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Related: About this forumCan I Send a Signal Faster than Light by Pushing a Rigid Rod ? (article)
https://www.physicsforums.com/insights/can-i-send-a-signal-faster-than-light-by-pushing-a-rigid-rod/One common proposal for achieving faster than light communication is to use a long perfectly rigid object and mechanically send signals to the other end by pushing, pulling, or tapping it. For instance; a hypothetical rigid rod linking two people several lightyears away. The fundamental idea is that when one end is moved the other end is disturbed instantaneously.
However, there is no such thing as a perfectly rigid rod: a mechanical disturbance at one end of any material can only move through the material at a finite speed. This speed is called the speed of sound in that material.
High stiffness materials like metal have a very high speed of sound and low stiffness materials like jello or air have a very low speed of sound. When you push on something made of jello, you can easily see that the disturbance propagates at a finite speed. When you push on something like metal, it is not so easy to see visually, but the disturbance still propagates at the finite speed of sound in the metal. (see e.g. https://www.physicsforums.com/showthread.php?p=4414855#post4414855)
The speed of sound in diamond is about 12000 m/s which is about 25 thousand times slower than the speed of light (299792458 m/s). But what about some hypothetical unobtainium? Why couldnt unobtainiums speed of sound be faster than the speed of light? The answer is that all materials, even unobtainium, are held together by electromagnetic forces at the molecular level. When one molecule moves then the change in its electromagnetic field propagates to its neighboring molecule at the speed of light. So even in principle it is not possible for any material to have a speed of sound faster than the speed of light.
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Can I Send a Signal Faster than Light by Pushing a Rigid Rod ? (article) (Original Post)
steve2470
Aug 2017
OP
Girard442
(6,088 posts)1. :) @ "Unobtanium"
Also known as "plotdeviceium."
marylandblue
(12,344 posts)3. If the material is unobtainium
Wouldn't it be held together by the unimaginable force moving at unbelievable speeds faster than the speed light?
GetRidOfThem
(869 posts)4. Thank you!
That post was a joy to read!
Warren DeMontague
(80,708 posts)5. ...
Cicada
(4,533 posts)6. Electrician bumper:186000 miles per sec. not just a good idea, it's the law