Information transfer that is faster than c?

[Puma24]

If I were to have some material, that was rigid, and was also say, 300,000,000 metres long. If I were to poke it at one end, would another observer see an instantaneous response at the other end? Ie, would the information I put into one end of the material travel faster than the speed of light to the other end?

I guess it woudln't be so easy. I assume that poking it counts as a sort of pressure wave that would have to be transferred through all the electrostatic processes along the way, which would be limited by c? Then I guess, can you argue that there is such thing as an incompressible material? (at least in regards to the force of my jabbing finger)

 

[Pengwuino]

I guess it woudln't be so easy. I assume that poking it counts as a sort of pressure wave that would have to be transferred through all the electrostatic processes along the way, which would be limited by c? Then I guess, can you argue that there is such thing as an incompressible material? (at least in regards to the force of my jabbing finger)

Correct, the electromagnetic processes have to carry the information the whole way, and no, by your previous thought process, you can't have an incompressible material.

 

[Puma24]

Alright then. So if we had the power to observe the material, would we see the side I poke move slightly, and then a sort of compression wave propagate through the material (like you could imagine a sound wave compressing air), warping the dimensions as it goes? Do you know if the speed of this wave has a speed that is constant, or is a consequence of the materials properties, like density I guess?

 

[Hurkyl]

and then a sort of compression wave propagate through the material (like you could imagine a sound wave compressing air),

I believe it literally is a sound wave.

 

[HallsofIvy]

I believe it literally is a sound wave.

Yes. And the speed at which the wave propogates is the speed of sound in that material.