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Say we have a civilization on the verge of becoming Type II, and are in the process of building a Dyson Sphere. They are aware that in the process, and especially after completion, there will be telltale signatures of this construction process to anyone observing the stars in their general vicinity, such as abnormal dimming and possibly what appears to be its total extinguishing after the sphere is up.

That in itself may still not be a full giveaway as unless any observer is sufficiently advanced in their understanding of all stellar phenomena, they should be unable to completely rule out natural bodies obscuring the star intermittently. However, if coupled with the telltale structure electromagnetic waves take when used as a communications medium, it may point out quite clearly that intelligent activity is occurring in the vicinity of the dimming star.

Assume the observers are equivalent in scientific understanding and technology to modern humans. Is there a way for the civilization to communicate without the observers realizing that the dimming star is not a natural phenomenon? For the purposes of this question assume

  1. The observers are already aware of the intermittent dimming of the distant star (approx 1400 light years away)

  2. The observers are actively trying to determine if intelligent life is behind the dimming by listening for telltale radio signatures

The civilization will be considered to have successfully evaded detection if one of the following is achieved

  1. They have a method of communication that cannot be detected at such large distances

  2. They manage to mask their communication by disguising the emissions to look like emissions of natural bodies (real or theoretical such as quasars, pulsars, exotic stars and any other -ars you can think of)

As an aside, I know of Tabby's Star and that's exactly what inspired this question. I'm also aware that there is no stealth in space, so I'm not exactly banking on scenario 1 but who knows.

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3 Answers 3

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Digitisation and encryption of radio signals means that they're indistinguishable from background noise unless you specifically know what you're looking for. However it may still stand out as a radio source.

The simplest option to disguise this is to use directional antenna. Usable both for broadcast and reception, you aim source at receiver and keep the power down to the minimum required. As long as you don't accidentally aim at the eavesdroppers they shouldn't get anything.

There's a big however here.

The technology level required to build a dyson sphere, let alone make it stay in the right place relative to the star once built, is high enough that they shouldn't be using radio. For that matter they shouldn't be using anything that's still limited by the speed of light.

Added to that, the 1400 light years distance means 1400 years before they could possibly pick up the signal. A narrow window of opportunity, then probably 100+ years before they can do anything about it. How people in 1500 years deal with a couple of visitors isn't really your problem! If it hasn't been discovered by then, you're probably alone in the galaxy.

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  • $\begingroup$ So like this question asks we can safely consider the possibility that at dyson sphere technology levels communication methods that we can conceive of will no longer be used? For radio communication detection, does it mean that effectively it's impossible to tell any radio signal from background noise unless you know the patterns to look out for? Meaning humans are limited by their knowledge and searches are only for patterns that we know of ourselves? $\endgroup$
    – SapphireFlame
    Dec 13, 2019 at 8:37
  • $\begingroup$ @SapphireFlame, the current level of digital encryption is remarkably hard to tell from background, so that's a given. You're free to speculate in your own world, but it's reasonable to assume there will be drastic changes to the technology for that sort of civilisation. Yes, we're limited to patterns we recognise, which probably means we're searching for civilisations with a very narrow technological range. $\endgroup$
    – Separatrix
    Dec 13, 2019 at 8:42
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    $\begingroup$ I'm curious why you think that the speed of light shouldn't be a limit for a civilisation that has a Dyson sphere? I don't see any obvious connection between the two, nothing about a Dyson sphere invalidates the reasons why FTL is commonly considered impossible. $\endgroup$
    – S. Move
    Dec 13, 2019 at 9:12
  • $\begingroup$ @S.Move dyson spheres are also commonly considered impossible ;) $\endgroup$
    – Separatrix
    Dec 13, 2019 at 9:13
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    $\begingroup$ Not really, or at least they are in vastly separate cathegories of implausibility. FTL leads to violent contradictions with our model of physics. Dyson spheres are just spheres. There is nothing non-physical about them (as long as you make reasonable demands for their composition like not being a passive and massive single structure). A Dyson swarm of satellites surrounding a star, or a very light Dyson bubble stabilized by radiation pressure of the star or by active support similar to a launch loop are all quite reasonable from a strict laws of physics perspective. $\endgroup$
    – S. Move
    Dec 13, 2019 at 9:21
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Using quantum entanglement for communication should be uneavesdropable.

EDIT: As pointed out by @S.Move , quantum entanglement does not allow communication like that.

But I've got another idea, why not use wormholes to send data by standard means? For now we don't know any way to intercept anything which goes through wormhole.

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  • $\begingroup$ You may want to elaborate a bit on this. While quantum entanglement allows for communication that can in principle not be decoded by some man-in-the-middle naively it would still be just as visible as communication as normal radio broadcasts are. I agree that it opens up the possibility of creating communication that is even more indistinguishable from natural radiation sources. $\endgroup$
    – S. Move
    Dec 13, 2019 at 9:15
  • $\begingroup$ Why it would be visible? So far as I know, quantum entanglement communication wouldn't need any transmission. You have basically two connected particles, when you change spin of one, spin of second is also changed, regardless of how far it's, that's why there would be nothing between to be eavesdropped. $\endgroup$
    – Guy with jewels' names
    Dec 13, 2019 at 9:40
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    $\begingroup$ You cannot transmit any information over quantum entanglement itself. Changing the spin of one particle does not change that of it's entanglement partner but rather as long as the two are not interacted with their measurement outcomes are correlated, so if you measure one you know the outcome of a measurement of the other. This can be used to generate encryption keys that are in principle unknowable to an eavesdropper or transmit quantum states over a classical channel - but you still need a classical channel for the actual communication. $\endgroup$
    – S. Move
    Dec 13, 2019 at 9:43
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    $\begingroup$ Yeah, you're right, it's not interacting with measurement thought, but with spin itself which brake entanglement, at least according to that: forbes.com/sites/chadorzel/2016/05/04/… $\endgroup$
    – Guy with jewels' names
    Dec 13, 2019 at 10:04
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If part of the Dyson sphere was intentionally left open at the point facing the observing planet then there would be no dimming. If directional sources were used for communication like laser beams and these were not pointed at the observers then there would be no communications to detect either.

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  • $\begingroup$ I used a specific observer in the scenario but it would be great if the disguise is non-directional, as in it could be applied to observers from any direction, without affecting the construction of the sphere itself. $\endgroup$
    – SapphireFlame
    Dec 14, 2019 at 0:22

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