Just remember, to the 'average' person (no such exists in reality), all
technology is magic. The TV remote is a magic wand that you wave at the
TV and recite the proper incantation (sometimes profane). You chant the
spell to your smart phone and you can talk to your friend anywhere in
the world. Everyone knows the 'spells' to make things operate, but have
no idea how they actually work. The math used with GPS is beyond most
(non-technical) college graduates.
One young child was asked how TV worked and he answered 'with gas. The
pipe (cable) bring the picture in and the electricity heats it up to
fill the screen'. He knew that things expand when heated and made the
connection. This (6 or 7 year old, if I recall) showed far more
scientific reasoning than most of our elected officials.
Most people understand faster, slower, bigger, smaller, but 'more
accurate' is a hard concept. 1% accuracy is bad until you realize you
are referring 1% uncertainty (99% accuracy). I'm currently have to
convince management that our 6-1/2 DMM (0.01% uncertainty) can't be used
to test the 0.1ppm DC Source that we're repairing.
My earlier comment of '1 nanosecond = 1 foot' really applies to GPS. If
the atomic clock on the satellites are allowed to drift, even a fraction
of a nanosecond, the accuracy of the whole system quickly degrades.
These clocks are updated at less than 4 hour intervals to keep this from
happening.
Mike
On 3/28/2012 7:43 PM, Hal Murray wrote:
jim77...@gmail.com said:
So when a member of the general public says:
Why do we need really accurate clocks?
What is your answer?
Personally I explain that accurate clocks enable you to pack a higher data
rate into your smart phone. They like that.
Any other thoughts?
Navigation? It goes back to Harrison. Dava Sobel's Longitude is good.
There is a version with nice pictures.
GPS is probably something they can appreciate.
If you have to explain why GPS needs accurate clocks, it might be simpler to
start with LORAN in 2D. Work out a simple example and then do it again with
one of the transmitters being off by a few microseconds.
I think of GPS as a bunch of satellites broadcasting "I'm Bob, my orbit
parameters are XXX, my clock says YYY." If you hear 4 of those, you have 4
equations to work out 4 unknowns. The unknowns are your position: X, Y, Z,
and T.
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