Fermi and the Great Scales
What would an advanced alien civilization look like?
In 1964, Soviet/Russian astrophysicist Nikolai Kardashev (1932–2019) released an essay titled “Transmission of Information by Extraterrestrial Civilizations.” While addressing the challenges of interstellar messaging, Kardashev argued that technologically developed civilizations could be classified based on the amount of energy they consume. From this, he proposed a three-tiered scheme that consisted of the following:
- Type I civilizations (aka. planetary civilizations) are those that are capable of using all of the energy available on their planet (~4×10¹² watts)
- Type II civilizations (aka. stellar civilizations) are those capable of using and controlling the energy of their entire star system (~4×10²⁶ watts)
- Type III civilizations (aka. galactic civilizations) are those that can control the energy of an entire galaxy (~4×10³⁷ watts)
This classification scheme has come to be known as the Kardashev Scale. While it is not a scientific tool in the strictest sense, the scale is a useful tool when it comes to the Search for Extraterrestrial Intelligence (SETI). In particular, it allows researchers to help address the all-important question, “What should we be looking for?”
For example, based on the parameters specified by Kardashev, a Type I civilization would have grown to occupy the entire surface area of its planet and colonized Low Earth Orbit (LEO). This would give them the ability to create space-based solar arrays that would provide the planet with consistent and abundant energy. In addition, they would be likely to have thousands of satellites in orbit for the sake of communication and scientific research.
The presence of these constellations in orbit (aka. Clarke Belts) would mean that the civilization could be detected whenever the planet transited across the face of its star. For other species observing the star edge-on, the Clarke Belt would pick up and reflect the light of the Sun.
A Type II civilization, according to Kardashev, was best exemplified as one that can construct a megastructure that would harness all the radiation of its home star (i.e., a Dyson Sphere) as well as multiply the amount of habitable space the civilization had in its home system. This idea was first put forward by famed British-American Freeman Dyson in 1960 as a thought experiment.
In the proposal paper, titled “Search for Artificial Stellar Sources of Infrared Radiation,” Dyson even suggested how SETI surveys could search for such structures by looking for unexplained sources of far-infrared radiation. These could indicate the presence of a massive shell that enclosed a star, absorbed all of its light, and radiated the excess energy outwards as heat.
A Type III civilization is tougher to characterize, but various scientists and speculative thinkers have advanced theories over the years. A popular idea is that a Type III civilization could build megastructures around their entire galaxy (or at least around the core region of their galaxy) and harness the energy of its supermassive black hole (SMBH).
Over time, many refinements have been made to the Kardashev Scale, with some suggesting that different metrics be used.
Information Mastery Scale
Once again, we owe a great debt to the famed physicist and science communicator Carl Sagan! In his book, The Cosmic Connection: An Extraterrestrial Perspective (released in 1973), Sagan postulated that a better means of measuring a civilization’s development could be its level of “information mastery.”
Civilizations, he argued, should be classified based on the amount of information they generate and store rather than energy. To this end, Sagan introduced a lettered scale (A to Z) where each letter represented an order of magnitude in data production. According to Sagan, a Type A civilization would be one that possessed about 10⁶ bytes of information.
By Sagan’s estimates, humanity had reached Type H, or mastery over 1⁰¹³ bytes of information, as of the early 1970s. Since then, humanity has advanced by several orders of magnitude, thanks to the development of modern telecommunications, personal and mobile computing, the internet, and its many associated applications.
As of the mid-2010s, humanity had reached what some analysts are now calling the “Zettabyte Era,” where global information usage surpassed one Zettabyte (or 10²¹ bytes) a year. By 2017, annual global information usage reached an estimated 2.7 Zettabytes (ZB), and nearly doubled to reach 4.4 ZB by 2019, and increased tenfold by 2020, reaching 44 ZB. By 2025, it is projected to reach 175 ZB, or 1.75 × 10²³ bytes .
By Sagan’s own scale, this means that humanity went from a Type H to a Type P between 1973 to 2015, advancing by 15 orders of magnitude in 42 years. Our current level of information mastery indicates we are Type Q right now, and by the middle of this decade, we’re expected to reach Type R. Sagan conjectured that no civilization could have reached Type Z yet, but humanity’s own exponential rate of growth has led some to question that assertion.
Planetary Mastery Scale
Another recent revision of the Kardashev Scale comes from Robert Zubrin, an American aerospace engineer, author, space exploration advocate, and co-founder of the Mars Society. In 2000, he released Entering Space: Creating a Spacefaring Civilization, where he shared his vision of human civilization that had branched out to colonize the entire Solar System.
At the same time, Zubrin presented yet another metric for measuring the development of a civilization. In his view, the key parameter was the level of “mastery” a species had attained (or how widespread a civilization had become in space) rather than energy consumption alone. When adapted to the Kardashev Scale, Zubrin’s scale would look like this:
- Type I: A civilization that has spread across its planet.
- Type II: A civilization that has extensive colonies in its respective stellar system.
- Type III: A civilization that has colonized its galaxy.
The Barrow Scale
But perhaps the most radical reinterpretation of the Kardashev Scale was made by English astronomer and cosmologist John D. Barrow. In 1998, Barrow released his seminal book, Impossibility: the Limits of Science and the Science of Limits, where he argued that a civilization’s technological progress should be measured in terms of how it had extended its control over the natural environment to increasingly smaller scales.
Basically, he argued that the true metric of a civilization’s development was not the amount of outer space it mastered but its mastery of “inner space.” Using human history as an example, Barrow demonstrated how the greatest technological leaps allowed humans to manipulate matter on smaller and smaller scales.
This included how ancient peoples relied on stone and metal tools to shape large-scale objects (like wood and stone), how chemical processes allowed people in the industrial era to manipulate matter on the molecular level (producing synthetic chemicals and catalysts), how atomic physics allowed us to harness electricity and split the atom, and how particle accelerators have helped advance our knowledge of subatomic particles.
From this, he created what is known as the Barrow Scale, a reverse classification that consists of the seven following categories:
- Type I-minus: a civilization that can manipulate objects similar in size to themselves (housing, mining ore, monuments, etc.)
- Type II-minus: a civilization that can manipulate and alter the development of living things (organ transplants, studying DNA, genetic engineering, etc.)
- Type III-minus: a civilization that can manipulate molecules and molecular bonds to create new materials.
- Type IV-minus: a civilization that can manipulate individual atoms, creating nanotechnologies and complex forms of artificial life.
- Type V-minus: a civilization that can manipulate atomic nuclei and engineer the nucleons that compose them.
- Type VI-minus: a civilization that can manipulate elementary particles (quarks and leptons).
- Type Omega-minus: a civilization that can manipulate the basic structure of space and time.
This scale has been adopted by many researchers and SETI theorists who believe that it is a more realistic assessment of an advanced civilization’s capabilities. Supporting arguments include recent advances in miniaturization and computing (aka. Moore’s Law), the “Digital Revolution,” materials science, biotechnology, and nanotechnology.
In particular, John von Neumann’s theory of self-replicating machines used for space exploration (aka. “Universal Assemblers,” or Von Neumann probes) is considered a sign of a truly advanced species. Moreover, theoretical works on nanotechnology — like Richard Feynman’s There’s Plenty of Room at the Bottom (1961) and Eric K. Drexler’s The Engines of Creation (1986) — are also cited.
These works outlined how, in the 21st century, humans would be able to engineer machines and materials on the nanoscale — i.e., measured in terms of nanometers (10^-9 m). As Drexler related, machines of this size would be able to manipulate matter at the cellular level (such as mitochondrial DNA), leading to endless medical, scientific, and engineering applications.
Taking things a step further, Feynman showed how universal assemblers would be able to build increasingly smaller robots. Thus, nanorobot assemblers would be able to build tinier and tinier versions of themselves, allowing for the manipulation of matter at even smaller scales, such as picometers (10^-12 m) and femtometers (10^-15 m) — what Feynman meant by “room at the bottom.”
Predictably, critics of the Kardashev Scale and other famous concepts that come up in the course of SETI (such as the Drake Equation) routinely take issue with the speculative nature of it all. Given the absence of evidence (goes the argument), these theories are effectively useless to us, are basically just guesswork, cannot be tested or falsified, etc., etc., etc. To this, there are several worthy counters:
- Of course they are speculative! Everything that takes place within the realm of SETI is speculative and will continue to be until at least one extraterrestrial civilization can be found.
- We have no idea what extraterrestrial life will look like, let alone intelligent life. Our very definition of “intelligence” comes down to language and tools, which is just another way of saying “intelligence as we know it.”
- These thought experiments help us to establish constraints on what we should be looking for. By defining what a civilization of a certain level of development might look like, we create testable hypotheses. This is a time-honored scientific tradition known as the Inductive approach, where we create hypotheses and then gather evidence to test them.
Granted, all of these thought experiments are derived using humanity and life on Earth as the template. This is why the words “as we know it” are constantly used in the course of SETI-related discussions. Like any scientist worth their salt, they understand that life and intelligence could come in any number of forms. And as long as we’re being completely honest with ourselves, there is still so much that we don’t know about life here on Earth.
So yes, the Scales and many other SETI concepts are speculation and subject to guesswork, cultural bias, anthropocentrism, and other idiosyncrasies. But it would be foolish to think that scientists engaged in the field of SETI research are unaware of this or that acknowledging it changes anything. In the end, all we have to work with is what we know, which is limited and all about ourselves.