spaceSpace and Physics

Moderately Advanced Aliens Could Easily Take Over A Milky Way-Like Galaxy, Simulations Show


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockJun 17 2021, 11:16 UTC
Alien spreading throughout a galaxy? That's more likely than you think... well, maybe. Marko Aliaksandr/

Aliens spreading throughout a galaxy? That's more likely than you think... well, maybe. Image credit: Marko Aliaksandr/

A new simulation has looked at how quickly a moderately advanced alien civilization would take to spread itself across a galaxy and the answer is not long at all, at least in relative cosmic terms. Even equipped with spaceships not much faster than our most advanced interplanetary probes, the whole ordeal could happen in just 1 billion years.

This might seem like a long time in terms of a human lifespan or even compared to the existence of our species as a whole, but when we consider the lifespan of a galaxy, it is pretty quick considering that the simulation didn’t require any super-fast spacecraft or physical tricks beyond our current understanding of the universe.


As reported in Research Notes of the American Astronomical Society, the team considers a civilization of Type II on the Kardashev scale. This is shorthand to describe the level of technological advancement of aliens that have spread throughout their star system and are using as much energy as their star can produce. Such civilizations might feel the need to spread to other star systems, and in this paper they do.

The research envisions an example of the process of a lone technologically advanced civilization in a Milky Way-like galaxy as it begins galactic expansion. They speculate the aliens' home star system and any newer settled systems would have technology (the mark of advanced civilization) for about 100 million years before dying out. They also wouldn't launch more than one settlement ship every 100,000 years, with these ships moving at a speed of about 10 kilometers (6 miles) per second and traveling less than 10 light-years from their original source. So at any one time, only a handful of stars would be available.

But stars move and that is key to the simulation. When the original civilization starts launching its generational spacecraft, as time goes by, due to the planetary systems' motion in the galaxies, it has access to different stars. At the same time, the newly settled systems will send out their own spacecraft.

“What’s neat is that in this simulation, because the ship range is small and ships are sent out infrequently, the wave [of expansion] goes slowly enough that it is actually the motions of the stars that do most of the work, and you can see how they take what might have created a bubble of inhabited stars and smear it out, like jam getting mixed into oatmeal or cream getting stirred into coffee,” lead author Professor Jason Wright, wrote in a blog post.


“Eventually, the front reaches the middle part of the galaxy where the stars are typically closer together than in the outer parts, and then the expansion proceeds very quickly, but the outer reaches of the Galaxy never get inhabited.”

The team is currently working on a new simulation that has softer limitations on how far they can move and how often a settlement happens.

This speculation might make you consider the Fermi paradox: the likelihood of other life in the cosmos is high so where is everybody? If it is easy to expand across a galaxy, why isn’t there an alien civilization already doing it in the Milky Way? As always, many answers are possible. Maybe there is one, or more, currently doing so. Maybe they have no interest in actually spreading throughout a galaxy. Maybe they even hope someone else would do it first.

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