The Fermi Paradox, first thought of by notable physicist Enrico Fermi, is a thought experiment that postulates how strange it is that humans have not yet detected any other life in the observable universe. Fermi’s explanation holds that the universe is vast enough, and old enough, that if life had time to evolve on Earth, then surely, it’s evolved elsewhere in the universe, if not in our own galaxy.
If just one tenth of a percent of the planets in the Milky Way that fall within in the habitable zone of their sun-like stars bore life, there would be one million planets in our galaxy with life on them. However, when we look to the stars, we see no example of any species like our own. There are no superstructures harvesting energy from stars, no sprawling space stations serving as a beacon to other intelligent life forms.
So, where is everybody?
One explanation is that life might just be more rare than we realized. Perhaps Earth is truly unique in ways we don’t yet understand, allowing complex carbon-based life to evolve in a way that is simply impossible to replicate elsewhere in the universe. This would mean we’re alone in this world, the lone intelligent species to ever achieve any degree of understanding of the natural world around us.
Another theory holds that life might not be rare at all, but that, instead, intelligent, complex life like our own planet boasts is very difficult to sustain. Some have proposed the human-like species that approach the capacity to travel though space might encounter some form of “Great Filter,” an extinction-level event that prevents them from creating technology humans could view from Earth.
This could be in the form of nuclear war, or some as-yet unknown danger inherent to interstellar travel we’ve yet to encounter.
Perhaps humanity is one of the rare species to actually make their way past the Great Filter in the first place. Given the age of the galaxy, we should have likely seen the technology, or at least the ruins of the technology, of advanced civilizations that have gone before us. Perhaps, however, we’re the first species to get past some Great Filter in our past that prevents intelligent life from ever leaving their home planet.
Consider, for instance, the Second World War and the advent of nuclear weaponry. Perhaps, by surviving such an event, humanity has set itself up as the most advanced civilization to yet live. If this is the case, the stars could be teeming with intelligent life, just life unable to make any impact on the stars, thus rendering them invisible to our efforts to detect them.