Astrophysicists have estimated the number of intelligent alien species that could possibly exist in our galaxy.
According to a study at the University of Nottingham, humans should be finding ways to make contact with 36 other intelligent civilisations in the Milky Way.
Intelligent life would evolve on other planets in a similar way to how it did on earth, according to the scientists.
This means alien life would require a habitable distance from a star like our sun.
The findings, published in The Astrophysical Journal, reveal the estimated age of one of these possible life-filled planets would need to be between 4.5 and 5.5 billion years old.
What is considered ‘intelligent’ life?
The team behind the study defined ‘intelligent life’ as being able to broadcast radio signals into space.
This concept is summarised by the acronym ‘CETI’ which stands for Communicating Extra-Terrestrial Intelligent civilisations.
Lead researcher,Professor Christopher Conselice, an astrophysicist at Nottingham University explained: “There should be at least a few dozen active civilisations in our galaxy under the assumption that it takes five 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,” he added.
"Our new research suggests that searches for extraterrestrial intelligent civilisations not only reveals the existence of how life forms, but also gives us clues for how long our own civilisation will last.
"If we find that intelligent life is common then this would reveal that our civilisation could exist for much longer than a few hundred years, alternatively if we find that there are no active civilisations in our galaxy it is a bad sign for our own long-term existence."
‘17,000 light years away’
While there may be life on more than 36 planets in the Milky Way, this life may only be at cellular level and not at all intelligent.
Even if these civilisations have more intelligence than a mere cell, the study’s requirement for such ‘intelligent life’ to be able to send and receive radio signals through space, certainly limits the numbers.
On Earth, humanity only developed to a point that it could broadcast radio signals in the last 119 years, when Marconi attempted to send the first radio signals across the Atlantic Ocean.
Those 119 years are a drop in the ocean compared to the 200,000 years humans have been estimated to walk this Earth.
The study calculated that if those 36 civilisations are spread out across the galaxy the nearest one to Earth would be a staggering 17,000 light years away.
As the name suggests, a light year is the distance that light can travel in a single year.
Since that figure is roughly six million million miles, these possible civilisations are likely too far away, making detection and communication "very difficult" with our current technology.