## Another data across long distances (nearly) instantly theory

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Luppoewagan
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### Another data across long distances (nearly) instantly theory

Imagine a very long string or cable that is attached to two stations very far from each other (maybe a light year, but doesn't matter.)

Now if someone at station 1 pulled on the cable, someone at station 2 would notice it instantly, would they not? (assuming it does not stretch)
Could this be used to transmit data faster than light?

ATCG
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### Re: Another data across long distances (nearly) instantly theory

Here is one of the threads discussing why this doesn't work.
"The age of the universe is 100 billion, if the units are dog years." - Sean Carroll

Gammashield
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### Re: Another data across long distances (nearly) instantly theory

That argment isn't giving a data transmission method sadly. Rather, what you've got there is a quick thought experiment that shows there's no such thing as a 'perfectly rigid' object. A side consequence of special relativity is that *any* material, unobtanium or otherwise, has some minimum compressability/extendability dictated by the speed of light. Compression waves in an object (aka, sound, or tugs/pushes) have a theoretical cap speed of the speed of light.

As a practical matter, of course, that speed is usually much, much lower.

Mettra
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### Re: Another data across long distances (nearly) instantly theory

*Chime in for agreement*

When you push that rod, what you are doing is pressing the atoms on the outside of it into the atoms right beside them. Those in turn press the atoms next in line and so on until you get to the end of the rod. Atoms cannot move faster than (or as fast as) light. This explanation is usually simpler to understand than Young's modulus and talks of rigidity.
zenten wrote:Maybe I can find a colouring book to explain it to you or something.

TheCoelacanth
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### Re: Another data across long distances (nearly) instantly theory

Good luck making the unstretchable cable.

taby
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### Re: Another data across long distances (nearly) instantly theory

The point here I think is that the interactions within the rod are heat conduction (also known as momentum, or energy flux), pressure (aka momentum flux), viscosity (aka momentum diffusion), and gravitation.

Since heat conduction is performed by photons, it's seen that the maximum rate that a change in temperature may transfer through the rod is c metres per second (according to special relativity). Photons also carry pressure, limiting the transfer of pressure to a rate of v = c. Likewise for the transfer of viscosity.

That said, even when the rod is modeled as a pressureless perfect fluid (no momentum or any of its derivatives), and gravitation is the only interaction worth considering, changes in the gravitational field still only transfer at v = c (according to general relativity).

So really, there is no way for change to transfer through the rod at a velocity faster than c (according to modern relativity).