My thoughts on interstellar relations when you can’t break the speed of light

5 min readAug 31, 2020

In the few science fiction series I’ve read, we often see societies with the capability to break the speed of light, travelling, or sending information, to other planets nearly instantaneously. Even Orson Scott Card’s Ender’s Game and Speaker for the Dead series, which maintain the speed of light as an upper limit for human travel until the end of the series, sets the precedent for instantaneous communication straight from the start.

Today, we’ll be discussing how I think interstellar civilizations would form and develop in the absence of faster-than-light travel or communication.

The nearest star to Earth, Proxima Centauri, is approximately 4.2–4.3 lightyears away.¹ There are 20 stars within 12 lightyears of Earth, and there are 45 stars within 17 lightyears.² But not all of those stars have exoplanets. According to Wikipedia (sorry, it’s the only place I could find a list), there are only 36 rocky planets within 42 lightyears of Earth (2 of which are within 6) ³, and of those, only 12 are in the conservative habitable zone, where liquid water could definitely exist given enough atmospheric pressure (although an additional 11 are in the optimistic habitable zone where water might be able to exist). Within 20 light years, we have 6 planets in the conservative habitable zone, and 5 in the optimistic one. However, we don’t know the chemical composition of most of these planets, so it’s unlikely that all of them could support life.

The point I’m trying to make with these numbers is that habitable exoplanets are relatively far between. You’d probably need to travel a few lightyears to even get to one outside your own system, and would only find a handful within 20 or so lightyears. The distance you’d need to travel and the time commitment you’d need to make to get between these systems would be humongous. But what effect would that have on the government and relationship between these star systems?

Lets start our analysis off by thinking about the relationship between a far future Earth and their interstellar colony on Proxima Centauri b, a planet in the habitable zone of the nearest star. If we develop the capability to send information through interstellar space using light, the colony would receive messages from Earth about 4 years and 3 months after we sent them. Due to necessary acceleration and deceleration, my amateur estimate is that manned missions would take at least 4 years 9 months (Assuming acceleration at 2g until you get to 99% of the speed of light)

4 years is a VERY long transit time, which would significantly inhibit our ability to communicate with and govern our colony. They would need to be self-sufficient and self governing, as it would take us about 9 years to receive word of any problems they might have and get someone over to help them.

Going to and from the colony would be a serious commitment, since travellers would be gone for minimum 9.5 years of their family’s lives. It would likely much longer since I doubt anyone would make that type of commitment only to stay at the colony for a few weeks. In fact, I bet a sizeable portion of travellers too and from the colony (at least at the beginning) would have no intention of ever returning.

Once the Centauri colony was firmly established, they wouldn’t ask for experts or laborers to come help with a single project, since in the decade it would take earth to receive the message and transport help over, the project would probably already be complete. If a long term project is important enough to uproot them from their friends and families for 10+ years, it’s important enough to give them a new life in the colony. Earthlings and colonists wouldn’t work together on science or technology projects: everything that’s developed would be distinctly from one planet or the other.

Over the centuries, the Centaurians would develop a distinct culture, probably multiple cultures. Their languages would diverge from earth languages over centuries, the rate at which it changes largely dependant on the volume of traders and new arrivals that travel to Centauri and from Centauri to earth. Eventually, we’ed get to a point where the colony would have a completely different set of languages, and completely different cultures than we do on Earth.

After centuries of culture change and linguistic drift, it is impossible to predict what the relationship between Earth and the Centaurians would look like. Traders might make a regular circuit between the planets, bringing news, passengers, and technological innovations. Trading like this would likely be a lifetime career that runs in certain families, since I find it doubtful that someone would uproot their entire life for just one or two trips. These traders would likely develop their own unique culture, never truly being a member of either planet they dock at. Time dilation as they travel at relativistic speeds would keep them around at least five times as long as ordinary humans: they’d see countries rise and fall, generations grow to maturity.

Once a culture of traders was well established, they could probably outlast periods of hostility from either planet. This would be made easier by the fact that both planets would likely have multiple countries that wouldn’t all be hostile at the same time. However, in order for these trading families to form, there’d need to be a long period where the planets were at peace and the advantages of trade were obvious. If Earth and Proxima Centauri weren’t interested in each other’s technology, if the governments didn’t see the need to maintain relations with peoples who live years away, Centauri might fade into Earth’s myths and legends, to be rediscovered by a new wave of explorers centuries or millennia later.

Calculations for my travel-time figures:

Manned missions would take even longer due to the need for acceleration and deceleration. Based on this Quora post and this book excerpt, I decided to assume a 2g upper limit for extended periods of acceleration in order to insure a human’s survival. Accelerating to or decelerating from .99 light speed (humans have mass so we couldn’t actually go light speed) would take nearly 6 months and cover roughly .2443 light years (I got this by integrating v=19.6t between 0 and 15357699.12, the approximate number of seconds it would take to accelerate to 99% the speed of light), making the entire trip take about 4 years and 9 months in earth time. Time dilation would make the 3.714 light years traveling at 99% light speed seem like a bit less than a month to the astronauts (my own calculation based off a formula on this website). Time dilation would also affect the acceleration and deceleration, but I have no idea how to do those calculations. My number in the article is a guess based on the fact that it couldn’t possibly take longer than a year given that acceleration and deceleration combined take less than a year, but wouldn’t get shortened to anywhere near a month given that relativistic effects don’t become noticeable until you reach about half the speed of light.