Milky Way Galaxy Alien Civilization
Photo credit: M. Kornmesser/ESO
Researchers at the University of Nottingham used the assumption that intelligent life forms on other planets in a similar way as it does on Earth to obtain an estimate for the number of intelligent communicating civilizations within our own Milky Way galaxy. They determined that there could be over 30 active intelligent civilizations in our galaxy alone. Read more for a video and additional information.

Technically speaking, there should theoretically be at least a few dozen active civilizations in the Milky Way under the assumption that it takes 5 billion years for intelligent life to form on other planets, like here on Earth. So, the idea is looking at a cosmic scale of evolution, called the Astrobiological Copernican Limit.

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The research shows that the number of civilizations depends strongly on how long they are actively sending out signals of their existence into space, such as radio transmissions from satellites, television, etc. If other technological civilizations last as long as ours which is currently 100 years old, then there will be about 36 ongoing intelligent technical civilizations throughout our Galaxy.” said the paper.