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First thing I've been wondering is how the gravitational field is emitted. Matter emits gravitational waves, and I guess that those waves travel at around the speed of light. If that's not the case, please direct me to something that explains that.
For now I'll assume that this emits a waves that travels at the speed of light.

Now those waves are emitted constantly without the apparent need of energy. Just the mass being there is enough to emit those waves, and the mass itself isn't consumed by the emission of gravitational waves. Again that's my assumption, please tell me if I'm wrong.

Now if we would be able to modulate the mass of an object, we would be able to modulate the gravitational waves this object emits. Hence we would be able to transmit information through those waves, if of course we'd have a device that detects gravitational waves with enough sensitivity.

Those waves would be transmitted at no cost, because the waves are emitted by the mass. The only cost of this transmission would be the "mass modulator", which has yet to be invented and which would require energy. However the actual transmission doesn't require energy, and the gravitational waves are harmless, unlike the EM ones.

So here comes my question (as in the title): would it be possible somehow to use the gravitational waves to transmit information?

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This question is quite speculative, since there is no direct evidence to support their existence. If this evidence exists, you should operate with gravitons rather than gravitational waves. In my opinion, it's not right to think about Gravitational waves as we think about electromagnetic. Effect of a gravitational wave is so small, and only the largest cosmic events are likely to generate detectable gravitational waves. –  Sigrlami Nov 10 '12 at 15:44
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Your statement about the strength of the waves implies that we need an enormous event that creates a massive amount of gravitational waves to detect it. I would say that a very sensitive detector would be another solution :-) –  Benoit Duffez Nov 10 '12 at 23:07

2 Answers 2

up vote 6 down vote accepted

First it's important to note that gravitational waves do require energy to produce. A good example of this is a binary pulsar, where the emission of gravity waves carries energy away so the two pulsars spiral in towards each other and will eventually merge.

Having said this, it is theoretically possible to modulate a gravitational wave and use it to transmit information. You don't need a mass modulator, you just need something with a changing quadropole moment - the simplest example of this is a spinning dumbbell, and indeed this is basically what the binary pulsar system is. If you can change the rotation frequency you can frequency modulate the gravitational wave.

However gravitational waves are exceedingly hard to generate in the sense that very little of the energy of your system is carried away as gravitational waves. At the moment we can't even detect gravitational waves let alone generate them. It doesn't seem likely we'll ever use gravitational waves for transmitting information.

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OK, the spinning dumbbell is a great example! But it'd cost energy to make it spin and actually change its rotation speed. I see that those waves are really either low power or hard to detect with our current technology. My background is that I'm an engineer in a company that designs mobile phones, tablets and 3G dongles. I wondered if it would be even conceivable to create a transmission technology based off of gravitational waves. –  Benoit Duffez Nov 10 '12 at 16:53
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One thing I don't get in your answer is the fact that it does require energy to produce a gravitational wave. Imagine the moon-earth system. The moon "knows" the earth is here because of its gravitational field, and both are attracted to each other by the gravitational force. This force doesn't consume energy, does it? Inert matter emits a gravitational field without consuming anything, right? –  Benoit Duffez Nov 10 '12 at 16:55
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@Bicou: that's the difference between a static gravitational field and an oscillating one. Consider the analogy with radio waves. An electron produces a static electric field and this doesn't cost it any energy as long as the field remains static. But to transmit information you have to make the electron oscillate and that does take energy, which the radio waves carry away. Exactly the same applies to gravity. –  John Rennie Nov 11 '12 at 7:33
    
Whoa, great. Thanks a lot. –  Benoit Duffez Nov 11 '12 at 8:47

The JASONs put together a reasonably extensive report on the use of high frequency gravitational waves for anything practical (including communication) in 2008. In the abstract they state that

the following are infeasible in the foreseeable future: detection of the natural “relic” HFGW, which are reliably predicted to exist; or detection of artificial sources of HFGW. No foreign threat in HFGW is credible, including: Communication by means of HFGW; Object detection or imaging (by HFGW radar or tomography); Vehicle propulsion by HFGW; or any other practical use of HFGW.

Here HFGW stands for high frequency gravitational waves, which includes the frequencies necessary for useful communication.

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protected by Qmechanic Feb 9 '13 at 23:15

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