Could Morse Code Be Instantaneous on a Million Light-Year Pole?

[friendlycello]

Suppose a pole could be constructed that was one million light years long and was completely incompressible. If someone on one end tapped out Morse code on their end, would a person on the other end be able to receive the message instantaneously?

 

[russ_watters]

Welcome to PF.

No, the impulse travels at the speed of sound in the pole.

 

[Uglybb]

In that nothing is incompressable the question is at heart wrong anyhow.

And no the speed of sound conduction in any given material is a lot slower than the speed of light (http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe2.html)

So your sound is going to take a lot longer than a million years to reach the other end of your rod.

 

[Pengwuino]

There is no such thing as an incompressible object. Motion through a material travels at that material's speed of sound.

 

[friendlycello]

What if the transmitting person just moved the pole a foot forwards? Would that still be considered sending a wave down the pole?

 

[Pengwuino]

sure, but same idea holds, that movement gets transmitted at the speed of sound.

 

[mishrashubham]

https://www.physicsforums.com/showthread.php?t=482577

 

[Ryan_m_b]

To quote myself from the link mishrashubham supplied above

Any object when pulled stretches somewhat. With some materials this is obvious (rubber) with others it is less so (concrete). Whilst some objects are elastic and stretch a lot before breaking others are not and quickly break (if you were to pull at a brick it would stretch ever so minutely before it broke). So if you had a pole that was any length (whether it was between Earth and Mars or your left and right hand) when you pull one end it ripples all the way down it's length at its speed of sound stretching.

Imagine it this way, you have 100 people each standing in 100 one metre wide squares. These people have to remain the same distance between either neighbor preferably exactly 1 metre from the person on either side. If i take the person at one end and move them 1 metre then you will observe a ripple as one by one every one hops one metre to catch up with the person that just moved.

If the person at the other end can't move then the line is stretched with the ripple passing back and forth as everyone tries to both maintain an equal distance between each other as well as trying to obey the rule of being 1 metre away from both neighbours in this now 101 metre line of 100 people. If i was to let the end person jump back to his original place the ripple would travel down again.

The "ripple" speed in an object is the speed of sound within the object. It is impossible to build a magic string where all objects move at the same time to reposition themselves because it would require each atom to react instantly to what happens to every other atom.

 

[mishrashubham]

I think this question should be added to the FAQ as it keeps coming up.

 

[Lsos]

I'm thinking almost everybody asked themselves this same question.

 

[FtlIsAwesome]

No, not this again!

I think this question should be added to the FAQ as it keeps coming up.

Yes.

 

[Uglybb]

I also want the stretch and contraction of the pole given a variation of 0.0001 degree in the temperature of space on a 1 million light year pole ... that's about as sensible :-)