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“Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” This sentiment, often attributed to science fiction author Arthur C. Clarke, captures the significant anxiety at the heart of humanity’s search for extraterrestrial intelligence. The first possibility suggests a lonely, perhaps meaningless, existence in a vast and silent cosmos. The second implies the presence of others who could be ancient, powerful, and potentially dangerous. But what if there is a third option? A paper by Robin H. D. Corbet proposes a less dramatic and less frightening middle ground, suggesting the truth may lie in a universe that is simply, and perhaps disappointingly, mundane.
This perspective, termed “radical mundanity,” offers a compelling explanation for the Fermi Paradox – the stark contradiction between the high probability of extraterrestrial civilizations (ETCs) existing and the complete lack of evidence for them. Instead of proposing exotic solutions like humanity being kept in a “celestial zoo” or aliens having transcended physical reality, the mundanity principle argues for a more straightforward scenario: the galaxy contains a modest number of civilizations, none of which have achieved the kind of “super-science” needed for galaxy-spanning engineering projects. This explanation for the “Great Silence” suggests a universe that is neither terrifyingly empty nor ominously crowded, but quietly and mundanely populated.
Measuring an Advanced Civilization
To understand the argument, it is first necessary to consider how we quantify the technological level of a civilization. The most common method used in the Search for Extraterrestrial Intelligence (SETI) community is the Kardashev scale, developed by Nikolai Kardashev in 1964. This scale classifies civilizations based on their energy consumption.
- A Type I civilization can harness all the energy available on its home planet. On a continuous scale proposed later, modern Earth rates at approximately 0.72.
- A Type II civilization can control and utilize all the energy emitted by its parent star. This would likely require massive astro-engineering projects, such as the theoretical Dyson sphere – a megastructure that completely encompasses a star to capture its power output.
- A Type III civilization can command the energy of an entire galaxy. It is difficult to conceive how this could be achieved, but it might involve constructing Dyson spheres around most of the stars in a galaxy.
The Kardashev scale is a useful, if crude, measure. Its primary limitation is its exclusive focus on power utilization, ignoring other aspects of development. Other scales have been proposed based on factors like information storage capacity, the ability to manipulate matter on smaller and smaller scales, or the intelligence level of artificial systems. For example, one could define a Type I civilization as one that has developed artificial general intelligence (AGI), while a Type II civilization might possess a collective machine intelligence equivalent to its entire population.
Despite these alternatives, the expectation remains that a truly advanced civilization would leave noticeable traces, or “technosignatures“. These could be powerful, deliberate beacons transmitting signals across the galaxy, waste heat radiating from massive engineering projects like Dyson spheres, or even physical artifacts left behind by robotic probes visiting our solar system. So far we have found nothing.
The Two Premises of a Mundane Galaxy
The principle of radical mundanity seeks to explain this silence with two core premises that favor the least extreme, most physically plausible scenarios.
- There is a fundamental limit to technological development. This premise suggests that while other civilizations may be far more advanced than our own, their technology does not involve radical leaps based on unknown laws of physics. They will eventually reach a technological plateau that is impressive, but still “mundane”. They might have controlled fusion and advanced AI, but not faster-than-light travel or the ability to manipulate dark energy.
- There is a modest, non-zero number of these civilizations in the Milky Way. The universe is not empty, nor is it teeming with life. This idea aligns with the Copernican mediocrity principle, which posits that humanity does not occupy a special or unique place in the cosmos. If our civilization was the only one, we would be extraordinary, violating this principle. A modest number of ETCs makes us one of many, but not one of billions.
These two premises, when taken together, paint a picture of the galaxy that neatly resolves the Fermi Paradox without resorting to fantastic explanations.
The Technological Plateau
The idea that technology might have limits runs counter to the narrative of exponential progress that characterized the 20th century, when many seminal SETI papers were written. While science still faces major unanswered questions, such as the nature of dark matter and dark energy, it is not clear that solving these mysteries would lead to technological revolutions on the scale of discovering electromagnetism or thermodynamics. For instance, even if dark matter is found to consist of exotic particles, there is no obvious way to harness this discovery for new technologies.
There are already subtle signs that progress may be slowing down or becoming more incremental. Studies have argued that scientific papers and patents are becoming less “disruptive” over time. The exponential growth of computing power described by Moore’s Law has slowed, and the performance growth of the world’s top supercomputers has flattened.
Furthermore, motivation, not just capability, is a important factor. Even if a civilization develops clean and abundant energy through nuclear fusion, there may be no compelling driver to endlessly increase its power consumption. Data from the United States shows that per capita energy usage has actually declined since 1979, suggesting that civilizations with stable populations may reach a point of energy equilibrium rather than pursuing an endless climb up the Kardashev scale.
This technological plateau has two significant implications for what we might expect to find. First, large-scale astro-engineering is likely impossible or pointless. If a civilization lacks both the god-like technology to build a Dyson sphere and the motivation to harness that much energy, such structures simply will not exist. Second, there will be no long-duration, high-power beacons. The cost of maintaining a beacon powerful enough to be detected across the galaxy for millions of years would be immense, and it would be far more logical to send probes to gather information directly.
Limited Colonization: The Animal Spirits of Fear and Boredom
The mundanity principle also addresses the question of galactic colonization. Calculations have shown that even with technology not far beyond our own, a civilization could spread across the entire galaxy in a relatively short astronomical timescale using self-replicating robotic probes. So why do we see no evidence of them?
The answer, again, comes down to means and motive. While interstellar travel to nearby stars may be technically feasible, a full-scale colonization of billions of star systems requires that the benefits outweigh the costs and risks. In the words of economist John Maynard Keynes, “greed must overcome fear”.
The primary risk is the “Berserker” hypothesis, named after the deadly probes in Fred Saberhagen’s science fiction novels. This is the fear that creating and releasing a vast number of intelligent, self-replicating machines into the galaxy could have unforeseen and uncontrollable consequences. This is not an exotic fear; it mirrors contemporary concerns on Earth about the development of advanced AI. From a mundane perspective, it is entirely reasonable to assume that other civilizations would share this caution.
The potential benefits, on the other hand, are subject to diminishing returns. The main reward for galactic exploration would be scientific knowledge. But after exploring thousands or millions of M-dwarf star systems – the most common type of star in the galaxy – and finding them to be broadly similar, the scientific gain from visiting the next one would be marginal.
This leads to a state of cosmic “ennui,” or boredom. A civilization’s exploration program would likely halt when the perceived risks of unleashing more probes outweigh the dwindling scientific rewards of encountering yet another similar star system or another civilization at the same mundane technology level. Exploration would be limited by a combination of fear and boredom.
Life in a Mundane Galaxy
This framework provides a clear picture of our cosmic neighborhood. The galaxy contains a modest number of technological civilizations, perhaps on the order of 100,000, that have all reached a similar technological plateau below Type II status. They are not building Dyson spheres, not broadcasting powerful beacons, and not launching fleets of self-replicating probes to every corner of the Milky Way.
When we examine the candidate technosignatures found so far through this lens, they align with the mundane prediction.
- The famous “Wow! signal” was a one-time event, never confirmed despite repeated follow-up searches. A mundane galaxy would produce persistent leakage radiation, not a single, powerful flash.
- Candidate Dyson spheres and the unusual dimming of “Tabby’s Star” all have plausible astrophysical explanations, which the mundane hypothesis prefers over claims of astro-engineering.
- The claim that the interstellar object ‘Oumuamua was an alien artifact is highly controversial, and the mundane view is skeptical, as it is unclear what would motivate such a flyby mission.
- Reports of UFOs/UAPs on Earth are unlikely to be extraterrestrial visitors, as our pre-plateau civilization would not be a particularly interesting destination for a modestly advanced ETC.
A Quiet Hope
The mundanity hypothesis resolves the Fermi Paradox in a way that is neither lonely nor terrifying. It suggests a universe that is quietly populated by civilizations not incomprehensibly different from what we might one day become.
This could mean that a detection is not impossibly far off. As our own radio telescopes become more sensitive, with instruments like the Square Kilometre Array (SKA) under construction, we may be able to detect the faint, unintentional “leakage” radiation from a nearby civilization – their equivalent of our television broadcasts and planetary radar. Such a discovery would be one of the most momentous events in human history, but it might also be slightly disappointing. We would not receive the secrets to faster-than-light travel or unlimited energy, but simply the quiet confirmation that we are not alone.
There is another, more hopeful implication. If technological civilizations arise in modest numbers, it strongly suggests that simple life is not rare at all. The galaxy may be teeming with planets that have some form of life, even if very few go on to develop technology. This gives us reason to be optimistic that future missions designed to search for biosignatures in the atmospheres of nearby exoplanets may well succeed.
The mundanity principle offers an elegant and objective solution to one of science’s most significant questions. It proposes a universe that is less extreme, less dramatic, and less terrifying than the one envisioned by Clarke. It is a universe where we are neither utterly alone nor in the presence of gods, but simply one of a modest number of civilizations making their way through the cosmos.
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