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TV on the Radio

October 13th, 2006

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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.

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  1. Jyril
    October 13th, 2006 at 08:20 | #1

    What is the probability that a relatively nearby star has a civilization whose technical level is comparable to ours (i.e. uses radio waves in planetary scale communication)?

    It took billions of years intelligent (that’s debatable ;) ) life to appear on the Earth. We have had the possibility to communicate using radio waves only for a few decades. Much less than a eyeblink in the history of the Earth. Not only that, the Earth’s “scream” is becoming less loud because more information is provided through cables etc.

    Despite the astronomical odds against finding any intelligent life, I think SETI is justified. If we don’t actively search for possible signs of intelligent life, it’s even more unlikely that we will ever find it.

    A strong argument against ETI is the Fermi Paradox, the problem that we haven’t seen them already; it takes a relatively short time to colonize the whole Milky Way (a few million years, anyway much less than its age). An optimistic counterargument (which I share) would be that we have an extremely naïve idea how truly advanced civilizations operate.

  2. qraal
    October 14th, 2006 at 07:50 | #2

    The odds of ETIs anywhere near us seem to get more remote the more we know of exoplanets, or it seems. Look at the recent estimate of Jovians – around about 6% of stars – and a Jovian in a decent orbit is arguably one requirement for a terrestrial planet’s habitability in the long term. The new work on planet formation around red dwarfs suggests terrestrials are unlikely to form in the habitable zone of such small stars. Mercury to Mars size, but no bigger – bigger worlds are out in the cold.

    I’m not saying there won’t be lots of habitats for small scale life – bacteria are likely to have spread all over the Galaxy after they first arose – but multi-cellular life as we know it needs at least a few percent oxygen in the atmosphere, which restricts conditions immensely.

    If habitable planets are so rare what will compel ETIs to spread out? Scientific interest would be served just as well by superscopes and unobtrusive probes.


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