Can Push Travel Faster Than Light?

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Discussion Overview

The discussion revolves around the hypothetical scenario of pushing a 1 lightyear long pole and the implications of such an action on the transmission of a light signal from one end to the other. Participants explore concepts related to the speed of sound in the pole and the nature of the push, considering factors like the time it takes for the push to travel and the visibility of the light signal.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant proposes that the time it takes for the light to reach the observer depends on the speed of push, suggesting a range from 2 years to many centuries based on various factors.
  • Another participant states that the speed of push is largely determined by the speed of sound in the pole.
  • A different participant calculates that the time would be roughly the length of the pole divided by the speed of sound in the rod, plus one year for the light to travel.
  • It is noted that when pushing on one end of the rod, the other end does not move instantaneously, as the push travels as a sound wave pulse.
  • One participant expresses gratitude for the clarification regarding the relationship between the push and the speed of sound, indicating a learning moment.
  • Another participant reiterates the importance of understanding that the push does not result in instantaneous movement of the other end of the rod.

Areas of Agreement / Disagreement

Participants generally agree on the concept that the push travels as a sound wave and does not result in instantaneous movement. However, there is no consensus on the exact implications or calculations regarding the time it takes for the light to reach the observer.

Contextual Notes

The discussion does not resolve the complexities of the scenario, such as the specific speed of sound in the pole or the exact conditions under which the push occurs. Assumptions about neglecting external factors like gravity and friction are made, but their implications remain unexamined.

PCNerdz
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TL;DR
Lightyear long pole, button activates light on the other end. How long does it take to reach you?
Been thinking about this since I was 12. Suppose you had a 1 lightyear long pole, and on the other end was a button 1 inch away that activates a light. The light is powerful enough for you to see it 1 lightyear away. You push the pole 1 inch forward. How long does it take for the light to reach you? Would you even be able to push the pole 1 inch?

My guess is it all depends on the speed of push, so anywhere from 2 years to many centuries, and it depends on how the pole is set up for the 2nd Question. We will say Gravity, Friction, air resistance and all that is negligible to help simplify it. An isolated system.

I think this requires you to know the speed of push, but I can’t find much on the internet on that subject. An exact answer would be great, but I’m mainly trying to create a discussion to see what some of you think about it.
 
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Welcome to PF.
It actually depends largely on the speed of sound in the pole.
 
It would be roughly the length divided by the speed of sound in the rod plus one year.
 
PCNerdz said:
I think this requires you to know the speed of push, but I can’t find much on the internet on that subject.
When you push on one end of the rod, the other end doesn't instantaneously move. It takes a while for the push to travel. This push is just a sound wave pulse.
 
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Thanks, I didn’t know the “speed of push” had to do with the speed of sound. This has been in the back of my mind for years as a question I wasn’t sure if I would ever find the answer to. I learned something new today. Thank you for taking the time to reply, have a good day.
 
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Mister T said:
When you push on one end of the rod, the other end doesn't instantaneously move. It takes a while for the push to travel. This push is just a sound wave pulse.
These things need to be said.
 

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