The observable universe is consists up to two trillion galaxies that are made of billions and billions of stars. In the Milky Way galaxy alone, scientists assume that there are some 40 billion earths like planets in the habitable zone of their stars. When you look at these numbers, there are a lot of possibilities of alien civilization to exist. In a universe that big and old, the possibilities of civilizations may start millions of years apart from each other, and develop in different directions and speed. So their civilization may range from cavemen to super advanced. We know that human started out with nothing and then making tools, building houses, etc. we know that humans are curios, competitive, greedy for resources, and expansionists. The more of these qualities that our ancestors had, the more successful they were in the civilization building process.
Like this, the other alien civilizations also might have evolved. Human progress can be measured very precisely by how much energy we extracted from our environment. As our energy consumption grew exponentially, so did the abilities of our civilization. Between 1800 and 2015, population size had increased seven fold; 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 for categorizing civilizations, from cave dwellers to gods ruling over galaxies into a scale called the Kardashev scale. It is a method of ranking civilizations by their energy use. It put civilizations into four categories. A type 1 civilization is able to use the available energy of their home planet. A type 2 civilization is able to use the available energy of their star and planetary system. A type 3 civilization is able to use the available energy of their galaxy. A type 4 civilization is able to use the available energy of multiple galaxies
. 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. On the lower end of the scale, there are type 0 to type 1 civilization. Anything from hunting, gatherers to something we could achieve in the next few hundred years. These might actually be abundant in the Milky Way. If that possible, why they are not sending any radio signals in space. But even if they transmitted radio signals like we do, it might not be very helpful. In such a vast universe, our signals may extend over 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 created huge structures, changed the composition and temperature of the atmosphere. If progress continues, we will become a full type 1 civilization in the next few hundred years. The next step to type 2 is trying and mine other planets and bodies.
As a civilization expands and uses more and more stuff and space, at some they may start a largest project that extracting the energy of their star by building a Dyson swarm. Once it finished, energy has become unlimited. The next frontier moves to other stars light years away. So the closer a species gets to type 3, they might discover new physics, may understand and control dark matter and energy, or be able to travel faster than light. For them, humans are the ants, trying to understand the galactic metropolitan area. A high type 2 civilization might already consider humanity too primitive. A type 3 civilization might consider us bacteria. But the scale doesn’t end here; some scientists suggest there might be type 4 and type 5 civilizations, whose influences stenches over galaxy clusters or super clusters. This complex scale is just a thought experiment but, still it gives interesting things. Who knows, there might be a type omega civilization, able to manipulate the entire universe, and they even might be the actual creators of our universe.
“Somewhere, something incredible is waiting to be known.” – Carl Sagan