For decades, radio dishes on Earth have scanned the skies for signals which would show signs of intelligent life - and found nothing.
But a strange pattern in high-energy radio signals thought to originate outside our galaxy has left scientists puzzled.
A repeating pattern of numbers found in ‘Fast Radio Bursts’ does not match what we know of cosmic physics - and could be transmitted from something totally unknown.
Astronomers have not ruled out the idea that this could be the first sign of an alien civilisation.
‘If the pattern is real,’ University of Hawaii researcher John Learned says, ‘It is very, very hard to explain.’
Radio telescopes have detected Fast Radio Bursts since 2001 – incredibly short, high-energy pulses which last for a few milliseconds and erupt with the energy the sun releases in a day, New Scientist reports.
The truly strange part is that the signals show a repeating pattern of numbers which doesn’t match what we know about cosmic physics.
An FRB was captured ‘live’ in November 2014, by the CSIRO Parkes Radio Telescope in Australia.
Michael Hippke of the Institute for Data Analysis in Neukirchen-Vluyn, Germany, and John Learned at the University of Hawaii in Manoa analysed the data, and say that all the known FRB signals have dispersion measures that are multiples of 187.5.
This implies that the signals all come from sources at distances at exactly spaced multiples of each other, billions of light years from Earth - a huge, improbably coincidence.
The astronomers suggest that there is a possibility that the signals could come from somewhere closer to home – and from something unknown.
Astronomers have previously speculated the signals could come from evaporating black holes, or even from distant alien civilisations.
Nigel Watson, author of the UFO Investigations Manual (Haynes), says, ‘Every unusual signal from outer space encourages us to wonder if it is from an alien civilisation.
‘It would be fantastic if this is an alien signal as the knowledge that we are not alone in this vast universe would have a dramatic impact on our perception of our place in the scheme of things.’
‘It would certainly give the opportunity for UFO spotters to say we told you aliens exist – and you didn’t believe us!’