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The Fermi Paradox is a perplexing one, even as exotic-sounding paradoxes go. Since the probability that alien life exists out there in some far corner of the universe is overwhelmingly high, it's a little weird that we simply haven't bumped into any of it yet.
It's confounding on a conceptual level, for sure, and the subject of countless stoned dorm room bull sessions. But it's also a legitimate mathematical conundrum. Assuming other advanced civilizations have built space-faring satellites and sent them out to explore the universe, some models suggest that one or more should have crept past and spotted us by now.
So would that mean that we humans—we glorious, perpetually warring, resource-extracting, sitcom-producing humans—are the only intelligent life on in the universe?
Nay, say some astro-braniacs at the University of Edinburgh. There's a mathematical explanation for all of this. In fact, alien probes could have already swung through the Milky Way. They might even still be here.
But they'd have to be self-replicating vessels made from space dust and gas that exploit the gravitational fields of small stars to slingshot themselves across galaxies. Got that? It's what Voyagers 1 and 2 did to pick up speed, but they notably lacked the ability to make copies of themselves out of stardust.
The researchers point out that "a single Voyager-like probe exploring the galaxy does so 100 times faster when carrying out these slingshots than when navigating purely by powered ﬂight."
Now, take an entire fleet of probes like that, programmed with the ability to multiply like robotic space amoebas, and we're talking alien explorers that can comb the galaxies so quickly they might have breezed on by us before we existed. According to the paper, the probes could scour the entire Milky Way in 10 million years, ample time to have slid by before human civilization had sprung forth.
Or, as the astronomers say, "we conclude that a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time to warrant the existence of the Fermi Paradox."
In other words, it's entirely mathematically possible that aliens may be out there. Then again, if they are, they might have a terrifying fleet of self-replicating spaceships.