Galactic civilizations may be impossible. Here’s why.
- For galactic-scale civilizations to exist in our Universe, they would have to overcome two major hurdles related to physics and biology.
- One is the sheer distance between each society. The other is biological life span.
- Astronomer Adam Frank outlines the difficulties with each problem.
My new guilty pleasure is the video game “Star Wars Outlaws” (guilty only because so many gamers seemed to hate it — they are wrong). Like all “Star Wars” stories, it’s set in a galaxy far, far away that hosts a vast interstellar civilization. And, like all civilizations, it’s a hotbed of politics and commerce, diplomacy and war, art and culture. Science fiction is full of these kinds of galactic-scale societies. Star Trek, Dune, and Asimov’s Foundation series — they all play out against the backdrop of star-spanning civilizations.
But are such things possible? Do the laws of physics and the dynamics of social arrangements (even alien ones) allow for galactic societies? As much as I love them (how else could I become a Space Pirate?), I fear the answer may be “no.”
Two challenges for galactic-scale civilizations
The problem for galactic-scale civilizations comes down to two numbers. The first is the time it takes to cross between the stars (we will call this the “crossing time”: Tc). Considering Tc forces us to deal with another number, which is a fundamental constant of nature: the speed of light (represented by the letter “c”). As Einstein taught us, the speed of light represents the upper limit for velocities in the Universe. Nothing can travel faster than c, which is about 700 million miles per hour. While this may seem pretty fast (it is), the distances between the stars are so great that it still takes centuries to hundreds of millennia for light to reach us from all but the nearest stars. That means the time for a ship to reach across reasonable fractions of the galaxy must also be measured in centuries to hundreds of millennia. If your ship travels slower than light speed (which is what we will be stuck with for a while), then your crossing time (Tc) is even longer.
The second timescale we need to consider is how long an individual in a species lives. Let’s call this the “generational time” Tg. This is the timescale where politics and culture play out. While there may be longer trends that occur across civilizations, societies are made of individuals who are the agents driving the immediate dynamics.
So where is the problem? Well, it’s physics that sets the limits of Tc and biology that sets the limits on Tg. On Earth, there are no vertebrates that live longer than a few centuries (the Greenland shark being the longest-living example, potentially living up to nearly 500 years). That means a high-tech civilization made of Greenland sharks would still face the problem that interstellar travel times are way longer than life spans (i.e. Tg << Tc). Let’s consider for a moment what that means for the possibility of galactic civilization and that most fundamental activity: trade.
Let’s say you want to sign a contract, deliver goods, and collect your credits across an interstellar trading route spanning 500 light-years. Every step of the negotiations requires cooperation across multiple generations. You send out an offer and then must wait 1,000 years for a reply. Well, actually, it’s your great-great-great grandkid who gets the reply, who then counter-offers and waits another 1,000 years to see whether the offer is accepted. After a few more rounds of this, you finally send out your trading ship which, even if it travels at almost the speed of light, takes 1,000 years to make the round trip.
You see my point by now. All things that make a society a single structured whole become impossible on galactic length scales unless the members of that society are remarkably long-lived (and there even may be biophysical reasons why this is impossible for “thinking” creatures). The distances between the stars are so vast that only collections of very nearby stars might possibly form loose cultural alliances, i.e. societies. And even these will have their problems because of relativistic time dilation, which occurs when individuals traveling at light speed experience the flow of time differently from those on their destination planets.
Now, I am not saying that galactic empires are impossible. Maybe there is a way around the light-speed limit (though relativistic time dilation might be a factor in warp drive/worm-hole travel too). Or maybe all intelligent life becomes post-biological and “lives” for timescales that dwarf interstellar crossings. You must be open-minded when you think about these things. But you can’t be too open-minded or your brain will fall out. If you really want to think hard about the possibilities for life beyond Earth, you can’t just wave your hands at the physics and the physics that limits biological processes.
So, are there galactic civilizations? I am stuck right now thinking “no” but still hoping “yes.” I’m clinging to that hope because I really want to be a space pirate (the good kind). And now back to “Star Wars Outlaws”!
