Is there anybody out there? Scientists say there could be 36 intelligent civilizations active in our galaxy
The average distance to these alien civilizations would be 17,000 light-years away, making detection and communication very difficult
How many intelligent life forms are there within our universe? This has been one of the biggest and longest-standing questions, and a new study now suggests that there could be 36 active communicating intelligent civilizations in our home galaxy, the Milky Way. However, the average distance to these civilizations would be 17,000 light-years away, making detection and communication very difficult with our present technology, says the research team from the University of Nottingham, UK.
Researchers calculate that a possible alien civilization would have to broadcast detectable signals for approximately 3,060 years for us to pick them up. Accordingly, to establish a two-way conversation with such a civilization, our civilization would need to survive at least another 6,120 years, they add.
Previous calculations along these lines have been based on the Drake equation, which was written by astronomer and astrophysicist Frank Drake in 1961. "Drake developed an equation which, in principle, can be used to calculate how many Communicating Extra-Terrestrial Intelligent (CETI) civilizations there may be in the Galaxy. However, many of its terms are unknowable and other methods must be used to calculate the likely number of communicating civilizations," says the research team in the study published in The Astrophysical Journal.
Accordingly, the researchers developed their own approach. Using the assumption that intelligent life forms on other planets in a similar way as it does on Earth, researchers obtained an estimate for the number of intelligent communicating civilizations within the Milky Way. The analysis 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, and television, among others. The team explains that if other technological civilizations last as long as ours, which is currently 100 years old, then there will be over 30 ongoing intelligent technical civilizations throughout our Galaxy.
"There should be at least a few dozen active civilizations in our Galaxy under the assumption that it takes 5 billion years for intelligent life to form on other planets, as on Earth. The idea is looking at evolution but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit," says Christopher Conselice, professor of astrophysics at the University of Nottingham, who led the research.
The Astrobiological Copernican limits come in two forms. At one extreme is the "weak" scenario, where a planet forms intelligent life sometime after 5 billion years, but not earlier. The other is the "strong" Astrobiological Copernican scenario in which life must form between 4.5 and 5.5 billion years, as on Earth. The analysis used the latter and said that under the strictest set of assumptions, there are likely between four and 211 civilizations in the Milky Way today capable of communicating with others, with 36 being the most likely figure.
"Our calculation involves Galactic star formation histories, metallicity distributions, and the likelihood of stars hosting Earth-like planets in their habitable zones, under specific assumptions which we describe as the Astrobiological Copernican Weak and Strong conditions. These assumptions are based on the one situation in which intelligent, communicative life is known to exist on our own planet," the findings state. The team also assumed that these new species would need to develop in metal-rich environments because human beings developed near such an environment, due to the metal present in the Sun.
"The classic method for estimating the number of intelligent civilizations relies on making guesses of values relating to life, whereby opinions about such matters 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," says author Tom Westby from the University of Nottingham. He explains, "The two Astrobiological Copernican limits are that intelligent life forms in less than 5 billion years, or after about 5 billion years - similar to on Earth where a communicating civilization formed after 4.5 billion years. In the strong criteria, whereby a metal content equal to that of the Sun is needed (the Sun is relatively speaking quite metal-rich), we calculate that there should be around 36 active civilizations in our Galaxy."
The study suggests that under the more relaxed assumptions of the weak Copernican scenario, there would be about 928 civilizations communicating in our galaxy today, meaning more of them at a closer range requiring an estimated 1,030 years to make contact.
The researchers say it is also possible that we are the only civilization within our Galaxy unless the survival times of civilizations like our own are long. They emphasize that if the search for intelligent life reveals nothing within a distance of about 7,000 light-years, this could mean one of two things. The first is that the lifetime of civilizations is much shorter than 2,000 years, which would imply that our own may be short-lived. The second is that life on Earth is unique, and intelligent life does not automatically form after 5 billion years on a suitable planet but is a more random process.
Conselice says that the new research suggests that searches for extraterrestrial intelligent civilizations not only reveals the existence of how life forms, but also gives 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 future and fate," says Conselice.