In 1964, Russian astrophysicist Nikolai Kardashev (April 25, 1932 – August 3, 2019) defined three levels of civilizations, based on the order of magnitude of power available to them (known as the Kardashev scale):
The Kardashev Scale
A Type I civilization, also called a planetary civilization can use and store all of the energy available on its planet. For the Earth-Sun system, this value is close to 7×1017 watts.
Also called a stellar civilization – a civilization capable of harnessing the energy radiated by its own star. Our Type I brains can hardly imagine how someone would do this, but we’ve tried our best, imagining things like a Dyson Sphere. The successful construction of a Dyson sphere would make a civilization’s status Type II, with energy consumption at ≈4×1033 erg/sec.
Variants of the Kardashev Scale
There are five and six-level variants of the Kardashev scale.
Carl Sagan, for example, suggested a new formula. As a result of his formulation, there should be a “Type 0” civilization, which controls almost no power on their home planet. As of 2012, humanity was at 0.7244 level on Sagan’s Kardashev scale.
At the other end of the scale, there are Type IV and Type V civilizations. A Type IV civilization can harness the energy of an entire Universe. A Type V civilization can control the multiverse, a collection of Universes. These two are highly speculative and we see no evidence of them.
So, let’s get back to the original Kardashev scale.
Why there is most probably no Kardashev Type-III civilization in the Universe?
There are studies about why there can’t be any (see notes 1), but for a simpler more colloquial explanation, see the video titled “Fermi Paradox: Imperial Pragmatism” published by the author and futurist John Michael Godier below.
We could definitely recognize a Type III civilization if we saw one
Some say Kardashev Type III civilizations could be here, all around us. But we’re just too primitive to perceive them. American physicist Michio Kaku says: “Let’s say we have an ant hill in the middle of the forest. And right next to the anthill, they’re building a ten-lane super-highway. And the question is ‘Would the ants be able to understand what a ten-lane super-highway is? Would the ants be able to understand the technology and the intentions of the beings building the highway next to them?'”
There are problems in this viewpoint. An ant doesn’t know what a highway is because it doesn’t know what anything is. It’s not that highways are too complicated for ants to understand, it’s that ‘understanding things’ isn’t what an ant’s brain does.
If a super-advanced alien civilization was doing some indescribable thing over there, we’d at least be able to say “Wow, that is some bizarre thing happening over there. We have no idea what that thing is, though”.
As John Michael Godier says “a Type III civilization like Kardashev imagined should stick out like a sore thumb”.
They would typically encase all (or most) of an entire galaxy’s stars in Dyson spheres. The end result would be a dark galaxy in visible light, but very bright in infrared from the waste heat generated by the Dyson spheres. Or in the case of a galaxy being colonized, it would have an expanding zone going dark as stars were encased. To date, we didn’t see any galaxy like that (see notes 1).
A single civilization simply cannot colonize an entire galaxy
Because a galaxy is a very, very big thing. For example, our Milky Way is around 150-200 thousand light-years in diameter. Unless there’s a way to travel and communicate faster than light (and there’s most probably not), a single civilization cannot colonize an entire galaxy.
Sending messages back and forth on either side of the galaxy would take hundreds of thousands of years. We know that cultures and languages change dramatically over just a few hundred years. And in a galactic civilization’s case, the receivers even may no longer any idea how to decipher the message. They can be even an entirely new species after that long time.
Because of that, all government necessarily would need to be local, rather than some imperial capital.
“Colonizing” even the next star system might be impossible: for instance, let’s assume that we built a big space ship (a generation ship) and sent it to colonize the nearest star system, Alpha Centauri. The journey would take a few thousand years. Within a few centuries, the colonizers will have become a new species. After that, why would they obey the orders of humans? Instead, most likely, they would build their own civilization.
There might be no reason to colonize an entire galaxy
A very advanced civilization most probably will abandon biology entirely and become a machine civilization. Let’s assume that a Kardashev Type II civilization has wrapped its star with a Dyson sphere (or a Dyson swarm).
Having abandoned their biology entirely and uploaded their brains to virtual reality, eternal-life paradise, colonizing a galaxy would be completely unnecessary and far too risky for them. At least until they have to move to another star system (for example, after their star began to change as our sun will).
- In 2015, a study of galactic mid-infrared emissions came to the conclusion that “Kardashev Type-III civilizations are either very rare or do not exist in the local Universe”.