The Defense Advanced Research Projects Agency (DARPA) recently announced the 100 Year Starship Study , an effort to encourage long-term thinking about the realistic prospects of interstellar travel, specifically with the goal of devising a workable mission-plan within the next century. This bold call to action is exciting, but let us consider the more plausible scenarios under which such a venture might eventually occur. Doing so should help us orient our efforts toward those proposals with the greatest likelihood of success.
This article proposes the theory that it is highly unlikely we will ever send humans beyond the solar system, not because it is fundamentally impossible — or even necessarily difficult — to do so, but because technologies that would circumvent such efforts will arrive before we would embark on such a mission. This not to suggest that we, as a civilization, will not voyage to the stars — merely that we will not travel there as flesh-and-blood humans. The technologies which will disrupt such a mission are two forms of computerized intelligence: artificial general intelligence (AGI, computers and robots endowed with human-level mental capabilities), and mind-uploading (MU, the transfer of an individual person's mind from the brain to an artificial and engineered substrate, i.e., a computer) [2-6,12-14]. As a consequence, when contemplating interstellar travel, we should focus less of our effort on the challenges of life support, generation-ships (arks) [15-17], social and psychological challenges of long-duration travel [18-20], and even suspended animation , despite their prima facie sense of importance. Rather, we should focus almost entirely on the underlying methods of interstellar propulsion and navigation since the results of such research will most readily apply to either potential crew type, computerized or biological. Furthermore, where mission design decisions are governed by the characteristics and needs of the crew and cargo, we should consider that such crew and cargo will most likely consist of small powerful computers and robotic vehicles (bodies), not humans in their present form.
The Historical Arrival of Technological Advancements
We can rightfully speculate that certain technologies should arrive before other technologies in the natural course of an intelligent species' scientific and technological evolution. As an exaggerated example, one would be hard-pressed to argue that the invention of the bow & arrow should logically follow the invention of the airplane. Let us consider the question of which order two technologies ought to arrive in as the repeated experiment of rerunning history over and over (even if it is only a thought experiment), and then inquiring about the proportion of trials in which one technology would logically be expected to precede another. That is, if we were to rerun history multiple times, which technologies should tend to precede other technologies in most of the resulting scenarios? This approach permits some stochastic plasticity in our analysis. As stated, we would generally expect the bow & arrow to precede the airplane in practically every timeline. It is actually rather difficult to think of pairs of existing technologies for which there is no expected order of arrival, i.e., for which repeats of history would yield 50/50 odds. Such an observation justifies speculation about future technologies. That is, we may assume that there is a correct order of arrival for anticipated technologies and we are justified in investigating what that order is.
Why do some technologies predictably arrive earlier than others? I propose three primary explanations. First, some inventions are direct prerequisites to others. Physical instances of an earlier technology may be actual components of a later technology (as is the wheel to the wagon) or alternatively may be tools critical to the construction of the other (as are pliers and screwdrivers to electronics or bellows to melted metal and glass). One might point out that rudimentary work on some technologies is often possible without earlier tools, but nevertheless, mass-production may still be precluded until the necessary tools are developed. Since it seems doubtful that AGI or MU are direct prerequisites to interstellar travel or vs/va, this explanation should not be of tremendous importance to our analysis.
Another reason is that some technologies require a larger and more organized society to either finance or physically construct, if not necessarily to mentally conceive of. Constructing a small sailing dinghy can be done by a lone individual, but funding and building a large ocean-going ship requires a mature economy, a large work force, experienced leadership, and centralized project management. In our modern era we appear to have achieved the necessary societal scale to actively research AGI and MU (the work is proceeding as we speak). In contrast, interstellar propulsion poses a notable economic challenge, especially since it cannot so easily benefit from tangential research in other domains (whereas AGI and MU steadily advance toward their own goals as a byproduct of ongoing computer AI and neurological research). This explanation therefore offers some insight into the primary thesis of
There is a third reason certain technologies should arrive later than others: they are fundamentally more complicated and should therefore arrive later in a society's technological advancement. They either require a more sophisticated understanding of the physical principles of nature or they cannot be constructed without mastering more difficult manufacturing techniques. For example, it is a safe bet that the steam engine should follow the printing press in most reruns of history. The printing press can be built almost entirely out of wood, and what few metal parts it has are fairly small. On the other hand, a steam engine requires large quantities of iron and steel, much more difficult materials to work with than wood. Of perhaps greater importance, a steam engine relies on a richer understanding of physics to either conceive of or to refine into a practical design. The mechanical principles underlying a printing press are comparatively simpler to discover and develop. For these reasons, the printing press should be expected to arrive before the industrial steam engine in most reruns of history. Despite the economic challenges mentioned above, the most basic methods of interstellar propulsion may actually involve simpler technologies that AGI or MU — they are barely more complicated than our conventional rockets. However, they involve such long travel times (tens of thousands of years) that the technical challenge of equipment longevity becomes preeminent in and of itself. On the other hand, the more advanced and therefore more theoretical propulsion ideas offer drastically reduced travel times and therefore simplify equipment longevity challenges, but they reintroduce the engineering challenges of highly speculative propulsion methods, as described later.
Future Technologies Relevant to Interstellar Travel
The primary hypothesis of this article is that AGI or MU will arrive before the necessary technologies for manned interstellar travel come together in a viable mission, such as interstellar propulsion and navigation, long-term hardware longevity, life-support, the ability to govern multi-generational societies, and possibly even methods of suspended animation although that technology may be a tougher call than the others (it may arrive earlier and therefore offer better competition to AGI and MU for the claim to first arrival).
If AGI or MU arrive before manned interstellar travel is fully realizable, it is highly unlikely we will ever bother to send flesh-and-blood humans to the stars. Sending AGI and MU is simply much easier. The evidence is our own history of space exploration. We have always sent machines and rudimentary robots throughout the solar system before following up with manned missions. We sent probes to the moon before sending people and we have yet to follow any of our robotic probes elsewhere in the solar system. Robotic probes offer significant advantages over humans in the realm of space travel. While a robotic probe may not weigh less than a human (although it certainly can, a la the infamous Mars Sojourner rover), its support infrastructure certainly weighs considerably less. With regard to a waking voyage (a generation-ship as opposed to suspended animation), people require large living habitats, food and water, air, heating, cooling, a pressurized atmosphere, radiation protection, gravity or methods of resisting muscle atrophy, limited exposure to accelerative G-forces — the list goes on. In addition, computers and robots can directly exploit the most readily available energy sources, such as electricity from nuclear reactors. Transforming such energy into food involves a necessary loss of efficiency.
Furthermore, there remains the well-studied, but never-the-less highly concerning, matter of psychological health during long missions, and such matters get worse the longer the mission. While some confidence may have been attained in the study of mental health during multi-year missions such as going to Mars [18-20], there is simply no precedent with regard to multi-generation missions. The psychological impact of knowing that one's entire life — even one's entire society — is merely an intermediate stage to a multi-millennial goal set in motion by long-lost ancestors, the rewards of which will only be reaped by distant descendants, are vague to say the least. Mutiny takes on a whole new level of meaning in this context. Another difference between a multi-year Mars mission and a one-way voyage of interstellar colonization is that the latter requires a significantly larger crew, again for reasons of mental health but also primarily to serve the basic needs of a nascent and utterly self-reliant society that hopes to not die out . Obviously, as the crew size grows with mission requirements, so grow the costs. Admittedly, many of these concerns are alleviated by the notion of suspended animation, which is considered below. The point is not that generation-ships are necessarily impossible, but rather that the prior arrival of AGI and MU obviate such a scenario entirely by easily outweighing the challenges associated with manned missions.
To briefly compare and contrast AGI vs. MU, it is worth pointing out that MU offers virtually all of the benefits of AGI (all the benefits of conventional robotic probes mentioned above) — plus one additional and crucial benefit: MU isn't just our tools, our stuff, our things. It is us. There are two reasons why we followed robotic probes to the moon, and why there is a pervasive undercurrent of cultural interest in manned space exploration (even if it is often relegated to book shelves and movie screens). The first is the fairly practical fact that up to the current time, humans have offered great advantages over robots in terms of physical agility, intelligence, and on-site decision-making. These advantages will wane in the future as AI continues to advance and as robotic bodies become more lithe and efficient. However, the second reason we followed probes to the moon was that the probes were not us. They were merely our tools, external extensions of ourselves. We didn't just want to watch the moon on TV; we wanted to walk on its surface and feel the soft dust beneath our soles, to bound in its low-gravity, to glimpse Earthrise with our own eyes. In short, we wanted to go on an adventure, and that drive will remain at the core of the human condition forever. MU offers just such a possibility. To send a MU-transformed person to the stars is to send ourselves.
Discussions about MU can become quite contentious on the topic of personal identity. Many people strongly believe that MU is in fact not you, but rather a simulacrum, something denigrated in its mental and psychological faculty, something inferior that we should detest. For example, some people believe that the mind resulting from a MU process cannot be conscious in the way that a human mind is — that at best it is a doppelganger or philosophical zombie (the idea that despite convincing external behavior there is nevertheless nobody home, no conscious experience . Some people go further by believing that we cannot even replicate the illusion of MU, that the suggestion of mind-like behavior exuding from anything other than the brain is a nonstarter. Such philosophical meanderings are fascinating — and anyone who thinks these matters can be casually dismissed as not having been considered in exhaustive detail by the MU community is selling the whole subject short [2-6,12-14] — but to pursue the matter here would utterly derail this article, so I must defer to existing works on this issue. For the time being, let us consider the possibility that MU is theoretically feasible and becomes available in the near future (this century).
This discussion cannot be considered fair and complete without accounting for the possibility of suspended animation. This is a popular motif in the canon of interstellar science fiction and has recently received serious consideration for near-term applications, such as preserving victims of battlefield or other traumatic injuries long enough to get them to a hospital [22,23]. The advantages for interstellar travel are immediately obvious: much smaller space requirements, potentially lower resource requirements (both mass and energy), a natural resistance to colder temperatures translating to lower heating and consequent power requirements, easier shielding against radiation (due to smaller enclosures), and the complete elimination of any social or psychological concerns. In addition, we are already making impressive advances in this technology. Wouldn't one then argue that suspended animation may actually arrive early enough to offer serious competition to AGI and MU as a candidate for interstellar travel? I consider this point in the next section.
The Likely Order of Arrival of AGI, MU, Suspended Animation, and Interstellar Propulsion/Navigation
Suspended animation is — if anything — poised to arrive well ahead of AGI and MU. In fact, in 2011 the first clinical trials were approved . It is therefore a safe bet that this technology will be completely ready by the time we plan the first interstellar mission. However, suspended animation is not enough. AGI or MU is not enough. We need interstellar propulsion and navigation. That will probably be the last technology to fall into place. Researchers report regularly on steady advancements in robotics and AI and many are even comfortable speculating on AGI [7-11] and MU [2-6,9-14]. It is true that there is wide disagreement on such matters, but the presence of ongoing research and regular discussion of such technologies demonstrates that their schedules are well under way. On the other hand, no expert in any field is offering the slightest prediction that construction of the first interstellar spaceships will commence in a comparable time frame. DARPA's own call to action is a 100-year window, and rightfully so.
We certainly won't be sending our first mission to the stars by mid-century (we'll be lucky if we get to Mars frankly). The difference between the potential arrival times of the first three technologies (AGI, MU, and suspended animation) and the last (propulsion/navigation) is enormous — on the order of several decades, possibly upwards of a century. By that logic, AGI and MU could arrive much later than the most optimistic predictions and yet still have time to arrive before the earliest interstellar mission. It appears that one must be remarkably pessimistic about the arrival of AGI or MU (barring philosophical positions that utterly preclude such technology) in order to invalidate the claim that they will precede interstellar propulsion — they seem to be decades ahead.
Consequently, even if suspended animation arrives before AGI and MU — admittedly, the most likely order of events — it is still mostly irrelevant to the discussion of interstellar travel since by the time we do finally mount the first interstellar mission we will already have AGI and MU, and their benefits will outweigh not just a waking trip, but probably also a suspended animation trip, thus undermining any potential advantage that suspended animation might otherwise offer. For example, the material needs of a computerized crew grow as a slower function of crew size than those of a human crew. Consider that we need not necessarily send a robotic body for every mind on the mission, thus vastly reducing the average mass per individual. The obvious intention would be to manufacture a host of robotic bodies at the destination solar system from raw materials. As wildly speculative as this idea is, it illustrates the considerable theoretical advantages of a computerized over a biological crew, whether suspended or not. The material needs of computerized missions are governed by a radically different set of formulas specifically because they permit us to separate the needs of the mind from the needs of the body.
Much of this theory rests on the observation that the likely time of arrival of interstellar propulsion is notably later than AGI and MU. Others seem to agree. For example, Seth Shostak, head of the SETI Institute, has advocated looking for computerized intelligence for similar reasons . There are many ideas for interstellar propulsion currently on the table. Some are pretty basic, relying on conventional science and engineering, but are still no where near first implementation. Of course, their interstellar travel times are the longest and they therefore pose the greatest mission-design challenges in terms of either a waking crew's psychological needs or alternatively the longevity of suspended animation equipment (potentially tens of thousands of years). Then there are more advanced proposals, trading plausibility and advancement of engineering principles against mission travel time. Ironically, since the more advanced methods generally offer shorter travel times, they actually simplify the psychological and hardware-longevity challenges. Some interstellar propulsion options are, in approximate order of feasibility: ion drives and gravity slingshots (we know how to do this today as a matter of fact), fission power, solar sails, fusion power, and antimatter power [25-29]. None of these methods will be mission-ready earlier than the second half of the century, and that's only for the simplest and consequently longest-travel-time options. On really long-term time scales, there is no reason to doubt that any of these technologies could work, but the question is, will they arrive before humanity perfects AGI and MU?
The purpose of this article is absolutely not to dissuade public interest in interstellar travel. Quite the opposite, I fully agree with people like Steven Hawking who argue adamantly that humanity's only chance for long-term survival is to spread beyond the confines of Earth , and doing so ultimately implies spreading beyond our solar system as well. As we look forward on the order of centuries or millennia, we can contemplate the long-term destiny of the human condition. What will our civilization look like in the far flung future? Will we still be confined to this one planet. Will we even be confined to this lone solar system? I would submit that we will either venture forth into the galaxy or we will eventually succumb to our own ennui and eventual extinction, but that the third alternative of prospering indefinitely within the white picket fence of our current solar system is veritably untenable. I highly commend DARPA for priming the public's interest in such projects...but at the same time, let us be realistic about — and plan accordingly for — the most likely circumstances under which our eventual emigration will take place.
The importance of adopting a realistic perspective on this issue is self-evident: if we aim our sights where the target is expected to reside, we stand the greatest chance of success, and the eventual expansion of humanity beyond our own solar system is arguably the single most important long-term goal of our species in that the outcome of such efforts will ultimately determine our survival. We either spread and thrive or we go extinct.
About the Author
Keith Wiley received his PhD in Computer Science from the University of New Mexico in 2006. He currently works as a research scientist in the Department of Astronomy at the University of Washington where his work focuses on the application of very large computing clusters (Hadoop) to massively parallel image data processing with applications to SDSS and LSST. When he isn't developing methods to reduce astronomical survey data, he can be found composing music, nurturing his love of photography, and seeking opportunities to travel. In the past he has also been an avid astrophotographer and rock-climber. Keith is also one of the original members of MURG (the defunct Mind Uploading Research Group). His contact is: firstname.lastname@example.org, http://keithwiley.com.
DARPA 100 Year Starship Darpa 100 Year Starship: http://www.100yss.org/
AGI, MU Introduction Paul, G., and Cox, E. Beyond Humanity: Cyberevolution and Future Minds. Delmar Thomson Learning, 1996.  Kurzweil, R. The Singularity is Near: When Humans Transcend Biology. Penguin, 2006.  Moravec, H. Robot. Oxford University Press, 2000.  Introduction to MU: http://www.ibiblio.org/jstrout/uploading/
AI, Robotics, AGI, MU Research Stanford Stanley Robot: http://cs.stanford.edu/group/roadrunner/stanley.html  IBM Watson: http://www-03.ibm.com/innovation/us/watson/  Blue Brain: http://bluebrain.epfl.ch/  Human Brain Project: http://www.humanbrainproject.eu/  AGI Conference: http://agi-conf.org/2011/  ASIM Research: http://www.carboncopies.org/  Singularity Institute: http://singinst.org/  Singularity Summit: http://www.singularitysummit.com/
Interstellar Arks Matloff, G. L. Utilization of O'Neill's Model I Lagrange Point Colony as an Interstellar Ark, Journal of British Interplanetary Society, Vol 29, 775-785, 1976.  Matloff, G. L. Deep Space Probes: To the Outer Solar System and Beyond, Springer, 2005.  Required crew: http://www.newscientist.com/article/dn1936
Long Term Space Flight Kanas, N. Expedition to Mars: Psychological, Interpersonal, and Psychiatric Issues. Journal of Cosmology, Vol 12., 3741-3747, 2010.  Le Scanff C., et al. Psychological Study of a Crew in Long-Term Space Flight Simulation. International Journal of Aviation Psychology. Vol. 7, No. 4, pp293-309, 1997.  ESA Mars500 Project: http://www.esa.int/esaMI/Mars500/
Philosophy of Mind Chalmers, D. The Conscious Mind: In Search of a Fundamental Theory. New York Oxford University Press, 1996.
Near-Term Suspended Animation Blackstone, E., Morrison, M., Roth, M. Hydrogen Sulfide Induces a Suspended Animation-Like State in Mice. Science, Vol. 308 (5721):518, 2005.  Clinical trials: http://www.forbes.com/sites/alexknapp/2011/05/05/names-you-need-to-know-dr-peter-rhee
SETI Should Search for Computerized Intelligence Shostak, S. What ET Will Look Like and Why Should We Care. Acta Astronautica, Vol. 67, No. 9-10, pp1025-1029, 2010.
Interstellar Propulsion Survey of methods: http://www.bukisa.com/articles/331671_five-real-life-methods-of-interstellar-travel  Survey of methods: http://knol.google.com/k/the-potential-of-interstellar-travel-by-advanced-propulsion-techniques  Dyson, G. Project Orion: The True Story of the Atomic Spaceship, Henry Holt and Co., 2002.  Projects Daedalus/Icarus: http://news.discovery.com/space/tau-zero-project-daedalus-icarus-110119.html  Project Icarus: http://www.icarusinterstellar.org/
Humanity Leaving Earth Steven Hawking: http://bigthink.com/ideas/21570
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