What Is Extraterrestrial Intelligence?

Extraterrestrial intelligence (often abbreviated ETI) refers to hypothetical extraterrestrial life that is capable of thinking and doing meaningful tasks. The question of whether other intelligent species dwell beyond our planet has been debated since ancient times, and shows no sign of slowing.

The modern form of this concept has its root in the Copernican Revolution, wherein it was proved that the Earth is a planetary body that revolves around the Sun instead of being stationary. Similarly, other planets revolve around the Sun—which raises the question of the possibility of intelligent life forms on these other planets. Recent discoveries in the new field of astrobiology have indicated that the existence and evolution of other “smart” species in the Milky Way is not improbable. In fact, more than 3,000 extrasolar planets have been discovered and water is likely to be present on Mars and on some moons of the outer solar system. These discoveries suggest that there could be other planets wherein life, or perhaps intelligent life, might be present. Extraterrestrial intelligence has become one of the most widely debated questions in astronomy and has become the core theme of many science fiction movies.

Star wars cosplay

Star Wars cosplay (Photo Credit : RyC/Wikimedia Commons)

Argument for Extraterrestrial Intelligence

The argument in favor of the probable presence of extraterrestrial intelligence is based on a popular philosophical notion called the principle of mediocrity. The principle suggests that there is nothing unusual about the evolution of the solar system, the evolution of the earth, and thereby the evolution of biological organisms and the human population. Just like the processes that led to life on Earth and eventually to thinking organisms, similar processes could have occurred elsewhere in the cosmos. There are three important assumptions in this argument:

  • Planets capable of nurturing life are common
  • Living organisms will spring up on such planets
  • Natural selection will play its course on the planet, which will intermittently produce intelligent species.

Hitherto only the first assumption has been proven—scientists have discovered several small rocky planets similar to Earth that have atmospheres and oceans germane for life.

Many eminent scientists, including Stephen Hawking, argue that the sheer size of the universe makes it improbable for the non-existence of other intelligent species elsewhere in the cosmos. Fermi’s Paradox, on the other hand, underlines the apparent contradiction between the lofty estimates of the possibility of the existence of extraterrestrial intelligent species and our lack of contact with them. To learn more about the Fermi Paradox, click here.

aliens meme

Search for Extraterrestrial Intelligence

Real extraterrestrial artifacts are yet to be found. At the onset of the 20th century, Percival Lowell, a Harvard graduate, claimed to see artificially made canals on Mars. Scientist later found that they were not proof of extraterrestrial intelligent species constructing canals on Mars, but rather a case of optical illusion!


Percival Lowell, an astronomer who theorized that an intelligent extraterrestrial community built canals on Mars. (Photo Credit : Wikimedia Commons)

The most competent mechanism for discovering an extraterrestrial community is to search for electromagnetic signals, especially radio and light waves. Many cosmologists believe that radio or light waves may have been beamed toward Earth from other life-supporting celestial bodies, either involuntarily (similar to the way we leak TV and radio signals into space) or deliberately (as a beacon signal).

Communication with extraterrestrial intelligence (CETI) is another way of searching for extraterrestrial intelligence. This method focuses on composing and decoding signals that could theoretically be comprehended by another technologically advanced extraterrestrial civilization. A famous CETI experiment was the Arecibo message, composed by the renown scientists Carl Sagan and Frank Drake in 1974. This experiment had a message composed of seven parts, which were encoded into a radio signal and sent to globular star cluster M13—a whopping 25,000 light-years from Earth. Sagan and Drake suggested that it would take at least 25,000 years for the message to reach the destination, given the technological advancement of humans. Rather than being an attempt to connect with supposedly existing extraterrestrial species thousands of light-years away from us, this experiment was a manifestation of the limitation of humanity’s technological advancement to communicate with them.

That’s why most of the seekers of extraterrestrial intelligence (SETI) these days do not send signals into the cosmos. Due to the sheer distance and limitation of speed that electromagnetic signals travel, two-way communication is nearly impossible. Researchers are focusing more on the signals received by our planet as a source of clues or hints that intelligent extraterrestrial species do exist somewhere in the vast emptiness of space!


  1. Cornell University
  2. SETI Institute
  3. Rochester Institute of Technology
  4. Penn State University
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Hussain Kanchwala is an Electronic Engineer from University of Mumbai. He is a tech aficionado who loves to explicate on wide range of subjects from applied and interdisciplinary sciences like Engineering, Technology, FinTech, Pharmacy, Psychology and Economics.

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