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June 17, 2020 03:30 am

Scientists Say Most Likely Number of Contactable Alien Civilizations Is 36

An anonymous reader quotes a report from The Guardian: They may not be little green men. They may not arrive in a vast spaceship. But according to new calculations there could be more than 30 intelligent civilizations in our galaxy today capable of communicating with others. In 1961 the astronomer Frank Drake proposed what became known as the Drake equation, setting out seven factors that would need to be known to come up with an estimate for the number of intelligent civilizations out there. These factors ranged from the the average number of stars that form each year in the galaxy through to the timespan over which a civilization would be expected to be sending out detectable signals. But few of the factors are measurable. "Drake equation estimates have ranged from zero to a few billion [civilizations] -- it is more like a tool for thinking about questions rather than something that has actually been solved," said Christopher Conselice, a professor of astrophysics at the University of Nottingham and a co-author of the research. Now Conselice and colleagues report in the Astrophysical Journal how they refined the equation with new data and assumptions to come up with their estimates. "Basically, we made the assumption that intelligent life would form on other [Earth-like] planets like it has on Earth, so within a few billion years life would automatically form as a natural part of evolution," said Conselice. The assumption, known as the Astrobiological Copernican Principle, is fair as everything from chemical reactions to star formation is known to occur if the conditions are right, he said. "[If intelligent life forms] in a scientific way, not just a random way or just a very unique way, then you would expect at least this many civilizations within our galaxy," he said. Under the strictest set of assumptions -- where, as on Earth, life forms between 4.5 billion and 5.5 billion years after star formation -- there are likely between four and 211 civilizations in the Milky Way today capable of communicating with others, with 36 the most likely figure. But Conselice noted that this figure is conservative, not least as it is based on how long our own civilization has been sending out signals into space -- a period of just 100 years so far. The team add that our civilization would need to survive at least another 6,120 years for two-way communication. "They would be quite far away ... 17,000 light years is our calculation for the closest one," said Conselice. "If we do find things closer ... then that would be a good indication that the lifespan of [communicating] civilizations is much longer than a hundred or a few hundred years, that an intelligent civilization can last for thousands or millions of years. The more we find nearby, the better it looks for the long-term survival of our own civilization."

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