The New Scientist is reporting on a new study by David Messerschmitt of UC Berkeley which claims our existing efforts to detect extraterrestrial attempts to contact us are looking for the wrong type of signal:

The simplest [message] would be a constant blast in all directions, but in a narrow range of frequencies, similar to early radio broadcasts – like a constant hum that would tell a listener it is artificial.

As Messerschmitt explains, broadcasting a continuous omni-directional signal would take colossal amounts of energy, which would be beyond the means of all but the most advanced alien civilizations. Therefore, he argues they would likely adopt a more practical method:

[I]nstead of a constant, narrow-band signal, he argues that ET would beep out short bursts in a wider range of frequencies – a broadband signal. This would take less energy to transmit, and could encode information.

And therein lies the problem, says Seth Shostak of the SETI Institute:

“The problem is that… encoding a message; means that any signal would vary quickly. To see such variations – to get the information in the signal – requires having enough sensitivity to see changes in a 10th or 100th of a millionth of a second. That requires antennas with collecting areas maybe 10,000 times larger than necessary to detect a steady signal.” No such antennas currently exist that would pick up the variations more than a few light years away.

Messerschmitt does provide one possible solution — to adapt SETI@Home to look for this type of burst broadband signal as well as the existing narrowband search, which sounds eminently sensible and doable, given how the rapid increase in CPU processing power has greatly improved the detection capabilities of the program.

While I understand his point, I’m not completely convinced by Messershmitt’s argument. The problem is that we simply do not know what the capabilities or the motivations of ET civilizations might be. If there are suitably old and advanced civilizations out there, their energy budget might not be an issue.

If intelligent life is rare in the Universe, there might well come a time in an ancient civilization’s history where making contact with alien life becomes a top priority. After all, once you have spent a hundred thousand years observing and studying a barely changing Universe, how else are you going to encounter something completely new and unexpected? Variety is the spice of life, after all, and intelligent life is a great source for that variety.

I have no quibble with expanding our SETI efforts to include other possible signal sources and types–that will undoubtedly increase the chances of success. Indeed, in my mind, ET civilizations serious about contacting alien life would likely employ as many of the communication methods likely to bear fruit as they can afford. Indeed, they very may well complement each other as in this bootstrap approach:

1. Broadcast a strong narrowband omni-directional “We Are Here” signal to tell ETIs where to point their radio telescopes.
2. Broadcast weaker broadband signal bursts (that can be picked up by a more intensive, follow-up observational effort) containing information about how to access a third, more technologically advanced high-bandwidth communications method.
3. Broadcast full contact information and (possibly) keep communications channels open on this third, high bandwidth method.

It’s all just speculation at this stage, but it is important that we continue to consider the possibilities and debate the issues, because of these days, we might just stumble across that one missing piece of the puzzle SETI needs to finally make contact.