160 light-years from Earth, 1000 years in the future, exists an alien civilization roughly equal in its technological advancement to modern civilization on earth. They fear the possibility of the expanding humans invading and destroying them. Future humans have already colonized almost all neighboring star systems. Surely humans would detect their radio emissions, not to mention that an expedition made to their home system would likely occur in the near future. How would these aliens avoid detection?

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    $\begingroup$ Welcome cxnhgfh. Could you tell us about your aliens, how they detected such an advanced humanity without being detected themselves? What sort of star/system they live in? Do they have nuclear power, space-flight, satellites orbiting? What's the atmosphere on their planet, its gravity/size? Is there abundant water in any form? Also, it's tricky to know what a 1000 year advanced humanity will look for in a planet or system for resources or colonisation, can you tell us what you've decided there? $\endgroup$ Commented Jan 16 at 4:59

4 Answers 4


It's not the Radio Transmissions that I'd be worried about

It's a planet that is capable of sustaining life. And that is probably the biggest hurdle to overcome. If Humans have Inter-stellar tech and the Aliens don't - then they are probably mostly out of luck...

There's a number of problems:

  • The Aliens don't know what the primary means of gathering information that Humans use. You mention Radio Waves - Do you humans use Radio Waves anymore? Or is that such an old-fashioned technology that it is considered Quaint and a Novelty?
  • as per my Title - I'd be more worried about a Human Surveyor going 'Mmmm Liquid water, breathable atmosphere, green plant life?!? Bust out the Flags boys, it's colonizing time!' - and that is something that we currently could not mask at a planetary level.
  • Too many Unknowns.

However... There's a few scenarios where we can somewhat address those questions in a plausible-ish manner, which allows us to fudge Technology with a bit of 'necessity' handwavium.

Option 1: You mentioned other planets were Colonized - if they also had intelligent, space-fairing life, then some of those Aliens could escape, warn your Planet about the Humans and what their capabilities are - If it's Radio Waves - then radio transmissions above a certain wattage are now illegal on pain of death, everything runs in Cables. Then, high above the Atmosphere, they let off a large number of Nuclear explosions.

The Humans observe the following: Regular radio traffic, indicating intelligent life, a mass of Nuclear explosions and a sudden cessation of all Radio Waves - they presume that the entire planet was irradiated in a global Nuclear war - and decide to give it a miss, not worth the effort.

Option 2: Human Nomads/Hermits - especially someone who was high in the Military/Colonization efforts and got disillusioned with the whole thing and sort out a place to be alone and die - met the Aliens and told them how they selected Planets. This then enables them to try and either fake signals or gives them a means to boost their technology up to the point they can disguise the habitability of the planet: perhaps sending an artificial signal to fool the sensors, perhaps good ol' fashioned camoflage on a global scale - dying the Oceans, putting netting over the crops etc.


To what length will they go?

There's a limit to this question, and to demonstrate that let me change the conditions a bit. If we ask how a medieval society could hide from today's tech the answer is, "they can't." Most of what we do today would, at least initially, look like magic to them. Even after they grew accustomed to our tech, they wouldn't understand it. As a world-wide population, they simply wouldn't know where to start to hid from (e.g.) a satellite.1

What makes more sense is asking how a newly post-industrial civilization (e.g., England about 1895) would avoid identification as a post-industrial society. Now we're talking about early radio, coal-fired pollution, railroad tracks, and a sudden increase in building sizes. Easy to see. Easy to detect. To be fair, even they would have the devil of a time hiding their very existence from we modern humans, but with some ingenuity (which they had), they could perhaps hide their tech level.

What do those examples suggest to us? You have two problems:

  1. As you've mentioned, your society has emissions. Principally electromagnetic, but also in terms of pollution and putting a significant amount of stuff into orbit. You also have considerable ground construction and ground-level light pollution. Just to name a few. How would such an advanced people hide? By ridding themselves of those emissions — green activism on steroids. OK, not steroids... PCP.

  2. But you also have people. There were large ancient cities... but not by today's standards. From the one data point we know about (humanity) we believe that there must be advancements in agriculture, medicine, sanitation, transportation, and other sciences to achieve seriously outrageous populations. So you could convince everyone to become vegans and live in tents, but the passing humans would inevitably think to themselves, "that's a honking lot of people living in tents and eating lettuce... I wonder how they're farming and moving all the lettuce... and where does all the crapola go?"

And, just to make a point, there's likely a third problem that we're simply going to ignore.

  1. Humanity has been throwing stuff out into space (emissions, satellites, etc.) for a long time — and we have yet to find evidence of another species.2 We're going to simply ignore this. Sometimes it's what you gotta do.

So, what could you do?

We have aliens who, for the sake of argument, act and think a lot like Humans with circa 2023 technology who got very lucky and happened to detect the wake of a passing relativistic craft at the very moment that no one on the craft cared a whit about looking at their planet. Cheers! The knowledge that they're not alone in the universe and, much to their chagrin, they also aren't top-dog on the technology pyramid has driven the more military-minded among them to take over the world's governments and act, as they say, for the preservation of their race. And they decided to do one or more of the following:

  • Strict population controls are put in place to permit decentralization of core population groups. This isn't unbelievable as we not only have advocates of such measures today but also have governments who have implemented such measures. [1], [2]

  • Development of thermal-based energy production. Geothermal comes to mind, but the goal here is to develop energy production that doesn't require (a) large surface structures (e.g., dams) or (b) substantial pollution (e.g., coal or nuclear).

  • Development of dense hydroponic food industries. The goal here is to get away from large surface agriculture to avoid not only large trivially discernable tracts of farmed/ranched land, but also large irrigation projects.

  • A serious focus on recycling.

And why do you need all this?

  • Because the only way to hide from such an advanced civilization is to move deep underground and hope that civilization doesn't look at your depopulated surface and think to themselves, "hey, there's an upopulated and unclaimed paradise down there!"

From a story standpoint you'll need to ignore a lot of things because unless your universe is unusually repleat with habitable planets, the fact that you have a habitable planet will be the single most difficult thing to hide... unless you're willing to destroy the surface. If not, every passing high-tech ship will be want to take a very close look at the planet.

1Let's ignore that there were a few thinkers who could imagine the fundamentals of the technology and, therefore, comprehend at least the basics of how they operate. They may not understand the mathematics of electromagnetic propagation... but they'd comprehend the basic operation of light. Random genius can get in the way of any worldbuilding effort... or be the convenient joker card that ensures success.

2We could point to the "Wow!" signal as possible evidence of extraterrestrial life. However, we humans are somewhat paranoid critters, evidenced by our penchant for conspiracy theories, and yet that signal has not driven us to hide from our potential alien overlords. Consequently, I suspect a believable story would require better proof than the "Wow!" signal, which begs the question others have asked... how can these people choose to act in the way you want and yet not have been discovered long before they could, themselves, detect a potential threat and act to avert it?


They wouldn't.

Humanity is vastly more advanced than them, and their planet is suitable for life. They have no real way of beating 1000 years plus super tech from earth.

They need to start their own colonization program.

160 light years is a long way. They can work on expanding out through their own solar system, colonizing all major resources, and fortifying it. Even a much more advanced earth is gonna have trouble conquering a whole solar system without ftl tech. Grab as many systems as you can, devote a huge amount of the budget to space travel and space techs, and build an enclave which can resist humanity or flee.


One way they could avoid detection is if the aliens and their entire life forms are sufficiently different from life on earth. Namely they life deep inside a gas giant. There system doesn't contain any planets that would be interesting colonizing targets for humans so no one goes there. Gas giants are plenty in space so there is no reason to go to that stellar system.


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