Humans have scoured the skies for clues of Intelligent civilizations elsewhere in the universe. And we’ve come up empty-handed. Not a single thing. So perhaps we shouldn’t be so focused on life, but rather on any kind of life. Sure, a little bacterium isn’t as exciting as trading stories with faraway aliens, but indicators of non-Intelligent life in our galaxy may be far more prevalent and easier to uncover. On Earth, life, including sentient life, evolved.
Our planet, on the other hand, shouldn’t be particularly noteworthy; it’s simply another random world in the cosmos. So, if Intelligent life exists here, it must be fairly frequent — common enough for humans to see it. So, where has everyone gone? This is the central argument in the iconic Fermi paradox, which has fueled the quest for extraterrestrial intelligence (SETI). At first glance, it appears to be self-evident that we are not alone in the cosmos, and that if we look closely enough, we will find proof of intelligence.
Maybe aliens are broadcasting radio signals for us to hear. Maybe they’re just blaring the radio in general and we chance to hear it. Perhaps they’ve left relics in the solar system to keep an eye on us or simply to observe us. Perhaps they’ll embark on massive engineering projects, such as encasing their star in a swarm of solar panels. Alternatively, they may just have fun and infect their star with heavy metals to proclaim their presence.
However, after more than half a century of SETI, we haven’t discovered anything. There are no radio signals. There are no artefacts. There will be no mega-engineering. We have found no evidence of sentient life in our galaxy, or even in the cosmos, despite over a hundred serious searches. Because Intelligent beings are capable of truly making their existence known, SETI assumes that life should be easier to detect than non-Intelligent life.