Is there life in the universe? If there is, can it communicate — and does it want to talk to us? If such a civilization is out there, how long could it survive? These are some of the fundamental questions astronomers regularly consider when they think about aliens.
Suffice it to say the answers are not as easy as Star Trek or Star Wars would make you believe. The most famous answer took place in 1961, when astronomer Frank Drake proposed what is now known as the Drake equation. You can read it on the Search for Extraterrestrial Intelligence (SETI) website here in full, but understand that it outlines the variables needed for a technological civilization to communicate with us.
A new paper in Astrobiology suggests there could be a way to simplify the equation, based on the observations of exoplanets that we have made since the first one was discovered in the 1990s. While the result is depressing — life was plentiful, but is likely extinct — it does have applications to help us extend our own civilization, the researchers said. The research was led by Adam Frank, a physics and astronomer professor at the University of Rochester.
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“The question of whether advanced civilizations exist elsewhere in the universe has always been vexed with three large uncertainties in the Drake equation,” Frank said in a statement.
“We’ve known for a long time approximately how many stars exist,” Frank added. “We didn’t know how many of those stars had planets that could potentially harbor life, how often life might evolve and lead to intelligent beings, and how long any civilizations might last before becoming extinct.”
Here are the elements that Frank and co-author Woodruff Sullivan (of the astronomy department and astrobiology program at the University of Washington) propose could be changed:
- How many stars have habitable planets? 1/5 of stars have planets in habitable zones. This is known due to the Kepler space telescope’s search of exoplanets as well as other planetary research.
- How long can civilizations survive? That question is very hard to answer, so the researchers instead asked “Are we the only technological species that has ever arisen?” More on that subject later in this article.
- How likely is it for advanced life to arise on a planet? The researchers instead tried to imagine a universe where humanity is the only one. By applying this probability question to the number of known stars the researchers found a probability of one in 10 billion trillion. In our own Milky Way, the number rises to just one chance in 60 billion.
The authors dub their result the “archaelogical form” of the Drake equation. Their equation multiplies the terms “Nast” and “fbt” to get the result. “Nast” refers to the “number of habitable planets in a given volume of the universe,” and “fbt” is the “likelihood of a technological species arising on one of these planets.”
The researchers say one in 10 billion trillion seems a very low probability that humanity is alone out there. But the vast distances of the universe, coupled with the uncertainty of how long civilizations exist, mean it may never be possible to communicate with anyone out there.
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Our civilization is 10,000 years old; unless a typical civilization lasts much longer, over the 13-billion-year lifespan of the universe it’s likely the others have gone extinct, the researchers added. But there is a practical application to keep us around longer, the researchers said.
“Our results imply that our evolution has not been unique and has probably happened many times before,” Frank said. “The other cases are likely to include many energy-intensive civilizations dealing with their feedback onto their planets as their civilizations grow. That means we can begin exploring the problem using simulations to get a sense of what leads to long lived civilizations and what doesn’t.”