Don't count on aliens to save us from our troubles. The “deepest and broadest” search for extraterrestrial intelligence yet conducted has found nothing indicative of advanced civilizations. The study was done on just one small section of the sky, and could only detect powerful signals at particular frequencies, so it in no way indicates aliens don't exist, but emphasizes how hard it will be to find them.
The easiest way astronomers can imagine to detect aliens is through their radio signals, but even this is an immense challenge. Radio telescopes not only need to be looking in the right place at the right time, but tuned to the appropriate frequency and with the sensitivity to pick up something at mind-bending distances.
The Murchison Widefield Array (MWA) telescope has the advantage of capturing an unusually large portion of the sky at a time while being relatively sensitive. Yet according to Professor Steven Tingay of the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) it couldn't detect the presence of an alien civilization emitting signals matching our own.
The MWA's range is similar to FM radio, Tingay noted. However, the Earth's most powerful transmitters are radar towers operating at much higher frequencies. If a transmitter with that power but the right frequency was located around the nearest star to the Sun, Tingay told IFLScience, the MWA would be unlikely to detect it. Snooping on a station playing Alpha Centaurian hits and memories is out of the question.
Given the obstacles, searching for aliens isn't the MWA's priority. However, when the telescope spent 17 hours seeking nitric oxide emissions in a particularly gas-rich part of the Milky Way at 98-128 Megahertz, Tingay and Dr Chenoa Tremblay realized they could also analyze the data for extraterrestrial signals.
The 400 square degree area, centered on the Vela supernova remnant, contains at least 10 million stars, five known to have planets. If a civilization based around one of them was trying to catch the galaxy's attention with a really powerful signal around 100 Megahertz, the MWA would be the instrument to find it.
Alas, Tingay and Tremblay report in Publications of the Astronomical Society of Australia, they struck out. However, Tingay is not disheartened. “As Douglas Adams noted in The Hitchhikers Guide to the Galaxy, ‘space is big, really big’,” he said in a statement. “And even though this was a really big study, the amount of space we looked at was the equivalent of trying to find something in the Earth’s oceans but only searching a volume of water equivalent to a large backyard swimming pool.”
The MWA is a precursor of the giant Square Kilometre Array telescope (SKA), construction of which will start at the same site in Australia's midwest next year. The SKA will be around 100 times the MWA's sensitivity, Tingay told IFLScience. Even with a smaller field of view, the SKA will survey so many stars over its lifetime it might find something if the signal is either exceptionally strong or, by galactic standards, unusually close.