Not long after the big bang that created our universe, the cosmos had cooled enough for its matter -- mostly hydrogen -- to form neutral atoms. Astronomers know that neutral hydrogen emits characteristic radiation at a wavelength of 21 centimeters, and for over fifty years they have studied neutral gas in our galaxy using this tracer radiation. Now astronomers are planning to build large new radio telescopes to study the neutral hydrogen gas at the remote edges of our known universe, gas that dates back to the early ages of the universe. Such research will provide important information about the shape and character of clusters of matter a few hundred million years after the big bang, when the first stars and galaxies are thought to have developed. But the powerful new telescopes offer an interesting side benefit.
Two CfA astronomers, Avi Loeb and Matias Zaldarriaga, have just published an article showing that the search for extraterrestrial intelligence (SETI) -- that is, intelligent life on other planets in the local universe -- can benefit in important new ways from the new generation of radio telescopes. Up until now, the scientists note, SETI searches have relied on searches at wavelengths where radio technology was most effective, namely, wavelengths with sensitive detectors and very low background noise levels. Frequencies near television or other broadcast stations, for example, where the vast majority of our radio transmissions occur, were avoided.
The two astronomers point out that the telescopes designed to study the primordial neutral hydrogen will by chance be tuned to the wavelengths where our civilization, and so possibly other local civilizations, broadcast loudly. Furthermore, they note that the nature of the cosmological searches, requiring the study of wide swaths of the sky for long periods of time, are fortuitously suitable to locate and identify SETI sources (assuming they arise on planets whose rotation and revolution can be monitored and used to identify the signal as artificial). The astronomers outline some steps that can be taken to insure that the data are properly analyzed for SETI information. The paper is a good illustration of the serendipitous power of astronomical surveys, and the importance of taking creative advantage of powerful new technological tools.