https://www.astronomy.com/science/the-g ... i-paradox/Many hypotheses have been proposed to resolve the Fermi Paradox, but all of these remain unproven. And in the 1990s, another possible explanation for our apparent aloneness in the universe was formulated by Robin Hanson — a postulate that has become known as the Great Filter.
The hurdles to interplanetary life
Simply stated, the Great Filter says that intelligent interstellar lifeforms must first take many critical steps, and at least one of these steps must be highly improbable. Indeed, the premise of the Great Filter is that there’s at least one hurdle that is so high virtually no species can clear it and move on to the next. But while the term the Great Filter suggests the conscious action of some sort of exogenous entity, in reality, the hypothesis is more a way of thinking about the relative likelihood of certain events happening — or not happening — in their own natural course.
So, what basic hurdles must be cleared in order to become a truly advanced, spacefaring civilization? Hanson suggested a few, paraphrased below:
A planet capable of harboring life must form in a star’s habitable zone.
Life itself must develop on that planet.
Those lifeforms must be able to reproduce, using such molecules as DNA and RNA.
Simple cells (prokaryotes) must evolve into more complex cells (eukaryotes).
Multicellular organisms must develop.
Sexual reproduction, which greatly increases genetic diversity, must take hold.
Complex organisms capable of using tools must evolve.
Those organisms must create advanced technology needed for space colonization. (This is roughly where humans are today.)
The spacefaring species must go on to colonize other worlds and star systems, while avoiding destroying itself.
Has humanity passed The Great Filter?
If the Great Filter is behind us, though, it bodes well for humanity as a species; the universe may be ours for the taking. If, however, the Great Filter still lies ahead, we may be doomed.
On the bright side, some have interpreted our apparent aloneness in the universe as a good sign — a blessing even — as it indicates we’ve safely made it through the bottleneck. Strange as it may seem, we may be the first species to have passed through the Great Filter (after all, someone has to be first).
On the other hand, if we were to detect a signal from a super-advanced technological species that makes us look primitive, it might imply that the Great Filter still lies ahead. Humanity could be destined to take a surprise cosmic test, one that we don’t know what to study for.
