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I'm making a hard-ish sci-fi universe where humans colonized nearby star systems and found not one but two civilizations in Alpha Centauri, each at home on a planet orbiting one of the two main stars. These aliens are slightly less advanced than humans. Both species have fusion powered spaceships that can cross distances between planets in a fairly short time (think Epstein drive from The Expanse) and communicate using radio. Year is 3620.

Meeting these aliens caught humans completely by surprise and my question is - is there a material that can distort signals so they don't get recognized by SETI but is also transparent (as we can see the Alpha Centauri system)?

Idea is that there is a gas/rock/ice/debris/whatever field between us and Alpha Centauri that could distort any signals that would give away the civilization, like radio, but letting visible, IR ... pass through. How could this be?

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  • $\begingroup$ Idea is that there is a asteroid/debris field between us and Alpha Centauri that could form asteroids? Typo in there somewhere? $\endgroup$ – nzaman Dec 4 '18 at 11:31
  • $\begingroup$ "500yrs behind humans" means what exactly? Is their tech at the level of the 1500s, 1600s, 1700s, 1800s, early 1900s? Then there were no signals to be detected. $\endgroup$ – AlexP Dec 4 '18 at 11:35
  • $\begingroup$ Two points at least that you need to fix to make this question clear: the last sentence is the first, and "500 years behind human when humans have fusion powered starships" gives no information to understand their tech level, since it's a technology we don't have. $\endgroup$ – L.Dutch Dec 4 '18 at 11:37
  • $\begingroup$ @L.Dutch I disagree that this is unclear. The question is: "Is there a naturally occurring material that can block radio signals without interfering with starlight?" The rest of the post pertains to the OP's specific environment, but isn't necessary to answer the question. Why did you hammer this shut? $\endgroup$ – Frostfyre Dec 4 '18 at 13:44
  • $\begingroup$ alien technology somewhat less than human, circa 3120 would be my guess. clearly both civilizations are advanced relative to today. the last sentence makes no sense. what is clear is you are looking for a menas of cloaking our presence from detection by these only slightly less techonologically sophisticated civilizations. $\endgroup$ – theRiley Dec 4 '18 at 17:23
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Space Chaff

Radar is slightly shorter wavelength than radio waves but the blocking principles apply. Chaff is used by the military to obscure targets from radar - for example a plane targeted by radar will release chaff to blur its outline and allow it to escape. Chaff as used by the military is made of lightweight metallized strips.

https://en.wikipedia.org/wiki/Radar_jamming_and_deception

Mechanical jamming is caused by devices which reflect or re-reflect radar energy back to the radar to produce false target returns on the operator's scope. Mechanical jamming devices include chaff, corner reflectors, and decoys. Chaff is made of different length metallic strips, which reflect different frequencies, so as to create a large area of false returns in which a real contact would be difficult to detect. Modern chaff is usually aluminum coated glass fibers of various lengths. Their extremely low weight and small size allows them to form a dense, long lasting cloud of interference. This cloud is unfortunately only effective in the range cell that it occupies. The slow movement of the chaff (compared to a flying target) makes it easily discriminated, based on the lacking Doppler shift. Ships on the other hand can benefit greatly from a slow moving chaff cloud. The cloud is released within the resolution cell of the ship, and moves with the wind in one direction. The ship then escapes in another direction.

For your purposes, your space chaff need not be lightweight because it is floating around in space. A field of angular metallic crystals would be a way to achieve this. I think ice can block radio waves. In any case, radio waves entering this field would echo crystal to crystal, blurring to incomprehensibility. It would need to be big to obscure a whole civilization - perhaps in a ring around the star or even a (more densely packed!) sphere encompassing their whole solar system in the way the Oort cloud encompasses ours.

https://space-facts.com/oort-cloud/

oort cloud

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  • $\begingroup$ the problem is that we'd already know it if something like this existed. $\endgroup$ – ths Dec 4 '18 at 23:40
  • $\begingroup$ @ths - I am not sure. If artificial radiowaves on the interior were scattered and rescattered such that their artificial nature was no longer evident, the radio emissions from something like this might just look like the random natural radio emissions from everything else in the universe. $\endgroup$ – Willk Dec 4 '18 at 23:57
  • $\begingroup$ even if we did know about it, it would still conceal the civilization on the other side until we sent a spacecraft around it $\endgroup$ – PecaWolf Dec 6 '18 at 13:59
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Asteroid material that can cause signal distortion.

Antimatter clusters at the Heliopause

Physicists have long puzzled why there is so little apparent antimatter in the universe - surely equal ammounts of matter and anti-matter should have been created at the big bang yes?

It turns out that in the time of your story some more evidence has been found that points towards a solution:

  • The Sun creates a solar wind of charged particles flowing outward in a three dimensional bubble. What stops this expanding infinitley is that every other star is doing the same so these bubbles push up against each other's solar wind at what is known as the heliopause.

enter image description here

  • There is a net flow of wind out from the centre of the galaxy's supermassive black hole's accretion disk is generating it's own wind.

  • It turns out that the buffeting at this edge creates swirls and eddies, some of which fade with time, others of which are permanent - still others suddenly pop into existence and are a hazard to navigation.

  • It also turns out that these eddies have a hidden secret - dense clusters of antimatter.

  • These clusters manifest as miniature antinutron stars (no more than a Km across) that have super-strong and chaotic magnetic fields that generate powerfull electromagnetic interference all the way from the milimetre range to long wave radio.

  • This in itself is not a problem in viewing the majority of the universe, but the trouble is, the bigest of these interfering eddies is almost in line of sight between Alpha Centauri and the solar system, and completley blocks long range communication

  • The obvious solution of placing a relay satellite off-axis at the heliopause won't work because of the instability of the ever shifting patterns in the interstellar winds - any such satellite, would incur a prohibitivley high fuel cost to stop it being pushed out of the galaxy altogether - if it weren't destroyed by a vortex popping into existence on top of it.

  • In extremis, a signal could be sent surely? Just increase the power! - It turns out that this is true but that the power required would be in the exawatt range (10^18W) - simply couldn't be generated for any length of time. (Compare current world annual electricity consumption approx 21 petawatts about 1 fiftieth of an exawatt.)

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  • $\begingroup$ Thank you for the amazing answer. However, I'm accepting a different one for storytelling reasons $\endgroup$ – PecaWolf Dec 5 '18 at 12:55
  • $\begingroup$ @PecaWolf thanks for the approbation, Willick's answer was always the less farfetched and unnecessarily elaborate. :) $\endgroup$ – Agrajag Dec 5 '18 at 13:15

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