The Fermi Paradox: Which proposed resolution is the most likely? – Part II

Welcome back! In our previous installment , we looked at some of the proposed resolutions to the Fermi Paradox made in the past few decades. These included the possibility that humanity is alone in the Universe, that intelligent life is periodically wiped out (or is naturally self-destructive), and that it may be avoiding contact with humanity. Today, we will examine other proposed resolutions and what makes them appear likely (and unlikely).

These include (but are not limited to) the possibility that intelligent life is merely listening to the cosmos and not messaging, that humanity may have arrived “early to the party,” that advanced civilizations have evolved to the point that we wouldn’t even recognize them, and the fact that we haven’t seen any evidence yet because, as they say, “space is hard.”

Which of these seems the most likely? You decide!

Everyone is listening, not transmitting

Perhaps the reason for the “Great Silence” is that all civilizations are listening for transmissions from others. Still, no one is sending messages of greeting – what is known as the “SETI Paradox.”

This could be because of an overabundance of caution since no one knows how other civilizations might react. This is consistent with the “Dark Forest Hypothesis” inspired by the Remembrance of Earth’s Past series written by famed Chinese SF author Liu Cixin.

The second novel in the series ( The Dark Forest ) argues that all civilizations are like a person wandering through a dark forest. They want to find their way but are naturally afraid of predators. Hence, they keep their ears open, listening for signs of movement while trying not to give away their location by lighting up a beacon.

Pros: This school of thought offers a plausible explanation for why civilizations would remain silent. Fear of the unknown and proceeding cautiously are instincts shared by most (if not all) lifeforms on Earth. It is also consistent with the controversy surrounding Messaging Extraterrestrial Intelligence (METI).

Cons: Once again, it only takes one civilization to break with this pattern for the “Great Silence” to end. Furthermore, humanity’s experience with METI – like the Arecibo Message and more recent attempts – demonstrates that messaging can still happen despite the controversy.

Humanity is “early to the party”

Another possibility is that while humanity is not alone in the Universe, we may be the first civilizations to emerge in our galaxy. In this respect, our SETI efforts are finding no evidence of technosignatures because we are “early to the party.”

Researchers from the Harvard-Smithsonian Center for Astrophysics (CfA) explored this possibility in a 2016 study, arguing that the probability of life in our Universe grows over time.

As a result, whether or not life will emerge on a planet could come down to the mass of its parent star. Using Earth as an example, we know it took roughly four billion years for complex, tool-using species (humanity) to emerge.

Massive stars, like Type-O and Type-A (blue giants), are short-lived, lasting only a few hundred million years, and therefore have less chance of forming life-bearing planets. G-type stars like the Sun have lifespans lasting billions of years, making them better candidates.

However, low-mass stars (like M-type red dwarfs) can remain in their main sequence for up to trillions of years. Based on their analysis, they concluded that the probability of life on planets orbiting red dwarf stars increases exponentially over this amount of time.

Pros: The study is consistent with what we know about the emergence of life on Earth and the long-lived nature of M-type stars. It also challenges one of the biggest assumptions about life in the Universe by rejecting the idea that life emerged long ago.

Cons: While stars like ours are rare, they still account for 7.6% of stars in our galaxy. This leaves over 15 billion stars in our galaxy that could have a comparable chance at supporting life. There is also considerable research that shows M-type stars may be inhospitable to life due to flare activity.

They have “transcended”

What if we haven’t heard from any ETIs because they’ve become so advanced that they are no longer recognizable? This hypothesis embraces the idea that technological progress is subject to acceleration and will lead to a point of inflection (the Technological Singularity).

This singularity could have come and gone a long time ago for a species much older than humanity, leaving them in a state so advanced that we wouldn’t recognize any of their technosignatures.

This is the basis of the Transcension Hypothesis , formally proposed by John M. Smart in a 2002 study . This hypothesis rejects the idea that advanced civilizations will expand to occupy more space and create larger and larger structures – a la the Kardashev Scale. Instead, it employs the Barrow Scale , which argues that advanced intelligence will seek “multidimensional mastery.”

This means they will instead develop technology that will allow them to manipulate matter at smaller and smaller scales to optimize the space they already occupy – i.e., nanotechnology , picotechnology, and femtotechnology.

As Smart related to Interesting Engineering via email:

“[E]very complex system in “outer space” is physically and informationally simpler, slower, more easily modeled, less conscious, less cooperative and competitive, less powerful, less immune, and less value-creating than systems that have successfully self-organized to go further inward. Said more simply, outer space is boring, slow, simple, weak, risky, and poor by comparison to our ever-accelerating inner space frontier. As a survival strategy, expansion very quickly becomes maladaptive, vs further localization and miniaturization of every leading complex system’s vital physical and informational processes.”

According to Smart, these advanced civilizations may not even live on planets anymore but have since migrated to regions surrounding black holes. In this environment, they would have inexhaustible energy and could perhaps observe the “seeds” of new Universes forming.

This would make advanced civilizations far older than humanity extremely difficult to notice.

Pros: This hypothesis also challenges a major assumption of the Fermi Paradox: that advanced life will always go “bigger and bolder.” It bases its predictions on developmental pathways that are arguably far more realistic and (according to many theorists) within humanity’s future.

Cons: The hypothesis does not preclude the idea that all advanced life will go this route. Once again, it would only take one (or a handful) of civilizations breaking with this pattern to break the “Great Silence,” at least with time.

Interstellar expansion is really difficult

The extreme challenges of interstellar travel will limit how far a civilization can spread through space. These include cosmic radiation, the danger of spending extended periods in microgravity, and the potential hostility of exoplanet environments and their biospheres. The “Aurora Hypothesis,” inspired by the 2015 novel by famed SR author Kim Stanley Robinson, summarizes these arguments.

There’s also the challenge that General Relativity poses for interstellar expansion. In a Universe where Faster-Than-Light travel is impossible and communications are limited to the speed of light, the idea of a “ galactic empire ” is unrealistic.

This is the essence of the “Percolation Hypothesis,” which argues that civilizations that attempt interstellar exploration and settlement will not expand uniformly or exponentially. Instead, they will “percolate” outwards, settling in some areas while failing to do so in others. This process will leave much of the galaxy unsettled.

Another major aspect of this hypothesis is the notion that not all civilizations will opt to send out ships to nearby stars and attempt to settle exoplanets. Instead, it posits that many ETIs will choose to remain at home, given the hazards and challenges of traveling between star systems.

Pros: This theory is appealing because it is realistic and based on established physics. It also eliminates the idea that extraterrestrials will have a “uniformity of motivation,” which makes many proposed resolutions impractical.

Cons: The theory assumes that Relativity is a barrier that can never be crossed, meaning that technologies like the Alcubierre Warp Drive and FTL communications are dead ends. At present, we don’t know if this is true or not or if it will remain that way forever.

Conclusions?

The following theories offer potential solutions to why humanity has not found evidence of ETI despite decades of research.

But “yet” is the operative word. As David Brin indicated in his seminal essay about the controversy surrounding SETI: “Few important subjects are so data-poor, so subject to unwarranted and biased extrapolations.” Until more evidence is collected and exoplanets characterized, nothing conclusive can be said either way. In the meantime, speculating about what we don’t know based on what we do is our only recourse.

However, these speculations are still useful. Theoretical predictions about what advanced ETI will look like – which is to say, what technosignatures they will produce – allow scientists to constrain and widen their searches. And while any proposed resolution to the Fermi Paradox is subject to bias, some are arguably more realistic.

For instance, the Percolation and Aurora Hypotheses are both grounded in established physics, biology, and what we know about the hazards of introducing life forms into unfamiliar environments.

The Transcension Hypothesis also addresses the assumption that ETIs will be older and more advanced than we are and offers an intriguing explanation that predicts future human development. The Great Filter incorporates many known cosmological dangers that could interfere with (or prevent) the emergence of advanced life.

Another common argument is that humanity is not searching for the right biosignatures, technosignatures, or in the right places. As David Brin told Interesting Engineering, the search has evolved considerably since Frank Drake first proposed his famous equation for estimating the number of ETIs that we could communicate with in our galaxy:

“The Drake Equation was always intended to lay on the table various topics for discussion or research. Frank never meant it as a predictive scientific formulation.  For 25 years, we’ve confirmed that planets are abundant. And even systems that lack an Earthlike “Goldilocks World” may still host ocean biospheres under the ice of Europa-like moons.”

“Every year, we discover more of the chemical steps that likely enabled the first cells to evolve out of early, organic ‘soups.’ Hence, I’ve been looking at later terms in the Drake Formulation. My top (out of a hundred) hypothesis for the Great Silence is that human beings got exceptionally smart, exceptionally fast! Indeed — and surprisingly, in light of our myriad past and present misbehaviors — it seems to me that humanity might also be (on average) exceptionally calm and wise.”

For example, most SETI surveys have focused on radio transmissions or searches for Dyson Spheres and other megastructures.

But as NASA noted in their Technosignature Report (released in 2019), there are many other potential technosignatures to look for. These include optic transmissions and directed-energy propulsion, using neutrinos and gravitational waves for communications, and quantum transmissions that take advantage of Solar Gravitational Lenses (SGLs).

James Maynard, the award-winning documentarian, filmmaker, science communicator, and publisher of The Cosmic Companion , beautifully summarized the challenge of SETI for Interesting Engineering :

“Everywhere we search around the Cosmos, we find the ingredients for life. Large bodies of water once thought to be exclusive to Earth, are now known to permeate the Solar System. Carbon does amazing things, and the building blocks of life – including all essential amino acids – are found throughout space. The idea that life only sparked on our lone planet seems to be the ultimate in human hubris.

“So why haven’t we found them yet? Only a handful of small bands of astronomers with meager budgets have, so far, carried out systematic searches over a tiny fraction of nearby stars, over minuscule portions of the electromagnetic spectrum. We ain’t yet begun to look!”