Unexplained signals from space could be signs that ancient alien civilizations have mastered interstellar travel, astronomers have proposed.
First detected in 2007, fast radio bursts - or FRBs - last only milliseconds, but are extremely powerful - and appear to come from a long time ago in galaxies far, far away.
Only 20 or so have been recorded since then, and no one knows what's making them.
"Fast radio bursts are exceedingly bright given their short duration and origin at great distances, and we haven't identified a possible natural source with any confidence," theorist Avi Loeb at the Harvard-Smithsonian Center for Astrophysics said in a statement on Friday (NZ time).
"An artificial origin is worth contemplating and checking."
Prof Loeb and fellow researcher Manasvi Lingam of Harvard University crunched the numbers on what it would take to manufacture something that could create FRBs.
They found it would take a solar panel twice the size of Earth, cooled by water - not something we could do, but nothing that breaks the laws of physics.
But why would aliens build something like this?
"The most plausible use of such power is driving interstellar light sails. The amount of power involved would be sufficient to push a payload of a million tons (907,000 tonnes), or about 20 times the largest cruise ships on Earth.
"That's big enough to carry living passengers across interstellar or even intergalactic distances."
Though the beams would be powered constantly, we'd only see them very briefly - a matter of milliseconds - because we're moving quickly through space, as is the source.
Prof Loeb says it's just an idea, and only time - and more research - will reveal the truth.
"Science isn't a matter of belief, it's a matter of evidence. Deciding what's likely ahead of time limits the possibilities. It's worth putting ideas out there and letting the data be the judge."
Scientists on Earth have started experimenting with light sails - the first craft predominantly powered by light pressure, IKAROS, launching from Japan in 2010.
The concept's not new, and featured in 1990s sci-fi show Star Trek: Deep Space Nine. During the episode 'Explorers', Captain Benjamin Sisko proves it was possible for the ancient Bajoran people to have travelled across space using photon-powered 'lightships', in a journey reminiscent of the real-life 1947 Kon-Tiki expedition.
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