Why haven't aliens visited Earth? Researchers suggests a disturbing answer.

Is it possible that we have never been visited by aliens? For decades, scientists have puzzled over the mystery, but two researchers have come up with a disturbing explanation: Advanced civilizations may be doomed to stagnate or die before they can reach their full potential.

In the new hypothesis, spacefaring civilizations reach a point of crisis when their innovation cannot keep up with energy demand as they grow in scale and technical development. Eventually, the civilization collapses. Researchers stated that the only other option is to reject a model of "unyielding growth" in favour of maintaining equilibrium, but at the cost of civilizations' ability to expand across the stars.

The argument, published in the journal Royal Society Open Science(opens in new tab), seeks to resolve the Fermi Paradox. The Fermi Paradox, named for Nobel Prize-winning physicist Enrico Fermi, highlights the contradiction between the vast size and age of the universe - two characteristics that would suggest alien life would be abundant - and the lack of evidence of extraterrestrial life. "So where is everybody?" Fermi remarked.

A new study may provide the answer, say the researchers.

"Civilizations either collapse from burnout or redirect themselves to prioritizing homeostasis(opens in new tab), a state where cosmic expansion is no longer a goal, making them difficult to detect remotely," astrobiologists Michael Wong, of the Carnegie Institution for Science, and Stuart Bartlett, of the California Institute of Technology, wrote in the study. "Either outcome — homeostatic awakening or civilization collapse — would be consistent with the observed absence of [galactic-wide] civilizations."

Studying studies of the "superlinear" growth of cities, the pair arrived at their hypothesis. Based on these studies, cities grow exponentially in size and energy consumption as their populations grow, making them prone to crisis points - or singularities - causing rapid crashes in growth and an even more precipitous, potentially civilization-ending, collapse. 

"We hypothesize that once a planetary civilization transitions into a state that can be described as one virtually connected global city, it will face an 'asymptotic burnout,' an ultimate crisis where the singularity-interval time scale becomes smaller than the time scale of innovation," they wrote. 

Researchers suggest that close-to-collapse civilizations would be easy for humanity to detect since they would be dissipating large amounts of energy in an unsustainable way. "This presents the possibility that a good many of humanity's initial detections of extraterrestrial life may be of the intelligent, though not yet wise, kind," the researchers wrote.

Civilizations could avert extinction by undergoing a "homeostatic awakening," redirecting their production away from unbounded growth across the stars to one that prioritizes societal wellbeing, sustainable and equitable development, and harmony with the environment, researchers suggested. While such civilizations may not completely abandon space exploration, they would not expand to scales great enough to make contact with Earth likely.

Researchers point to several of humanity's "mini-awakenings" that addressed global crises on Earth, such as the reduction of nuclear weapons stockpiles from 70,000 to 14,000 warheads; the halting of the hole in the ozone layer by banning chlorofluorocarbon emissions; and the 1982 international whaling moratorium.

They stress that their suggestion, however, is merely a hypothesis, taken from the observation that certain laws seem to govern life on Earth, and is meant to "prompt discussion, introspection, and future research."

This proposal joins a multitude of other scientific and popular theories as to why we have never made direct contact with celestial visitors. The many practical challenges of interstellar travel; the possibility that aliens may actually be visiting in secret; and the possibility that aliens arrived on Earth too early in the universe (or humans too early) for direct contact.

According to another theory published in The Astrophysics Journal(opens in new tab), the sheer size of the universe could mean it would take 400,000 years for one advanced species to reach another - a timescale that is far greater than the brief period humans have been able to scan the skies.