Are we alone in the Universe? Could there be countless sentient life forms out there just waiting to be found? Will we meet them someday and be able to exchange knowledge? Will we even recognize them as intelligent life forms if and when we see them? Or worse, will they recognize us as intelligent life? When it comes to astrobiology, the search for life in the Universe, we don’t know what to expect. Hence, the speculation and theoretical studies into these questions are so rich and varied!

One such study was conducted by famed Soviet and Russian astrophysicist and radio astronomer Nikolai Kardashev (1932 – 2019). While considering an important question related to the Search for Extraterrestrial Intelligence (SETI) in 1964, Kardashev proposed a classification scheme for ranking a civilization’s development. This would come to be known as the Kardashev Scale, which remains one of the most influential concepts in SETI to this day.

In 1960, the first modern attempt to detect extraterrestrial communications (“Project Ozma“) was made in the United States. Led by Frank Drake, creator of the Drake Equation and hailed as the “Father of SETI,” this experiment was conducted using the radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia.

This experiment monitored two nearby Sun-like stars – Tau Ceti and Epsilon Eridani – for radio signals in the 1420 MHz range, corresponding to the frequency of cold hydrogen gas in interstellar space. While the project failed to detect anything beyond radio static, Ozma paved the way for far more ambitious SETI (and METI) efforts. It also inspired astrophysicists worldwide to consider what future surveys should be on the lookout for.

At a time when a search for extraterrestrial intelligence was more a thought experiment than an actual discipline, physicists in the Soviet Union formulated many of the seminal ideas that would endure until this day. Of these, Nikolai Kardashev was one of the earliest and most consequential thinkers, and his ideas remain foundational to the field of SETI.

Nikolai Kardashev

Coming of age in the postwar era, Kardashev studied under Josef Shklovskii (1916-1985), the celebrated author of Intelligent Life in the Universe. This book was the first general treatise on how humans could search for technologically capable beings in the cosmos. Shklovskii’s book was translated (and added to) by Carl Sagan and became the inspiration for many scientists after it was published in 1966 in the West.

For much of his formative years, Kardashev was on his own. His mother and father were both victims of the Great Purge in 1937 and 38 (respectively), and he was sent to an orphanage. He was eventually released into the custody of his aunt (on his mother’s side), who died in 1948 when Kardashev was 16. His father was eventually shot while his mother worked in a prison labor camp until she was released in 1956.

A year before, Kadashev graduated from Moscow State University, where his studies focused on radio astronomy, an emerging field at the time. He then worked at the Sternberg Astronomical Institute in Moscow, earning his Ph.D. in 1962. Kardashev’s early exposure to the fundamental premises of SETI led him to turn his inventive mind to how radio astronomy could be used to detect transmissions that were not terrestrial in origin.

One of his earliest contributions to SETI came in 1963 while Kardashev was studying CTA-102, a radio source located 8 billion light-years from Earth. Based on previous studies, this object was known to vary in intensity and send out irregular emissions. Kardashev famously suggested that this might be a deliberate attempt by extraterrestrials to send out coded messages.

This theory would eventually be discarded as astronomers learned that CTA-102 is an Active Galactic Nucleus (AGN), aka. a quasar, which astronomers know to be variable in nature. Nevertheless, Kardashev shared this theory and other imaginative ideas in a paper that would establish him among the astronomical community.

Birth of the Scale

This paper, titled “Transmission of Information by Extraterrestrial Civilizations,” was published in 1964. The paper’s purpose was to suggest what types of radio frequencies (and at what energies) SETI researchers should be looking for. In keeping with the idea that there may be some civilizations billions of years older than humanity, it stood to reason that these civilizations would be able to harness levels of energy that were not humanly possible.

To characterize the potential level of a civilization’s development, Kardashev proposed a three-level scale based on the amount of energy they could harness. This Scale included:

Type I – Planetary Civilizations: This refers to those that have developed the means to harness and store all of their home planet’s energy. According to
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