Information transmission

[PBRMEASAP]

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:

[pervect]

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'.

[PBRMEASAP]

That makes sense. Thank you!

JP