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This is an impossible scenario, however I would like a physical explanation of what should happen if such a scenario occurred.

Considering that:

  • Light speed in vacuum is 299792458m/s.
  • I have an hypothetical wand of 299792458m.
  • The wand is almost mass less but not zero (assume that moving the wand is has much difficult as moving a branch).
  • Two planets are involved in the scenario they are 299792458.1m apart.
  • You can consider the planet are static.
  • I am able to move the wand of 0.1m in 0.1s.
  • You can omit the distance from me to the ground.
  • Consider everything is in vacuum.

Let's say that I move the wand 0.1m toward the other planet, please explain what should see an observer that can see the full wand, and what will another observer on this other planet witness.

My hypothesis

(I am of course not a physicist). I think the wand would get distorted a bit like a rope when kids play the snake game. Therefore speed of light would still be respected since the wave would move along all the wand and reaching the observer on the other planet after 1.10000000033s.

Am I wrong?

Greg7000
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1 Answers1

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You are sort of right! The key is that disturbances in a solid medium (such as a displacement) generally propagate at the speed of sound in the medium. The speed of sound is guaranteed to be slower than the speed of light in vacuum. So when you push the rod, that force will be conveyed much slower than the speed of light, thus preserving relativity. The other end won’t move for a while after your push! You would have been better off just sending a light signal like everyone else.

Gilbert
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  • Thx for the answer I was mainly intrigue by what would happen in a solid medium. That's why I did not target the other planer with a laser beam. – Greg7000 Feb 24 '20 at 15:23