Are We Alone?


The material factors which ultimately limit the expansion of a technically advanced species are the supply of matter and the supply of energy.

— Freeman Dyson, an English-born theoretical physicist and mathematician, in his article “Search for Artificial Stellar Sources of Infrared Radiation”, published in the journal Science in 1960

A scheme for classifying advanced technological civilizations was proposed by the Russian radio astronomer and SETI theorist, Nikolai Kardashev in 1964. His original classification of the three types of civilizations, based on their energy consumption, is given below:

I – technological level close to the level presently attained on the earth, with energy consumption at ~4 × 1019 erg/sec.

II – a civilization capable of harnessing the energy radiated by its own star (for example, the stage of successful construction of a “Dyson sphere”); energy consumption at ~4 × 1033 erg/sec.

III – a civilization in possession of energy on the scale of its own Galaxy, with energy consumption at ~4 × 1044 erg/sec.”

Kardashev calculated how powerful an extraterrestrial radio signal would have to be in order to be detected, “by conventional radio astronomical techniques.” The numbers he came up with were rather large, which formed the basis of his ranking of the civilizations.

Since the publication of Kardashev’s seminal paper, there have been various extrapolations of Kardashev’s original classification by scientists. The following quote is from David Darling’s website “The Encyclopedia of Astrobiology, Astronomy, and Spaceflight”.

“A Type I civilization would be able to marshal energy resources for communications at a planet-wide scale, equivalent to the entire present power consumption of the human race, or about 1016 watts. A Type II civilization would surpass this by a factor of approximately ten billion, making available 1026 watts, by exploiting the total energy output of its central star. Freeman Dyson, for example, has shown in general terms how this might be done with a Dyson sphere. Finally, a Type III civilization would have evolved far enough to tap the energy resources of an entire Galaxy. This would give a further increase by at least a factor of 10 billion to about 1036 watts. [Carl] Sagan pointed out that the energy gaps between Kardashev’s three types were so enormous that a finer gradation was needed to make the scheme more useful. A Type 1.1 civilization, for example, would be able to expand a maximum of 1017 watts on communications, a Type 2.3 could utilize 1029 watts, and so on. He estimated that, on this more discriminating scale, the human race would presently qualify as roughly a Type 0.7.”

Human Civilization is not even in Kardashev’s scale yet

Currently, human civilization is able to harness only a portion of the energy that is available on Earth. Although intermediate values were not discussed in Kardashev’s original proposal, Carl Sagan calculated humanity’s civilization type to be 0.7 in 1973 by interpolating and extrapolating the values. The current state of human civilization has been named Type 0.

In the table below, the International Energy Agency’s past and projected values for planetary power production yield is shown against the corresponding Kardashev scale estimates.

Year 1900 1970 1973 1985 1989 1993 1995 2000 2001 2002 2004 2010 2030
Terawatts 0.67 0.6 8.2 9.2 10 11 12 13 13 14 14 16 22
Kardashev Scale 0.58 0.68 0.69 0.7 0.7 0.7 0.71 0.71 0.71 0.71 0.72 0.72 0.73

If the data is fit to a linear model, Type 1 status in Kardashev’s scale will be reached around the year 2250, when human civilization is expected to harness most forms of energy available on Earth. This is consistent with Freeman Dyson’s estimates that, within 200 years or so, we should attain Type I status.


In fact, growing at a modest rate of 1% per year, Kardashev estimated that it would take 3,200 years to reach Type II status, and 5,800 years to reach Type III status.

According to Kardashev, the possibility of detecting a Type I civilization using an Ozma-like search would be extremely low. Instead, he suggested SETI programs should concentrate on looking for the kind of intense radio signals that might originate from Type II or III activity. Of particular interest were two radio sources whose California Institute of Technology designation numbers were CTA-21 and CTA-102.

In 1964, G.B. Sholomitskii used the Crimea Deep Space Station to examine the radio source CTA-102 at a frequency of 923 MHz and reported periodic variations in its radio flux (period of 102 days) in accordance with Kardashev’s claim that this was indicative of a possible signal from a Type III civilization. However, subsequent studies found the variability of radio flux of CTA-102 had another explanation. CTA-102 was actually a quasar and further studies led to the discovery of a new and fundamental property of quasars—variability of their radio emissions.

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