[curiosity (OP)]

I've researched a bit on sound and light waves, however my key question is still not answered.

Is there any kind of light or sound wave, or any other form of man-made anything, that can travel through the entire Earth?

I am Curiosity.

[Dr B]

Do you mean a man made source being input at one position and being received at any point on the earths surface?

I think the answer is no regarding through the Earth.  This is because waves would refract on their journey and prevent the wave reaching the point directly on the other side.  

I think the answer is theoretically yes for a surface wave spreading around the Earth but frictional effects of shaking all that rock makes it a practical no!

Dr B
Istanbul

[daveshorts]

Sound waves can travel through the whole earth, this is how we have some idea of what is down there, but seismologists use the vibrations from earthquakes that occur naturally rather than man made explosions, although vibrations caused by underground nuclear tests will probably penetrate pretty deep. Dr B is right that the waves are refracted all over the place, but with enough earthquakes you can build some sort of  picture of what is going on down there.

Some very low frequency radio waves (as in 30-300Hz) can be detected all over the surface of the earth, they use them to talk to submarines, I am not sure if they go straight through or around the edge, or if it is actually meaningful to ask that question as the wavelength is comparable to the size of the earth.

The other things that can penetrate the earth quite easily are neutrinos, which are produced by nuclear reactions and will pass through without even noticing. They are not much use for imaging though as they interact with matter so weakly that the detectors needed tend to be the size of cathederals!

[Dr B]

Agreed, you would need multiple sources to get complete coverage through the Earth.

Interested to know more about the vlf radio waves ...

Dr B
Istanbul

[daveshorts]

The data rate for elf is extreemly low - I think considerably less than one bit per second, but it means that base can send a message to the missile submarines which says 'come nearer to the surface' and then the actual message can be sent, by more conventional means - satellite or shortwave or whatever.

reading:
http://jproc.ca/radiostor/vlfelf.html
the data rate is about 3 characters in 15mins!

[curiosity (OP)]

Thanks for all the responses. Basically I'm working on a project to communicate with something on the other side of the Earth without using Satellites or multiple base stations of contact. In other words, a straight-shot form of communication through the Earth from one point to another.

Not sure if it's possible, but it was an idea that popped in my head and decided to make a project of it.

On the note of Satellite communication, anyone know if there's public satellites that can be used by anyone? I'd like to learn more about Satellite communication as well.

I am Curiosity.

[daveshorts]

Isn't the traditional means to use shortwave radio, although it is very dependent on ionospheric weather...

 Be careful if you start using ELF as various governments probably won't want you accidently telling their submarines to do stuff - a mate of mine has a story that runs along similar lines and ended with a visit by a few very polite gentlemen in suits who suggested that he did it a different way...

[tweener]

I can answer the question on VLF/ELF radio waves.  They do not go through the earth, but are propagated between the earth's surface and the ionosphere.  Because they are such long wavelengths they will not be absorbed by the earth or the atmosphere very effectively and they will thus be detectable anywhere on the surface of the earth.  And yes, the antennas are huge as the transmitting wires need to be at least a half wavelength, longer if possible.  The data rate is very low because the available bandwidth is very narrow - you are using a carrier that is only a few hertz, so the modulation bandwidth cannot be more than a few percent of this value at the most.

And I fully agree that you need to check out the legal and licensing ramifications BEFORE you start transmitting.  ALL radio frequencies are controlled in some fashion and most are monitored fairly closely.  If you start transmitting in a protected band, you will indeed receive a "suggestion" to communicate a different way.

----
John - The Eternal Pessimist.

[Soul Surfer]

The only narrow beam communications that can go straight through the earth that I can think of are neutrinos and there is an experiment going ahead using a beam of neutrinos going through the earth but this is more to do with measuring if neutrinos flip between one sort and another as they travel.  The bandwith of a device like this if it was used for communication is extremely low  probably in bits per day!

Underground nuclear explosions create sound waves that can be detected all over the world  so that gives you an idea of the sort of power levels you would have to use.

Agree radio out for through the earth communications but short wave radio will work well between two locations at specific times of day for most parts of the sunspot cycle.  G-1 theory I am supprised at you calling Top Band  (160m)  VLF when it is clearly MF lying beeween the medium wave broadcast band and the start of short wave proper at around 50m.

Another interesting long range radio communication technique is sporadic meteor scatter using VHF where channels open briefly for a few seconds because of the ionised meteor trails and burst communication between stations is possible

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