### Question

If you have a very long and rigid pole and have an observer on each end, if one of them pushes the pole how soon will the other one feel it? Can this response time be shorter the time it would take light to travel the length of the pole?

The rigidity of any pole depends on the material from which it is made, but there is no material that is infinitely rigid. A push on one end of a pole only appears to be transmitted instantaneously to the other end because of its relatively short length compared to the speed of transmission. Each atom must influence its neighbor along the pole via electromagnetic force, which in turn is carried by (guess what?) 'light' photons!

So yes, the speed at which a push on one end of the rod travels to the other end is subject to the same universal speed limit, the speed of light, as any other physical phenomenon. Therefore, you could NOT use a 'rigid' pole to transmit signals faster than light to another observer.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

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### Science Quote

'As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality.'

Albert Einstein
(1879-1955)