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Waves and Strings

  1. May 28, 2005 #1
    If I attached a long string from the ground to a geostationary satellite in orbit, and plucked it, would the wave created by the string be affected by gravity? The particles in the string move sideways, so the wave itself should not be affected by the Earth's gravity, should it?
  2. jcsd
  3. May 28, 2005 #2


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    It will be affected by gravity in a rather subtle way: the tension in the wire would vary with distance from the earth so the wave speed would also vary.

    By the way, a wire from the earth to "stationary orbit" would not stay in position. Stationary orbit is where there is no vertical force on points at that height. Every part of the wire below stationary orbit would be pulled downward so if you stop at stationary orbit, there will be a net downward pull. Of course, if you extend past stationary orbit, each part of the wire above it will be pulled upward. In order to get zero net vertical pull, you would have to extend MANY times that distance above stationary orbit ("many times" because of the drop off in gravitational force).
  4. May 28, 2005 #3
    Ok, let's assume that space station is attached with a string at a point where it will be stable. The only thing that should vary, in theory, is the wave's speed.

    What if we were to drop a string strong enough, attached from a ship, past the event horizon of a black hole?
  5. May 31, 2005 #4
    You would never see the string go past the event horizon...
  6. May 31, 2005 #5
    No, but it is said that no information can be transmitted out of anything past the event horizon. However, since particles in a physical string are not affected by the downwards pull, it should be possible to send mechanical waves out past the EH the same way a mechanical wave would travel in the first post.
  7. May 31, 2005 #6


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    Maybe you should consider the exact nature of these "mechanical waves" and figure out why they are nothing more than EM interactions/light. If light can't escape the event horizon, how do you propose these "mechanical waves" can?

  8. May 31, 2005 #7
    If there can be no interactions between particles past the event horizon, then everything just "breaks down" when past it?
  9. May 31, 2005 #8


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    How would you get a string (even an ideal one) to stand up to a gravitational force strong enough to stop photons?

    I know you're doing a thought experiment, but you must accept the fact that matter will not withstand the forces generated within a BH.
  10. Jun 22, 2005 #9
    Ok I've just come across another explaination. Even assuming the string to be unbreakable, and I'm quoting here, "space around the event horizon dilates to infinity, and infinite wavelength = 0 frequency, therefore no info travel out of EH". Any validity in that?
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