How can you tell if a signal from space is an alien communication?
Humanity scans the skies, hoping to hear from other intelligent species. But how can you be sure you’ve tuned in to aliens and not just got interference? Andy Norton explains.
Astronomers working at the Arecibo radio telescope in Puerto Rico have detected a weird radio signal , spotted when pointing their telescope at the nearby star Ross 128 . They’re not getting too excited about the prospect of an alien civilisation contacting us just yet though. “In case you are wondering, the recurrent aliens hypothesis is at the bottom of many other better explanations,” said Abel Mendez , the scientist leading the campaign.
Of course, this doesn’t stop others speculating that the signal may be just that. And it begs the question, how do you work out if a strange signal from space really is a message from aliens? The simple answer is that you have to rule out everything else first and only then can you think it may be aliens. As Sherlock Holmes said: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” But eliminating all the other possibilities isn’t exactly easy.
When radio pulsars were first detected in 1967, “little green men” were at least considered a possibility — before it was that they are rapidly rotating neutron stars. The discovery opened up a whole new area of astrophysics, so could hardly be considered a disappointment.
There have been other cases. In 1977, astronomers detected a radio burst dubbed the “WOW signal” — and they have been debating its origin for decades. Only recently was it suggested that there could be a natural explanation: emission from a passing comet that happened to lie in the right part of the sky. However, other astronomers have cast doubt on the comet idea, so it can’t be considered to be settled just yet.
Another mysterious signal is that from Tabby’s star , which displays strange quasi-periodic dips in its brightness. Could this be evidence of orbiting alien megastructures , or is it merely a cloud of natural debris surrounding the star? Once again, the jury is still out on that one, but we have certainly not ruled out…