Nikolai Kardashev, born in Moscow in 1932, is a leading Russian astrophysicist. He is perhaps most well known for his system of ranking interstellar civilizations by their technological ability, but he has also long been involved in Russian efforts in the Search for Extra-Terrestrial Intelligence (SETI). While American attempts at SETI have largely focused on looking for radio signals from alien civilizations, Kardashev emphasised looking instead for other signs a technologically advanced civilizations would create – for example heat generated from the use of vast amounts of energy.
Kardashev was one of the first to consider the possibility that an alien civilization may be millions or even billions of years more advanced than we are. A key feature of increasing technological growth is an increase in energy use – our global industrial civilization uses energy in a scale completely unimaginable to someone living in the Roman Empire 2000 years, just as their energy use was many times greater than that of primitive hunter-gatherer societies thousands of years before. Extrapolating these trends one can imagine that a civilization that spans multiple star systems would use energy equivalent to the output of several entire planets, while a galaxy spanning civilization would use more energy than output by entire stars.
Kardashev proposed classifying the technological development of a civilization by the total amount of energy used. Under his scale the following civilization types were defined:
- A type 1 civilization would have a technological level similar to that currently seen on Earth (or perhaps in 1964, when Kardashev proposed his scale), and an energy consumption of 4×10^12 W.
- A type 2 civilization would be capable of harnessing the energy output of it’s home star, perhaps by constructing a “Dyson sphere“. Kardashev suggested that this would imply an energy consumption of 4×10^26 W.
- A type 3 civilization would be capable of using energy on a galactic scale, and would have a total energy consumption around 4×10^37 W.
Notice that these definitions are quite vague. For example, a civilization that forms on a planet around a dwarf star would find it much easier to reach type 2 than a civilization forming around a much brighter star. This vagueness of definition has allowed a lot of modification to the Kardashev scale. It is not uncommon to see attempts at expanding the scale to include galaxy clusters and even the entire Universe, or to see it rebased around absolute numbers.
Carl Sagan, a famous US astronomer and SETI enthusiast, suggested that we should not yet consider ourselves a type 1 civilization as we are not yet able to control all of Earth’s energy output. According to Sagan’s calculation humanity currently lies at about 0.7 on the Kardashev scale, and will reach type 1 in another 100-200 years.
The Kardashev scale can be a useful way to break potential alien civilizations into broad categories. There are certainly going to be huge differences between a Type 1 and Type 2 civilization, and between a Type 2 and Type 3 civilization. Indeed, if a type 3 civilization already existed in our galaxy we should already see clear signs of their energy use and technological influence on the natural galactic environment. The fact that we don’t seems to indicate that no such civilization exists in our galaxy. Scans of nearby galaxies have also shown little evidence of such technologically advanced galaxies.
However, I don’t believe there is much benefit in trying to build the Kardashev scale into a serious system for categorising civilizations. We still know very little about the possible forms of civilization – the only examples we have are our own human civilizations. We also know little about how civilizations may evolve over time, it may be that all civilizations eventually move away from endless growth as a metric for success and develop into something else. The Kardashev scale is useful in as much as it provokes thought and question, but it is not yet sensible to make it into a rigorous system.