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As John Micheal Godier states in this video: SETI and Alien Quantum Communications.

Alien civilizations might use different methods of communication beyond radio for several reasons. J.M.G uses quantum communication as an example due to the encryption methods inherent with it. This led me to ponder about other communication methods, one of them being gravitational waves.

Now, barring the practicality and possibility of actually sending and detecting transmissible data as gravitational waves; could anything stop these waves? As these waves move at the speed of light, they fill the same niche as electromagnetic communication and unlike radio waves, are not absorbed or scattered by cloud dusts or intergalactic media, for which an advanced space faring civilization would likely want to avoid. This last point in dependant If anything can actually stop them. From my understanding, Gravitational waves are just fluctuation and stretching of the fabric of spacetime, which permeates everything, so it seems likely to me that nothing much could stop them. Then again, I could be wrong, so I ask this question.

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  • $\begingroup$ Gravitational waves can certainly be absorbed, otherwise we couldn't detect them. In principle, just about anything can absorb energy from passing gravitational waves. It's just that gravity is a very weak force so the amount you absorb is very small. $\endgroup$
    – knzhou
    Dec 29, 2021 at 2:21
  • $\begingroup$ Well, we do not use energy absorption to detect gravitational waves. LIGO uses a perpendicular set of lasers to detect gravitational waves. The minute distortion in space causes slight, yet detectable differences in the emission and detecting of laser light in the facilities mirrors. Wonders of modern technology. $\endgroup$
    – C-Consciousness
    Dec 29, 2021 at 4:02
  • $\begingroup$ @C-Consciousness: I believe that gravitational waves cause an oscillating strain in matter, which I assume creates heat, thus absorbing some of the energy from the waves. Is this true? If so, then I think knzhou was implying that detection is not possible without an energy absorption of some sort. The following answer agrees that matter attenuates gravitational waves. astronomy.stackexchange.com/a/28550/20370 $\endgroup$
    – James
    Dec 29, 2021 at 14:13

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Interesting thought about using gravitational waves to communicate - I find it to be exceedingly unlikely, but I like the creativity. As to whether or not they could be blocked, not really - when covering gravitational waves in a general relativity course, they are generally non-dissipative (this is the only case I am familiar with). This is essentially because gravity couples so weakly to matter (say compared to the electromagnetic force, which dissipates much faster in materials). For similar reasons, they experience much weaker scattering. If I recall correctly, they will be dissipative at higher orders (usually one only covers the first order case first time round).

Interestingly, I believe a few years ago someone actually found exact oscillating solutions to the Einstein Field Equations, but take that with a pinch of salt, because I can't find the source on a cursory search. As to why they would be a poor method of communication, just think about how hard we find it to detect them from black holes these days! LIGO really is a masterpiece of engineering - to use gravitational waves you would have to be able to move very heavy objects in a predictable manner, and detect waves which would should be orders of magnitudes smaller than those at LIGO. Still, like I said, points for creativity.

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  • $\begingroup$ Thank you for your insight and comments. I agree, using gravity waves to communicate seems nigh impossible, without invoking advanced technology and the "Aliens of the Gaps" scenario. I any case, I think you have opened a whole separate can of worms with the oscillating solutions of the GR equations; a rabbit hole I will now regrettably dive into. Thank you once again! $\endgroup$
    – C-Consciousness
    Dec 29, 2021 at 4:04
  • $\begingroup$ Exact solutions for gravitational waves in GR have been around since (at least) the 1950s. (And no they do not show any dissipation) $\endgroup$
    – TimRias
    Dec 31, 2021 at 0:25

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