Our Galaxy alone is possibly home to around 36 intelligent extraterrestrial civilizations.


How many intelligent extraterrestrial civilizations exist amid the hundreds of billions of stars that make up the Milky Way’s spiral arms? The answer, according to a fresh computation, is 36.

This figure implies that life on Earth evolves in a manner similar to how life evolves elsewhere in the cosmos – on a rocky planet a proper distance away from a suitable star, after around 5 billion years. If that assumption is correct, mankind is not entirely alone in the cosmos, but any neighbors are almost certainly too far to meet.



On the other hand, the assumption that life would evolve on a similar timetable to life on Earth is a massive assumption, according to Seth Shostak, a senior astronomer at the SETI Institute in Mountain View, California, who was not involved in the current study. That is, the apparent accuracy of the computations is deceptive.

“If those large, massive assumptions are relaxed, those figures may be anything,” Shostak told Live Science.

Of course, the subject of whether humans are alone in the cosmos is a complete mystery. However, astronomer Frank Drake proposed a new method of thinking about the probabilities in 1961.

Known as the Drake equation, this formulation summarizes the elements that influence the likelihood of humans discovering (or being discovered by) intelligent extraterrestrials: The average annual rate of star creation in the galaxy, the proportion of stars having planets, the fraction of planets with ecosystems, and the even smaller fraction that evolve life. Following that is the proportion of planets with life that support intelligent life, as opposed to, instance, alien algae.


This is subdivided further into the proportion of intelligent alien species that develops observable communication from space (humans fit into this category, as humanity has been communicating with radio waves for about a century).

The third variable is the average duration of communication between alien cultures. The Milky Way is estimated to be around 14 billion years old. If the majority of sentient, speaking civilizations endure for a few hundred years at most, the chances of Earthlings connecting with them are minuscule at best.

It is impossible to solve the Drake equation since the values of the majority of the variables are unknown. However, astronomer Christopher Conselice of the University of Nottingham and his colleagues were interested in having a crack at it using fresh data on star formation and the presence of exoplanets, or planets orbiting stars beyond our solar system. They reported their results in The Astrophysical Journal on June 15.

Conselice told Live Science that “this study could not have been produced a few years ago.”

The researchers assessed the age distribution of stars in the Milky Way, looking for those that are at least 5 billion years old and likely old enough to support a human-like civilisation. They discovered that 97% of the stars in the Milky Way are more than 5 billion years old. Conselice explained that because our solar system is a relative newcomer to the galaxy at 4.5 billion years old, it makes logical that many stars in the Milky Way are older.

The researchers then determined the number of dense and stable stars capable of hosting planetary systems. A third of stars older than 5 billion years met the qualification criteria. The researchers then approximated the number of rocky planets inside the habitable zones of those stars using what astronomers presently know about the distribution of exoplanets.

Additionally, they estimated which stars are metal-rich enough to have rocky planets around them that have the components necessary to create, say, a radio transmitter. Finally, they established a bottom limit of 100 years for the lifespan of a communicative civilisation, based on Earth’s chronology with radio technology thus far.


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As a result? If life on other planets follows the same trajectory as it does on Earth, there are currently 36 sentient, communicative alien civilizations coexisting with humans throughout the Milky Way. This estimate is subject to error, with a range of four to 211 additional civilizations. If extraterrestrial civilizations are scattered evenly over the Milky Way, our nearest neighbor would be around 17,000 light-years away.

That means we’re extremely unlikely to contact you. According to the researchers, a hypothetical extraterrestrial civilisation would have to transmit detectable signals for around 3,060 years in order for mankind to discover them. That means that mankind (and the aliens) would have to hold it together for another 6,120 years in order to start a two-way dialogue with such a society.

There are more hopeful situations for encountering ET. If life may evolve at any point after 5 billion years, but not necessarily at 5 billion years, the number of probable civilizations in the Milky Way increases to around 928. In this situation, a civilisation can establish contact after just 1,030 years of communication.

The issue with these statistics is that they fill in some of the gaps in the Drake equation using astronomical data while excluding some of the most intricate and contentious elements, Shostak explained. Is it possible for life to evolve on every rocky planet inside a sun-like star’s habitable zone?

Is it true that intelligent life consistently appears around 4.5 billion years later? After instance, had an asteroid not collided with Earth some 66 million years ago, wiping out the dinosaurs, the history of Earth’s origin of sentient species may appear considerably different. Perhaps the most constraining aspect, according to Shostak, is the assumption that a communicative civilisation broadcasts signals for just a century.

That appears bleak, even for human civilization, which has challenges but is unlikely to abandon radio waves in the next few months, he added.

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The Drake equation’s solution “is very dependent on the likelihood of life emerging on a world, the probability of [intelligent life developing on a world, and the longevity of intelligence,” Shostak told Live Science. “All of those are significant factors that might alter the outcome by an order of magnitude.”

According to Conselice, the computations provide a means of comprehending humanity’s existence — and future. If there are more civilizations in the galaxy than the new math predicts, this indicates that either life can evolve under far broader conditions than those seen on Earth, or that civilizations have a much longer lifespan than ours has thus far.

“If we discover a large number of them, it’s a good omen that our civilisation may have a very long lifespan,” Conselice added.

On the other hand, if the hunt for alien life continues to provide negative results, it may imply that life evolves seldom or that civilizations tend to self-destruct swiftly. Perhaps the Milky Way was more vibrant a few billion years ago, but those life-giving sparks have since died away. Finally, Shostak stated, there is only one way to discover.

“You will be able to create a report in which you can make any estimate of the number of extraterrestrial cultures once you discover one or two,” Shostak explained.


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