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Changing speed of light

  1. Jun 28, 2014 #1
    If the speed of light is changing, does this mean that the permattivity and/or permeability are dynamically changing quantities? are these "constants" derivable yet or are they still only experimentally measured quantities?
  2. jcsd
  3. Jun 28, 2014 #2


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    What makes you think the speed of light (in vacuum) is changing?
  4. Jun 28, 2014 #3


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    The speed of light, vacuum permettivity and vacuum permeability are all determined by the system of units. In natural units they are all equal to 1, and in CGS the vacuum permeability and permittivity do not even exist.

    What you should really be asking is if the fine structure constant is derivable or only experimentally measured. That is a dimensionless number and so is independent of the system of units. It characterizes the physics rather than the units.

    The answer is that the fine structure constant is experimentally measured, not yet derivable.
  5. Jun 29, 2014 #4


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    Has there been a follow up to..


  6. Jun 29, 2014 #5
    I just assumed he was referring to vacuum

    what's CGS?
  7. Jun 29, 2014 #6
  8. Jun 29, 2014 #7
    the speed of light will be changed when the light goes from the vaccum into the media due to the change of the permability and permittivity. the speed of the light is related to these material properties by checking the wave equations in the medias.
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