If the Aliens Have Cities, Will We Be Able to See Them ?

Day 2,202, 08:10 • Published in Belgium Spain • by just Djox


Did you hear the one about the two astrophysicists on the bus? It was January 2010, during a workshop in Abu Dhabi, when they took off for a tour of Dubai—a city so bright it could be seen from outer space, the guide boasted. Later that day the astrophysicists, Avi Loeb of Harvard and Edwin Turner of Princeton, tried figuring out how far from Earth they’d have to go before the lights of Dubai became invisible. Then they turned their perspective around and wondered what it would take to seek alien civilizations by looking for distant analogues of Dubai, or Las Vegas, or Times Square.

Up until now, the search for extraterrestrial intelligence, or SETI, has primarily involved listening for radio signals deliberately or inadvertently sent by alien cultures into space. But away from the academic grind, Loeb and Turner saw city-spotting as an alternative way to hunt for ET. One virtue of the scheme was that it made few assumptions about the aliens. They didn’t have to be beaming messages at us; they merely had to share our fondness for artificial light, something common to every modern society on Earth. But the astronomers’ initial back-of-the-envelope calculations were not encouraging. Detecting light pollution from planets orbiting other stars is far beyond the capabilities of today’s instruments, they realized.

Loeb and Turner shelved the notion, but then they talked to Freeman Dyson, the physicist renowned for his seminal contributions to quantum field theory and equally famous for his provocative speculations. In the 1960s he conceived of Dyson spheres—structures manufactured by advanced civilizations that would completely surround stars, capturing most of their energy. More recently he suggested that parabola-shaped plants (which he called “sunflowers”) could survive on the solar system’s cold fringes by concentrating the weak sunlight available there. When Loeb mentioned the concept of searching for the lights from extraterrestrial cities, Dyson urged him to write it up.





Signature of Urban Lights
To prepare a paper for publication, Loeb and Turner worked out some hard calculations based on the most detailed views afforded by the Hubble Space Telescope. They concluded that Hubble could detect a city as luminous as Tokyo at 1,000 times the distance between the Earth and the sun. That would place it deep in the outer solar system, well beyond the Kuiper belt where Pluto resides.

Why Tokyo? The researchers homed in on the city not only because it is one of our planet’s brightest urban centers but also because Turner—a self-described Japanophile—happened to be there at the time. After the Fukushima nuclear disaster, moreover, he had ready access to detailed information about Tokyo’s power consumption, much of it used for illumination.


Cities Around Other Stars
The reality is that astronomers barely know the basics about Kuiper belt objects, much less whether they harbor life. They are so small and distant that they look like points of light in even the largest telescopes. Brightness changes are in fact one of the few things we can study about these enigmatic frozen bodies, so every scrap of information is bound to turn up something new.

“At the very least, we’ll learn a lot about Kuiper belt objects, gaining insights into their shape, spin, and reflectivity,” says Loeb. “We’ll extract new information, and we’ll do it statistically, for a large number of objects, so we can do good science even if there are no civilizations to be found.”

Someday, with more powerful technology at our disposal, we might go further, spying on an alien city (or gambling strip) on an Earth-like planet elsewhere in our galaxy. Spotting ET's urban glow out to about 30 light-years—roughly the distance to the nearest known stars with potentially habitable planets—would take a telescope at least a million times as powerful as the Hubble Space Telescope orbiting Earth.

Instead of Hubble’s 2.4-meter (7.9-foot) primary mirror, then, astronomers would have to build a telescope with something like a 2,400-meter mirror. That is about a mile and a half wide. Building such a huge instrument is out of the question using current technology. For now we will have to rely on human ingenuity to come up with the tools needed to see planets bathed in urban light.

Perhaps ET has beaten us to the punch. They could be monitoring our cities now, watching the latest giant casino switched on in Vegas or towers of light sprouting in Dubai.