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Imagine an advanced civilization which can manipulate gravity like we manipulate electromagnetic radiation. Could they already be using gravitational waves for data transmission across different galaxies?

Unlike electromagnetic radiation which can be shielded, gravitational waves appear to travel through any medium at speed of light. Perhaps this explains why SETI is a wasted effort?

EDIT: didn't realize there was a similar question already raised: Would it be possible to transmit information through gravitational waves?

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javaPhobic
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    You are answering your question yourself by assuming that advanced civilisation can manipulate it. The tech only required is to detect weakest GW , since generating strong detectable waves require lot of energy. – Anubhav Goel Feb 16 '16 at 04:53
  • If I imagine that, then the result is an empty set. There are no such civilizations. I do agree with you that SETI is a wasted effort, though. Not even mankind would use the SETI frequencies if we really wanted to communicate. – CuriousOne Feb 16 '16 at 05:24
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    @JohnForkosh: Does your cell phone use AM radio to set off the ring tone? Of course not. The theory of optimal communication over electromagnetic waves is worked out in quite some detail these days and it is rather straight forward. SETI is basically a hail mary pass of physicists who know better. These guys aren't stupid... but sometimes the social animal side of things ($) gets in the way of doing things right and that's where I would put the current status of search for intelligent life in the universe. The professional side is the exoplanet searches with which SETI will merge soon enough. – CuriousOne Feb 16 '16 at 07:09
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    Just for interest, Larry Niven wrote a short story about an alien device, found on Mars, that turns out to be exactly this - a GW radio set. It contained a micro black hole that was made to oscillate thus producing modulated gravity waves. – Oscar Bravo Feb 16 '16 at 07:43
  • Gravitational waves travel through any medium at the speed of light? Well, mostly accurate, but do you realize that the speed of light changes in each medium? – Mooing Duck Feb 17 '16 at 00:46
  • Also, I suddenly find myself very skeptical that electromagnetic waves can be shielded, but gravitational waves can't. I don't know enough about physics to say you're wrong though. – Mooing Duck Feb 17 '16 at 00:47
  • @CuriousOne On the other hand, your cell phone isn't trying to communicate over intergalactic or interstellar distances, with an entire universe of stuff happening and generating ubiquitous noise. Consider the following: you're in a really noisy club. You can barely hear the person next to you talking. Walking across the room isn't feasible. How do you get the attention of someone across the room (a server/bartender, perhaps)? You sure don't speak to them, even though that's usually the efficient way. You use something less likely to be lost in the noise: waving your hands, say. – zibadawa timmy Feb 17 '16 at 02:36
  • @zibadawatimmy: I would stay where I am and use my cell phone and call the person on exactly the same frequency on which I will be talking to them. You are over-thinking the communication problem. Nobody is desperate for your attention at the cost of wasting energy. If anybody wants to communicate to us, they will do so on a good frequency knowing that we are smart enough to figure out how to build a transceiver for that one frequency. It's not that hard, either, just a lot more costly than SETI, which is the main reason why it hasn't happened, yet. – CuriousOne Feb 17 '16 at 02:43
  • @CuriousOne In this analogy "using your phone" is meant to be distinct from "talking to him", which was implicitly meant to involve nothing but your mouthy bits (and necessary systems for vocalizing). But one way or another, I suppose your complaint boils down to: SETI is checking for guys waving their hands around, when we should be checking for guys trying to call us on their cell phones. – zibadawa timmy Feb 17 '16 at 03:28
  • @zibadawatimmy: That's the point... nobody with a phone will wave their hands around or start a signal fire. The cool thing about this is... in this case the phone is the same equipment (a telescope) that one would use to see if anybody is at home, at all. Keep watching the rapid progress in exoplanet search, then imaging and, finally... optical communication. – CuriousOne Feb 17 '16 at 04:23
  • I wonder whether you could have "gravitational noise canceling" (on a stellar scale). Acoustic noise cancellation profits from the low speed of sound; the device is able to detect sound, compute anti-sound and control a forward-lying membrane in time to arrange the canceling motion. Canceling a gravitational wave would not be possible that way; it would have to be a self-canceling setup driven by the wave proper, much like vibration dampeners on archery bows, or earth-quake dampeners in Tokio skyscrapers. – Peter - Reinstate Monica Feb 17 '16 at 10:50
  • @CuriousOne, probably true in general. But I do know a deaf person who used sign language to someone in the bleachers on the other side of a basketball court during a game. :-) – WGroleau Jan 13 '20 at 18:41

3 Answers3

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We can already manipulate gravity like we manipulate electromagnetic waves. Tie something at the end of a rope and swing it around your head: you're now generating gravitational waves. And yes, you can transmit information with gravitational waves in the same way you can transmit information with any other modulable wave.

The problem is not generating waves, it's generating strong enough waves; the waves you generate by swinging something around are completely undetectable by any technology we have the resources or engineering capacity to build, and so they'd be useless for transmitting readable information to someone else. It would be like trying to contact someone far away by whispering at them.

Asher
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    Good answer, however what i meant by manipulate is generating very strong gravitational waves that are detectable across galaxies. We are not there yet obviously. – javaPhobic Feb 16 '16 at 04:45
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    The power scale is just too high. The event LIGO detected released three solar masses worth of energy, and still only produced a distortion about 1/1000th the width of a proton here. And that was at a distance of only a few percent of the radius of the visible universe. Somehow I doubt any civilization will ever use power on that scale to generate gravitational waves when electromagnetic or kinetic methods would be much more effective. – Asher Feb 16 '16 at 05:41
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    @javaphobic: If general relativity is correct and complete (at the level of classical waves), then there is no chance that we will ever communicate with gravitational waves. The coupling of mass to spacetime is just too small. In another thread I estimated based on an example from Misner, Thorne, Wheeler chapter 36 that a 400+ ton steel bar rotating at almost 300rpm emits a gravitational wave with a flux equivalent to one visible photon per three centuries... that's just not good enough for anything. Can you see the escape clause in that statement? :-) – CuriousOne Feb 16 '16 at 07:17
  • @CuriousOne Equivalent in detectability or equivalent in energy? – JiK Feb 16 '16 at 10:38
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    @JiK: Equivalent in total power. There is no known technology that could even detect a single photon in 300 years on top of background noise... let alone a gravitational wave of equivalent power. There is a remote possibility that torsion needs to be added to general relativity and I have heard in a talk some twenty years ago that in that case gravity might couple strongly to spins rotating at gamma-ray frequencies (at least in some naive models)... but I have a feeling that the resulting modification to the standard model is probably already ruled out by LHC. – CuriousOne Feb 16 '16 at 10:45
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Can gravitational waves be used to transfer information?

Yes, the two black holes did just that.

The waveform held information allowing scientists to

  • estimate their masses, including error bars
  • estimate their location in the sky (roughly)
  • estimate their distance and the time of the event

All of this information is part of the exact increase/decrease of the detected wave amplitude and frequency in conjunction with the matching data of the sister detector.

If you want to know more on the general issue, I suggest topics such as

  • fourier transformation
  • signal encoding theory
  • modulation of waves (acoustic, electromagnetic)

Can aliens use GWs to transport information? If they know how to carefully swing black holes around, then yes. But I'd be skeptical. It's so much easier to use electromagnetic waves by carefully swinging electrons around. Or carve something in stone and send by snail mail, like the Voyagers do :-)

Jens
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In theory, yes. The recent observation of gravitational waves is nothing but information transfer via gravitational waves captured by us, humans. The information conveyed is not an email (sorry gmail) but it tells us that two black holes merged. However, whether GW or EM waves, the source has to be unimaginably powerful to communicate over galactic distances. Also, because GW can not be shielded, therefore, they can not be pointed in a particular direction like we can do with EM waves. So, the source has to be even more powerful. But if a civilization is that advanced, it may have figured out some other more practical means of communication.

anukul
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kpv
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    More practical means of communication... like... electromagnetic waves? :-) – CuriousOne Feb 16 '16 at 05:22
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    Probably yes, as they can be boosted on the way. May be some sort of quantum communication, extra dimensional communication... worm holes.. Should not rule out new research, which we can not even think of. – kpv Feb 16 '16 at 05:38
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    Quantum communication uses electromagnetic waves. One can do very short distance baryonic quantum communication, but it wouldn't be very practical. All I am saying is that I am so surprised that people are asking for something "better" than electromagnetic waves, even though the universe has communicated its state at 300,000 years after the big bang to us trough them... that's really, really far! – CuriousOne Feb 16 '16 at 05:42
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    I agree, for our civilization at the moment. GW might add few more hundred years if we are lucky/successful. What I meant was that it is possible for such an advanced civilization to figure out some kind of FTL transmission including some that I mentioned, and others that we may not be able to imagine today. – kpv Feb 16 '16 at 05:49
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    I mean FTL without violating relativity -:) – kpv Feb 16 '16 at 05:56
  • No problem, just borrow some exotic matter from your friendly alien neighbor. :-) – CuriousOne Feb 16 '16 at 06:22
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    I will, once I get a quantum entanglement experiment equipment here on earth, and have verified my theory. Then I will have something as a return gift for him -:). SE warning me to move it to chat.. – kpv Feb 16 '16 at 06:31
  • The quickest way to check if one will receive the Nobel Price for the development of a time machine is by using the time machine... in case that the result is negative, one can always buy a few lottery tickets with next week's numbers and throw a party... – CuriousOne Feb 16 '16 at 06:34