Many have heard of the Fermi paradox, which raises a completely philosophical question: given the high probability of the existence of alien life in the universe, why has no one contacted humanity? If there are so many other civilizations, perhaps far more advanced than we are, why don’t they do what we do in search of life?
One explanation for this is the Great Filter. The Great Filter is a hypothetical barrier that prevents the spread of life from simple beginnings to advanced civilizations, reports iflscience.com.
This concept suggests that the probability of a species advancing to a certain level is extremely low and that, at some point in the evolution of life, a barrier must exist to prevent further progress.
This barrier could be due to a variety of causes, including disease, environmental disasters, or even self-inflicted destruction. The concept of the Great Filter is used to explain why humanity has not encountered any advanced extraterrestrial civilizations in the universe.
We don’t know if we have passed the “great filter” or if it will happen in the future. Could it be that the majority do not live to see single-celled life, and we have passed this filter? Or are we, like other alien civilizations, going to destroy ourselves at some point before we can leave Earth, perhaps due to war or running out of our resources before we can escape?
Some philosophers and scientists have suggested that if we found life on, say, Mars, it would have less than ideal implications for where we are in relation to the Great Filter.
Oxford University philosophy professor Nick Bostrom says that he hopes the search for extraterrestrial life turns up nothing.
If we found very simple life forms, Bostrom argued in an article published in the MIT Technology Review in 2008, then we could conclude that the filter happens sometime after that point of life. If we found multi-cellular life, this would narrow down the point at which the Great Filter could take place.
Bostrom thinks that in order to narrow down the scope of the filter, we need to look at life on Earth to see what moves are unlikely.
“One criterion is that the transition should have occurred only once,” he wrote. “Flight, sight, photosynthesis, and limbs have all evolved several times here on Earth, and are thus ruled out.”
He also argued that evolutionary features that took a long time to occur even after prerequisites were met would indicate that this evolutionary step was improbable, eg the original emergence of life. The step from animals to humans took place over a relatively short time period, geologically speaking, suggesting it’s a weak candidate for a Great Filter event.
If we were to find evidence of vertebrates on Mars (very unlikely, but we can dream!) he believed that would be terrible news, as it would suggest that the bulk of the Great Filter is still in our future, and we’ll have to face the probability that we will go extinct before we are technologically mature enough to travel through the galaxy.
“Such a discovery would be a crushing blow. It would be by far the worst news ever printed on a newspaper cover,” Bostrom wrote. “This is why I’m hoping that our space probes will discover dead rocks and lifeless sands on Mars, on Jupiter’s moon Europa, and everywhere else our astronomers look. It would keep alive the hope for a great future for humanity.”
While there are many other possible solutions to the Fermi paradox worth looking at, if Bostrom is right, this means that finding evidence for advanced civilizations is good news, but finding the wrong stages of life that evolved independently in our own Solar System would be the worst possible news we could receive.