What is the Great Filter?
Is intelligent life common, or rare in our Milky Way galaxy? If it’s common, why haven’t we encountered it? While discussing UFOs on a walk to lunch in the year 1950, the physicist Enrico Fermi is famously said to have asked, “But where is everybody?” Scientists today call that riddle Fermi’s Paradox. Now a new paper by NASA scientists explores one possible answer to the paradox. The answer may be what’s called the Great Filter.
Economist Robin Hanson first proposed the Great Filter, in the late 1990s. It’s the idea of that – even if life forms abundantly in our Milky Way galaxy – each extraterrestrial civilization ultimately faces some barrier to its own survival. The barrier might come from without (for example, an asteroid striking a planet, and wiping out all life forms). Or it might come from within (for example, all-out nuclear war).
Hanson proposed that a Great Filter might be at work within our Milky Way galaxy. He argued – from what we can see here on Earth – life expands to fill every niche. And so, he argued, we should see signs of intelligent life beyond Earth in nearby star systems, perhaps even in our solar system. But we don’t see this.
Is humanity facing a Great Filter?
The authors of the new paper take Hanson’s idea further. They explore the idea
that humanity may now be facing a Great Filter. The authors wrote:
We postulate that an existential disaster may lay in wait as our society advances exponentially towards space exploration, acting as the Great Filter: a phenomenon that wipes out civilizations before they can encounter each other … In this article, we propose several possible scenarios, including anthropogenic and natural hazards, both of which can be prevented with reforms in individual, institutional and intrinsic behaviors. We also take into account multiple calamity candidates: nuclear warfare, pathogens and pandemics, artificial intelligence, meteorite impacts, and climate change.
And they offer solutions, beginning with, as they say:
… a necessary period of introspection, followed by appropriate refinements to properly approach our predicament, and addressing the challenges and methods in which we may be able to mitigate risk to mankind and the nearly 9 million other species on Earth.
In a sense, the authors of the new paper – including lead author Jonathan H. Jiang of NASA’s Jet Propulsion Labortory in Pasadena, California – are engaging in a “necessary period of introspection” by the act of writing their paper.
And, with their paper, they’re laying out the challenges we’re facing and methods of addressing them.
We’ve already survived some ‘filters’
The scientists point to life’s resilience. Life on Earth has already survived a number of filters in the form of mass extinction events. The Permian-Triassic extinction – aka the Great Dying – occurred 250 million years ago and nearly ended all life on the planet. This extinction event wiped out about 96% of marine life and 70% of land species. The exact cause of the Great Dying is still a matter of study, but some scientists have said it was a combination of warming temperatures and decreasing oxygen.
But these previous filters, or extinction events, have been natural, arising from the evolution of our planet and solar system, including volcanic eruptions and asteroid impacts.
A Great Filter of our own making
But now, clearly, humanity may be facing a Great Filter of our own making, and one that other intelligent civilizations in the galaxy have faced … and failed to withstand. Perhaps it’s no surprise that the technological advancements humans have achieved might ultimately lead to our undoing. Perhaps that’s nature’s way. As the new paper said:
It seems as though nearly every great discovery or invention, while pushing back the borders of our technological ignorance, is all too quickly and easily turned to destructive ends. Examples such as splitting the atom, biomedical innovations and resource extraction and consumption come to mind with disconcerting swiftness. Still, some have suggested artificial intelligence (AI) as yet another factor, which, pending substantial technical hurdles, may yet have its chance to prove friend or foe.
Here’s a look at some of the issues that might compose Earth’s Great Filter.
Unchecked population growth
One of the factors Earth faces, according to the paper, is unchecked population growth. Earth just passed a milestone on November 15, 2022, when it reached 8 billion human inhabitants. The paper said with our current population figures, Earth has experienced:
… an exponential rise from about 1.6 billion [people] at the start of the 20th century.
Technological advancements in farming, energy production and distribution have made such a large population possible on Earth. But, as the paper said, these advancements cannot:
… indefinitely offset the multifaceted stresses imposed by an ever-escalating population.
When will Earth’s human population reach its peak size? Some projections report that education in developing nations might allow Earth’s population to peak at 10 billion in the 2060s. But, of course, no one really knows.
While warfare has long been a factor of life on Earth, only in the past century has humanity had a weapon that could destroy all nations, not just those participating in a nuclear war. The scientists said the greater the number of democracies in the world, the better our chances for avoiding nuclear war. The scientist also saw other encouraging signs, including:
Peace agreements in the historically troubled Middle East, a vast reduction in nuclear warheads since the height of the Cold War and a wide coalition of nations rallying their support for the besieged in Eastern Europe.
Pathogens and pandemics
The threat of illness and pandemics continues to grow simply because our world is so interconnected. Spreading diseases have a much easier time in our global society. But on the positive side, advancements in medicine have also given us an edge. The scientists said that having current and reliable data is crucial:
… in predicting how future pandemics will spread, how deadly they will be and how quickly and effectively we will be able to leverage our knowledge of
the life sciences to counter this manifestation of the Great Filter.
While true artificial intelligence as a separate sentient being is not yet reality, the authors of the paper urge a proactive plan to peacefully share Earth. They project that computer sophistication will one day rival that of the human mind. The scientists said:
As for whether AI would be benign or otherwise, self-imposing a Great Filter of our own invention, that will depend on the evolving nature and disposition of Earth’s first high-tech species.
Asteroid and comet impacts
Here’s an extinction event from the past that could still spell our doom in the future. While large impacts are exceedingly rare, there is, as the scientists said:
… a non-zero percentage [of asteroids or comets] which are large enough to survive passage through the atmosphere and, impacting the surface, cause catastrophic destruction to our sensitive biosphere.
The odds of a mass extinction level event in the coming years is vanishingly small. But, over time periods extending into the very distant future, the odds increase toward 100%. Meanwhile, with projects such as the DART mission, and given enough lead time, humanity has a way of defending itself.
Climate change has become one of the most studied threats to life on Earth. Because the threats from climate change happen on a slower time scale than, say, the time it takes to launch a nuclear weapon, the efforts to curb these effects have not been as rapid as they could have been. The scientists said:
The major impediment to taking more decisive actions, however, are the challenges imposed by transitioning to non-carbon-based energy sources such as solar, wind, nuclear power. Here again, rapidly advancing technologies in areas such as modularized nuclear power plants and carbon capture and sequestration (CCS) are among the best hopes for avoiding slow-motion ensnarement by this lulling but lethal Great Filter.
Avoiding the Great Filter
So you see there’s not just one possible Great Filter for Earth, but many. Any one of them could be our downfall. These scientists are suggesting something that sounds simple on its face, but is (apparently) hard to do. That is, in order to avoid the Great Filter, humans must work together and recognize the big picture. As the paper said:
History has shown that intraspecies competition and, more importantly, collaboration, has led us toward the highest peaks of invention. And yet, we prolong notions that seem to be the antithesis of long-term sustainable growth. Racism, genocide, inequity, sabotage … the list sprawls.
Meanwhile, we continue to look outward, peering at the dark depths between the stars, hoping for a sign that we aren’t alone in the universe. Ultimately, our quest to find life beyond Earth is part of trying to understand life on our planet and where we fit in. As Carl Sagan said:
In the deepest sense, the search for extraterrestrial intelligence is a search for ourselves.
Bottom line: Scientists say the reason we haven’t found intelligent civilizations in the galaxy is that they may not have survived the Great Filter. And they say we may be facing down our own Great Filter.