If there were civilizations on distant planets, how would we know? Sure, we could turn some of our massive telescopes toward those planets, but we're still at least "two or three generations of telescope away" from being able to detect the light of a large city in another solar system, Ed Turner tells Time. But in the meantime, he and fellow astrophysicist Avi Loeb came up with a novel solution for looking a bit closer to home in the Kuiper Belt, which surrounds our own solar system.
Rather than just look for the light of a distant city, Loeb and Turner figured out that we can look for changes in light intensity. As light sources move closer and further away in the Kuiper Belt's elliptical orbit, light reflected from the sun will get dimmer much faster than light created by an original source, like a street lamp or neon sign. So by looking at how much light intensity changes as an object in the Kuiper Belt moves, astronomers can figure out if it is just a lifeless rock—or if it is producing new light, like a city does. Of course, Loeb and Turner realize that it is incredibly unlikely there are any cities out in the Kuiper Belt, but they say the only way to know for sure is to look.