[ExI] Is this FTL Communication?

[John Clark]

On Feb 21, 2010, at 9:19 PM, Will Steinberg wrote:

> Imagine we build a very, very long, very, very solid rod.  One end of the rod is located very, very far away.  Will pushing one one end of the rod effect an immediate response on the other?

If the rod was infinitely rigid then yes it would enable faster than light communication, but unfortunately infinite rigidity is not possible; the atoms in the rod must be held together by some force and even the strong nuclear force, the most powerful known, is not infinitely strong.

If I push at one end of a rod when the other distant end will move depends on the speed of sound of the material in the rod and on its density. At the same density the more rigid the material the faster the speed of sound. In diamond the speed of sound is 12,000 meters per second and that's 35 times what it is in air and is the fastest known, but light moves at 300,000,000 meters per second.

 John K Clark

 



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