[time-nuts] Measuring speed of light or reproducing a metre

[Brian Alsop]

You need to know the wavelength.  You can get that from a diffraction 
grating without any knowledge of the speed of light.

Brian

On 6/24/2013 21:56, Jim Lux wrote:
> On 6/24/13 5:21 AM, Brian Alsop wrote:
>> The time issue was effectively eliminated by the Michaelson-Morley
>> interferometer.  One used a monochromatic light and an array of mirrors
>> which split the light in opposite directions around the track.  The two
>> beams were recombined and an interference pattern resulted.  One counted
>> the number interference fringes passing by  while moving one mirror in
>> one path.
>>
>> Knowing the number of fringes, wavelength of light and the mirror
>> movement, one could compute c.
>
> There are easier ways to measure wavelength of an EM wave (Young's
> double slit experiment, for instance), or measuring the voltage along a
> transmission line carrying a reflected wave.
>
> BUT, then, an interferometer (or melted marshmallows in the microwave
> oven) tells you the wavelength of the EM radiation.  But you need to
> know the frequency of that signal in order to calculate c from that
> measurement.
>
> and we're back to the "what can be done simply to measure time/frequency"
>
> (I guess.. it's all really arbitrary.. a meter is so many wavelengths of
> the light from a Krypton lamp)
>
>
>
>
>>
>> htt
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