Do light waves change over distance within a vacuum?

  1. Specifically, does the amplitude of a wave of light change if it does not encounter any matter?
     
  2. jcsd
  3. we can have a gravitational redshift were light will change wavelength
    moving away from a stong gravitational field ,
     
  4. So, if the universe consisted of a uniform spherical mass and light, when the light waves emanate radially away from the mass would the light waves decrease in amplitude or only wavelength? What exactly happens?
     
  5. k i know that when the light travels outward into a weaker gravitational field
    the wave-length becomes longer and the frequency increases but im not sure
    about amplitude
     
  6. HallsofIvy

    HallsofIvy 40,673
    Staff Emeritus
    Science Advisor

    As a spherical wave spreads out, without touching anything, the total energy in it does not change. However, it is spread over a greater area (the area of a spherical surface is proportional to the square of the radius) so the intensity at any point on that surface decreases as the inverse square.
     
  7. MATLABdude

    MATLABdude 1,724
    Science Advisor

    Over a great enough distance (and we're talking cosmological distances here--millions of light years, i.e. the distance between galaxies), the wavelength gets longer as well. Owing to the expansion of the universe, cosmological redshifting (as opposed to regular redshifting from receding objects) occurs.
    http://en.wikipedia.org/wiki/Cosmological_redshift#Redshift_velocity_and_recessional_velocity

    The planned James Webb telescope is an IR telescope because the "first light" (emitted when the universe was a wee billion or two years old) has travelled so far that it's been stretched out and is now in the infrared.
    http://en.wikipedia.org/wiki/James_Webb_Telescope

    ...But for the most part (on earth or within the solar system, for instance), the wavelength doesn't change to any measurable extent.
     
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