Aliens aren't real

It's just us on this ride, for now.

I have long believed that settling the stars is the single most pressing moral concern and today I wanted to explain why.

The main reason is that, based on the best evidence we have, Humanity is, probably, the only technologically advanced life in the observable universe.

To think about this idea clearly, we must first engage with a couple of facts.

Fact 1:

We have yet to discover any evidence of extrasolar life at all, let alone evidence of advanced extrasolar life.

Fact 2:

The observable universe is indescribably large, ~200,000,000,000,000,000,000,000 stars, the Milky Way alone has ~100–400 billion stars.

Fact 3:

The observable universe is incredibly old, ~13.8B years.

Fact 4:

It would take Humans ~50 million years to colonize the entire Milky Way under extremely conservative assumptions.¹

Fact 5:

Life has existed on Earth for ~4B years, with anatomically modern Humans - meaning a person who would be able to perfectly blend into modern society if raised from infancy - existing for ~300k years.

Taken together, these facts create a genuine puzzle. If anything like Humanity had arisen at any point in the last 13.8 billion years and begun to spread, it would have colonized the entire galaxy in less than a billion years. We should expect to see evidence of such a civilization everywhere. We don't.

The puzzle becomes doubly mysterious when you consider Arthur’s Dyson Dilemma. What this says is essentially that as a stellar-based civilization captures more and more of their sun’s energy, the relative composition of their “light” signature would shift into their “waste heat” signature. In practice, this would look like a star having a much lower light spectrum than would otherwise be plausible given the star’s size, etc. Well, we have looked, and found no examples of this anywhere. What this means is that nowhere we can see is there any evidence any civilization is significantly capturing their sun’s light, an action that Humans would inevitably undertake somewhere in the galaxy over the next billion years. This is to say nothing of the fact that there is no evidence of galactic “gardening,” or the arrangement of stars so they are more ‘useful’ such as avoiding ruinous collisions, something, again, we Humans would certainly do.

Finally, consider the problem of timing. A person could respond to everything I’ve said so far by saying “advanced alien civilizations do exist, but they simply haven’t developed to the point we can detect them yet.” However, when you consider it carefully, it falls apart, since for it to work it would require that every civilization capable of expanding across the galaxy happened to arise within roughly the same ~50 million year window, a blink of an eye against 13.8 billion years of cosmic history. If even one civilization had appeared just a hundred million years earlier, it would have left an unmistakable footprint.

I don’t want to oversell the evidence for an absence of aliens because of course we have imperfect instruments; however, as the evidence of NO alien life continues to mount, it is increasingly in the court of the alien-life believers to substantiate their hypothesis.

Still, we cannot rule out exotic possibilities like humans living in some sort of alien zoo, or the life undergoes a “sublimation” process where it normally “steps out” of reality, either through constructing enormous Nozick-esque experience machines or by literally undergoing apotheosis. I personally find this implausible, and since these theories are by construction impossible to disprove, I will put them aside for this article.

So where does this leave us?

If we take the evidence at face value - and I think we should - then Humanity is very likely alone, at least as a complex technological civilization. Not just alone abstractly, but alone in a galaxy of hundreds of billions of stars, possibly even alone in the entire observable universe of 200 sextillion stars.

Why?

If we accept that the absence of aliens is, probably, real, the natural question to ask is: why? Why would a universe this old and this large produce precisely one technological civilization?

The most convincing answer is Robin Hanson’s Great Filter Theory. What this postulates is that rather than thinking about the probability of life emerging and becoming technological as a binary event, we should instead think about it as a series of “filters,” where even if each one is only moderately unlikely, the combined product can yield a world where even the possibility of one technological civilization is quite small.

To concretize this, consider just the following subsample of filters with probabilities I think are plausible, both behind and ahead of us.

Suitable star ~15%

Right type, metallicity, not in a binary system so the temperature remains stable, and not too close to the galactic core where radiation would sterilize everything.

Rocky planet in the habitable zone ~10%

Planet needs to have water, and for that water to not boil or freeze.

Planetary stability over billions of years ~20%.

Venus lacked plate tectonics, which led to a runaway greenhouse gas cycle and Mars lacked a sufficiently active metallic core and so its atmosphere was stripped away.

Abiogenesis ~10%.

The literal emergence of life:

The Eukaryotic Transition ~0.1%

You probably remember from your high school biology classes that the mitochondrion is the powerhouse of the cell, but what you might not know is that it has its own genetic lineage and is in many ways its own living organism. What occurred is that billions of years ago one prokaryote engulfed another, and rather than absorbing it they instead “fused” together and conquered the entire planet. Literally all eukaryotic life today - every animal, plant, and fungus, or about 80% of biomass - descends from this event, which occurred precisely one time in four billion years.

Photosynthesis and surviving oxygenation ~50%.

In order for life to escape being trapped around volcanic rims and capture the enormous energy potential of the sun, photosynthesis had to evolve. This alone is by no means guaranteed, but there is an additional wrinkle. A side effect of photosynthesis is that it produces huge amounts of free oxygen in the atmosphere. Oxygen is dangerous in two ways: first, it is directly poisonous to anaerobic life, and on Earth this process resulted in a devastating mass extinction event; second, oxygen is extraordinarily reactive, and without a sufficiently large biosphere sink it will eventually quite literally burn the entire surface to a crisp.

Complex multicellular life ~10%

The emergence of differentiated tissues, coordinated body plans, and complex organ systems took a billion years of evolution after the rise of eukaryotes.

Land colonization ~30%

For a number of reasons that are wonderfully outlined in this video, life had to move out of the ocean to have any hope of developing space travel. For this to occur, a planet would need an ozone layer, which requires oxygen created by photosynthesis.

Mental and anatomical prerequisites for technology ~1%

We have yet to find any fossil record of animals which shared the triple punch of Humans: we are highly social creatures, we have highly adaptable limbs which lend themselves to tool use, and we are brilliant. Dolphins and octopuses are of course genuinely intelligent, but even given a billion years they would never accomplish what Humans have. Similarly, early hominid ancestors shared many of the same traits as Homo sapiens but lacked the social machinery to conquer the Earth.

A cumulative culture ~10%

Even with anatomically modern Hmans you need writing and other cultural systems to develop which allow for the gradual accumulation of technology and society.

The Scientific Revolution & Energy Bootstrapping ~50%

To get from an agrarian civilization to an industrial civilization you need at least two things. First, a society has to arrive at empiricism or some other system to exponentially increase knowledge; and second, you need a source of easily capturable energy. Earth happens to have a large store of hydrocarbons which are the result of millions of years of captured biomass.

Survival to interstellar expansion ~50%

We of course have yet to “escape” and are still haunted by the shadow of nuclear war, engineered pandemics, an AI apocalypse, or a collapse in fertility leading to a world run by the Amish.

Taking just these probabilities you get a p≈1.125×10^12 per star.

Which would imply, at most, ~0.45 interstellar civilizations in the Milky Way.

You can of course add more filters or quibble about the probabilities, but the idea is hopefully clear.

So are we fucked?

If you have bought everything I’ve written so far, the natural question to ask is “where” in the Great Filter process we stand. Humans have yet to do anything that we ourselves would be able to identify from afar, and so it is plausible that billions of civilizations have reached this point in the Milky Way alone and then collapsed in the transition from industrial to multiplanetary civilization.

The semi-recent news from Mars makes this story somewhat darker, since in July 2024 NASA’s Perseverance rover collected a sample from a rock called “Cheyava Falls” in Jezero Crater which showed potential biosignatures consistent with ancient microbial life, for which scientists have found no strong abiotic explanation. Now this isn’t proof of life on Mars, but it is suggestive evidence that microbial life may have existed at one point, and this would imply that in our solar system alone life existed on AT LEAST two of the three planets within the Goldilocks zone. Note I say existed, not originated, because it is possible life was carried from a single source around the chaotic early solar system.

But even if Mars experienced independent abiogenesis, and we radically assume that life always arises when the conditions are right, the math barely changes.

Since the core principle is the layering of moderately low-probability events where each individual step is mostly irrelevant. In short, we cannot know for sure, but given how steep the cliffs we have already climbed are and the relative believability of the challenges ahead, I personally lean towards the belief that we have already passed the most daunting filters and, barring catastrophic mismanagement, have a very solid chance at “escaping.”

Why does this matter? - for paid subscribers only

Assuming you bought even half of what I’ve written, you may be feeling some combination of fear, pride, and overwhelming duty at the realization that all future consciousness in the observable universe, not just Human consciousness, all consciousness that will ever exist, probably depends on what happens to us in this century. Our lives will largely determine the trajectory of the entire fanning web of future possibilities.