16 July 2007

do we need to go to Mars now?

A Survival Imperative for Space Colonization, from today's (Tuesday's) New York Times.

There's something called the "Copernican principle" which states, basically, that if we know nothing about how long a given process has been going on, we ought to assume that there is nothing special about the current moment. Therefore, if we look at something that is currently going on, the probability is one-half that we are in the first half of the thing's lifetime, and therefore it'll keep going on for longer than it's already gone on. For example, if you didn't know anything about history, you should assume that the United States has an even chance of lasting another 227 years. The usual practice in statistics is to form a 95% confidence interval; that works out to be that we are not in the last 2.5% or the first 2.5% of the United States' lifetime, that is, there's a 95% chance that the U.S. will last between 227/39 years (a little less than six years) and 227*39 years (about nine millennia).

Or another 400 years, since the Jamestown colony in 1607? When did the United States start? That makes this sort of analysis tricky.

The Copernican principle's principal exponent is J. Richard Gott III, and a long list of times when the principle works is given here. I'm a bit skeptical, because throughout the paper he predicts 95% confidence intervals. And then he says "well, 90% of the time the results are within the 95% interval" -- or 100% of the time -- and claims that's good enough. It's hard for me to be convinced. I'd be more convinced if he made predictions about the distribution of the remaining lifetime, or even predictions of the form "the U.S. has a 50% chance of lasting between 227/3 and 227*3 years".

Anyway, Gott goes on to argue that because of this Copernican principle, we ought to start trying to develop a colony on Mars in the next fifty years or so, because the spaceflight program has a significant chance of going extinct soon. But I don't think this is so. Gott has tested his principle on things like how long world leaders stay in power, how long Broadway shows last, and so on -- these are things for which there is a large sample. We have no idea how long space programs tend to last, because there have only been at most a handful in human history. Furthermore, I would guess that we are near the beginning of that part of human history when we are capable of spaceflight, given that we don't just wipe ourselves out as a species -- it seems unlikely that we'll forget how to go into space, given the distributed nature of information these days. (Then again, I suppose the people in charge of the Library of Alexandria would have said the same thing.)

I agree with the idea that if we want to perpetuate the human species into the far future, then we should attempt to colonize other planets, especially since we seem to be ruining the planet we have. But the probabilistic logic underlying this is hardly ironclad. Maybe it's reasonable to say that spaceflight will continue to exist as long as the human species itself does.

1 comment:

Michael Cassidy said...

Bah, we should go to Mars because it will fun . I'm in favor of more Rovers also.