TV on the Radio
SETI and the idea of alien life are the stuff of endlessly fascinating speculation. I remember wild late-night conversations with my freshman dorm mates when we should have been writing lab reports and studying for chemistry exams. To date, however, the SETI hasn’t turned up anything, and the Fermi Paradox seems as perplexing as ever. Proponents of the conventional SETI approach argue that this is because we’ve barely scratched the surface in terms of the number of stars that we’ve observed. Build a bigger telescope, they argue, scan more stars, and success will come.
If I look at my own behavior, the trend has been toward increasingly frequent correspondence with more and more people. The cell phone rings many times a day. I send a lot of e-mails via wireless internet. I look on flickr to see if my photos have accumulated views or comments. My life revolves around connectivity. I rarely send letters through regular post, and I have little interest in conversations with a response time of 8.78 years. I’m not inclined to beam coded messages to the sky, and I don’t shine high-power collimated lasers at nearby stars. My behavior is similar in aggregate to many, many others here on Earth.
It seems reasonable, then, that the most promising strategy for a succesful SETI is to look for behaviors that resemble our own. I think it’s much more likely to detect another civilization through their signal “leakage” rather than through reception of a directed message. If I knew that it was going to take at least 8.78, and in all likelihood millions of years for my photos to accumulate views, I’d soon start neglecting to post them.
When I was at the CfA last week, I had an interesting conversation with Avi Loeb, who pointed out that at present, the largest sources of artificial terrestrial radio emission are military radars, FM radio broadcasts, and television broadcasts, all of which emit their power in the frequency range between about 40 and 800 Mhz. SETI searches, on the other hand, have focused in the frequency range above 1 Ghz.
Loeb is involved in the Mileura Wide Field Array (MWA), which is a low-frequency radio telescope designed to study highly redshifted 21 centimeter emission from hydrogen. By mapping the spatial distribution and redshift distribution of 21 centimeter emission, the Mileura project will be able to make a 3-dimensional map of the distribution of atomic hydrogen in the early universe.
The MWA will provide an enormous increase in sensitivity at exactly the frequencies that we here on Earth broadcast. Loeb recently received a grant from the FQXi foundation to run a SETI-search on data obtained during the course of MWA survey observations. The cosmic signals received will be combed for telltale artificial emissions from nearby stars. The array will be sensitive enough to detect Earth-like leakage from more than 1000 of the nearest stars, a list that includes oklo.org Southern Hemisphere favorites such as Alpha Centauri B, Beta Hyi, GJ 780, and Tau Ceti.
Loeb informs me that he’s posted an overview paper on astro-ph. Look for it on Sunday night, 5PM PST.
While we’re on the topic, I recently participated in a panel discussion on SETI that closed up the AIAA Space 2006 meeting in San Jose. I argued that the resolution of the Fermi Paradox lies in the fact that we’re inward bound. My understanding is that the video of the discussion will go up on the web at some point, but for the moment, here’s a .pdf (4MB) file with the transparencies that I showed in my 10 minute summary.