How do you classify extraterrestrial civilizations?

In the search for extraterrestrial intelligence (SETI), it is important to conceptualize how one might identify the existence of extraterrestrials. Such conceptualization informs SETI operations – where to point sensors and what sorts of sensors to use, for instance. The most well-established classification system for extraterrestrial intelligence is the Kardashev scale, which classifies a civilization’s level of technological advancement according to how much energy it can use. But there are other ways to conceptualize classification. Valentin Ivanov of the European Southern Observatory has worked on an alternate classification system. We spoke to him to learn more.


Why is it important to develop ways of classifying extraterrestrial civilizations?

It may come as a surprise, given that we are discussing such an abstract and hypothetical topic as extraterrestrial civilizations (ETCs), but the main reason is strictly utilitarian. It has to do with answering the question of how to search for ETCs. The brute force approach of covering every surface on Earth or the Moon with radio telescopes and filling nearby space with them is economically not viable. We have to prioritize our goals and optimize our search strategies. Classifications of ETCs – albeit hypothetical ones – help describe the parametric space and establish a framework for the problem.

What are the shortcomings of the Kardashev scale?

I wouldn’t use the word shortcoming here. In his seminal paper from 1964, Nikolai Kardashev answered a very specific question – if communications on interstellar distances were technically feasible with radio. The answer was positive. The required energies, he found, were high but not prohibitive when considering the energies available on a planet or within a stellar system. The classification was not the main point of his paper, but it established a convenient comparison to describe the available energy.

It is naive to expect that a civilization would use all its resources towards the sole goal of communicating with other civilizations. ETCs, for instance, would need to have sufficient remaining resources to create content that is worth sending to other ETCs.

Today, our own situation makes it readily apparent that an ETC might not spend all its energy on communication. In the 1960s, before the rise of fears about ecological problems like “burning” out our own planet, this was less apparent. Today, though, we can obviously see that much of our energy use is driven by growing consumerism that has nothing to do with creating worthy content to send to the stars. This forces us to consider classifying ETCs according to how they spend energy, not just according to how much energy they use.

What are you proposing as a way to classify extraterrestrial civilizations?

Our team also includes the Chilean astronomers Juan Carlos Beamín, Claudio Cáceres, and Dante Minniti. We focus on the interaction of an ETC with its environment as its defining characteristic. We propose a new classification scheme, consisting of the following four classes.

Class 0 is when the ETC uses the environment as it is (like most animals). Class 1 is when the ETC modifies the environment (as humans do now, exemplified by the clothes we wear and the buildings in which we live). Class 2 is when the ETC modifies itself to fit the environment (genetically improved humans, in the not-too-distant future, would be an example of this). Class 3 is when the ETC merges with the environment, converting dead matter into thinking matter (admittedly, this is the most speculative category). In practice, the borders between these categories blur. Some animals, such as ants, build quite sophisticated structures, for instance.

ETCs can – as our own history shows – progress from purely mechanical modification of the environment to more complex manipulation on chemical, atomic, nuclear, and presumably other levels. This sequence of modifications allow ETCs to achieve larger impacts and, more importantly, impacts that were not possible with simpler levels of interaction.

An important point that follows from this observation is that increasing sophistication does not necessarily result from ever increasing energy consumption. Biosciences show this. The opposite notion, that more energy consumption leads to more sophistication, is probably a bias arising from the fact that the radio astronomers and physicists leading SETI research come armed with the idea that progress is embodied by more powerful accelerators or radio transmitters.

The two classification schemes – Kardashev’s and the one we propose – are not directly correlated. There are three main takeaway points from our work. First, the gross amount of available energy is not a unique measure of ETC progress. More energy is not necessarily better, in other words. Second, it is possible that ETCs may exist in the Milky Way that are advanced (e.g., Kardashev Type III ETCs) but that are not energy hungry. Third, our SETI programs perhaps ought to look for beacons specifically set up by advanced ETCs to contact young civilizations like ours or it ought to search for ETCs at technological levels similar to ours.