Communication with a Million-Mile Pole: A Relativity Puzzle?

Click For Summary
SUMMARY

The discussion centers on a thought experiment involving Bob and Alice, who attempt to communicate over a million-mile-long pole using Morse code. The key conclusion is that communication is not instantaneous due to the limitations of the speed of sound in the pole's material, which is significantly slower than the speed of light. The resolution highlights that in relativity, no rigid bodies exist, and thus the speed of sound cannot exceed 'c', confirming that there is indeed a delay in their communication.

PREREQUISITES
  • Understanding of basic principles of relativity
  • Knowledge of the speed of light ('c') and its implications
  • Familiarity with the concept of signal transmission speed in different materials
  • Basic understanding of Morse code communication
NEXT STEPS
  • Research the implications of relativity on communication methods
  • Explore the concept of rigid bodies in physics and their limitations
  • Study the speed of sound in various materials and its effect on signal transmission
  • Investigate other relativity puzzles and their resolutions
USEFUL FOR

Physics enthusiasts, educators, and students interested in the principles of relativity and communication theory.

PBRMEASAP
Messages
191
Reaction score
2
Here's a scenario I thought of a few days ago. I know there must be an easy explanation, but it hasn't come to me ...

Bob and Alice (no Eve this time) are separated from each other by about a million miles, and they would like to communicate with each other without the five second delay of radio waves. Fortunately, there lies between them a million-mile-long pole. After talking back and forth over radio, they agree to communicate by poking each other in Morse code with the long pole. Are they communicating with no five-second delay? Is this a problem?

I wouldn't be surprised if this is a well-known relativity-style "puzzle". If someone could explain what's wrong with the reasoning, I'd appreciate it.

thanks,
JP :biggrin:
 
Physics news on Phys.org
The signal will travel down the bar at the speed of sound in the material, which will be far less than the speed of light.

It's a standard puzzle, the resolution is that there are no rigid bodies in relativity, a rigid body would have an infinite speed of sound, while the actual speed of sound is less than 'c'.
 
That makes sense. Thank you!

JP
 

Similar threads

Undergrad General Relativity rocket puzzle
  • · Replies 84 ·
3
Replies
84
Views
8K
Graduate More questions about relative speeds.
  • · Replies 12 ·
Replies
12
Views
3K
Graduate Communicating Through an Einstein-Rosen Bridge Without Causality Violation
  • · Replies 1 ·
Replies
1
Views
3K
High School Quantum Entanglement information transmission idea to knock down....
  • · Replies 41 ·
2
Replies
41
Views
6K
Graduate Entanglement Swapping and FTL Communication
  • · Replies 63 ·
3
Replies
63
Views
10K
Undergrad No relativistic Bohmian mechanics and superluminal causation
  • · Replies 37 ·
2
Replies
37
Views
5K
High School Delayed choice experiment and FTL communication
  • · Replies 15 ·
Replies
15
Views
4K
Graduate Astronomical Implications of Quantum Entanglement?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Progress In Calculating The HLbL Contribution To Muon g-2
  • · Replies 0 ·
Replies
0
Views
4K
Graduate Influence of strong measurements in a Two Slit Interferometer
  • · Replies 8 ·
Replies
8
Views
2K