In recent weeks, I’ve been writing a lot about Fermi’s Paradox (“Where is everybody?” aka. where are all the aliens?) As you can imagine, this has involved a lot of research! So much has been said and so much ink has been spilled on the potential reasons why humanity has not found evidence of cosmic counterparts, despite seventy years of looking and the sheer vastness of the Universe.

Today, I thought I might share some of my own thoughts and speculations on that front. In terms of which hypothesis is the most likely, my thoughts are pretty simple and straightforward. But in terms of which hypothesis I think is the coolest and most mind-blowing (in part for the sake of science fiction writing), that’s where things get a bit crazy!

Most-Likely Scenario:

I think that Robin Hanson summarized it best with his Great Filter Hypothesis. Basically, if the ingredients for life are everywhere and there’s no shortage of places for it to have emerged – and enough time has passed that some of it ought to be colonizing entire galaxies! – then there must be something that in the evolutionary process that keeps life from reaching advanced stages.

According to Hanson’s theory, the evolution of life on Earth can serve as a template for addressing Fermi’s big question. If we assume that life follows a similar course in all parts of the Universe, then we can boil that down to a multi-step process that might look something like this:

  1. A star system with potentially habitable planets and organic molecules
  2. Reproductive molecules (e.g. RNA)
  3. Single-cell life
  4. Complex single-cell life
  5. Sexual reproduction
  6. Multi-cell life
  7. Tool-using animals with intelligence
  8. An advanced, technologically-dependent civilization (we are here)
  9. Colonization of space

As the argument goes, wherever you place the filter in this process will have inevitable implications for humanity and life on Earth. If the filter is at an early stage, it means life has beaten the odds just by getting this far. If it is at a later stage, it means humanity could be nearing a precipice. Neither of these scenarios is particularly cheery because they mean that we’re either likely to die soon, or we shouldn’t be here in the first place!

Given the challenges and existential threats that life on Earth is facing today, there are many theorists who argue that the filter belongs between steps 8 and 9. As intelligent species grow and multiple, so will their dependence on technology and their impact on their natural environment. Eventually, they will reach a bottleneck, where they will either get off-world, or they will collapse before they get the chance.

Now for the Crazy Stuff!

Hands down, my favorite proposed resolution to the Fermi Paradox is the Transcension Hypothesis. This theory has deep roots but owes its existence largely to cosmologist and theoretical physicist John D. Barrow – who passed away on Sept. 26th, 2020. In 1998, he published a study called “Impossibility: Limits of Science and the Science of Limits” where he proposed a revised version of the Kardashev Scale.

For those unfamiliar, Kardashev proposed that civilizations could be divided into one of three categories based on how much energy they could harness:

  • Type I civilizations could to harness the energy of an entire planet
  • Type II civilizations could harness the energy of their entire sun
  • Type III civilizations could harness the energy of an entire galaxy

In contrast, Barrow observed that humans have benefitted far more from extending their abilities into increasingly smaller scales rather than larger ones. Therefore, he proposed a scale that extended downward, where civilizations would be capable of manipulating matter from the scale of objects, down to the genetic, atomic, subatomic, and finally, space and time itself.

By 2002, John M. Smart, the CEO of Foresight University and founder of the Acceleration Studies Foundation, synthesized Barrow’s work and the increasingly-popular theory of the Technological Singularity to propose another resolution to the Fermi Paradox. In a paper titled “Answering the Fermi Paradox: Exploring the Mechanisms of Universal Transcension,” he claimed the “Great Silence” could be explained by technological evolution.

He updated these arguments in a 2011 essay titled “The transcension hypothesis: Sufficiently advanced civilizations invariably leave our universe, and implications for METI and SETI.” In summary, Smart argued that the process of evolutionary development (evo-devo) will inevitably guide species to optimizing their space rather than attempting to expand and fill more of it.

Rather than trying to colonize more star systems, they will be more likely to convert matter within their own system. This could include disassembling planets to create clouds of computronium, shedding their physical bodies to live out their lives in simulations, and soaking up all the energy they need from their sun. Or, as Smart offered, they might relocate to live around the Event Horizons of black holes!

Black holes could be the ultimate source of energy since matter that falls into rings around them is accelerated to relativistic speeds (near the speed of light) and they also emit energy in the form of Hawking Radiation. Beyond that, black holes allow for all kinds of revolutionary physics that only a super-advanced species would be able to harness.

Bottom line, a species that has reached this state of evolutionary development would likely be “radio-quiet” and undetectable by conventional SETI means. Moreover, they would likely lose interest in broadcasting their existence to the outside Universe and would prefer to observe it passively.

Honorable Mention

If you really want to get into the weird and scary theories that make you paranoid and want to question everything, there are few theories better than the Planetarium Hypothesis. This theory states that the reason there’s the “Great Silence” is that humanity is living inside a simulation or engineered environment (that would be the “planetarium”) built by a super-advanced species.

This species could have emerged millions (or billions) of years before we did and is making sure we’re unaware of their existence by making sure the simulation presents us with no evidence of intelligent life beyond Earth. And all the while, they are watching and studying us, maybe for the sake of research, maybe for entertainment, maybe because they created us, or maybe just to keep us controlled so we never threaten them.

It’s like a cross between the Truman Show, The Matrix, and 2001: A Space Odyssey. It’s also akin to the Zoo Hypothesis, which states advanced civilizations are avoiding contact with humanity (and any other less-developed species) out of some version of the law of non-interference (think of Star Trek’s “Prime Directive“.) You could say the Planetarium Hypothesis is the Zoo Hypothesis’ evil sister!

Some theorists have raised the question of how we might test this hypothesis. It’s been suggested that the physics of a simulated universe would have tell-tale signs of structure (“lattices”) that would indicate that it’s artificial. This theory takes its cue from the concept of Lattice Quantum Chromodynamics (QCD) environments, where quantum-level interactions are harnessed to create artificial environments (think of a “Holodeck“).

However, this approach is based on the idea that the physics model that is used in the simulation would be reliable – or at least the same as what exists in the real Universe. An inevitable counter-argument arises from this: if the laws of physics (as we perceive them) are part of our simulated reality, how can we trust them to reveal that it’s just a simulation?

That’s what makes this hypothesis so intriguing, as far as I’m concerned. If the very laws of physics were written as part of the simulation, it would make sense that those laws would be in place to prevent us from ever finding out. Even more mind-boggling is the idea that they could be specially-tuned to limit humanity’s growth.

When it comes to becoming an interplanetary and interstellar species, there are two forces that are holding us back: Gravity and Special Relativity. To break free of Earth’s gravity, one needs to generate an escape velocity of 11.19 km/s (6.95 mi/s), which takes a LOT of energy. As for Relativity, it establishes that the speed of light (299,792,458 m/s) is constant and a physical absolute.

One of the consequences of this law is that the faster an object gets, the more massive it becomes. As a result, it takes progressively more energy to accelerate the closer you get to the speed of light. In order to actually reach it, you’d have to generate an infinite amount of energy. Because of all that, traveling to even the nearest star is prohibitively expensive and could take many decades (at least).

That’s what makes this hypothesis interesting to me, from my perspective anyway. If I were a super-advanced species and in the habit of keeping less-advanced species confined in an artificial environment, I would include a physics model that imposes these very kinds of limitations. In other words, I am intrigued by the Planetarium Hypothesis because it’s exactly what I would do!


No spoilers, but all this research also gave me some big ideas for future novels. I would preview what these are, but I prefer to do that when the idea is in the works, and that won’t happen for a long time! I got a few standalone books to finish in the meantime, a trilogy that’s waiting on the release of the third installment, and then a second trilogy to prepare for.

Speaking of which, more new on that front will be coming soon! Stay tuned!

5 thoughts on “Fermi and the Great Filter. Or, Some Thoughts on Why We Haven’t Heard from Aliens (Yet!)

  1. Remarkable story Matt, thanks again. I enjoy sharing lots of stories on my blog. Maybe I can send this out to my audience as well, with your permission of course. Great work!

  2. Checkout Ciuxin Li’s Three Body Problem trilogy and the Dark Forest Hypothesis that is core to the story and very related to the ideas you write about here.

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