A small team of researchers has estimated how long it would take before humanity will hear from an alien civilization, and their response was approximately 400,000 years, a study published in The Astrophysical Journal said.
The authors of the research, Wenjie Song and He Gao, both of Beijing Normal University's Department of Astronomy, suggested that the number of Communicating Extraterrestrial Intelligent Civilizations (CETIs) is tied to how long we have to wait to hear from one. And humans still cannot be sure extraterristrial civilizations even exist.
"As the only advanced intelligent civilization on the Earth, one of the most puzzling questions for humans is whether our existence is unique," the research reads. "There have been many studies on extraterrestrial civilization in the past few decades."
Indeed, the researchers, as well as numerous academics, have approached the subject as if it were a thought experiment, using strict scientific procedures. According to some estimates, there might be 36 CETIs in the Milky Way.
"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 question. We can only learn from a single known data point (ourselves)," the authors wrote.
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The team utilized the Drake Equation, which attempts to predict the number of CETIs in our galaxy based on our developing understanding of it.
"Most studies on this problem are based on the Drake equation," they pointed out. "The obvious difficulty of this method is that it is uncertain and unpredictable to quantify the probability that life may appear on a suitable planet and eventually develop into an advanced communicating civilization."
Why So Many Years Before 'Hello'?
The study is concerned with two parameters, both of which are mostly hypothetical. The first is how many livable terrestrial planets there are and how often life evolves into a CETI on these worlds. The second question is when a CETI would be born in the evolution of a host star. In their calculations, the researchers made each of these parameters a variable. The chance of life arising and evolving into a CETI is (Fc), and the stage of evolution required by the host star is (F).
The scientists used different values for these variables in a series of Monte Carlo simulations. They came up with two scenarios: one optimistic and one pessimistic. F = 25% and Fc = 0.1% were utilized in the optimistic scenario. Before a CETI may appear, a star must be at least 25% of the way through its lifetime, and there is barely a 0.1% possibility of a CETI forming on each terrestrial planet.
Over 42,000 CETIs are created by these optimistic variables, which is actually quite a small number when dispersed across the galaxy at different periods of time. Furthermore, to develop two-way communication, we'd have to endure for another 2,000 years.
As for the pessimistic calculations, F = 75% and Fc = 0.001% in the gloomy scenario. As a result, a star cannot host a CETI until it is much older, and the chances of any single terrestrial planet hosting a CETI are extremely slim. In the Milky Way, this estimate yields only about 111 CETIs. And we would have to wait another 400,000 years for us to be able to communicate with them.
"However, it has been proposed that the lifetime of civilizations is very likely self-limiting, due to many potential disruptions, such as population issues, nuclear annihilation, sudden climate change, rogue comets, ecological changes, etc," the study said. "If the Doomsday argument is correct, for some pessimistic situations, humans may not receive any signals from other CETIs before extinction."
So Little Known, So Much to Know
Notably, the majority of the research assumes that CETIs have the ability to emit radio signals in the same way that humans do. Radio transmission in cosmic space, on the other hand, will result in a decrease in flux as a function of distance. The problem of signal attenuation will make communication between CETIs even more difficult. Therefore, people will have to solve the problem of more reliable transmission and reception of signals in space.
Nevertheless, the scientists admit that "the values of Fc and F are full of many unknowns" in those estimates, as it happens.
"It is quite uncertain what proportion of terrestrial planets can give birth to life, and the process of life evolving into a CETI and being able to send detectable signals to space is highly unpredictable," they explained.
The study said that "until any positive detection is made," the issue of the intelligent life out there able to communicate with us "will remain entirely in the domain of hypothesis." Still, it is pointed out that scientists can come up with useful models based on logical assumptions "that may at least produce plausible estimates of the occurrence rate of such civilizations."
Perhaps humanity will live for a long time. Perhaps Earth will become unsuitable, and humanity will seek refuge on Mars or elsewhere. Alternatively, we may perish long before we can accept a conversation invitation from another system.