[time-nuts] Best reason

Michael Blazer mblazer at satx.rr.com
Thu Mar 29 03:09:14 UTC 2012


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:
> jim77742 at 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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