March 14th, 2009
Not every scientist has an interest in science fiction or anything resembling the ability to think like a science fiction writer.
I was reminded of this again today in regard to this story about how to focus SETI searches.
Basically, the idea is that it is easier in principle to find and characterize Earth-like planets when you can see them eclipsing their system’s star. Therefore if we want to talk with ETIs, we should be targeting our searches in the plane of the ecliptic. “Plane of the ecliptic” is just a technical term for the directions in space that would see us eclipsing the Sun. The aliens living in star systems in the plane of the ecliptic, so the reasoning goes, would then be the ones most likely to have spotted us and be trying to communicate with us.
Maybe a teeny-tiny bit more likely, but overall a dumb reason to restrict searches in my opinion. (Somehow the article I linked to talks about using the idea to “broaden” searches, but that’s just bad reasoning or writing, in my opinion. The only way to use the idea is to restrict searches.) Let me explain why I think the idea isn’t very good or logical, setting aside my scientist cap for my science fiction writer cap.
We are at the dawn of the era of discovery of exoplanets. We haven’t quite found Earth-like planets yet, but we’re approaching the technology and time required to do so. We’ve gone from no exoplanets known 15 years ago to many hundreds now, and the eclipse-finding technique is just the latest step. We’ll be able to image Earth-like planets around other stars in the relatively near future, and in all likelihood, a century from now barring some catastrophe in our civilization, we’ll have the technology to do a whole lot more. A big enough space telescope could do the job of spotting Earth-like planets in principle, whether or not they are in eclipsing systems.
So, the only way I think this makes any sense as a strategy is if the aliens are essentially at the same technology level we are, and not a century or more advanced.
If you think that high-technological civilizations are short lived (centuries or less), the chances of finding one anywhere nearby is tiny, let alone in the highly-restricted plane of the ecliptic.
If they’re long-lived (much longer than centuries), they will have the technology to spot us whether or not we are an eclipsing system as seen from their world and we should be looking everywhere for their signals, if in fact they are sending us such signals.
This argument can be quantified, which would take time away from things more important to me that this flawed proposal, in order to say exactly how small the benefit would be from adopting this strategy, if in fact there is any benefit at all. It is not at all clear to me that it is one. In fact, I will go as far to say that I think the study is wrong. If civilizations are long-lived, we’d be idiots to restrict searches as there are a lot more systems outside the plane of the ecliptic than in it. There would only be a benefit for short-lived civilizations, which would be unlikely to be there and broadcasting anyway, and then it becomes a contest between the exact time-frame a civilization has advanced technology versus the number of stars in and out of the plane of the ecliptic.
Here is the original paper, by the way. The author seems to want to have it both ways, assuming an optimistic million-year lifetime for a civilization but claiming that finding Earth via direct imaging is unlikely for anyone except very nearby ETIs. The million-year lifetime, however, suggests that nearby ETIs are likely to exist, and that they are likely to have technology hundreds of thousands of years more advanced than our own. Hundreds of thousands of years. And only “nearby” ETIs are going to bother to do anything but eclipse studies to find Earth?
OK, he does try to respond to my point, even though his search restriction only improves search efficiency by a factor of “16-40.” Damn small gain to weigh against the competing issues. His counterargument relies on the assumption that it will take the aliens “hundreds of thousands of years” to find Earth via proper motion or other sorts of studies, which is ridiculous.
It’s like he can’t imagine technology or resources very much more advanced than our own, or, when he does, still claims eclipsing is easier and we should neglect searching 90+% of the sky.
Remember, according to some we’re supposed to have the Singularity in a couple of decades and get superpowers. I think a civilization just a thousand years more technological advanced than ours will not have any problems finding us if that’s what they want to do.
OK, done picking on a guy thinking in interesting ways about an interesting problem. He’s been very quantitative about some easy things, and neglected the hard questions like what is the lifetime of a civilization and would it really be hard for a much more advanced civilization to find us without eclipses. “Hundreds of thousands of years” seems like a laughable strawman to me. I mean, we went from an era 50 years ago where people got PhDs for studies of samples of a few objects, to today when people do projects studying millions of objects. The number of stars in the galaxy does not seem daunting to me in the face of advancing technology.