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The universe should be teeming with life or there must be no life at all, according to a new study that reformulates the Drake equation using probabilistic logic.
A common axiom in the search for extraterrestrial information (SETI) if we find technologically advanced aliens, there will likely be many, many cases of alien life out there rather than having two cases (us and the new discovery).
In a new paper, astronomers David Kipping of Columbia University in New York and Geraint Lewis of the University of Sydney describe how this logic works, based on a probability distribution first introduced by biologist and mathematician JBS Haldane once in 1932. Let’s imagine some of it Earth-like exoplanetsall with similar characteristics. Given their slight differences, we would expect life to emerge on all or any of them; there is no obvious reason why half of these are nearly identical planets would support life and not give half, for example.
We can then show the different outcomes in a U-shaped graph, with the probability on the y-axis and the fraction of planets with life on the x-axis. The two pennies of the U shape correspond to one or a few planets with life, and many planets with life. The U-shaped valley, which corresponds to a low probability, means that half of the planets have life.
Related: The Drake Equation: Estimating the Probability of Finding ET
Now Kipping and Lewis have brought Haldane’s logic to the famous The Drake equation. Developed by an astrologer Frank Drake before the first ever SETI conference, at Green Bank Observatory in 1961, as a means of providing an agenda for the workshop, the Drake equation has subsequently taken on a life of its own, being used to number the technological life forms in the The Milky Way Galaxy.
The Drake equation is written as N = R* x fp x ne x fl x fi x fc x L, where N is the number of civilizations, R* is the star formation rate, fp is the fraction of stars that have planets , ne is the number of potentially habitable planets, fl is the fraction of those habitable planets that develop life, fi is the fraction that develops “intelligent” life, fc is the fraction that has life they communicate, and L is the average lifespan of the civilizations.
Astronomers know the star formation rate (less than 10). solar masses per year in our galaxy) and the fraction of stars that have planets (almost all stars have planets) very well. The number of potentially habitable planets is less known, but astronomers are learning more about them every day as they investigate exoplanetary atmospheres with the James Webb Space Telescope and to characterize those lives. The values of the other four terms are still a complete mystery, making any attempt to use the Drake equation less than satisfactory because so much of it is guess work.
However, Kipping and Lewis point out that the first six terms in the Drake equation describe the “birth” of what they call extraterrestrial technological instantiations, or ETI. This is how they refer to the technological alien life, terms like “civilization,” “species” and “intelligence,” which are not only problematic (for example, how do we define intelligence?) but potentially inaccurate. also when describing alien life. Meanwhile, the final term, L, refers to “death,” or another ETI event.
By splitting the terms of the Drake equation in this way Kipping and Lewis can simplify the formula, as follows: The average number of ETIs in the galaxy is the birth rate of ETIs multiplied by their death rate.
“The beauty of our approach is that it is completely general,” Kipping told Space.com. This means that there is no need to worry about the terms of the Drake equation that we do not know.
“We are not accepting any particular birth mechanism or methods,” Kipping said. “The births could happen by spontaneous emergence, or panspermia seeding, or empire building or whatever else you want – it’s just a birth rate.”
Kipping and Lewis assume what they call the Drake equation for the steady state, where there is a more or less equal level of birth and death rates in an equilibrium that is inevitably reached after enough time. The two astronomers then link this back to Haldane’s introduction (“prior” is the name for a type of probability distribution, such as the U-shaped curve) through a characteristic called the occupation fraction, F. In the exoplanet example mentioned earlier in this article, a high value of F – close to 1 – would correspond to all planets having life, and a low value – close to or equal to 0 – would correspond to no planets having any life.
The problem facing SETI scientists is that, based on observations so far, F is probably not close to 1; otherwise, we would like to note by now that we are not alone, assuming that intelligent aliens are competent to spread throughout the galaxy, building megastructures such as Dyson shares while sending out radio signals. This means that if we are not truly alone in the Universe, then the occupation fraction must be closer to 0.5, placing it in that unlikely valley of the U-shaped curve. Based on that U-shape, we’re probably pretty isolated — that the technological world is rare in other parts of the world.
“These are instances of life that come to light, first through the signals they produce and then through their colonization where they would be seen through megastructures,” Lewis told Space.com. “If such an ETI had arisen in the life of the Milky Way, then they could have colonized the entire galaxy in 10 million to 100 million years, and even after they fell, then they would have their debris around for a long time. It means we don’t see anything out there, they’re long gone and their signatures are gone and we’re back to our original premise. – ETIs appear to be rare in time and space.”
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But neither Kipping nor Lewis advocates giving up on SETI. If we ignore the lack of evidence for a moment, the Drake equation predicts a steady state of congestion globe as likely as we are lonely. For a crowded universe, the occupation fraction must be close to 1, and this may still be possible under certain circumstances. Perhaps ETI remains in its own region, and ours solar system which just happens to be in a region that no one has spread into yet. That would mean that the aliens are quite far away, and our strategy of looking for them around nearby stars is the wrong one. These inhabited regions may be more clearly observed in other galaxies. “I would certainly support extragalactic SETI,” Kipping said.
Or maybe interstellar travel and building megastructures is too difficult, or perhaps ETI don’t even need them to live more frugally, less colonially. And in the absence of radio or optical signal detection, SETI has barely had the resources to be particularly comprehensive in its search so far, and we could easily be lost signal.
It is also possible that there is plenty of complex life, but that the development of technological life is rare.
It’s also possible that ETI birth and death rates haven’t reached a steady state after all, meaning that the new ETI would still have time to arrive on the scene and increase the occupation fraction. However, due to the age of the universe and the limited lifetime of ETI, this is unlikely to be the case.
The research is currently available as a preprintand submitted to the International Journal of Astrobiology for peer-reviewed publication.
