In Hollywood movies, when aliens invade our innocuous little blue planet, they usually have a ludicrous motivation. Sometimes they’re after our water or want to colonise us or are just being plain nasty. Space travel is incredibly difficult and expensive — so why would aliens actually bother to come and invade us? Today’s Needull is an interesting book-excerpt that will give you a more logical perspective on alien attacks.
As an astrobiologist I spend a lot of my time working in the lab with samples from some of the most extreme places on Earth, investigating how life might survive on other worlds in our solar system and what signs of their existence we could detect. If there is biology beyond the Earth, the vast majority of life in the Galaxy will be microbial—hardy single-celled life forms that tolerate a much greater range of conditions than more complex organisms can. To be honest, my own point of view is pretty pessimistic. Don’t get me wrong—if the Earth received an alien tweet tomorrow, or some other text message beamed at us by radio or laser pulse, then I’d be absolutely thrilled. So far, though, we’ve seen no convincing evidence of other civilizations among the stars in our skies.
But let’s say, just for the sake of argument, that there are one or more star-faring alien civilizations in the Milky Way. We’re all familiar with Hollywood’s darker depictions of what aliens might do when they come to the Earth: zapping the White House, harvesting humanity for food like a herd of cattle, or sucking our oceans dry. These scenarios make great films, but don’t really stand up to rational scrutiny. So let’s run through a thought experiment on what reasons aliens might possibly have to visit the Earth, not because I reckon we need to ready our defenses or assemble a welcoming party, but because I think considering these possibilities is a great way of exploring many of the core themes of the science of astrobiology.