”One of the three big uncertainties has now been constrained."
Are we alone out there? The question of whether or not other advanced civilizations exist somewhere in the vast universe has long been one of the most perplexing uncertainties in science. But new research suggests that the odds of humans being the only intelligent species to have ever existed are next to zero.
In a recent study published in the journal Astrobiology, researchers Adam Frank and Woodruff Sullivan used newly obtained data to reformulate the famous Drake equation, which calculates the probability that intelligent life currently exists in the universe, to measure the probability that intelligent life has ever existed in the universe. Introduced by Dr. Frank Drake in 1961, the original Drake equation identified specific factors thought to play a role in the development of advanced civilizations in order to estimate the number of technological civilizations that may currently exist in our galaxy. Over the past half a century, it has been the most widely accepted tool in the scientific community to predict the current existence of other advanced civilizations.
Yet three large uncertainties plague the original Drake equation. "We've known for a long time approximately how many stars exist,” Frank explained in a statement. “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… Thanks to NASA's Kepler satellite and other searches, we now know that roughly one-fifth of stars have planets in 'habitable zones,' where temperatures could support life as we know it. So one of the three big uncertainties has now been constrained."
Although it is still completely unknown how long other civilizations might survive, a simple change of semantics to the proposed question eliminates this issue altogether. By looking at the probability of how many times in the history of the universe life has evolved to an advanced state, Frank and Sullivan estimate a one in 10 billion trillion chance that humans are the only intelligent species to have ever existed. “One in 10 billion trillion is incredibly small,” Frank said. “To me, this implies that other intelligent, technology-producing species very likely have evolved before us.”
While the odds are extremely high that we aren’t the first intelligent civilization to have ever existed, the original question still remains: Are there any other advanced civilizations that currently exist? "The universe is more than 13 billion years old," explains Sullivan. "That means that even if there have been a thousand civilizations in our own galaxy, if they live only as long as we have been around—roughly ten thousand years—then all of them are likely already extinct. And others won't evolve until we are long gone. For us to have much chance of success in finding another "contemporary" active technological civilization, on average they must last much longer than our present lifetime."