An observable universe is a big place that’s been around for more than 13 billion years. Up to two trillion galaxies made up of something like 20,000 billion billion stars surround our home galaxy.
In the Milky Way alone, scientists assume there are some 40 billion earth-like planets in the habitable zone of their stars. When we look at these numbers, it’s hard to imagine that there is nobody else out there. It would change our perception of ourselves forever if we found others.
Just knowing that this vast place is not dead would shift our perspective outward, and could help us get over our irrelevant quarrels.
But before looking for our new best friends, or worst enemies, we have a problem to solve:
What are we actually looking for?
In a universe that big and old, we have to assume that civilizations start millions of years apart from eachother, and develop in different directions and speeds. So not only are we looking over distances of dozens to hundreds of thousands of light years, we’re looking for a civilization ranging from cavemen to super advanced.
So, we need a conceptual framework to enable us to think better thoughts that make us able to search better.
Are there universal rules that intelligent species follow?
Currently our civilization sample size is only one, so we may make incorrect assumptions based solely on ourselves. Still, better than nothing.
We know that humans started out with nothing but minds and hands that could build tools. We know that humans are curious, competitive, greedy for resources, and expansionist.
The more of these qualities our ancestors had, the more successful they were in the civilization building game. Being one with nature is nice, but it’s not the path to irrigation systems, or gunpowder, or cities. So it’s reasonable to assume that aliens able to take over their home planet also have these qualities.
And, if aliens have to follow the same laws of physics, then there is a measurable metric for progress:
Human progress can be measured very precisely by how much energy we extracted from our environment, and how we made it usable to do things. We started with muscles, until we learned to control fire.
Then we made machines that used kinetic energy from water and wind. As our machines got better and our knowledge of materials expanded, we began to harness the concentrated energy from dead plants we dug up from the ground. As our energy consumption grew exponentially, so did the abilities of our civilization.
Between 1800 and 2015, population size had increased sevenfold, while humanity was consuming 25 times more energy.
It’s likely that this process will continue into the far future. Based on these facts, scientist Nikolai Kardashev developed a method of categorizing civilizations, from cave dwellers to gods ruling over galaxies:
The Kardashev Scale; a method of ranking civilizations by their energy use.
The scale has been refined and expanded on over the decades, but in general it puts civilizations into four different categories.
- Type 1 civilization is able to use the available energy of their home planet.
- Type 2 civilization is able to use the available energy of their star and planetary system.
- Type 3 civilization is able to use the available energy of their galaxy.
- Type 4 civilization is able to use the available energy of multiple galaxies.
These levels differ by orders of magnitude. It’s like comparing an ant colony to a human metropolitan area. To, ants we are so complex and powerful, we might as well be gods. So to make the scale more useful, we need subcategories.
On the lower end of the spectrum, there are Type 0 to Type 1 civilizations: Anything from hunter-gatherers, to something we could achieve in the next few hundred years. These might actually be abundant in the Milky Way. But a civilization that is not actively transmitting radio signals into space might be as close as our nearest stellar neighbor, the Alpha Centauri system, and we would have no way of realizing they exist.
But even if they transmitted radio signals like we do, it might not be very helpful. On an interstellar scale, humanity is practically invisible.
Our signals may extend over an impressive 200 light years, but this is only a tiny fraction of the Milky Way.
And even if someone were listening, after a few light years our signals decay into noise, impossible to identify as the source of an intelligent species.
Today, humanity ranks at about level 0.75.
We have altered our planet: we’ve created huge structures, mined and stripped mountains, removed rainforests, and drained swamps. We’ve created rivers and lakes, and changed the composition and temperature of the atmosphere.
If progress continues, and we don’t make Earth uninhabitable, we will become a full Type 1 civilization in the next few hundred years.
Any civilization that becomes a Type 1 is bound to look outside, because it’s likely that it’s still curious, competitive, greedy and expansionist.
The next reasonable step towards transitioning to Type 2 is trying to alter and mine other planets and bodies. This might start with outposts in space, transition to infrastructure and industries near the home planet, move on to colonies, and end with terraforming other planets, by changing their atmosphere, their rotation, or position.
As a civilization expands and uses more and more stuff and space, its energy consumption scales with them, so at some point, they may embark on the largest project a lower Type 2 civilization can take on: harnessing the energy of their star by building a Dyson Swarm.
Once this megastructure is finished, energy has become practically unlimited for molding the home system however they see fit. If they are still curious, competitive, greedy and expansionist, and now have complete control over their home system, stellar infrastructure in place, and the energy output of a star, the next frontier moves to other stars light years away.
For a Type 2 civilization, the distance to other stars might feel like the distance between Earth and Pluto does to us today: Technically within reach, but only with immense investments in terms of time, ingenuity, and resources.
This begins their transition towards Type 3.
This step is so far beyond us that it becomes hard to imagine what exactly these challenges will look like, and how they’ll be solved. Will they be able to find a solution to the vast distances and travel times of hundreds or thousands of years?
Will they be able to communicate and keep a shared culture and biology between colonies light years apart? Or will they split into separate Type 2 civilizations? Maybe even different species? Are there deadly challenges between the stars?
So the closer a species gets to Type 3, the harder it becomes to fathom what it might actually look like. They might discover new physics, may understand and control dark matter and energy, or be able to travel faster than light. We might be unable to grasp their motives, technology, and actions.
Humans are the ants, trying to understand the galactic metropolitan area. A high Type 2 civilization might already consider humanity too primitive to even talk to.
A Type 3 civilization might feel about as like we feel about the bacteria living on the anthill. Maybe they wouldn’t even consider us conscious, or our survival relevant. We could only pray that they’re nice gods.
But the scale doesn’t necessarily end here. Some scientists suggest there might be Type 4 and Type 5 civilizations, whose influence stretches over galaxy clusters or superclusters, structures comprising thousands of galaxies and trillions of stars.
Ultimately, there might be a Type Omega civilization, able to manipulate the entire universe, and possibly others. Type omega civilizations might be the actual creators of our universe, for reasons beyond our comprehension. Maybe they were just bored. As flawed as this classification may be, this thought experiment is already telling us interesting things.
If our ideas about the nature of species that form interstellar civilizations is sort of correct, then we can be pretty sure that there are no civilizations of Type 3 and beyond near the Milky Way. Their influence would in all likelihood be so all-encompassing, and their technology so far above our own, that we couldn’t miss them.
The galaxy should flash with their activity in thousands of star systems. We should be able to see or detect their artifacts or movements between different parts of their empire.
Even if a Type 3 civilization did exist in the past, and died a mysterious death, we should be able to detect some of the remnants of their empire.
But when scientists looked, they didn’t find remnants of harvested stars, decaying megastructures or scars of great interstellar wars. So they’re very likely not out there and never were.
In a sense, this is very sad, but also very reassuring. It leaves the galaxy to us and others similar to us. So the most promising civilizations to look for may be somewhere in the spectrum from Type 1.5 to Type 2.5. They wouldn’t be too advanced to understand them and their motives.
They may have finished their first megastructures, and they might be in the process of moving staff between stars, transmitting enormous amounts of information into space, by accident, or on purpose.
They would probably also look to the stars and look for others. Then again, maybe we’ve got it all wrong.
Maybe progress to Type 2 does not mean expanding outwards, and humanity is still too immature to imagine otherwise.
For now, all we really know is that we haven’t seen anybody yet. But, we’ve only just started looking. Until we finally find friendly super aliens and can ask them to explain the rules of the universe to us, most of us have to make do with learning stuff ourselves.