With 200 billion trillion stars (
This is the basic question of the Fermi paradox, the tension between our suspicions of the potential for life in the universe (given planets found in
One solution, or at least a way of thinking about the problem, is known as the Great Filter. Proposed by Robin Hanson of the Future of Humanity Institute at Oxford University, the argument goes that given the lack of observed technologically advanced alien civilizations, there must be a great barrier to the development of life or civilization that prevents them from getting to a stage where they are making big, detectable impacts on their environment, that we can witness from Earth.
“You start with billions and billions of potential germination points for life, and you end up with a sum total of zero extraterrestrial civilizations that we can observe,” Nick Bostrom, also of the Future of Humanity Institute,
Hanson
The right star system (including organics)Reproductive something (e.g. RNA)Simple (prokaryotic) single-cell lifeComplex (archaeatic & eukaryotic) single-cell lifeSexual reproductionMulti-cell lifeTool-using animals with big brainsWhere we are nowColonization explosion
“The Great Silence implies that one or more of these steps are very improbable; there is a ‘Great Filter’ along the path between simple dead stuff and explosive life,” Hanson wrote in the original paper. “The vast vast majority of stuff that starts along this path never makes it. In fact, so far nothing among the billion trillion stars in our whole past universe has made it all the way along this path.”
Searching the galaxy for star systems amenable to life, stars for planets, and planets for biospheres and technosignatures could tell us more about where the Great Filter lies. Could it be that the conditions for even simple life are rare (which doesn’t seem likely given
The good news is that finding life on other planets could tell us about where we are in relation to the Great Filter, or our own extinction.
“Searching for technosignatures alongside biosignatures would provide important knowledge about the future of our civilization. If planets with technosignatures are abundant, then we can increase our confidence that the hardest step in planetary evolution – the Great Filter – is probably in our past,” as one
It could be that common threats, such as asteroids, wipe out civilizations before they have a chance to begin colonizing their galaxies, or that at some point in a technological species’ development, they inevitably learn about some technology (such as nuclear weapons, or another concept we have not discovered yet), or that
The original paper on the Great Filter “The Great Filter – Are We Almost Past It?” is available on the