An obvious objection to the idea of human journeys to the stars is time — if we can’t find ways to reduce travel time to well within a human lifetime, so the thinking goes, then we’ll have to stick with robotics. But expand the timeframe through multi-generational ships and you change the parameters of the debate. The notion of a multi-generational ‘worldship’ whose crewmembers have long forgotten their actual circumstance is a classic trope of science fiction, with obvious references like Robert Heinlein’s story “Universe” (1941), later reprinted in Orphans of the Sky, and Brian Aldiss’ Non-Stop (1958), published in the US as Starship.
But maybe such a crew wouldn’t forget where it was going. For that matter, would the people aboard a true worldship, one that took, say, 5000 years to make the average interstellar crossing, really consider themselves a crew? They might prefer the term ‘inhabitants’ when describing themselves, because they would be living inside a structure so vast and commodious that it would simply have become a home. By the time they reached their destination, they might well decide to study it for a few generations and then move on to the next distant world.
All of which depends, of course, on our ability to build vast structures in space, huge living worlds that take their inspiration from Gerard O’Neill’s colonies, on which entire ecosystems could flourish. Such mega-engineering is hard to imagine if you’re thinking in terms of 20th Century technologies, but by the end of this century, molecular nanotechnology could conceivably be applied to the task, turning fields of building material like the asteroid belt into workable structures. If off-planet living becomes a serious option, then generations accustomed to living aboard enormous space colonies will surely find among their number some who decide to make the interstellar journey, even if thousands and thousands of years are involved.
Michael Anissimov discusses space colonization in terms that relate to this in a fascinating post on his Accelerating Future weblog. Noting Marshall Savage’s projection that the asteroid belt could theoretically house 7,500 trillion people if exploited in its entirety (this is drawn from the latter’s The Millennial Project), Anissimov goes on to ponder the motivations for space exploration itself. Here’s one relevant bit:
Why expand into space? For many, the answers are blatantly obvious, but the easiest is that the alternatives are limiting the human freedom to reproduce, or mass murder, both of which are morally unacceptable. Population growth is not inherently antithetical to a love of the environment – in fact, by expanding outwards into the cosmos in all directions, we’ll be able to seed every star system with every species of plant and animal imaginable. The genetic diversity of the embryonic home planet will seem tiny by comparison.
Thus one model for interstellar colonization. Rather than building a starship capable of carrying a tiny crew to another star in less than a century, we first turn to exploiting the resources of our own Solar System. Eventually we make a wide variety of space-based habitats available, where colonies of all sizes and descriptions can flourish. Our expertise with nanotech engineering will teach us how to make the most of the abundant resources we have within reach of our planet. At some point, pushing ever deeper and farther out, we may well see the first enterprising colonists depart Sol forever.
Of course, such a perspective demands a different view of time than anything we’re familiar with today. Those of us who believe our expansion into the stars is inevitable also know that the time scale is unknowable. The one thing we can predict with certainty is that it will take the efforts of generations to build the necessary base for such journeys, and to put the technologies available at each step of the way to wise use. Worldships are only one possible outcome of this work, but the reason Centauri Dreams supports continuing research into all aspects of interstellar flight is that building that base is critical if we ever hope to make the interstellar vision a reality. Ad astra incrementis.
The fast interstellar flight is the most exciting of all. Why do we need worldships to reach the stars in time frame thousands of years if we could reach them in less than a life time? I hope that a breakthrough in space ship propulsions will happen soon and then it will terminate that kind of sci-fi in the article.
A breakthrough propulsion technology is hopeless because even if we manage 0,99c – which is highly unlikely – it’ll take hundreds of thousands of years for interstellar travel. Millions, even billions of years for intergalactic travel.
The problem must be approached from a different perspective.
There were times when it was deemed acceptable for a journey or an expedition to take a year or two. At times when most people reached an age of maybe 40 this was very aproximately 5% of their lifespan or 10% of their adult lifespan.
To travel to our nearst interesting neighbour, it may take 40 years. This would be deemed appropriate by an individuum having a lifespan of say 500years.
Another interesting neighbour may be Eta Cassiopeiae at 200years travel.
We soon reach a lifespan of say 1000years to find travel acceptable.
The technology to enter an age of spaceship building is around the corner,
but we also urgently need to be masters of our DNA to enable us to enjoy the results of journeys of this magnitude.
So it is not only technology we should develop to fulfill centauri-dreams, but also biology. And then andromeda-dreams will still be dreams.
Hi Philip, I disagree. If a ship successfully reach 99,9999% of speed of light then the astronauts on board will experience the so called Time dilation wich means that for them(the astronauts) time will slow down. A journey to the center of our galaxy(The Milky way) will only be 21 years(ship time) wich is measured in 30 000 years normal time. A journey to Andromeda galaxy will take 28 years and a circumference of the known universe in 56 years, but the astronauts will return in distant future(billions of years). The high relativistic speed turns a starship in a time machine. Even of we build antimatter engines wich will help us to reach that kind of speed a future interstellar economy will still be impossible. If we depend of resources from a planet 50 ly from Earth then Earth will have to wait that big vessel one half century. “Time is money”! If we want to survive then we must find a way to exceeding the light barrier!
Hi Phil
I agree on life extension/suspension for IS travel, but your statements are a bit fuddled. If you could do 0.99c the time dilation is about 7. Thus a trip to Eta Cassiopeia is 20 years planet time, but less than 3 years in ship time. It’s 200 if you are doing 0.1 c, but that’s not how you started your post.
Assuming very advanced mass-beam technology a constant acceleration could be sustained for the whole trip. At 20 gees a subjective time of 1 year would allow one-way voyages of about 770 light years. A subjective time of 1.82 years at 20 gees gets you to Andromeda.
Given that we haven’t managed to figure out how to build an interstellar probe for an economically-feasible price tag, even for a flyby of another star (let alone entering orbit around another star), speculation on manned interstellar missions is interesting but probably premature/irrelevant at this stage. We currently don’t even have the infrastructure to transport people beyond low Earth orbit.
Philip suggests that increasing human lifespan may be necessary to make an interstellar journey worth the time it will take. This leads me to another thought.
Whether looking at flights that take many generations or half of an individual’s lifespan, humans must be physically and psychologically adapted to living in space. Heinlein’s Orphans Of The Sky has ‘muties’, like two-headed Bobo, resulting from living in the outer levels of the ship. But his muties are simply that – mutants, not adaptations.
In Dan Simmons’ Hyperion books there is a nomadic society, the Ousters, who have become physically adapted to living and traveling in space. Some mutations are probably accidental but many are intentional. For instance, some Ousters sport opposable thumbs on their feet and prehensile tails. When taken in context, rather than an evolutionary reversal these traits are an advancement.
So there’s an idea. Not only will humans need a new understanding of time for interstellar and intergalactic travel, but also perhaps a new understanding of what it means to be human.
Hey, a post mentioning my blogs name. ;-)
Anyways, as far as “time” goes, time is merely a concept. We currently measure it by how long it takes Earth to travel around the Sun.
Regardless on your perception of time, you will still age no matter what. Unless there is a way to extend the human lifespan, are great, great, great, great grandchildren may be the only ones to see the fruit of the interstellar expedition.
PS
What about worm holes? Any possibility of constructing those?
As I see it with my admittedly limited 21st century mind, we have two non-mutually exclusive ways to go: Conventional propulsion (which includes Bussard ramjets, solar sails and fusion engines) and long-generation starships. We don’t really have the technology for arks yet, whether we talk of a self-sustained closed system or adaptation of the travelers. The exotic variations (FTL, stable wormholes) may remain forever in the realm of SF. Even so, it will be wonderful to travel out.
Darnell, I already asked Adam about the black holes. You can see his answers here.
https://centauri-dreams.org/?p=1335
If we could control black holes, then we will produce negative energy for a worm hole.
Athena, FTL will not forever be sci-fi. Remember that. Maybe we are more close than we can imagine.
…it may well turn out to be complete and utter fantasy. Wormholes may not be possible – these kind of things are pushing our physical models into regimes where they may not apply, and it may turn out that these kind of tricks do not work.
andy, we will see who is right after some decades ;)
Hi Lubo & andy
Perhaps our models aren’t daring enough – we’re on the verge of learning about higher dimensions once the LHC is up and running. We’ve a few vague ideas on what that might mean, but there’s a whole Unknown Country awaiting us.
As I argued before in a previous post, I do not really believe in multi-generation ships/arks, O’Neill Colonies, worldships, etc., for the fundamental reason that any extended time in space, especially if combined with reduced space/population, increases risk. In other words: the longer the time spent and the smaller the colony (in terms of both living space and population), the greater the accumulated risk.
This holds true for islands and small nature reserves on earth (island theory, island biogeography), and probably much more so during space travel. Risks varying from accidents (internal, external), disease and inbreeding, conflict, resource exhaustion, or simply ‘collective amnesia’ about the purpose.
I do believe in the usefulness of suspended animation/hibernation and the like, because this can actually reduce needs and risks during travel.
I also do not believe that leaving earth would ever serve the purpose of reducing population pressure or resource depletion, because for the same investment there would always be cheaper and easier solutions here on earth.
The real purpose of colonizing the MW galaxy would be exactly that: colonizing the galaxy for the purpose of spreading (our) life ánd spreading extinction risk.
I love Anissimov’s description of ‘seeding the galaxy’ with life (note: as far as it does not already have its own life!).
But I still think it will have to happen relatively fast per each step, on the order of 0.1 c – 0.9x c, as long as we don’t master any exotic FTL propulsions.
Mind you, between 10 and 50 ly there are several dozen very promising sunlike stars. Supposing we travel at 0.5 c average (accel/decel) these could be reached within several decades. Even at 0.1 c it would ‘only’ be a few centuries (in hibernation), not a terribly long time for a whole new world.
But, as proposed for Mars as well, we would probably first send small robot probes, then unmanned ships for ‘preparation’, possibly seeding and/or terraforming a new world, and lastly a small number of humans and other species.
Lubo: I am not saying that I think FTL is definitely impossible (though I would not be surprised if it were), just that right now there is precious little reason to think that it is possible, let alone merely a few decades away. But who knows…
Of course, if FTL is a possibility, it would put an interesting constraint on solutions to the Fermi paradox.
Sustainability: A Tedious Path to Galactic Colonization
Authors: Y. Dutil, S. Dumas
(Submitted on 12 Nov 2007)
Abstract: Civilization cannot sustain an exponential growth for long time even when neglecting numerous laws of physics! In this paper, we examine what are fundamental obstacles to long term survival of a civilization and its possibility to colonize the Galaxy. Using the solar system as a reference, resources available for sustained growth are analyzed. Using this information, we will explore the probability of discovering a civilization at its different stage of energy evolution as estimating some possible value of L, the typical life time of an extra-terrestrial civilization.
Comments: 4 pages, to appear in the proceedings of “Bioastronomy 2007”, ed. Meech et al
Subjects: Popular Physics (physics.pop-ph); Astrophysics (astro-ph)
Cite as: arXiv:0711.1777v1 [physics.pop-ph]
Submission history
From: Stephane Dumas [view email]
[v1] Mon, 12 Nov 2007 14:13:18 GMT (20kb)
http://arxiv.org/abs/0711.1777