Where Are All the Extraterrestrials?

A traveler stands under the Milky Way galaxy as seen from the Atacama desert in northern Chile.

Ever since I was a child, I presumed the universe would be teeming with alien life. Star Wars and Star Trek reinforced this belief, and I yearned for the day when we would meet and communicate with other intelligent beings.

But as every potential alien discovery turned out to be natural, and our initial assumptions about the chance that life can naturally emerge from non-living materials turned out to be wildly optimistic, perhaps it is time to honestly reappraise the likelihood of us ever detecting, let alone communicating with other technologically intelligent extraterrestrial species.

In this vast universe, there appear to be around one septillion stars (one trillion trillion stars [1 × 1024]) spread out across trillions of galaxies, vastly more numerous than all the grains of sand on all the world’s beaches. If there is only one planet for every ten stars, then there are 100 billion trillion planets in the visible universe.

Given how enormous the universe is and how many planets exist, where is everybody? Even if we assume only one planet in a thousand is Earth-like; and only one in a thousand of those developed life, and only one in a thousand of those developed intelligence; and only one in a thousand intelligent species developed space travel and exploited their stellar neighborhoods by creating megastructures; there should be at least a hundred billion intelligent species who’ve developed megastructures that are visible across the universe.

And yet, we find nothing, no matter how hard we look. Every possible discovery of aliens has been proven to be either natural or man-made. There are no Kardashev Type III civilizations. There are no detectable Type II civilizations. At the very least, we should’ve observed or encountered one instance of non-biological extraterrestrial intelligence, like a sentient robotic probe, since the bar for their creation and spread throughout the cosmos is vastly lower than the development of megastructures.

The existence of extremophiles shows life can exist in environments that are fatal to most life. This means a world does not need to be within the “Goldilocks Zone” (the distance from a star where water is in liquid form on a body’s surface) as a condition for life to exist, which gives more possible places for life to exist.

If the non-living/living-cell barrier can naturally be traversed given the right conditions, then, statistically speaking, life, especially the single-celled kind, should be everywhere in the universe because life self-perpetuates, spreads, and adapts to different environments.

Even if a condition for life is the presence of liquid water, its existence beneath the surface of planets and satellites due to tidal forces and internal planetary heating means the likelihood of finding extraterrestrial life in our own solar system (say, beneath Mars, Enceladus, Europa, and Ganymede) is not zero. And since the barrier between single-celled and multicellular life has been breached many times, the likelihood of extraterrestrial multicellular life, even in just our solar system, shouldn’t be zero either.