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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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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 at 4:53
    
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 at 5:24
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@CuriousOne The seti frequencies aren't meant to communicate, per se. They're "hailing frequencies" -- it's guessed they'd be used by a civilization meaning to announce its presence to anybody listening. Subsequent communication of detailed information would be different. But, anyway, I agree it's likely a wasted effort, but only because it's very unlikely anybody's out there. Nevertheless, the risk (cost) is pretty low, while the benefits of success would be spectacularly high (unless they ate us for lunch), so why not? – John Forkosh Feb 16 at 6:58
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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 at 7:09
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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. – Owen Boyle Feb 16 at 7:43

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.

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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 at 4:45
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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 at 5:41
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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 at 7:17
    
@CuriousOne Equivalent in detectability or equivalent in energy? – JiK Feb 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 at 10:45

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 :-)

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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.

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More practical means of communication... like... electromagnetic waves? :-) – CuriousOne Feb 16 at 5:22
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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 at 5:38
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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 at 5:42
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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 at 5:49
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I mean FTL without violating relativity -:) – kpv Feb 16 at 5:56

protected by Qmechanic Feb 16 at 21:23

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