Information travelling faster than light

  • #1

Main Question or Discussion Point

I dont know if this has been asked but

if you imagine a pipe that theoretically extends from one end the universe to another

two people at each end, and by twisting the pipe left means "yes" and right means "no"

if you twist it what happens
 

Answers and Replies

  • #2
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There is a theorem that states that no completely rigid bodies exist. So If one person twists the pipe, the twist will travel along the pipe in a similar fashion to a wave, but at a speed that is less than the speed of light.

Quantum Entanglement seems to be something that does violate the speed of light, but (I may be wrong on this) since nothing useful is transmitted, the speed of light is not violated.
 
  • #3
how can a twist be a wave ?????
 
  • #4
ZapperZ
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The material that makes up the pipe is connected via electromagnetic forces which can transmit their forces only as fast as the speed of light.

Zz.
 
  • #5
phinds
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how can a twist be a wave ?????
A twist, a bang, any mechanical motion that you impart to a "rigid" body will travel down it as Senti31 said, NOT rigid. The wave will travel at the speed of sound in the material, which is much faster than the speed of sound in air (if the material is something like steel) but utterly trivial compared to the speed of light.
 
  • #6
sorry but why is it travellin at the speed of sound not the speed of light
 
  • #7
Bandersnatch
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sorry but why is it travellin at the speed of sound not the speed of light
Speed of sound in a material is the average time it takes for two neighbouring molecules to affect each other mechanically(scaled to SI units). That is, if you push or pull one, it will push or pull on the next one - but not instantenously.
The time lag involved is related to the amount of empty space between molecules(e.g., density), whether or not the molecules are arranged in a rigid structure(e.g., crystals, metals vs fluids), and probably other factors like molecular weight and type of bonds.

It's very much like billiard balls on a pool table. You hit one, and it takes some time before it reaches the next and transfers the momentum.
 
  • #8
sophiecentaur
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sorry but why is it travellin at the speed of sound not the speed of light
Have you never heard a thunder clap occur some time after seeing a lightning flash? There is no essential difference with your 'rigid' connecting rod situation.
 
  • #9
@bandersnatch

cool thanks now i get it

@sophiecentaur

so the thunder is connected to the lightning?
 
  • #10
Bobbywhy
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“The origin of audible thunder is the expansion of the rapidly heated lightning channel. During the lightning stroke, typically with currents of 30,000 amperes, the channel heats the air to about 30,000 degrees K in less than 10 microseconds. It follows that the channel pressure must rise in response to the temperature rise. The average channel pressure is about 10 bar during the first 5 microseconds. This channel overpressure results in an expansion of the channel behind a shock wave. The acoustic radiation pulse (thunder) travels about 1 kilometer in 3 seconds.”
REFERENCE: “The Lightning Discharge”, by Martin A. Uman, Dover, 2001
 
  • #11
@bobbywhy

ok thanks oh so basically the lightning heats up the sky light a microwave heatas up a popcorn and then it pops cuz it gets hot
 
  • #12
Bobbywhy
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Yes, you've got the general idea!
 
  • #13
sophiecentaur
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“The origin of audible thunder is the expansion of the rapidly heated lightning channel. During the lightning stroke, typically with currents of 30,000 amperes, the channel heats the air to about 30,000 degrees K in less than 10 microseconds. It follows that the channel pressure must rise in response to the temperature rise. The average channel pressure is about 10 bar during the first 5 microseconds. This channel overpressure results in an expansion of the channel behind a shock wave. The acoustic radiation pulse (thunder) travels about 1 kilometer in 3 seconds.”
REFERENCE: “The Lightning Discharge”, by Martin A. Uman, Dover, 2001
I was told thunder was due to the clouds bumping together. :devil:
 
  • #14
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There is a theorem that states that no completely rigid bodies exist. So If one person twists the pipe, the twist will travel along the pipe in a similar fashion to a wave, but at a speed that is less than the speed of light.

Quantum Entanglement seems to be something that does violate the speed of light, but (I may be wrong on this) since nothing useful is transmitted, the speed of light is not violated.
Is there a name for that theorem? I'd like to have a look-see :)

I imagine it's a similar story for all the words we use in mechanics, such as "light", "inextensible" and "point"
 
  • #15
phinds
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@bobbywhy

ok thanks oh so basically the lightning heats up the sky light a microwave heatas up a popcorn and then it pops cuz it gets hot
Badly stated, to get at the actual point. The heat and the pop happen at the same time but you SEE the lightening right away but you HEAR the thunder quite a bit later. It is the difference between the two perceptions, because of the difference in speeds, that is the point.
 

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