(ORDO NEWS) — If there are so many galaxies, stars and planets, where are all the aliens and why have we not heard anything about them? These simple questions are at the heart of the Fermi paradox. In the new paper, a pair of researchers are asking the obvious question: How long do we have to live to hear about another alien civilization?
Their answer is 400,000 years.
Four hundred thousand years is a long time for a species that has only been around for a couple of hundred thousand years and only discovered agriculture 12,000 years ago. But 400,000 years is exactly how long we need if we want to hear anything from alien civilizations. This follows from a new study on extraterrestrial intelligent civilizations (CETI).
The work is called “The number of possible CETIs in our Galaxy and the probability of communication between them.” The authors of the work are Wenjie Song and He Gao, both from the Department of Astronomy at Beijing Normal University. The article was published in The Astrophysical Journal.
“As the only advanced intelligent civilization on Earth, one of the most puzzling questions for humans is the uniqueness of our existence,” the authors say.
“Over the past few decades, there have been many studies of extraterrestrial civilizations.” Of course there were, although it is difficult to study something that we are not even sure exists. But that doesn’t stop us.
Studying other civilizations in any way is confusing, because we have only one point of reference – people on Earth. However, many researchers treat this question as a kind of thought experiment using strict scientific principles. For example, one study from 2020 concluded that there are likely 36 CETIs in the Milky Way.
The question of how many CETIs can exist is related to how long we have to wait to hear about 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 difficult question. We can only get information from one known data point (ourselves)…”, the authors write.
This is where the Drake equation comes in. Based on our growing knowledge of the Milky Way, the Drake equation attempts to estimate how many CETIs our galaxy might have. The Drake Equation has its drawbacks, as many critics explain.
For example, some of its variables are nothing more than guesses, so the number of civilizations it calculates is not reliable. But the Drake equation is more of a thought experiment than a real calculation. We have to start somewhere, and it helps us to start.
The authors of the new study also started with it.
“Most of the research on this problem is based on the Drake equation,” the researchers write. “The obvious difficulty of this method is that it is impossible to quantify the likelihood that life could appear on a suitable planet and eventually develop into an advanced communicative civilization.”
If you are skeptical about all this, you are not alone. We cannot scientifically know how many other civilizations exist, or if they exist at all. We do not have sufficient knowledge. Research like this is part of a constant conversation with ourselves about our predicament. Each of them helps us to think about the context of our civilization.
How did they arrive at the figure of 400,000 years if we don’t even know how many CETIs can exist?
Researchers are not the first to tackle this issue. Their article describes some of the previous scientific efforts to understand the prevalence of other civilizations in the Milky Way. For example, they cite a 2020 study that says there are 36 CETIs in the Milky Way.
This number was derived from calculations involving the history of galactic star formation, the distribution of metallicity, and the likelihood that stars have Earth-like planets in their habitable zones.
This work clarifies that “… the topic of extraterrestrial intelligent and communicative civilizations will remain exclusively in the field of hypotheses until any positive discovery is made …”. But they also point out that scientists can still create valuable models based on logical assumptions.
This study echoes these ideas to some extent. It considers two parameters, both of which are poorly understood. The first concerns how many terrestrial planets are habitable and how often life on those planets turns into CETI. The second is at what stage in the evolution of the host star CETI can originate.
In their calculations, the researchers gave each of these parameters a variable. The probability of the appearance and development of life in CETI is (fc), and the necessary stage in the evolution of the host star is (F). Song and Gao ran a series of Monte Carlo simulations using various values of these variables. They came up with two scenarios: optimistic and pessimistic.
In the optimistic scenario, the values F = 25% and fc = 0.1% were used. Thus, a star must travel at least 25% of its life path before CETI can occur. And for each terrestrial planet, the probability of CETI occurrence is only 0.1%.
These optimistic variables create over 42,000 CETIs, which sounds like a lot but isn’t when spread across the galaxy at different times. Further, we will need to live another 2000 years to achieve a two-way communication with us. It almost sounds like within reach.
But this is an optimistic scenario in which the universe seems friendly and populated by other hospitable civilizations. Perhaps some of them are already talking to each other and we just need to join them.
Now about the pessimistic scenario.
In the pessimistic scenario, F = 75% and fc = 0.001%. Thus, a star cannot host CETI until it is much older, and the chance of any terrestrial planet hosting CETI drops to a measly percentage. What is left for us?
This pessimistic calculation gives only about 111 CETIs in the Milky Way. Even worse, we will have to live another 400,000 years to have a two-way communication with them. (For the record, Star Trek begins in the middle of the 22nd century.)
This is where the Great Filter comes into play. The Great Filter is what prevents matter from turning into life and then becoming an advanced civilization.
The authors touch on this topic when they write: “However, it has been suggested that the lifespan of civilizations is likely to be self-limiting due to a variety of potential disruptions such as demographic problems, nuclear annihilation, sudden climate change, runaway comets, environmental changes, etc. etc.”
If the doomsday argument is correct, then in some pessimistic situations humans may not receive any signals from other civilizations until extinction.”
In their work, the scientists write: “… the values of fc and F are full of many unknowns.” This is what happens in all these jobs. This work, and others that address the same question, are more usefully regarded as thought experiments than as reliable results.
We cannot know anything with complete certainty, but we cannot but be compelled to investigate it. This is part of human nature. “It is completely unknown what proportion of terrestrial planets can give rise to life, and the process of evolution of life and the ability to send detectable signals into space is highly unpredictable,” they write.
Will humanity ever meet another civilization? This is one of the questions that most concern us, and it is almost certain that no one living today will have an answer to it.
First, there must be other CETIs, and then we must exist simultaneously with them and somehow communicate. It is possible that other CETIs had already detected life on Earth before they were destroyed by the Great Filter, or perhaps by a natural disaster such as a supernova explosion. We will never know.
Perhaps mankind will live for a long time. Perhaps the Earth will become uninhabitable and humanity will flee to Mars or somewhere else. But would a Martian outpost on a long-vanished planet, populated by the ragged descendants of a destroyed Earth, count as CETI?
We like to imagine that other civilizations have successfully dealt with the problems we are still struggling with. Will it be true? Or will the first CETI we discover turn out to be nothing more than the descendants of a once-proud civilization that exuded confidence until the Great Filter came along?
Who knows? If humanity ever encounters another technological species, it could be so far into the future that our descendants will be almost unrecognizable to modern humans.
Or perhaps we will never have an answer and the Great Filter will prevent us from finding it.
But if humanity needs a purpose, something to cling to that can hold on to hope, then the dream of fellowship with another CETI can do it.
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