Humans have pointed radio telescopes at the sky for decades, hoping to hear signals from another intelligent civilisation in our galaxy - and heard nothing.
But a new study has suggested that it might be a long time before we hear anything from intelligent aliens - so long, in fact, that the human race might have wiped itself out before we hear the call from E.T.
Using computer simulations, researchers Wenjie Song and He Gao worked out that in an optimistic scenario, we’ll hear from aliens in 2,000 years - and in a pessimistic one, it’ll be 400,000 years.
In that case, the human race may well have succumbed to runaway climate change or nuclear annihilation before then the researchers warned, according to ScienceAlert.
The researchers wrote: “As the only known intelligent civilisation, human beings are always curious about the existence of other communicating extraterrestrial intelligent civilizations (CETIs).
“There have been many studies on extraterrestrial civilisation in the past few decades.
“Based on the latest astrophysical information, we carry out Monte Carlo simulations to estimate the number of possible CETIs within our Galaxy and the communication probability among them.
“We have always wanted to know the answers to the following questions. First, how many CETIs exist in the Milky Way? This is a challenging problem. We can only learn from a single known data point (ourselves).
“As the only known CETI, the question we are most interested in is how long we need to survive in order to receive signals from other CETIs.”
The researchers used Monte Carlo simulations (which use randomness to simulate possible results, calculating the results over and over again).
They used variables including the probability of life appearing, how long civilisations are likely to last, and the stage of its host star's evolution.
In an optimistic scenario, there might be 42,000 communicating civilisations in our galaxy - which means it would take 2,000 years from now for one of them to get in touch.
In a pessimistic scenario, there would be only 111 communicating civilisations in the Milky Way - meaning it would take 400,000 years for one to have two-way communication with us here on Earth.
But by that point, humanity may well be extinct.
The researchers said: “The reason why we have not received a signal may be that the communication lifetime of humanity is not long enough at present.
“However, it has been proposed that the lifetime of civilisations is very likely self-limiting (known as the Doomsday argument), due to many potential disruptions, such as population issues, nuclear annihilation, sudden climate change, rogue comets, ecological changes, etc
“If the Doomsday argument is correct, for some pessimistic situations, humans may not receive any signals from other CETIs before extinction. Nevertheless, it is also possible that no two CETIs in the Milky Way could ever communicate with each other.”
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