disruptive breakthrough in science or technology), but we must learn to see this limitation as being at the same time an opportunity. Relativistic interstellar travel, and the spacefaring civilization that emerges from such voyages, will contribute materially to the existential viability of a civilization. This is the great opportunity that lurks within the limitations imposed by relativistic travel.

In my first post to Centauri Dreams, Existential Risk and Far Future Civilization, I argued that the existential viability of civilization is contingent upon three conditions: 1) knowledge, 2) redundancy, and 3) autonomy. Knowledge transforms uncertainties into calculable risks that can be managed; redundancy assures that if one center of civilization succumbs to an existential risk, other centers of civilization will remain to continue the life of civilization; autonomy among centers of civilization assures that distinct centers will pursue distinct existential risk mitigation strategies, therefore lowering the likelihood that multiple redundant centers of civilization would all succumb to the same existential risk.

A spacefaring civilization established by relativistic interstellar travel secures all three of these conditions in an especially robust manner. And it does so, as Carl Sagan said, in virtue of, “another and quite unexpected method.” The unexpected method of securing existential risk mitigation is what I call the establishment of a temporally distributed civilization, i.e., a civilization that is distributed not only in space, but also in time.


The idea of a temporally distributed civilization is something that I began to develop in my 2012 100YSS presentation, “The Large Scale Structure of Spacefaring Civilization.” There I observed that we tend to think of human expansion into the universe as distribution in space, but in a relativistic universe, distribution in time cannot be separated from distribution in space. As the engineering innovations of industrial-technological civilization bring us gradually ever closer to the possibility of a 1G starship, our spatial distribution in the universe will at the same time become a temporal distribution through time dilation: the faster we go and the farther we go, the more time will have elapsed at our point of origin.

Time dilation is not only subject to misconception, but the way in which the “twin paradox” has been commonly presented seems almost as though calculated to elicit a poignant response: one of two twins remains on Earth, while another flies to a distant star at relativistic velocities. When the traveling twin, who has experienced acceleration, returns, the twin who has remained on Earth is now old, while the returning traveler is yet young. The greater the speed of travel, the greater the time dilation effect, so that a 1G starship would allow a traveler to not only exceed the age of a twin, but to exceed the age of the Earth, and this would be sad indeed. It sounds like madness to undertake such a voyage.


[Image credit: http://physicsforme.wordpress.com/2012/04/26/the-twin-paradox-in-relativity-revisited/]

Even if many or most individuals are dissuaded from interstellar travel by time dilation, or are risk averse and would never fly to the stars out of fear, it would ludicrous to argue that no one will take the risk, or that no one would be willing to leave the world behind. Even under the conditions of total separation I strongly suspect that there would be a few individuals and small groups willing to cut their ties to their homeworld and go on a one-way journey to the stars. And it is highly likely that among the first to make the journey to the stars, some will never be heard from again (Some of these may prove to be questions as fascinating to the public as the fate of Amelia Earhart.) They will be as lost to us as early ships lost at sea. Perhaps they will go farther than any of us; perhaps they will be waiting for us at the edge of the universe when we finally arrive, en masse, as a civilization.

This, however, represents a limiting case of relativistic travel. To give an accurate picture of the large scale structure of spacefaring civilizations, the twins paradox must be recast in terms of populations rather than individuals. As in evolutionary biology, it is the population that is the unit of selection, although in this context it is a human population that is temporally selected, or rather selects itself. The vanguard of spacefaring civilization will consist of populations who desire their differentiation from the civilization of source (eocivilization); this process will be strongly selective of those who feel alienated from the civilization of their birth and are willing to abandon it.

There will be long-term socio-political consequences of the establishment of initial interstellar settlements by those least attached to the civilization that made spacefaring possible, but these socio-political consequences will be limited by the small size of the communities in question. In the same way that any communicating civilization would be overtaken by any traveling civilization, because of the technological innovations that would occur during the period of time while waiting for a signal to travel interstellar distances and then return, so too any civilization that experiences less time as a result of time dilation would be overtaken by a non-accelerated center of civilization. Later technological innovations from the original center of civilization will eventually overtake the vanguard, but the scales of space, time, and technology involved will mean that it will be an open question whether these vanguard communities will have transformed themselves into something unrecognizable in the interim.

It is likely that the greater part of innovation in propulsion technologies (and therefore that attainment of greater velocities) will occur wherever the greater part of the human population is to be found, which in the initial stages of a spacefaring civilization means that most advances in propulsion technologies will occur on a given species’ home planet while its initial starships will be isolated from these innovations. Thus technologies on the home world will surpass those who have made the first interstellar journeys.

In so far as such interstellar travel is continually improved and refined, it would not be isolated groups, but rather large groups that will eventually travel, or many individuals or small groups who could rendezvous at an appointed place and time. Collectively, such a group of travelers would bring its contemporaneous civilization along with it—they would both travel to the stars, and have their familiar civilization, although that civilization would not continue to mirror the civilization of source indefinitely as it independently developed, though later voyages are likely to diverge less from the source of civilization than earlier voyages.

Beyond a certain threshold, when off-planet population clusters approach the levels of density required for innovative scientific research on an industrial scale, and as innovations from the original center of the civilization result in cheaper, more effective, and more widely distributed transportation technologies, the bias will shift from the certainties of settled planetary life to the possibilities of life on a larger scope and scale that represents an increase in an order of magnitude of the choices and opportunities available. For the same reasons that populations have steadily moved from rural areas to urban centers, driving further urbanization once urbanization had become a viable way of life for the formerly-rural masses, populations will steadily migrate from settled planetary life to an accelerated life that joins the time-dilated community once this becomes a viable way of life for the civilized masses.

As civilization enlarges in scope, it is subject to a greater degree to the natural forces that govern the large scale structures of space-time. At the largest cosmological scale, the theory of relativity would prove to be constitutive of civilization. The farther a civilization extends in space, the greater number of frames of reference it encounters and the greater the diversity of these frames of reference. It is this process that will yield a temporally distributed civilization.

In the context of a temporally distributed civilization, a distinction must be made between the chronological age of a civilization and the temporal span that a civilization covers, since the cosmological distribution of centers of civilization at relativistic velocities means that accelerated populations cover a greater span of time than unaccelerated populations remaining at the original source of civilization. The temporal span of a civilization is the total portion of the age of the universe occupied by a given spacefaring civilization. This temporal span will be much larger in its scale of time than the chronological age of the civilization.

More significantly, distinct centers of civilization widely dispersed in space and time (i.e., separated by a significant temporal span) may be chronologically very close in age. When velocities close to the speed of light are attainable, this temporal span may be dramatic. Centers of civilization separated by thousands or even millions of light years may be chronologically only a few years apart, so that essentially the same civilization exists millions of years apart in terms of its temporal span. Separation of months or years or even decades amounts to little more than a rounding error in terms of the scale of time involved.

This distribution of essentially the same civilization throughout widely separated spans of time will result in a very high degree of existential risk mitigation, since these temporally distributed centers of civilization will not even be subjected to the same natural disasters occurring on a cosmological scale, as they will inhabit different ages of the universe. A sterilizing gamma ray burst may doom the unfortunate center of civilization coeval with that disaster, but other coeval centers of civilization will be spared this particular risk, though they may be subject to other existential risks.

These coeval centers of civilization, approximately the same chronological age, but widely separated across the universe as faster and farther travel takes us ever greater distances from the original source of our civilization, will be like stepping stones across the cosmos. An interstellar traveler might pass from one arm of the Milky Way galaxy to another, always having a familiar center of civilization to stop and to pause. Some would choose to stay and maintain that center of civilization (and its coeval character), while others may choose to go farther. Such stepping stones across the cosmos might eventually take us from galaxy to galaxy, cluster to cluster, and supercluster to supercluster.

The new centers of civilization that result from interstellar voyaging, and which can serve as stepping stones across the cosmos, will be connected to each other as peer civilizations. It is only when you seek to retrace your steps that you come “back” to a near-peer civilization (i.e., a civilization sufficiently removed in time that it is no longer a peer simpliciter), now removed by degrees of separation in time, or even to a non-peer civilization, the farther and faster you go back to the former source of civilization. If homeworld civilization stagnates, one might even return to something like a peer civilization, but even a peer civilization would be unrecognizable, as the continents of Earth rearrange themselves and all our cities and monuments disappear and are replaced by new structures, until the Earth is no longer habitable.

The cosmos itself forces us to confront the fact that you can’t go home again. Earth is our cosmological home, and once we leave it for the stars we will not be able to return to the world that we left behind. But we will take our terrestrial civilization with us to the stars, and these new centers of civilization established by interstellar voyaging will possess the knowledge, redundancy, and autonomy requisite to mitigating any existential risk.

The civilization that I have described will be both strikingly similar to and radically different from the civilization that we know today, and we will have to formulate new modes of self-understanding in order to conceptualize our place within such a cosmic order. The advent of temporally distributed civilization will mean that the historical consciousness that human civilization has laboriously constructed, and which we have greatly expanded since the formulation of scientific historiography, will have to be expanded and extended once again by the expanded and extended human experience of a civilization that spans the geometry of spacetime across the galaxy and eventually across the universe, step by step.


Comments on this entry are closed.

  • Tarmen January 17, 2014, 11:48

    If we are graced with this much time and space, it looks like a ‘wild west’ type of expansion. A ‘wild west’ but far far larger scaled and longer lasting. It looks like the law would fall far behind the wagon trains. There would be only the local ‘ sheriff ‘ idea of law. Plenty of shootouts, bandits, massacres. Plenty of boom towns and ghost towns. Boom worlds and ghost worlds. Religious offshoots of all kinds. Relics from by gone days alongside modern here-and-now tools. Lots of conflict between diverging peoples of totally different mindsets. Perhaps after a long time, the older settled regions would submit to a regional authority. But then the various regional authorities would conflict where ever they overlap in time and space. By then it’s looking like Romulans vs Klingons vs Federation. Eventually we would fill up our given time and space and bump against truly alien zones.

  • webwalker January 17, 2014, 15:06

    We are going to have to come together as a people united in the world before anything like leaving here and spreading out is ever attempted. We have far too many prejudices and selfishness to overcome. I think the world of Star Trek is a beautiful thing and it is a socialist based society. An episode comes to mind about Kirk or was it Picard’s disdain of some captitalists. Look at the condition of our country at this moment because of the actions of a few greedy investor crooks in the last 3 or 4 years and our own government bailing out the very bunch that did it with no one being held responsible. That will have to change.
    I understand the longing and feeling of home one gets when you look at the stars probably because it is where we came from… We are Star stuff.
    We have to mature as a people and be better stewards of the Earth before we spread out. It’s a beautiful world we have here and we have our little corner of the universe to explore, take care of and make better.

  • RonSmith January 17, 2014, 16:11

    This is a bit off topic, but I have never understood the claim that travel in a 1G starship would result in relativistic time dilations.
    I do understand the concept of relativity, at least to an extent, but the specific claim that a 1G starship would result in such dilations does not make sense to me.
    We here on earth are constantly exposed to 1G acceleration. Eintein’s principle of relativity, as I understand it, states that there is no difference between gravitational acceleration and acceleration due to change of velocity. So the gravity of Earth has, in all ways, the same effect on us that the 1G acceleration experienced by travelers on such a spaceship would have.
    Therefore I can only surmise that someone in a spaceship accelerating away from the earth at 1G would age at EXACTLY the same rate as someone staying behind on the 1G spaceship called Earth.
    As I said this is a bit off topic, and I don’t expect an explanation from anyone here, but maybe someone could point me to a resource that would explain this?

  • Wojciech J January 17, 2014, 16:59

    For various reasons the vision of the civilization doesn’t seem likely.

    First of all, the assertion that we are alone is based on our very limited observations.
    Humanity likes to take pride from its technology but the fact is that our tools and methods are still very lacking.
    Just think-a mere 100 years ago-a less than a blink on cosmic scale-humans believed sincerely in abundance of life on Venus or Mars. Using the best telescopes and science they had.
    And less then 30 years ago, we barely could even confirm if there are planets around other stars.
    Our methods and telescopes are still very, very basic and we know little about universe.
    We have been searching for signs of civilization that would be advanced by 100 or 300 years from us, while statistics dictate it would be older by hundreds of millions of years if not more. Only lately have we discovered traces of things that maybe, just maybe are products of technology advanced far more than ours like Dyson Spheres or hypervelocity stars.And it is far more likely these are just natural phenomena anyway.
    There is a lot for us to discover and we may yet verify our assumptions about alien life in universe.

    As to the civilization-it follows the often made assertion of endless expansion, which seems flawed in its basic assumptions. As I have mentioned before, when you have technology to colonize other stars you no longer need to. Artificial habitats, virtual reality and modification of the species would allow to limit the need for expansion tremendously.
    While I do not claim that some form of space exploration and colonization would happen(especially due to fringe groups), it doesn’t seem likely that massive interstellar community beyond a dozen or hundred light years would happen.
    Even our world is slowly stabilizing in regards to population growth and we now value conservation of natural eco-systems more and more.

    So far now I would wait for observations in next 30-50 years by telescopes which are bound to change our understanding of humanity’s position in universe.

  • Tom West January 17, 2014, 17:08

    RonSmith: You’re not accelarting towards the Earth (excluding those times you are jumping in the air). Hence we are not “constantly exposed to 1G acceleration”, hence no time dilation


    What I woudl like to see is travel times for various intersellar/inter-galactic distances for those *on* the ship, given constant 1G acceleration. (Well 1G hafl way there, and -1G the other half). My quick mental calculations imply you could reach most of the galaxy in 15 years of on-ship time.

  • Alex Tolley January 17, 2014, 17:45

    @Ron Smith – it is the velocity that affects time, mass and length. The Wikipedia page is a useful place to start.

  • Michael January 17, 2014, 17:46


    ‘This is a bit off topic, but I have never understood the claim that travel in a 1G starship would result in relativistic time dilations.’

    Given enough time at 1G it is not long before we are going relativistic, for example at 1G acceleration we will be traveling 0.5c in about 176 days. In 318 days of 1G acceleration we will be going 0.9c which has a time dilation of about 2.29, which means things appear to be taking about just over twice as long to be done, things also appear to shrink to 0.43 of normal.

    ‘WE LIVE ON A 1G SPACESHIP. So the gravity of Earth has, in all ways, the same effect on us that the 1G acceleration experienced by travelers on such a spaceship would have.’

    But because we are not moving away from the earths reference frame (clock) therefore we experience no perceivable time dilation, but when compared to free space people on earth are aging slower than further away in space in which there is little moving/mass to distort space-time, it is however very little.

  • Alex Tolley January 17, 2014, 17:56

    There are some interesting consequences of this expansion based on technology change and civilization length.

    If starships take centuries to reach the pinnacle of 1G acceleration, then the earlier travelers should choose short distances to prevent being overtaken by later travelers. Only when the technology has reached its maximum development should really long range travel occur. The only reason for early travelers to want to attempt long distances is because they want to meet an advanced civilization at the destination. One wonders if simple suspended animation on Earth, or a circular journey (c.f. Planet of the Apes [movie version]) makes more sense in this case.

    If the length of a civilization is much shorter than the galaxy’s dimensions in light years, almost any civilization upon reaching a star will find itself alone in time, at least in the early stages. For example, if the civilization lifetime is 2000 years, unless there are very many other travelers that stopped close by in time and space, that civilization would be cut off from all other civilizations and the distance and/or time between civilizations would be greater than 2000 years. This might be either desired, or a lonely experience, depending on the civ’s culture.

  • Alex Tolley January 17, 2014, 19:18

    Even if the colony ships were small and rare, any ship that landed could increase its population a billion fold in a millenium with just 2% pa growth.
    So I don’t see that as a stumbling block for civs to plant themselves throughout the galaxy.

  • Joy January 17, 2014, 21:18

    Olaf Stapledon believed in a punctuated equilibrium model for the advancement of genus Homo, the fall of each species setting up the conditions for the rise of the next. Another scenario would be that the early H. sapiens experiments with first agriculture and now technology come to ruin as degradation of soils, aquifers, ores, and the atmosphere advance faster than belated attempts at remediation. Climactic feedbacks result in an end Permian die off in the ocean and an Eocene thermal maximum on land. Homo in the year 100,000 CE would consist of dwarfed circumpolar hunter gatherers and a semi-aquatic tropical marine species. No matter, the universe is patient and would still be there if our genus wished to try the technological thing again.

    Ok, that might qualify as extreme pessimism for Centauri Dreams. But surely such a Stapledonian scenario is at least consistent with geological natural history. Relativistic starflight? Impossible to prove a negative, but there is no credible evidence that this is possible in our universe.

  • Michael January 17, 2014, 21:55

    One way to preserve some sort of civilisation constant would be to communicate with each other at the ‘speed of light’ virtually. i.e. transmit information to each other about what is going on in each civilisation node. But alas each node of civilisation will become independent because there will ultimately be an increasing delay of information to each node. This transmission of information could also possibly aid our propagation if for instance one of the nodes discovers a better drive or survival technology.

  • James D. Stilwell January 18, 2014, 11:57

    It’s pointless to avoid having a child simply because one may never live to meet one’s great grandchildren…hence building worldships to forever leave earth is sensible and a goal worth pursuing…
    Few want to imagine the Singularity coming about either…
    Which is the accomplished artilect or synthetic man with an IQ of 200….
    Synthetic men will be required to build worldships in orbit anyway….
    They’ll build worldships for the cost of their manufacture and repair….
    Assuming we first develop a civilization friendly to artilects….
    Celebrating the day they achieve consciousness on their own….
    Heinlein’s “The Moon Is A Harsh Mistress” offers insights….

  • Alex Tolley January 18, 2014, 12:09

    @Joy, JM Nielsen. Does the model of expansion break down if starflight is not relativistic? I don’t see why it wouldn’t hold even if flight is a small frction of c. The method of travel changes, but I don’t see why the outcome should.

  • Alex Tolley January 18, 2014, 12:48

    BOE calcs for starship speed differentials, civilization lifetime (L) and destination strategy.

    If a later ship travels at 99% c while the earlier manages 98% c, then every ~100 ly allows a later group to catch up 1 ly with the earlier group. A 100k ly journey across the galaxy means that the 2nd group could reach the destination 1000 years before the first group. Plenty of time to build a civilization to meet the 1st group. For a journey to Andromeda M31, 2.5 Mly away, the time differential is 25,000 years. If L << 25,000 yrs, the second group leaving thousands of years later, could arrive first, build a new civ that flowers and dies, so that the 1st group arrives finding a dead or moribund civ with possibly very advanced monuments littering the local star system or cluster.

    This leaves 3 possible strategies:
    1. Target nearby stars to ensure that you are the first colonizers and can build your new civ,
    2. Target distant stars in the hope than the target will have become a high tech civilization founded by a later, faster traveling group, by the time they arrive.
    3. Target really distant targets so that a later group will have developed a civ, but decayed, allowing the first group to arrive to enjoy the fruits of teh remaining infrastructure.

    Which you choose may depend on what you are. Are you a founder civ, or a parasite or predator?

    This all gets complicated by multiple journeys, local expansion, and whether your slight is relatively early in the expansion phase or late.

    However, despite this, I don't think it changes the initial premise that star flight will result in new civilizations being embedded in time, as well as space. It does affect whether these civs are isolated in spacetime, or not.

  • Eniac January 18, 2014, 15:33

    Alex Tolley: I severely doubt you will ever find ruins without a civilization around. This “lifetime” L strikes me as ill-defined and irrelevant. There has never been a civilization that disappeared without another one taking its place, and I think there never will be. So, depending on how exactly you define “civilization”, L is either infinity, or it is irrelevant because you have forgotten to take into account that civilizations do not just “decay” away without replacement.

    Some of the greatest ruins on Earth had to be painstakingly dug out from under busy city streets….

  • Heath Rezabek January 18, 2014, 16:57

    @Eniac – It’s worth remembering, however, that a civilization which falls and fails to be replaced by one that has the wherewithall to strive for greater things (such as to become an interstellar civilization) won’t really be a peer civilization to one that eventually discovers it lolling about in the ruins of its forebears.

    This would be the Xrisk category known as Permanent Stagnation. So, if that state is reasonable as a potential outer boundary risk to a civilization’s ability to be a peer to another more advanced than it, then L remains relevant.

  • Brett Bellmore January 18, 2014, 18:40

    “It is likely that the greater part of innovation in propulsion technologies (and therefore that attainment of greater velocities) will occur wherever the greater part of the human population is to be found,”

    I think the contrary is arguable. It’s true that a large population implies a large number of minds possibly devoted to the problem, and large resources which can be brought to bear.

    However, advanced interstellar travel most likely requires high energies, which a densely populated society may be conservative about experimenting with. And a high population divides those resources among more people.

    I think it’s likely that self-reproducing infrastructure will predate interstellar travel, just because it will be necessary for interstellar travel, to produce the needed ratio of infrastructure and energy resources to population where a large enough excess exists to do expensive things.

    So, imagine, the colony arrives in a new system. Infrastructure starts out on an exponential growth curve, with a doubling time in the weeks to months, but eventually saturating out due to heat dissipation requirements and available resources. An S shaped curve. Population also begins an exponential increase, followed by declining growth rates, but on a longer scale.

    It’s the ratio between the two curves which dictates resources available for interstellar travel, and that peaks long before population.

  • Roger January 18, 2014, 18:53

    The fact that we have not been “found” by ET may very well be due to ET’s reluctance to engage with an immature space faring civilization and an immature erratic unpredictable fratricidal “global” civilization. I would think that in spite of our technological advances, we must seem infantile and perhaps dangerous to advanced space faring civilizations – who can probably cloak there whereabouts with ease. We are probably on the “do not visit list – wait a few hundred years”!

  • Jer January 18, 2014, 20:30

    …of course, if we create instantaneous communication (quantum entanglement to ansible facebook anyone?) and/or indefinite lifespans (or indefinitely prolonged and developing consciousness identities) this dislocation may not come to pass, but would rather just be this incredibly dense information field propagating and self-reinforcing itself within us, as we choose, over time. I believe that these technologies are just as likely as mass/rapid transport to the stars given enough generations or centuries.

  • Alex Tolley January 18, 2014, 21:15

    @Eniac – I think we have had this discussion about what constitutes a civilization. You may be right that there are no isolated civilizations without immediate replacement by another, but it is undeniable that civilizations operate differently. We see that in the case of the withdrawal of the Roman occupation of Britain, which resulted in roman structures being torn down for their stone without comparable structures being built. Had Genghis Khan not died and his empire had overrun Europe, the cities and towns would have been destroyed or left to ruin.

    Suppose our current global civilization fails and we are extinguished. Any of the big existential risks we know about might cause this. Then there would most definitely be some value for L. (No argument that the average lifetime may be a power law function, rather than a simple gaussian).

    My point is simply that by changing parameters, we may get different expansion types when you feed this into the simulations.

  • Gerry January 18, 2014, 21:51

    I read something by Adam Crowl a while back speculating about a 1-G starship propelled by a baryon-burning drive. If I remember correctly, this drive would convert matter into a beam of neutrinos, providing thrust in a manner analogous to an anti-matter photon rocket. I suppose you might get over 20 tons of thrust per gram of fuel converted each second. He envisioned coupling it with a ram-scoop to provide a continuous feed of raw matter for conversion. The neutrino beam would have useful momentum, but would be far less dangerous to ship and crew than a beam of gamma rays would be.

    I haven’t found anything else about this idea, except that it seems similar to some ideas Frank Tipler had about artificial sphalerons and such. I know it’s all at the very edge of what’s barely conceivable, but then so is the idea of a 1-G star ship in general. I do hope Dr. Crowl or someone else will someday elaborate further on the physics and engineering ideas (and challenges) behind such an engine.

    At any rate, if we are lucky, perhaps by the time we have advanced relativistic star ships, we’ll also be in a position to bring wormhole mouths along with us to our destinations, to serve as threads preserving a connection to where and when we originated even as we spread across space and time.

    Perhaps some colonists through accident or deliberate intent will lose or destroy their wormhole connections, thus leaving themselves truly isolated from galactic civilization.

  • Tarmen January 19, 2014, 10:23

    Almost the instant that each of these envisioned colonial launches leave for another stepping stone, the ones on board will begin to differ from those left behind. Even before launch they will have self-selected to a degree. Then later, when they choose a new place to settle of have a place chosen for them, they will rapidly evolve in outlook from who they were on board. How could a group of colonists not be changed by a whole other world with wierd sunlight, strange calander and chemistry? Let alone if they need to compromise with native life. Some very creepy cultures will inevitably arise under the pressure to survive somehow some way. I would forsee later arivals could be shocked at what has been established at many far places. So are they really all the same civilization? I’d say no.

  • Sean M. Brooks January 19, 2014, 13:10

    Very interesting article by Mr. Nielsen. I’m reminded of how Poul Anderson touched on some very similar ideas in many of his works. Examples being his Kith stories, STARFARERS, ORBIT UNLIMITED, and the stories collected in NEW AMERICA. These works were based on what might happen if only slower than light, relativistic star traveling was used.

    ORBIT UNLIMTED speculates on what might happen if a discontented minority used relativistic travel to leave an Earth they consider hostile to their ideals and beliefs. By contrast, Anderson’s Kith stories focuses on a culture which remained space based and hence outlasted the rise and fall of civilizations on Earth and its colonies on other worlds.

  • Wojciech J January 19, 2014, 17:35

    Alex Tolley
    “Even if the colony ships were small and rare, any ship that landed could increase its population a billion fold in a millenium with just 2% pa growth.
    So I don’t see that as a stumbling block for civs to plant themselves throughout the galaxy”

    I don’t really expect entities capable of long range space flight beyond local cluster of stars to be determined by old biological need of constant reproduction and endless growth. Especially across a timescale of millenium.
    Considering that any other civilization would have to be millions of years ahead of us in development, then the lack of visible overpopulation of galaxy suggests this is not a strategy they pursued. And there are good arguments for this.

  • Andrew Palfreyman January 20, 2014, 0:59

    I am curious if anyone has run the algebra on a straightforward symmetric accelerate/decelerate interstellar trajectory. According to SR as applied to a photon rocket, whereby about half the mass of the craft is utilised on each half of the trip, it appears to be impossible to exceed 0.6c. That means that destinations like Andromeda are right out of the question, even with super-advanced energy storage capabilities.

    If you want to dig in deeper, feel free to email me: andrewppp at att dot net

  • Michael January 20, 2014, 15:26

    @Andrew Palfreyman

    ‘I am curious if anyone has run the algebra on a straightforward symmetric accelerate/decelerate interstellar trajectory. According to SR as applied to a photon rocket, whereby about half the mass of the craft is utilised on each half of the trip, it appears to be impossible to exceed 0.6c. That means that destinations like Andromeda are right out of the question, even with super-advanced energy storage capabilities.

    If you want to dig in deeper, feel free to email me: andrewppp at att dot net’

    try this site


    Although the photon rocket is very efficient it might be better to send a stream of pellets/fuel stream, timed, out towards the target and then send a craft after it which collects and uses the fuel, each pulse giving it enough energy to get to the next pellet/stream. Remember 1G for 318 days gets us to 0.9c The advantage of both methods is that the structural components to store, ignite the fuel etc. are much smaller than for a craft that is required to carry all the fuel. The energy of moving the ‘fuel’ is paid for by accelerator/s which are quite efficient with heavy generators. Slowing the craft down could be achieved say by a load pellets or fuel stream been sent decades ahead but slower and again timed. This pellet/fuel stream can then be picked up by the craft near the target system and used as fuel to slow it down again or even using the fuel and still going ahead but dumping light mag/light sail probes in the ionised exhaust which slow them down.

  • RonSmith January 20, 2014, 16:27

    @Tom West
    Sorry, but we ARE constantly exposed to 1G acceleration otherwise we would be flung off into space by the Earth’s rotation.

    @Alex Trolly
    Thanks for the link. This clears things up for me somewhat, but there are still some details that don’t make sense. I will continue reading.

  • Alex Tolley January 20, 2014, 16:27

    @Andrew Palfreyman
    Why is staging not considered?

  • Alex Tolley January 20, 2014, 17:09


    I don’t really expect entities capable of long range space flight beyond local cluster of stars to be determined by old biological need of constant reproduction and endless growth. Especially across a timescale of millenium.
    Considering that any other civilization would have to be millions of years ahead of us in development, then the lack of visible overpopulation of galaxy suggests this is not a strategy they pursued.

    I tend to agree with your analysis, but disagree with the conclusion. Endless expansion of physical numbers is unsustainable. That doesn’t mean that we cannot have periods of a few thousand years where there is logistic growth to high population numbers at a distant target star or star cluster. There could also be many reasons why we don’t see aliens nearby that used this strategy.

    I personally think that the idea of humans (us or our near term post human versions) traveling as physical entities is highly unlikely because either the targets will be living and incompatible with us and our necessary ecosystems, or dead and need massive terraforming that would take millennia at a minimum. Far more likely is that we send tiny (relatively) ships that contain the information to reproduce sentient cargo. I further suspect that sentient cargo will be machines, or machine like, rather than complex biologicals. Machines that could live anywhere and not require a massive, ecosystem support system. So I see seedships, carrying the information to build sentient machines that will use local resources to replicate their civilization in time frames far shorter than any humans could do.

    Obviously we don’t see them either, and so we are back to the Fermi paradox.

    If real resources are not a sustainable goal, then virtual worlds are the way to build rich, vibrant civilizations, here on earth, or the solar system. They could contain a mix of human and artificial intelligences, with the humans initially physically embodied in flesh, but later not. An extended The Matrix scenario. Whether computational requirements would be less than actual physical ones is an interesting question, but in principal an endless dream world should be possible.

  • william collins January 20, 2014, 21:05

    Very enjoyable and thought provoking article! Predicting the future development of Human civilizations (post-interplanetary civilization) would be as difficult for as for citizens of previous human societies to predict the the current state of human societies in the early 21st century. Since I have become convinced albeit relucantly that traversable wormholes and warp drive propulsion systems arefaniful dreams I believe that humans will spread across the cosmos over the course of untold millenia- I hope. Earth may become a distant legend for these folks who will live in another part of Milky Way Galaxy – if it is not forgotten altogether.

  • Andrew Palfreyman January 21, 2014, 7:56

    I am incorrect in assuming that we consume half the mass up to the midpoint. What actually happens is that we consume the same mass fraction for acceleration as for deceleration, assuming these are both the same acceleration value.

  • ljk January 21, 2014, 10:11

    william collins said on January 20, 2014 at 21:05:

    “Earth may become a distant legend for these folks who will live in another part of Milky Way Galaxy – if it is not forgotten altogether.”

    Like in the Foundation Series by Isaac Asimov, where Earth is the mythical and legendary world of human origin (in Asimov’s galaxy, there are no ETI).


    And Battlestar Galactica, except in this case it is the lost Thirteenth Colony of the human race.

    This is another way the messages and information carried aboard the twin sets of Pioneer and Voyager space probes may be come invaluable to future generations across the Milky Way: They point the way to Earth and give some details about the early decades of the Space Age:


    Much of that may be lost over thousands of years of space and time. Thus my plea again that every deep space mission carry information about us and our world for future generations, human and alien.

  • william collins January 21, 2014, 18:16

    My interests in this blog relate to the sociological/cultural aspects of future spacefaring human societies. How will our descendants who explore, settle and exploit interplanetary space – a necessary precursor to human expansion out to nearby solar systems. How will they govern themselves; how will mobilize the resources of our solar system; how will power and wealth be distributed; if future humans are longer lived in more robust way that includes greater adaptaion to hostile environments, i.e. deep space, Mars, Moon, etc.will there emerge a great divide between the spacefarers and the billions of humans who will probably never go beyond NEO? Interstellar space exploration at even relativistic speeds could cause the emergence of human societies which will develop in unforeseen ways. Propulsion system development is key of course but not as important to me as the development of the people who use these future systems. Since I believe that humans will hopefully
    survive to spread across the galaxy as Nick Nielsen describes.

  • Eniac January 22, 2014, 23:53


    We are probably on the “do not visit list – wait a few hundred years”!

    Who’s list whould that be, exactly? If there is one star-travelling ETI, then there are hundreds, or millions, of societies. Are you suggesting they all share and synchronize their do-not-visit lists?


    Had Genghis Khan not died and his empire had overrun Europe, the cities and towns would have been destroyed or left to ruin.

    Really? Are you saying Mongols are an inferior race? Do you think you can make such statements about alternate history at all?

    It is just as plausible that the result would have been an early Renaissance in a flowering Greater Mongol Empire, followed by the advent of modern technology several centuries earlier than actually happened.

  • william f collins January 23, 2014, 10:58

    I tend to agree. I suspect that there is no interstellar quarantine set up on us; it is more likely the tremendous distances, the enormous energy outputs, and the humongous costs of travel around the galaxy that would be greater explanations for the lack of apparent visitors. There could be a great number of other civilizations in our galaxy- or not. Maybe the clue lies in the fact that wormholes probably do not exist and FTL & warp drive propulsion are not feasible or possible means of getting around deep space. ( By the way, while it is clear that Mongols are not inferior to any other humans, their destruction of Baghdad among many other cities may have served as the model for the type of civilization that they may have left in their wake . Who knows?)

  • ljk January 23, 2014, 13:36

    Places that cooperated with the Mongols (and some did because they saw the potential benefits) were spared and became part of their empire. Those that did not were utterly destroyed. The Romans had a rather similar policy, though they only destroyed a place if it were a threat, like Carthage.

    Even the Vikings eventually settled down and became part of the cultures they had initially invaded. Though they were no fun for their targets during their pillaging and plundering era.

    If our civilization collapsed and humanity did not go extinct, would we repeat these cycles again ala A Canticle for Leibowitz, or would humanity decide – willingly or otherwise – to remain in a rural agricultural and hunter-gatherer state?

    It might sound nice, but we would be defenseless against such things as a planetoid or comet strike. There is some historical backing on this, as recent evidence indicates a piece of Comet Halley may have struck Earth in 536 C.E., causing widespread famine in the early days of the European Dark Ages.


  • Alex Tolley January 23, 2014, 17:08

    @Eniac. I am not clear why you would interpret my comment as “superior civilization/people = city dwellers”. The Mongols destroyed non-surrendering cities and all the people in them. When you do that, and you have a nomadic ancestry, the chances are the cities will stay fairly empty and decay. If you have killed everyone, it is going to be a bit tricky repairing the infrastructure that breaks. No so different from allowing the railways to decline in the US, because automobiles and trucks have become the preferred transportation mechanism. Car people are not superior to train people or vice versa.

    As for a renaissance stimulated by Mongol rule, what evidence is there that this happened anywhere in the succeeding century of Mongol Empire?

    I don’t disagree with the difficulties of alternative history, but the Mongols did defeat the Hans in China

  • Dexter Trask January 24, 2014, 18:02

    Vernor Vinge did an excellent treatment of human civilization spread spatially and temporally in “A Deepness in the Sky.” The Stross novels “Singularity Sky” and “Iron Sunrise” also deal with the same issue (although resulting through very different mechanics).

  • Eniac January 25, 2014, 0:07

    Alex Tolley: As LJK mentions, the Mongols are not the only ones apt to destroy cities. In fact, the largest and most efficiently destroyed cities in all of history were Dresden, Hiroshima, and Nagasaki.

    That said, I am not defending my version of Mongol alternate history. I am just saying that my version is equally as plausible as yours (meaning: not very), and it is simply not possible to pick one over the other, except maybe for dramatic effect.

    To my earlier point: Most of those cities destroyed by the Mongols have later been (and are still now) thriving. So have Dresden, Hiroshima, and Nagasaki. And the Han have long since recovered from their defeat at the hands of the Mongols and are now getting ready to take second place in line for world domination.

  • James D. Stilwell January 26, 2014, 13:58

    I’m looking forward to renting a studio apartment in the American Quarter of the planned Chinese Lunar colony called New Hong Kong…..They’ll be doming over a small lunar crater with reflectve flex material say by about 2030 and by 2040 tourist will be able to don a pair of wings and fly about the crater’s interior atmospheric pressure…..all they’ll need to get going is a fleet of Skylons, lunar water and several trillion dollars…JDS

  • william collins January 29, 2014, 22:20

    The possible directional paths for longer-lived humans who have conquered all of the age- related infirmities and , who exploit the resources of the solar system to an advanced degree, and are able to sucessfully survive and thrive in the very dangerous environment of interplanetary space are fascinating to contemplate. Without economic incentives, threats of extinction, population pressures, or the long range discovery of inhabitable planets in nearby star systems, I expect small scale expeditions out to nearby star systems and beyond to be the likely norm – of course, small scale could mean world ships transporting afew thousand people or a whole lot less.