A wealthy, 22nd century trillionaire, for whatever reason, builds an EIS (Embryonic Interstellar-Ship). He sends a ship with frozen human embryos, and an AI system to grow and educate them, to a planet known as Alpha Sigma Iotia IV (although it would be known as "Serkis" by the eventual inhabitants). When they arrive to their destination, the children are grown, educated, and build their own society: The one problem, they aren't aware of greater interstellar society.

So, let's say about 150 years later, this isolated rogue human colony develops 1950s level technology. Could they detect the large interstellar human society (which is 100 light years away from them) and if so, what methods would they have to use to do so?

  • 2
    $\begingroup$ We need a better definition of an "interstellar society" - what does this society do that can unmask them? We know what we, as people, do now in the early 21st century and how aliens may be able to detect that - but what would we be doing some 400-500 years in the future? $\endgroup$
    – Alexander
    Jan 6, 2021 at 2:30
  • $\begingroup$ Any sort of probe craft is going to have much better legs than a colony ship, assuming a similar technology base, and the extant interstellar civilization has had another 150 years to make it better. Is there a reason why they're avoiding the rogue colony? $\endgroup$
    – notovny
    Jan 6, 2021 at 11:17
  • $\begingroup$ @notovny: They don’t really noticed then. The United Terran Federation has about 100,000 planets under its dominion, the existence of Serkis’s rogue colony flew under the radar. $\endgroup$
    – DT Cooper
    Jan 6, 2021 at 13:17
  • $\begingroup$ This detail need further clarification: you state the colony will be founded with 22nd Century technology but somehow only has pre-1950s tech for most of its existence. Why do all of their communications/radio telescopes/etc cease working? Why is knowledge of their origins kept from them? $\endgroup$
    – rek
    Jan 6, 2021 at 15:33
  • $\begingroup$ @rek: the guy who founded the colony wanted it to be an unspoiled colony, so all of the more futuristic tech (besides the robots) were immediately destroyed after everything was set up. Obviously. $\endgroup$
    – DT Cooper
    Jan 6, 2021 at 16:40

2 Answers 2


So, let's say about 150 years later, this isolated rogue human colony develops 1950s level technology

First of all, whatever the originator planned for (even possibly including a Safehold-level religious control), the colony has to know they are human colonists from somewhere else and have a good guesstimate about where. If those data were included in the original ship's cargo, they knew from the very beginning. Otherwise, it would quickly become obvious anyway.

  • no fossil record with the human Bauplan found
  • planetary biochemistry is visibly "hacked together"
  • bioweathering and other indicia point to the colony not being older than 150-300 years at most
  • technology started from a way higher level than you'd expect
  • no archaeological remains of earlier settlements anywhere
  • oral tradition still easily goes back to Landing Day, but no further

So, "we came from the stars, already pretty advanced". Which star? In 1950 the local G-class stars of our neighbourhood were acceptably mapped. I'd expect no less from the colonists. "If we arrived here, our Sun must have been visible from the mythical Home; it follows that Home's Sun should be visible from here".

So the colonists would build radio and optical telescopes, with a much keener spirit than ours was, and would point them to nearby G-class stars, which would be exactly the most likely to host the recently established Human Federation of Planets.

It's just a matter of time before they detect radio waves and laser light from those sources.

  • $\begingroup$ How hard would it be to guess which Star was the origin? $\endgroup$
    – DT Cooper
    Jan 6, 2021 at 13:25
  • $\begingroup$ Exactly... probably pretty hard. They'd have to make a guesstimate about how far the arkship could have gone (and if it was deliberate or accidental). This depends on how much of the arkship is still available for study. They would probably restrict the choice to several dozen G-class stars in their stellar neighbourhood. Without space-based telescopes I very much suspect that's the best they could do. $\endgroup$
    – LSerni
    Jan 6, 2021 at 18:34

Radio Telescopes

Radio telescopy was discovered in the 1930s and large dishes were being build and operated by astronomers in the 1950s.

Firstly your planet is 'only' 100 years from Earth which is virtually next door in galactic terms. Secondly you are also talking about a scenario where Earth itself has established an interstellar society. This presumably involves high levels of space based energy output (including radio waves) from infrastructure orbiting numerous solar systems and from ships and signals traveling between those systems. This means the chances of early radio telescopes picking up stray transmissions is greatly improved.

(As opposed to our current real world situation where the chances are very slim.)

  • $\begingroup$ The other issue, of course, is that assuming there's been no breakdown of society, the interstellar human community should be well aware of the ship and where it went. It would be fairly trivial to set up a dedicated radio telescope that both listens for them and broadcasts a "Have you figured out how to answer yet?" signal to them. $\endgroup$ Jan 7, 2021 at 17:27

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