There Could Be 36 active alien Civilizations in Our Galaxy
According to a new study in The Astrophysical Journal, there could be dozens of intelligent alien civilizations hiding in our galaxy, all capable of communicating.
One of the biggest and longest-standing questions in the history of human thought is whether there are other intelligent life forms within our Universe. Obtaining good estimates of the number of possible extraterrestrial civilizations has however been very challenging.
A new study led by the University of Nottingham and published in The Astrophysical Journal has taken a new approach to this problem.
Using the assumption that intelligent life forms on other planets in a similar way as it does on Earth, researchers have obtained an estimate for the number of intelligent communicating civilizations within our own galaxy the Milky Way.
They calculate that there could be over 30 active communicating intelligent civilizations in our home Galaxy.
Professor of Astrophysics at the University of Nottingham, Christopher Conselice who led the research, explains:
“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.”
Conselice also explains that, “The idea is looking at evolution, but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit.”
First author Tom Westby explains: “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.
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 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.
However, the average distance to these civilizations would be 17,000 light-years away, making detection and communication very difficult with our present technology. It is also possible that we are the only civilization within our Galaxy unless the survival times of civilizations like our own are long.
Professor Conselice continues: “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.”
Story source
Journal reference
The Astrobiological Copernican Weak and Strong Limits for Intelligent Life
Abstract
We present a cosmic perspective on the search for life and examine the likely number of Communicating Extra-Terrestrial Intelligent (CETI) civilizations in our Galaxy by utilizing the latest astrophysical information.
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. This type of life has developed in a metal-rich environment and has taken roughly 5 Gyr to do so.
We investigate the possible number of CETI civilizations based on different scenarios. At one extreme is the Weak Astrobiological Copernican scenario such that a planet forms intelligent life sometime after 5 Gyr, but not earlier. The other is the Strong Astrobiological Copernican scenario in which life must form between 4.5 and 5.5 Gyr, as on Earth.
In the Strong scenario (under the strictest set of assumptions), we find there should be at least ${36}_{-32}^{+175}$ civilizations within our Galaxy: this is a lower limit, based on the assumption that the average lifetime, L, of a communicating civilization is 100 yr (since we know that our own civilization has had radio communications for this time).
If spread uniformly throughout the Galaxy this would imply that the nearest CETI is at most ${17,000}_{-10,000}^{+33,600}$ lt-yr away and most likely hosted by a low-mass M-dwarf star, likely far surpassing our ability to detect it for the foreseeable future, and making interstellar communication impossible.
Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M dwarfs, which may not be stable enough to host life over long timescales. We furthermore explore other scenarios and explain the likely number of CETI there are within the Galaxy based on variations of our assumptions.
