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Amplitude of EM waves in vacuum ~

  1. Aug 21, 2007 #1
    Amplitude of EM waves in vacuum~~~

    As we know, amplitude of waves decreases with distance due to energy loss.
    But what if EM waves in the space??
    Since there's no matter around, I was wondering if there is any energy loss when EM waves travel through vacuum.
  2. jcsd
  3. Aug 22, 2007 #2
    If you have an EM-emitting source somewhere in an otherwise empty space, the energy flux through a closed surface completely sorrounding the source is constant regardless of where the surface i placed.

    If the surface is made larger by expanding it further away from the source, the intensity, i.e. energy flux per unit area, diminishes since the same energy is distributed over a larger area.
  4. Aug 22, 2007 #3


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    There are some theories that propose that light diminishes in amplitude and/or frequency over distance (so-called "tired light" theories), but these are not generally accepted due to their lack of experimental proof. If such an effect does occur, it is too small for current instrumentation to detect. By all te observed data avialable, EM enegry does not diminish over distance unless it inmteracts with something else.
    Photons are forever.
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