The search for alien intelligence is back in the news again, with the launch last month of a new project, 'Breakthrough Listen', to scan the skies for signs of transmissions from extra-terrestrial civilisations. Starting in January 2016 The sky will be scanned in hugely more detail than in the past, by three highly sensitive telescopes in radio and optical wavelengths, searching for any unusual signals that can't be explained conventionally.
If you talk to your friends about the possibility that aliens may be beaming out signals, the chances are that you will meet with some raised eyebrows and jokes about ET calling home – is this serious science? This project was launched at the Royal Society in London and is backed by a number of high-profile scientists, including Professor Stephen Hawking, so make your own judgement.
But how will the observers be able to tell if a signal has been sent by intelligent life? Should we also be making efforts ourselves to make contact with any beings out there?
And how likely is it that anything at all will be found? The search for extra-terrestrial intelligence (known briefly as SETI) has been on the astronomical agenda since the start of the space age, but to date has turned up not a single unequivocal piece of evidence that there is someone else out there.
One intriguing transmission was picked up in 1977 – an abnormally strong radio signal at a single frequency from a very small area of the sky. Known simply as the 'WOW' signal (due to a researcher's brief comment on the computer printout), it lasted only 72 seconds, and a repeat signal was never detected despite repeated searches in the same area. It was narrow and focussed, suggesting an artificial source rather than a natural one, and no reasonable explanation for a human-made source has ever been found. So it could well have been a transmission from an alien civilisation, perhaps a beacon emitting a pulse at long intervals - but without detecting a repeat signal, it is impossible to say more.
Human, natural or alien origins?
A major difficulty with this sort of search is distinguishing between possible sources: how can you tell the difference between an artificial source and a type of natural source that has never been observed before? For example, as mentioned in an earlier post, when pulsars were detected for the first time, they were jokingly nicknamed 'Little Green Men'.
Also, there are many possible man-made artificial sources of signals, some of which may not seem obvious at first – like the mysterious microwave signals that baffled astronomers at the Parkes Observatory in Australia for 17 years, before they finally discovered earlier this year that they were caused by the microwave oven in their own kitchen!
Listening quietly for incoming signals is not the same as trying to make contact ourselves, and this is probably just as well. Strong arguments are being made these days against inviting attention from any possible alien life, on the basis that any civilisation advanced enough to pick up a signal from Earth and visit us, would most likely wipe out or enslave humankind.
Perhaps we were a bit more naïve in earlier stages of space exploration – the Pioneer and Voyager spacecraft, launched in the 1970's are now hurtling beyond our solar system into interstellar space, carrying handy maps of how to find our planet and information about our culture. Let's hope that if any of them are ever found, the finders will be better behaved towards newly-discovered civilisations than the human race …..
http://www.theguardian.com/science/2015/jul/20/breakthrough-listen-massive-radio-wave-project-scan-far-regions-for-alien-life
http://news.discovery.com/space/alien-life-exoplanets/the-wow-signal-130524.htm
http://www.theguardian.com/science/2015/may/05/microwave-oven-caused-mystery-signal-plaguing-radio-telescope-for-17-years
1. http://www.gb.nrao.edu/gallery/gbt/index.html
2. Wikimedia Commons
3. NASA