According to renowned astrophysicist Stephen Hawking, aliens are not to be trifled with. In his new Discovery Network TV series, Hawking says it's likely that aliens exist, given the vastness of the universe, and that we don't want them down here on Earth, since they're likely to view our blue marble of a planet as a tasty, exploitable resource.
"If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the native Americans," Hawking said.
OK, so we shouldn't be down on the beach waving "hello" to those incoming galleons, metaphorically speaking. Should we be peering through the trees — make that spying on the skies — in an effort to spot aliens in secret, before they spot us?
Signs of life
In the past, we earthlings have launched spacecraft with drawings of humans and directions to our planet. We have beamed radio waves towards the skies as a sort of electromagnetic greeting. This sort of active Search for Extra Terrestrial Intelligence (SETI) is just the sort of thing Hawking believes we should not do.
But there are other ways. A recent paper from a scientist at the Fermi National Accelerator Laboratory suggested an alternative to conventional SETI, called "interstellar archaeology".
In essence, this involves scanning the cosmos for the equivalent of Earth's Egyptian pyramids, or the Great Wall of China — signs of intelligent life that can be seen from space.
Fermi scientist Richard Carrigan's paper, Starry Messages: Searching for Signatures of Interstellar Archaeology, was first posted on the blog of the Project on Government Secrecy of the Federation of American Scientists.
Truth be told, this study is pretty involved. Built structures visible from space are just the starting point — it also covers possible atmospheric changes as signatures of civilisation and galactic-scale engineering. An example of the latter, says the study, might be a Dyson sphere — a hypothetical megastructure, first dreamt up by physicist Freeman Dyson, in which a star is surrounded by orbiting solar-power satellites as a means of capturing a high percentage of energy output.
Passive SETI research could also involve just listening for "we are here" alien radio transmissions that are similar to the sort of thing we earthlings have broadcast into the unknown.
But aliens looking for other worlds might not necessarily be friendly, writes Carrigan in an echo of Hawking's warning.
