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The Kardashev Scale: Exploring Other Forms of Life

The universe is so vast and old, that it is incredibly unlikely that Earth is the only planet to host life; yet, not a single sign of life outside of the blue planet has ever been observed. This contradiction is termed the "Fermi Paradox" (de Schrijver, 2021), and has been explained in an earlier article. There are many different solutions to this paradox, some more difficult to accept than others. It is possible that although life in the universe is abundant, intelligent life is not. Although humans like to think that their brains are the pinnacle of evolution in the history of life on Earth, intelligence comes at a cost. The brain comprises only about 2% of the body’s mass, though it consumes about 20% of a person's energy (Pulido & Ryan, 2021). The precious resources required to sustain a well-functioning brain in humans might have been spent on the growth or strength of body muscles in other animals. With this thought, Alexander Kotrschal experimented with the selective breeding of a specific type of fish, guppies (Kotrschal et al., 2013). Kotrschal bred two populations of guppies. First, he bred guppies with small brains to create progeny with even smaller brains. Additionally, Kotrschal bred a population of big-brain guppies. Kotrschal showed that the brain mass of the latter group was 9% bigger. The body of the smarter guppies had changed quite substantially, however. Because more energy was needed to sustain the brain, the smarter guppies had smaller guts and fewer progeny. In other words, it may not be intrinsic to evolution that intelligent life, whatever that may be, develops.

Still the statistical unlikelihood, a direct consequence of the estimated 40 billion Earth-like planets in the Milky Way alone, is all but reassuring that humans are indeed the only form of (intelligent) life in the universe (Petigura et al., 2013). While vast sums of money are spent on trying to detect forms of life by NASA and ESA, among others, other scientists theorise about what these other forms of life may look like. The difficulty with this reasoning is that the assumptions may be heavily biased, given that humans are the only example on which assumptions can be based. Because the Earth is thought to have only been around for about 30% of the universe’s existence, if other lifeforms do exist, they are likely substantially more advanced in terms of technology than humans (Jacobsen, 2003). Quantifying this "advancement", however, has proven difficult. Though the human population has exponentially grown in the past centuries, which has gone hand in hand with new medical and technological advancements, according to the United Nations, it is likely that the human population will not grow beyond 10 and a half billion people (United Nations Department of Economic and Social Affairs, Population Division, 2022). Nonetheless, technological advancement is likely only to accelerate. In other words, human population size may not be the best indication of advancement.

Figure 1: The past and the projected population size between 1950 and 2100 (Roser & Rodés-Guirao).

Something that has been steadily increasing throughout human evolution, however, is energy consumption. A few hundred thousand years ago, energy consumption was limited by the amount of energy extracted from foods. A little later, humans mastered fire. Next, humans started taking control of animals and crops, after which our ancestors made small machines to turn water flow into movement. This progressed into enormous buildings, in which engineers were able to burn oil and coal resulting in steam, which could power machines. And now, even more sophisticated scientists work on enormous dams and power plants to facilitate electricity generated from nuclear and hydrothermal energy. As it turns out, all these achievements have exponentially increased the amount of energy consumed by the human population: in the past two centuries, the human population increased seven-fold, while the amount of energy used has increased by a factor of 25 (Our World in Data, 2021; 2022). Energy consumption is therefore much more closely correlated with human evolution than population size.

With this in mind, the Russian astrophysicist Nikolai Kardashev developed a thought experiment termed the "Kardashev Scale" in 1964 (Kardashev, 1964). This scale represents a classification of civilisations based on energy consumption, and it has been evolving over the past half-century. Though originally Kardashev came up with Type I, Type II, and Type III civilisations, the current version is a continuous scale that can be extrapolated to practically an infinite number. Consequently, Arabic numbers have been preferred over the original Roman system (Type 1.0, Type 2.0, etc.). This scale is logarithmic, where Type 1.0 represents a civilisation with an energy consumption of 10^16 Watts, Type 2.0 represents a civilisation with an energy consumption of 10^26 Watts, and so on (Gray, 2020). These numbers roughly correspond to the amount of energy on Earth and its Sun, respectively.

Figure 2: The scale on which energy is made available for civilisations of type 1.0, 2.0, 3.0, and 4.0 (Zuritksy, 2020).

Type 0.0 civilisations harness the energy from biological metabolism, exclusively. Type 1.0 civilisations control the full energy potential of their home planet: they can modulate the weather, extract energy from volcanic eruptions and other natural disasters, and can use every landscape to their advantage (What If, n.d.). Type 2.0 civilisations consume energy at an amount equivalent to the energy found in the civilisation's star. Finally, a Type 3.0 civilisation uses the amount of energy equivalent to the full galaxy it finds itself in, and a Type 4.0 harnesses an amount of energy that is equivalent to the energy available in its supercluster of galaxies. Scientists estimate that human civilisation currently finds itself at a level of about 0.75, which sounds rather unsophisticated when compared to theoretical civilisations of level 4.0 or even higher (Gray, 2020). It is estimated that the Homo sapiens could reach level 1.0 in as little as a few hundred years, though there is no certainty in this (Gray, 2020). If humans stay as curious and expansionist as they are right now, they might be able to advance further; people have already come up with ways to terraform Mars or Venus, and scientists have even come up with designs to harness all of the Sun’s energy, including a Dyson Sphere (Dyson, 1960).

In total, the Sun produces an immense amount of energy, close to about 10 to the power of 24 W (Anissimov, 2023), but the amount of sunlight that reaches the Earth is only a fraction of that number. Yet, the amount of energy that reaches the Earth in only a single second is more energy than the total energy that humans use in a year (Chandler, 2011). On top of that, solar panels are only about 20% efficient, meaning that the vast majority of the sunlight that reaches the solar panels is refracted (Enelx, n.d.). In other words, there is enormous potential in harnessing solar energy to exponentially increase energy production, which is precisely what a Dyson Sphere is for. Dyson came up with this design as a thought experiment to think about how to detect more advanced civilisations (Dyson, 1960). He noted that, given that more advanced civilisations probably need a certain amount of energy, they likely try to exploit the energy of the sun completely. Originally, Dyson described an enormous ring around the sun with structures to collect solar energy, although he did not make any detailed design. Nowadays, multiple designs exist, which are too complicated to go into in this article. One thing that is intrinsic to a Dyson Sphere, and not dependent on its design, is the need for energy release: a structure built to absorb a large amount of solar energy will likely melt. Consequently, it will require a system through which energy can be discarded, most likely, in the form of infrared waves or heat, and these infrared waves should be detectable. In other words, Dyson proposed to look for large and dark objects that emit a lot of heat: these objects would be dark, simply because the light emission of the star is absorbed.

Figure 3: A hypothetical design of a Dyson Sphere (Roche, n.d.).

Although it is interesting to think of intelligent life as much more advanced than human life, this thought experiment comes with intrinsic flaws and biases. All the assumptions made are based exclusively on human beings. Advanced civilisations may have completely different psychology and motivations. With respect to humans, it could be like comparing human civilisation to that of an ant. Although there are some similarities, the complexity is vastly different. The truth is that no one knows whether there are alien civilisations in the vastness of the universe; and if there are, no one will know what they look like, or how advanced they are, until humans are introduced to them. Within this context there is one thing that scientists are fairly sure about: quantification of a civilisation's "advancement" is done best through the quantification of its energy consumption.

Bibliographical References

Anissimov, M. (2023, February 02). How much energy does the sun generate? All the Science.

Chandler, D. L. (October 26, 2011). Shining brightly. MIT News.

De Schrijver, S. (November 6, 2022). Fermi Paradox: Are we Alone?. Arcadia.

Dyson, F. J. (1960). Search for Artificial Stellar Sources of Infrared Radiation. Science, 131(3414), 1667–1668.

Enelx. (n.d.). Solar panel efficiency: what is it?.

Gray, R. H. (2020). The Extended Kardashev Scale. The Astronomical Journal, 159(5), 228.

Jacobsen, S. B. (2003). How old is planet earth? In Science (Vol. 300, Issue 5625, pp. 1513–1514).

Kardashev, N.S. (1964). Transmission of Information by Extraterrestrial Civilizations. Soviet Astronomy, 8, 217-221.

Kotrschal, A., Rogell, B., Bundsen, A., Svensson, B., Zajitschek, S., Brännström, I., Immler, S., Maklakov, A. A., & Kolm, N. (2013). Artificial Selection on Relative Brain Size in the Guppy Reveals Costs and Benefits of Evolving a Larger Brain. Current Biology, 23(2), 168–171.

Our World in Data. (2021). Chart: Population, 1800-2019. Based on: Gapminder (v6); United Nations - Population Division (2022); HYDE (v3.2); Gapminder (Systema Globalis).

Our World in Data. (2022). Chart: Global primary energy consumption. Based on: BP Statistical Review of World Energy; Vaclav Smil (2017), Energy Transitions: Global and National Perspectives, 2nd edition, Appendix A.

Petigura, E. A., Howard, A. W., & Marcy, G. W. (2013). Prevalence of Earth-size planets orbiting Sun-like stars. Proceedings of the National Academy of Sciences, 110(48), 19273–19278.

Pulido, C., & Ryan, T. A. (2021). Synaptic vesicle pools are a major hidden resting metabolic burden of nerve terminals. Science Advances, 7(49), 9027.

United Nations Department of Economic and Social Affairs, Population Division (2022). World Population Prospects 2022: Summary of Results. United Nations.

What If. (n.d.). What if we become a type 1 civilisation?. The What If Show.

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