Mysterious signals from 1000 light years away

New Scientist magazine is reporting the discovery of a mysterious radio signal from space that "happens to be the best candidate yet for a contact by intelligent aliens in the nearly six-year history of the SETI@home project." As an astrophysicist myself (at least by training), I'm skeptical but this is an interesting observation. It could well be a telescope defect (only one telescope has detected this signal, but Arecibo is the largest, and therefore most sensitive telescope, and the signal is weak). There is no detectable star, let alone planet, in the direction of the signal. But until the scientists can conclusively demonstrate a cause for the signal, the possibility of having detected an alien broadcast will excite many people's imagination.

I have always been somewhat skeptical of the SETI project. The signal is found at the frequency of hydrogen's 21 cm line. This is the frequency of light emitted or absorbed when the electron in hydrogen flips spin relative to the proton. SETI scientists believe this frequency is "one of the main frequencies at which hydrogen, the most common element in the universe, readily absorbs and emits energy." There are plenty of "fundamental" frequencies associated with hydrogen, e.g. the 13.6 eV binding energy (the energy that holds the electon and proton together to form hydrogen) or the Lyman alpha line. The only thing that is special about the 21 cm line is that it is in the radio regime, which we humans use for electronic communication. Just because we use radio does not mean some other alien species would as well. But the scientists have to make some assumptions on what to look for, so choosing the 21 cm line is a practical necessity.