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Wavelength as a yardstick

  1. Jun 25, 2010 #1
    Could electromagnetic wavelength be used as a legitimate distance pattern? I mean is it OK to exchange geometrical length with physical wavelength? For example, given a bundle of light rays following geodesics in empty space, can the length between a given pair of geodesics be equivalent to a wavelength?
    I recall vaguely that the General Conference on Weights and Measures in 1983 adopted as a primary length standard, or reference length, the wavelength of the iodine stabilized HeNe laser,He−Ne = 632.99139822 nm.Thus, in physical metrology seems to be a common practice to use an appropriate wavelength of electromagnetic radiation as the reference length. But I don't know if it is physically straightforward to interchange geometrical lengths with wavelengths as in switching in a given Physics formula the wavelength with an equivalent geometrical length.

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  3. Jun 25, 2010 #2


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    There are devices that count wavelength cycles to determine distance (moved) for very precise measurements.
  4. Jun 27, 2010 #3
    I understand wavelengths are interchangeable with lengths in every physical situation.
    Anyone thinks otherwise?
  5. Jun 27, 2010 #4


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    Lengths are lengths. If doesn't matter what the length measures.
  6. Jun 27, 2010 #5

    Andy Resnick

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    It's not clear what you are asking; electromagnetic radiation is used as a *time* standard, not a length standard (frequency vs. wavelength). However, because 'c_0' is a constant, it's possible to think of the meter being standardized in terms of a wavelength as well- as long as you mean wavelength in vacuum, or otherwise correct for the index of refraction.

    That said, 'length' is 'length'... I don't understand what you mean by 'geometric' length vs. 'physical' length. Certainly, it's possible to scale physical parameters in an equation to obtain nondimensional groups (scaling the navier-stokes equation to obtain the Reynolds number, for example).
  7. Jul 2, 2010 #6
    I Googled 'geometrical length' to try and find out what the OP is talking about.

    I came up with this thread as the only reference. :rofl:
  8. Jul 2, 2010 #7
    The speed of light is 'by definition' 299,792,458 metres per second. So yes, a wavelength is as good a distance measure as nature offers.
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