Kardashev scale

The Kardashev scale is a method of measuring a civilization's level of technological advancement based on the amount of energy it is capable of harnessing and using. The measure was proposed by Soviet astronomer Nikolai Kardashev in 1964, and was named after him.
Kardashev first outlined his scale in a paper presented at the 1964 conference that communicated findings on BS-29-76, Byurakan Conference in the Armenian SSR, which he initiated, a scientific meeting that reviewed the Soviet radio astronomy space listening program. The paper was titled "Передача информации внеземными цивилизациями". Starting from a functional definition of civilization, based on the immutability of physical laws and using human civilization as a model for extrapolation, Kardashev's initial model was developed. He proposed a classification of civilizations into three types, based on the axiom of exponential growth:

A Type I civilization is able to access all the energy available on its planet and store it for consumption.
A Type II civilization can directly consume a star's energy, most likely through the use of a Dyson sphere.
A Type III civilization is able to capture all the energy emitted by its galaxy, and every object within it, such as every star, black hole, etc.

Under this scale, the sum of human civilization does not reach Type I status, though it continues to approach it. Extensions of the scale have since been proposed, including a wider range of power levels and the use of metrics other than pure power, e.g., computational growth or food consumption.
In a second article, entitled "Strategies of Searching for Extraterrestrial Intelligence", published in 1980, Kardashev wonders about the ability of a civilization, which he defines by its ability to access energy, to sustain itself, and to integrate information from its environment. Two more articles followed: "On the Inevitability and the Possible Structure of Super Civilizations" and "Cosmology and Civilizations", published in 1985 and 1997, respectively; the Soviet astronomer proposed ways to detect super civilizations and to direct the SETI programs. A number of scientists have conducted searches for possible civilizations, but with no conclusive results. However, in part thanks to such searches, unusual objects, now known to be either pulsars or quasars, were identified.

Origin of the classification

First publication (1964)

Kardashev presented for the first time a classification of civilizations according to the level of the rate of their energy consumption, or ability to harness power, in an article entitled Transmission of Information by Extraterrestrial Civilizations, published in 1964 first in Russian in the March–April issue of the Astronomicheskii Zhurnal, then in English in the September–October 1964 issue of the Soviet Astronomical Journal. In this article, the scientist presents a calculation of the evolution of the power needs of humanity. Assuming that overall human power use will continue to increase, he calculated that the rate of energy consumption will cross specific mileposts. Kardashev proposed a typology of technological civilizations based on the evolutive attainment of the three power harnessing mileposts he described.
A civilization known as "Type I" has achieved a technological level close to the one attained on Earth at the time Kardashev's article was submitted, with a rate of energy consumption evaluated at about 4 x 10¹² watts. A civilization known as "Type II" would surpass the first by fourteen orders of magnitude, matching the entire power emitted by the Sun in about 3,200 years, i.e, Earth's home star's "output" at that time, predicted at 4 × 10²⁶ W. Finally, a civilization known as "Type III" reaches the milepost set in 5,800 years when humanity's rate of energy consumption is predicted by the author to match the power emitted by the approximated 10¹¹ stars in the Milky Way galaxy, which involves harnessing power of up to an estimated 4 x 10³⁷ W.
Assuming the development of radio, Kardashev predicted that in the following two decades it would be possible to build antennas of 100,000 m² capable of detecting Type II and III civilizations. A Type I civilization like that of Earth would be able to receive the extraordinary energetic emissions of the other types of civilizations, which would supposedly be able to emit continuously.
Kardashev then examined the characteristics of a transmission from an artificial source. He mentioned the two cosmic radio sources discovered in 1963 by the California Institute of Technology, CTA-21 and CTA-102 in particular, which would have characteristics close to those of a presumed artificial source. The most suitable region of the galaxy for observing Type II and III civilizations would then be the Galactic Center, due to the high density of the stellar population it harbors. He then recommended that the search programs for such artificial sources should focus on other nearby galaxies, such as the Andromeda Galaxy, the Magellanic Clouds, M87, or Centaurus A. Kardashev concluded his paper by noting that the possible discovery of even the simplest organisms on Mars would increase the likelihood that Type II civilizations exist in the galaxy.

Second publication (1980)

Towards an energetic definition of civilization

In 1980, Nikolai Kardashev published a second article entitled Strategies of Searching for Extraterrestrial Intelligence: A Fundamental Approach to the Basic Problem, in which he stated that:
According to the Soviet astronomer, the Earth's civilization would be too young to be able to contact another civilization that would certainly be more advanced; the Solar System is too young with its five billion years, and the first ancestors of today's man appeared only 6 million years ago at the earliest; the oldest celestial objects are between 10 and 14 billion years old; it is clear that the other civilizations are incomparably older than the human civilization. Therefore, the knowledge of these civilizations must be greater than Earth's, and, he reasoned, they must surely be aware of what humans are doing.
Kardashev believed it is probable that the present state of Earth's civilization is only one of the stages through which civilizations pass during their evolution. It is thus possible to define civilization on the basis of this universal characteristic, which allowed Aleksandr Lyapunov to define life as "a highly stable state of matter, which uses information encoded by the states of individual molecules to produce maintaining reactions", which Kardashev calls the "functional definition of civilization". He therefore suggests thinking of civilization as a "highly stable state of matter capable of acquiring, making abstract analysis of, and utilizing information to obtain qualitatively new information about its environment and about itself, to improve its capabilities of gathering new information for producing sustaining reactions."
Civilization is therefore characterized by the quality of the information acquired by its operating program, and by the energy required to implement these functions. By "information about its environment and about itself", Kardashev specified that it is data about organic or inorganic nature, science, technology, economy, culture, arts, etc. From this definition, he proposed a diagram representing the interactions between a civilization and its environment, and enumerated a number of scientific problems arising from these interactions with the information available in the Universe.
From this definition, Kardashev drew three conclusions. The first postulated that because of the vast and unlimited set of activities required by scientific problems, the period during which civilizations must transmit and communicate is necessarily long, even unlimited. On the other hand, since our present development covers only a negligible fraction of this communication phase, Kardashev hypothesized the high improbability that we will meet "brothers in intelligence" who are at the same stage of evolution as are we. After all, highly advanced civilizations know and use the laws of physics to a degree that we have yet to suspect. Kardashev asserted that "this last point should be taken into account in the research programs of extraterrestrial civilizations" and concluded that it is very likely that our present state is only one of the stages through which every civilization passes during its evolution.

Two strategies for searching for intelligent signals

Kardashev then analyzed various models and hypotheses of the evolution of civilization. Answering the question of the Russian astronomer Iosif Shklovsky, who in an article published in 1977 entitled Possibility of the Intelligent Life in the Universe Being Unique found it strange that the "shock wave of intelligence" of a supercivilization had not yet reached the limits of the whole Universe, Kardashev put forward two explanatory hypotheses. In the first, he postulated that it would not be useful for a supercivilization to expand the space it occupies in order to maintain its activity, and in the second, it is possible that a civilization, instead of dispersing itself in space, would rather continue its activities of information analysis in order to discover new fundamental laws.
However, such civilization activities require the use of abundant energy. According to the laws of thermodynamics, an important part of this consumed energy must be converted into radiation of a bolometric magnitude approximately equal to that of the radiation background surrounding the source. The spectral distribution of this intensity must be close to that of a black body. This would be a possible way to search for extraterrestrial civilizations. Such energy consumption would also require a large amount of solid matter for stellar engineering activities, which Kardashev called "cosmic miracles". In short, information about the possible existence of an extraterrestrial civilization would come in the form of electromagnetic radiation.
With regard to the fate of civilizations, Kardashev saw two concepts, from which two strategies for the search for extraterrestrial civilizations can be derived. The first, which he called "terrestrial chauvinism", is based on the principle that civilizations can only stabilize or perish at a level of development close to ours currently reached. The second, which he called the "evolutionary concept", holds that civilizations are capable of reaching higher levels of development than that of contemporary humanity. In the first case, the best search strategy using astronomical detection means would be to observe the most powerful sources of radiation in space.
The observer will then be able to determine if they are natural emission sources, and only then can the search focus on objects with weaker radiation. In the second case, he recommended to search for new and powerful sources of radiation, especially in the poorly known regions of the electromagnetic spectrum. These sources could be significant or periodic monochromatic signals from the galactic center, from other galaxies or from quasars and other exotic cosmic objects.
Kardashev believed that the search should focus on the millimeter wavelength spectrum, close to the maximum intensity of the cosmic microwave background, rather than in the 21-centimeter band. According to Kardashev, in order to capture the significant radiation of an advanced civilization emitted by a megastructure, a radio telescope with a diameter larger than that of the Earth would have to be placed in orbital space.
Kardashev concluded by predicting that the search for extraterrestrial civilizations would lead to positive results in the next decade, giving humanity access to a vast amount of information about the Universe and its evolution over a period of several billion years.