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Re: [hackers-il] Re: Fwd: The case of the 500-mile email.

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  • Oleg Goldshmidt
    ... There are two factors (at least) that affect the speed of propagation. One is the material filling the fiber, and the other is geometry. Just the second
    Message 1 of 6 , Nov 26, 2002
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      Shlomi Fish <shlomif@...> writes:

      > What if everything that connected these networks were fiber optics
      > Point-to-Point lines? Maybe they have a close to vacuum light-speed.

      There are two factors (at least) that affect the speed of
      propagation. One is the material filling the fiber, and the other is
      geometry. Just the second one would reduce the group velocity. The
      material in fiber is some sort of glass. I don't know what its
      refraction index is (anyone?). The refraction index of the ordinary
      glass is about 4/3, meaning that the speed of light in the glass is
      3c/4.

      > BTW, from what I remember from my studies, the speed of light within
      > certain materials can exceed the speed of light within vacuum, for some
      > particular frequencies.

      This can be the case for phase velocity, not group velocity, which is
      the one we are discussing here (to make the long story short, it is
      the one that determines how fast information can be transmitted by
      light).

      > Still passing information from one point to another
      > can only be done at the speed of light.

      Yep, and that's what matters.

      --
      Oleg Goldshmidt | ogoldshmidt@...
      ========================================================
      First binary search algorithm - J. Mauchly, 1946
      First correct binary search algorithm - D.H.Lehmer, 1960
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