“The question of the existence of advanced civilizations elsewhere in the universe has always been clouded by three large uncertainties in the Drake equation,” says Adam Frank, professor of physics and astronomy at the University of Rochester. “We have known for a long time how many stars there are approximately. We do not know how many of these stars have planets that may have harbored life, how often life could have evolved and lead to intelligent beings; how long a civilization can exist before it dies out.
We don't even know if a highly developed technological civilization can survive for more than a few centuries. However, new work by Frank and Woodruff Sullivan is allowing scientists to start leveraging everything they know about planets and climate and simulate the interactions of highly energy-dependent species in their homeworld.
“Our results indicate that our biological and cultural evolution was not unique and may have happened many times before. Other cases could include many energy-dependent civilizations trying to cope with the crisis on their planets as civilizations grow. We can start to investigate this problem using modeling to get an idea of what leads to longevity of civilization and what does not."
The new study shows that the recently discovered exoplanets, combined with a broader approach to the issue, allow to determine a new empirically significant probability of the existence of advanced civilizations throughout the history of the universe. And it shows that unless the chances of life on the planet are infinitely small, humanity will not be the only and not the first advanced technological civilization.
The work, published in the journal Astrobiology, also shows for the first time what “pessimism” or “optimism” means in the context of assessing the likelihood of advanced extraterrestrial life.
“Thanks to research by NASA's Kepler satellite and others, we now know that about one-fifth of stars have planets in 'habitable zones' where temperatures allow the life we know to exist. Therefore, one of the three biggest uncertainties can already be contained.”
Frank says Drake's third biggest question - how long civilizations could have existed - is still completely incomprehensible. “The fact that humans have had rudimentary technology for about ten thousand years doesn't tell us whether other societies will tinker with it just as long or even longer,” he explains.
In 1961, astrophysicist Frank Drake developed an equation to estimate the number of advanced civilizations that could exist in the Milky Way galaxy. It looks like this: N = R * (fp) (ne) (fl) (fi) (fc) L, the decoding of each variable is below. Based on the simplest statistics, it is easy to calculate that somewhere there may be thousands, even millions of alien civilizations:
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R *: The rate at which stars form in our galaxy.
fp: Percentage of stars with planets.
ne: the number of terrestrial planets around each star that has planets.
fl: The percentage of terrestrial planets that have evolved life.
fi: The percentage of planets with life on which intelligent life has evolved.
fc: The percentage of sapient species that have made it to technology that can be discovered by forces of an external civilization like ours. For example, radio signals.
L: The average number of years it takes an advanced civilization to detect detectable signals.
Drake's equation has become the basis for research, and space technology has deepened the knowledge of scientists about several variables. But to find out the possible duration of the existence of other advanced civilizations - L - is almost impossible.
Frank and Sullivan have proposed a new study that addresses a slightly different question. What if some civilizations evolved over the course of the history of the observable universe? Frank and Sullivan's equation relies on Drake but removes the need for L.
“Instead of asking how many civilizations can exist today, we are asking: are we really the only technologically advanced species?” Sullivan says. "This shift in focus removes the need for the question of the duration of civilization and allows us to tackle the so-called 'question of space archeology' - how often in the history of the universe has life evolved to a technologically advanced state?"
Serious uncertainties remain in calculating the likelihood of advanced life appearing on inhabited planets. And here Frank and Sullivan make a U-turn. Instead of calculating the odds of an advanced life emerging, they are calculating the odds against its emergence, that is, whether humanity could be the only developed civilization in the history of the observable universe.
“Of course, we have no idea how likely it is that an intelligent technological species will appear on a single planet,” says Frank. “But using our method, we can tell exactly how unlikely we are going to be the ONLY civilization in the universe. We call this the pessimistic trait. If the probability goes beyond the line of pessimism, then the technological species and civilization appeared before."
Using this approach, Frank and Sullivan calculated how unlikely evolved life would be if there were not a single example of it among the two hundred billion trillion stars in the universe. Or even among the hundreds of billions of stars in the Milky Way.
What's the result? Applying new data on exoplanets to the universe as a whole, Frank and Sullivan found that a civilization would be unique to space only if the chances of a civilization appearing on an inhabited planet were less than one in 10 billion trillion, or 1 in 1022.
“One in ten billion trillion is very little,” says Frank. “It's obvious to me that other intelligent technologically advanced species most likely evolved before us. Think about it in the following way. Before our results, you would be considered a pessimist if you counted the likelihood of a civilization on an inhabited planet, say, in one in a trillion. But even if we assume that there was one chance in a trillion, then what happened to humanity on Earth happened at least 10 billion times throughout our cosmic history."
If we take the smaller volumes, then in our own galaxy, the Milky Way, a different technological species has appeared, if the chances that it will not appear are less than one in 60 billion.
Good. If these numbers give "optimists" reason to rejoice at the existence of extraterrestrial civilizations, Sullivan says that the complete Drake equation - which determines the likelihood of civilizations existing today - can comfort the pessimists.
"The universe is over 13 billion years old," Sullivan says. "This means that even if thousands of civilizations in our galaxy existed in our time - all these ten thousand years - they all have probably disappeared." Others did not appear. For us to succeed in the search for another technologically advanced civilization, it must, on average, exist more than we currently exist.
“Given the vast distances between the stars and the fixed speed of light, we will never be able to contact another civilization, talk to it, anyway,” says Frank. "If they were 50,000 light years away, messaging would take 100,000 years."
But from a philosophical point of view, it does not matter at all whether we can contact another civilization. It is important that it existed. And this already makes you think deeply.
ILYA KHEL