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

[Chris Albertson]

Using only "moderately" accurate equipment, like mechanical clocks and
meter sticks Albert Michelson has able to measure the speed of light and
determine it was a constant in all directions.   It was this work the
prompted Albert Einstein to think about what t means for C to be constant.

They were working at about the turn of the last century or before 1890 to
about 1905 and did not have lasers or HP universal contours.   They used
sunlight.

One experiment was done here where I live up at the Mt. Wilson Observatory.
They put light from a slit onto to a rotating mirror and then bounced it
off a fixed mirror back to the rotating one.  If the speed were infinate
the light would go right back up the slit.  But in reality the light misses
because the rotating mirror moves a little while the beam is in flight.

The advantage of this is that it is a direct measurement of the speed of
light that does not depend on many assumptions and can be done with
technology that was available in the late 1800's   One big limitation is
the atmosphere.  You need very stable air over the long path length

This was the experiment that got Einstein thinking.  He said he started at
age 16 to think about how the light from a moving lamp could be the same
speed as one from a stationary lamp.  It was total non-sense and impossible
at the time.   We have to remember that those experiments at the time were
are considered to be "Failed Experiments" because "C" could not be constant.





On Mon, Jun 24, 2013 at 4:26 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 6/23/13 10:48 PM, DaveH wrote:
>
>> Something a bit similar was first published by Nick Hood in 2007.
>>
>> Here is a copy:
>>
>> http://www.sciencebuddies.org/**science-fair-projects/project_**
>> ideas/Phys_p056<http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p056>
>> .
>> shtml
>>
>> Here is Nick's website:
>>
>> http://cullaloe.com/
>>
>> Some people use marshmallows.
>>
>> Dave
>>
>>
> the only problem is that you don't have a very accurate measurement of the
> microwave oven frequency and the mode pattern isn't very "sharp". So this
> might get you 1 sig fig. Granted, most folks only use 1 sig fig 3E8 m/sec,
> but that's just a happenstance since c happens to be close to a round
> number.
>
> And that gets back to another time-nuts kind of question..
>
> How accurately can you measure length and time?  (in a science demo sort
> of way.. without getting a Rb or GPSDO, etc.)  For most school age kids,
> the sources of time available are fairly lengthy (e.g. 1 second ticks from
> wwv by phone, stopwatches built into iphones, etc.)
>
> Tape measures and meter sticks are readily available.
>
>
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-- 

Chris Albertson
Redondo Beach, California