[BRIEF NOTE] On generation starships

[rfmcdonald]

At his blog, Charlie Stross wonders how you could give a generation starship a society and a culture viable for centuries. What is a generation starship, exactly? See my extensive quote from Wikipedia below.

A generation ship is a hypothetical type of interstellar ark starship that travels across great distances between stars at a speed much slower than that of light. Since such a ship might take from as little as below a hundred years to tens or even hundreds of thousands of years to reach even nearby stars, the original occupants would either grow old or die during the journey and leave their descendants to continue traveling, depending on the life span of its inhabitants and relativistic effects of time dilation.

Such a ship would have to be almost entirely self-sustaining, providing energy, food, air, and water for everyone on board. It must also have extraordinarily-reliable systems that could be maintained by the ship's inhabitants over long periods of time. Humans might create large, self-sustaining space habitats before sending generation ships to the stars. Each habitat could be effectively isolated from the rest of humanity for a century or more, but remain close enough to Earth for help. This would test whether thousands of humans can survive on their own before sending them beyond the reach of help. Small artificial closed ecosystems, including Biosphere 2, have been built in an attempt to work out the engineering difficulties in such a system, with mixed results.

The social issues, as Stross notes, may well be key, and not only in the sense of having enough genetic diversity among the crew to avoid terrible inbreeding.

Generation ships would also have to solve major biological, social and moral problems, and would also need to deal with complex matters of self-worth and purpose for the various crews involved. As an example, a moral quandary might exist regarding how intermediate generations (for example, those destined to be born, reproduce, and die in transit, without actually seeing tangible results of their efforts) might feel about their forced existence on such a ship.

Estimates of the minimum viable population vary. The results of a 2005 study from Rutgers University theorized that the native population of the Americas are the descendants of only 70 individuals who crossed the land bridge between Asia and North America. Other researchers tend to propose a higher minimum number. Anthropologist Dr. John Moore estimated in 2002 that a population of 150-180 would allow normal reproduction for 60 to 80 generations, equivalent to 2000 years. Careful genetic screening and use of a sperm bank from Earth would also allow a smaller starting base with negligible inbreeding. An initial population of two female humans should be viable as long as human embryos are available. The health of the population depends on the diversity of the gene pool, which in this case would be directly decided by the quantity of preserved embryos.

I'm profoundly skeptical about the idea of generation starships. The only states that I can think of offhand with lifespans even close to a millennium are Japan and the Venetian Republic, both polities which changed massively over time. In any case, isolated island societies--the closest parallels we have to generation starships at present--tend not to work out well, as Jez Weston observed in the comments.

All societies, even democracies, seem to be quasi-stable, with outbreaks of violent change occurring following a power-law distribution - small changes are frequent, larger changes less frequent, but never reaching a cut-off point. The problem for a society in a generation ship is that the maximum size of violent change is sharply limited. Beyond a certain level of disorder, everyone dies, whether through a catastrophic failure (war that punches a hole in the ship skin) or a systematic failure (extinctions in the biosphere, extinction of the knowledge to run the biosphere).

This means that there'll be a requirement for the society to be responsible and self-limiting. However, there is no requirement for that society to be just, fair, or compassionate.

One example is Pitcairn Island. It's probably the most isolated example of a long-term community that we've got, a spec in the depths of the South Pacific, with a population that's varied between 50-250 since 1790. The history began with the mutiny on the Bounty, went through murder, slavery and alcoholism, had a successful transition to extreme religion, and spent the Twentieth Centry in what we'd call the systematic sexual abuse of twelve-year old girls. Many of the men there, including the Mayor and his deputy, called this "a normal part of Pitcairn life".

This continued over generations, because of the requirement for social stability. What else is going to happen? Without the community working together, then the place economically falls to pieces. When you're all your eggs in one social and economic basket, you're not going to tip that basket over, and if you're mad enough to try, then everyone else will try to stop you.

The problem was only resolved by outside force, namely intervention by the British Government. Pitcairn also had a safety valve - substantial emigration to much larger communities. That's not available on a generation ship. Without safety valves, it's going to get messy, eventually.

Besides, if you've the technology necessary to accelerate a massive starship to 2 or 3% of the speed of light, why not use that same technology to accelerate a substantially less massive starship to a substantially higher fraction of light-speed, one that would hopefully not require nearly as many desperate tricks to keep its payload from self-destructing? Do starships really need to carry that many people to colonize another planetary system? Assuming that such settlement is possible, of course.

Thoughts?