Nikolai Kardashev, a Russian astrophysicist, was one of the founders of the search for extraterrestrial intelligence (SETI). In 1964, Kardashev published a paper proposing a way to categorize a planet’s energy use, a system that has come to be known as the Kardashev Scale.

In 1964, when Kardashev published his paper, SETI was still a very young field. But now, a growing number of researchers are actively looking for technosignatures that indicate intelligent life elsewhere in the galaxy.

Pinchen Fan is one of those researchers. An astrophysicist at Penn State University, Fan searches for radio and laser technosignatures using ground-based telescopes.

“A technologically advanced civilization will leave behind evidence of their existence,” she says. “So we’re trying to find evidence of their technological activity. They’re gonna leave something behind.”

Even though SETI has been around for 60 years or so, we’ve still not explored much of the galaxy. Fan points to a 2018 paper by Jason Wright, also at Penn State, which estimates that the amount of space SETI has searched compared to the entire galaxy is about that of a hot tub compared to the water in all the Earth’s oceans.

“We have filled a hot tub with ocean water and haven’t found any fish,” Fan says. “But that doesn’t mean there are no fish in the ocean.” 

Read More: Could the Multiverse Help us Find Alien Life? Expert Paul Sutter Explains

The Kardashev Scale

When using the Kardashev scale to discover extraterrestrial life, it measures a civilization’s level of technological advancement based on the amount of energy it can use. The scale organizes hypothetical civilizations into three categories.

Type I 

This type of civilization uses energy sources available on its own planet, but only energy available there. The energy use of this type of civilization, according to Kardashev’s original scale, would match the energy use of humanity in the 1960s.

Type II

A civilization at this level harnesses energy from its star. A civilization with a Dyson sphere, a giant structure built around a star to collect its energy, would be at stage II on the Kardashev Scale.

Type III

At this stage, a civilization harnesses energy from all the stars in its galaxy, perhaps using multiple Dyson spheres or some other as yet unimagined technology.  

Kardashev admitted that his figures were estimates. However, the point of the paper was not so much to specify the precise amount of energy used at each level but to estimate the detectability of extraterrestrial intelligence using the technology then available.

If civilization is not unique to Earth, Kardashev wrote, then the possibility of using radio physics capabilities to make contact with other civilizations is “entirely realistic.” 

Read More: Life Elsewhere in the Universe: When Did We First Consider the Possibility?

Detecting Alien Technology

There are several possible reasons we might not find advanced civilizations, even if they’re out there. For whatever reason (fear of colonization by other civilizations, perhaps?), a technological civilization might intentionally try to reduce its detectability. 

You can imagine this being done in several ways, says Julia DeMarines, an astrobiologist at the University of California Berkeley’s SETI Research Center who studies how to search for alien life. They might use a minimal amount of off-planet communications or even decide not to communicate off-planet at all.

“You could even think of some cool sci-fi things they could do, such as creating some sort of artificial dust cloud to hide behind,” she says. 

More likely, the reason we haven’t yet found extraterrestrial life is that they’re just too far away for us to detect them.

“Electromagnetic signals decay exponentially over distance,” explains DeMarines, “so the farther away you are, any signal we might get would be so unintelligible by the time it reached our telescopes that any information that might have been encoded, whether it was intentional or not, might be lost on us.” 

Global development is making the search more difficult as well. Radio frequency interference makes it difficult to tease out the signal from the noise, according to DeMarines.

“You try to keep these big radio telescopes in a radio quiet zone, but you still get bombarded with local or satellite communication,” says DeMarines.

There’s still a lot we don’t know about what technosignatures extraterrestrial life might present, but schemas like the Kardashev Scale help scientists get their minds around the possibilities so they’ll know what to look for and how best to look.

Read More: New SETI Tool Expands the Search for Intelligent Life in the Universe

Article Sources

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Avery Hurt is a freelance science journalist. In addition to writing for Discover, she writes regularly for a variety of outlets, both print and online, including National Geographic, Science News Explores, Medscape, and WebMD. She’s the author of “Bullet With Your Name on It: What You Will Probably Die From and What You Can Do About It,” Clerisy Press 2007, as well as several books for young readers. Avery got her start in journalism while attending university, writing for the school newspaper and editing the student non-fiction magazine. Though she writes about all areas of science, she is particularly interested in neuroscience, the science of consciousness, and AI–interests she developed while earning a degree in philosophy.