# Thread: communicate over light years of distance?

1. I possibly should have this in the psuedoscience forum, I wasn't sure though I don't see that its far off of physics anyway.

This stems from hearing that electricity actually only travels at a speed of about 1 inch per minute but its like a train. if the front carriage moves they all move instantly.

I was thinking, if you had a theoretical piece of string say 3 light years long, you could communicate with say Morse code with someone at the other end of the string. thoughts?

also a quick question, I find I often have many questions at a time to ask, am i best to post multiple topics with one question and topic per post, or should i stop spam and post them all in one topic. I have found though that posting many questions in one post gets only 1 of the questions answered and the rest ignored

2.

3. a) I'm pretty sure electricity moves at light speed.
b) why have a cable when you can just radio them?

4. Originally Posted by somfooleishfool
I possibly should have this in the psuedoscience forum, I wasn't sure though I don't see that its far off of physics anyway.

This stems from hearing that electricity actually only travels at a speed of about 1 inch per minute but its like a train. if the front carriage moves they all move instantly.
They don't move instantly. Depending on the type of conductor, the delay between a signal entering one end and being detected at the other will be the equivalent of a speed of 66-99% of the speed of light.

I was thinking, if you had a theoretical piece of string say 3 light years long, you could communicate with say Morse code with someone at the other end of the string. thoughts?
The speed at which the impulse would travel through the string would be limited to the speed of sound in the string. And the limit for the speed of sound though any object is less than the speed of light. So, no you cannot comunicate paster than the speed of light by this or any other means

also a quick question, I find I often have many questions at a time to ask, am i best to post multiple topics with one question and topic per post, or should i stop spam and post them all in one topic. I have found though that posting many questions in one post gets only 1 of the questions answered and the rest ignored
It depends on whether the questions are related to each other or not.

If you are only getting the first question answered, it may be that the responder feels that the answer to the first question makes the rest of the questions moot.

5. Originally Posted by 15uliane
a) I'm pretty sure electricity moves at light speed.
b) why have a cable when you can just radio them?
1)the flow of electrons in a DC current moves at about 84 millimetres per hour

2)radio waves travel at the speed of light. it would take 3 years to send a radio message to your friend. but a tug on an 100% taught string (or really any other material would do for the theoretical example) would pass a message instantaneously I would think.

wow... I think this might be the first time ever on "thescienceforum" where I have corrected someone . everyone is too much smarter than me haha

6. Originally Posted by somfooleishfool
.... but a tug on an 100% taught string (or really any other material would do for the theoretical example) would pass a message instantaneously I would think.

wow... I think this might be the first time ever on "thescienceforum" where I have corrected someone . everyone is too much smarter than me haha
Wrong.

A tug on a string propagates a stress wave at approximately the speed of sound (there is a weak dependence on amplitude and sound speed is the limit of vanishingly small amplitude). That is very much slower than light speed.

One of the implications of special relativity is that there is no such thing as a rigid body.

7. wow I wouldn't have guessed the string tug was limited by the speed of sound. so what about in the example of a solid steel rod stretching out 3 light years. if you gave this a fast shunt forwards by say 5 metres using a hydrolic machine or something, where does that 5 metres go for 3 years(minimum)? does the rod just contract?

8. Originally Posted by somfooleishfool
wow I wouldn't have guessed the string tug was limited by the speed of sound. so what about in the example of a solid steel rod stretching out 3 light years. if you gave this a fast shunt forwards by say 5 metres using a hydrolic machine or something, where does that 5 metres go for 3 years(minimum)? does the rod just contract?
Same answer. The stress wave propagates at approximately the speed of sound in steel.

9. Originally Posted by DrRocket
Originally Posted by somfooleishfool
.... but a tug on an 100% taught string (or really any other material would do for the theoretical example) would pass a message instantaneously I would think.

wow... I think this might be the first time ever on "thescienceforum" where I have corrected someone . everyone is too much smarter than me haha
Wrong.

A tug on a string propagates a stress wave at approximately the speed of sound (there is a weak dependence on amplitude and sound speed is the limit of vanishingly small amplitude). That is very much slower than light speed.

One of the implications of special relativity is that there is no such thing as a rigid body.
I had posted my reply that you quoted before janus had responded (I was writing it as he posted) and funnily enough the last post I made was written while you posted this message.

10. Originally Posted by DrRocket
Originally Posted by somfooleishfool
wow I wouldn't have guessed the string tug was limited by the speed of sound. so what about in the example of a solid steel rod stretching out 3 light years. if you gave this a fast shunt forwards by say 5 metres using a hydrolic machine or something, where does that 5 metres go for 3 years(minimum)? does the rod just contract?
Same answer. The stress wave propagates at approximately the speed of sound in steel.
I love this forum . Another issue solved that otherwise would have bothered me for years.

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