How many civilizations are there in the Milky Way?

Are there other thinking creatures in the universe? Researchers recently determined that life should be at least relatively common. In terms of intelligence, however, the results, which were based on an analysis of its development on Earth, were less clear.

A new article published in the Astrophysical Journal has come to somewhat more encouraging results. Astrophysicist Tom Westby, one of the authors, explains his group’s approach: “The classic method for estimating the number of intelligent civilizations relies on making guesses of values relating to life. Opinions about such matters, however, vary quite substantially. Our new study simplifies these assumptions using new data, giving us a solid estimate of the number of civilizations in our galaxy.”

The value that the researchers came up with was 42. Okay, not really, that was just a little joke. Westby continues:

“The two astrobiological limits are that intelligent life forms in less than 5 billion years. For the case of the Earth, it was 4.5 billion years. In addition, a star with at least the metallicity equal to that of the Sun is needed. With those constraints, we calculate that there should be around 36 active civilizations in our galaxy.”

The paper also shows that the number of civilizations strongly depends on how long they transmit signals of their existence out into space, for example, by means of satellites, TV broadcasts, etc. In this respect, our civilization is only 100 years old. If other technological civilizations last at least as long as humankind, then there should currently be about 36 of these civilizations in our galaxy. On average, these would be about 17,000 light-years apart from each other, which would make their discovery and any subsequent communication between them extremely difficult with current technology.

Christopher Conselice, lead author of the study, adds: “Our new research suggests that searches for extraterrestrial intelligent civilizations not only reveals the existence of how life forms, but also gives us clues for how long our own civilization will last. If we find that intelligent life is common, then this would reveal that our civilization could exist for much longer than a few hundred years. Alternatively, if we find that there are no active civilizations in our galaxy, it is a bad sign for our own long-term existence. By searching for extraterrestrial intelligent life—even if we find nothing—we are discovering our own future and fate.”

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