The universe is mind-bogglingly vast, with trillions of stars spread across billions of galaxies. With so many worlds, it seems reasonable to expect that life would have arisen countless times throughout cosmic history. Yet despite searching the heavens, we find no evidence of advanced alien civilisations attempting to contact or visit us. This striking absence was highlighted in 1950 by physicist Enrico Fermi’s famous question, “Where are they?“
The continued lack of observable extraterrestrial intelligence has become known as the Fermi Paradox. So, to solve this puzzle, we need to explain what stops technological life from thriving on other worlds and spreading across the galaxy. One interesting theory says that the odds are really low at the most important evolutionary steps, creating a “Great Filter” that stops spacefaring societies from appearing. It’s really important for humanity’s future to understand the step that almost all species mess up.
The Great Filter As Solution to Silent Skies
The Great Filter theory outlines a series of transitions, each with associated probabilities, required to produce an advanced spacefaring civilization. These include planetary conditions allowing life, emergence of replicating chemistry, evolution of complex eukaryotes, development of intelligence, and spreading across interstellar frontiers. With so many dice rolls across a 14 billion-year universe, you’d expect loads of species to have traversed this staircase. But the fact that we don’t see any signs of their astroengineering means there’s probably a filter – one ultra-unlikely step that’s eliminated almost all aspiring galactic civilisations.
This filter could be down to the struggle to go from simple life forms like RNA/DNA to complex cells, or from single-celled bacteria to technological intelligence.Or it might be triggered by running out of resources or by self-destruction from nuclear war, engineered pathogens, unconstrained artificial superintelligence, or other existential threats that could plausibly arise with technological power. And then there are things like asteroid impacts, which could be resetting the clock of evolution across different worlds. So, identifying the unlikely step helps us make sense of why we don’t see more life in space, even though everything seems to be pointing to the opposite.
The Great Filter Lies Behind Us
An optimistic perspective on the Great Filter suggests humanity has already cleared the most improbable transition by developing technological capacities to communicate across interstellar gulfs. We may be among the first torchbearers – early risers who have navigated past the Great Barrier.
So, when we look at the development staircase, we’ve got solid proof that habitable worlds, organic chemistry, simple life and intelligence are all possible across the cosmos. Earth shows us this. With these things in place, we’ve got a good shot at taking over the galaxy, but only if we’re careful with our technology and don’t end up destroying ourselves.
We’ve passed some important milestones, but getting to the stars and exploring space is still really tricky. Right now, we’re only sending out basic radio signals, not the more purposeful beacons we’d really need. Our probes have barely left the solar system, and they’re moving really slowly. No human has even gone beyond the Moon in 50 years. And when we send probes to Mars and other places, we find out that the environment can change really quickly from being able to support life to being totally sterile.
So, we’ve still got a few hurdles to jump before we can reach even a small part of our galaxy. Mastering propulsion, hibernation, recycling, climate control, governance, and cooperation on an unimaginable scale for millions of years through unpredictable galactic changes is going to be a real challenge.
The Great Filter Lies Ahead of Us
But we might be the last of our kind, about to trip on the Great Filter that’s stopped everything before. The lack of alien civilisation ruins, artefacts, or communications suggests that no one has crossed the threshold to expansion yet. And if some of the tech we develop in the next hundred years ends up destroying us, that would explain why there are no other civilisations out there.
We’d be doomed to repeat the mistakes of countless other experiments in a vast universe, all doomed by technologies that could lead to terminal wars, engineered diseases, unconstrained AI, environmental devastation, or other ways of making defeat seem like success. The silence means most of us never find the narrow path through the dangers of being a new technology.
Conclusion
In the next few decades, we’ll get to know more about exoplanets, prebiotic chemistry and signs of alien industry. This will help us decide whether the Great Filter is real or not.
It’s a bit unsettling, but it gets us thinking about the big decisions and risks that a species faces when it’s got powerful control over its environment and existence. If we can see the challenges that all new technological civilisations are likely to face, we might be able to move towards a more sustainable path through the tough times ahead.
