A thought experiment for surpassing the speed of light

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Discussion Overview

The discussion revolves around a thought experiment involving a long, inelastic rod used for communication via Morse code. Participants explore whether information can travel faster than the speed of light by extending the rod to communicate across vast distances, such as from Earth to another galaxy.

Discussion Character

  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant proposes that the information would travel faster than light, although acknowledges that it does not actually reach the destination.
  • Another participant argues that information will travel along the rod at the speed of sound in the material, which is significantly slower than the speed of light.
  • A different viewpoint emphasizes that no perfectly inelastic material exists, and thus the propagation of force would still be limited to the speed of sound.
  • Some participants challenge the notion that the displacement of the rod could propagate faster than sound, suggesting that the nature of the material and its properties must be considered.
  • One participant references a previous discussion on the same topic, indicating that this thought experiment is frequently revisited.
  • Another participant asserts that electromagnetic interactions limit the speed of any transmission through the rod, reinforcing the argument that nothing can transmit faster than light.

Areas of Agreement / Disagreement

Participants express differing views on the speed of information transmission through the rod, with no consensus reached on whether it could exceed the speed of light. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants note the limitations of the thought experiment, including assumptions about the rod's material properties and the nature of wave propagation. The discussion highlights the complexity of the underlying physics without reaching definitive conclusions.

Who May Find This Useful

This discussion may be of interest to those exploring concepts of information transmission, the properties of materials, and the implications of relativity in theoretical physics.

k4ff3
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You have a straight, light, hard, inelastic rod at hand. It's pretty long, long enough so that you can hold it out of your window and into your friends window at the other side of the street.

The way you and your friend communicate is through morse code. You move the rod a distance x so that it hits your friend's wall and makes a sound. *Bump--BumpBump-Bump* The morse code is easily heard and interpreted.

Extrapolate.

Make your rod reach from your house to another galaxy, and place your friend there. Continue communicating as usual. Will the information now travel faster than the speed of light?
 
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This is a known thought experiment, but I have never heard an answer for it.

My answer would simply be Yes. It doesn't actually travel there however.
 
No. The information will travel along the rod at the speed of sound in the material. For most solids the speed of sound between 1 and 10 km per second, which is much slower than the speed of light.
 
k4ff3 said:
You have a straight, light, hard, inelastic rod at hand. It's pretty long, long enough so that you can hold it out of your window and into your friends window at the other side of the street.

The way you and your friend communicate is through morse code. You move the rod a distance x so that it hits your friend's wall and makes a sound. *Bump--BumpBump-Bump* The morse code is easily heard and interpreted.

Extrapolate.

Make your rod reach from your house to another galaxy, and place your friend there. Continue communicating as usual. Will the information now travel faster than the speed of light?

No, because there is no such thing as a perfectly inelastic material. The force of pushing one end will propagate at the speed of sound through the material to the other end.
 
Doc-Al: Sorry, I did not know that.

However, it seems like the you overlook the fact that the rod is inelastic. The same thing goes for the answers in the thread you linked to.

And even if the rod was elastic, I do not buy your answer that the information/displacement will propagate as a wave pulse with the speed of sound in the medium. I am displacing the whole rod, so that the displacement is much higher that the wavelength of the pulse induced.
 
k4ff3 said:
Doc-Al: Sorry, I did not know that.

However, it seems like the you overlook the fact that the rod is inelastic. The same thing goes for the answers in the thread you linked to.

And even if the rod was elastic, I do not buy your answer that the information/displacement will propagate as a wave pulse with the speed of sound in the medium. I am displacing the whole rod, so that the displacement is much higher that the wavelength of the pulse induced.

Nobody is overlooking anything. Your question has been answered.
 
k4ff3 said:
Doc-Al: Sorry, I did not know that.

However, it seems like the you overlook the fact that the rod is inelastic. The same thing goes for the answers in the thread you linked to.

And even if the rod was elastic, I do not buy your answer that the information/displacement will propagate as a wave pulse with the speed of sound in the medium. I am displacing the whole rod, so that the displacement is much higher that the wavelength of the pulse induced.

Er.. hello? What do you think holds the material that make up the rod?

If you've learned any amount of solid state physics, you'd know that these are linked by various types of BONDS, and they interact with the lattice ions via electromagnetic interactions! Light is a form of electromagnetic interaction! This means that anything done to the rod can't transmit something faster than what light can do!

Zz.
 

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