[ntp:questions] National time standard differences

unruh unruh at wormhole.physics.ubc.ca
Thu Feb 11 18:36:28 UTC 2010

On 2010-02-10, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
> unruh wrote:
>> On 2010-02-10, David J Taylor <david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid> wrote:
>>> "David Woolley" <david at ex.djwhome.demon.invalid> wrote in message 
>>> news:hksmaf$1cm$2 at news.eternal-september.org...
>>>> David J Taylor wrote:
>>>>> I remember the flying of caesium or other atomic clocks round the 
>>>>> world, and that folks had to invoke relativistic corrections.  Were 
>>>>> these better than microseconds as well?
>>>> That's called Navstar (GPS) and GPS position solutions do have to 
>>>> include a general relativity correction to the satellite clocks.
>>> Not today's GPS, but some forty or more years ago:
>>>   http://www.hp.com/hpinfo/abouthp/histnfacts/timeline/hist_60s.html
>>> 1964:
>>> "The highly accurate HP 5060A cesium-beam atomic clocks gain worldwide 
>>> recognition as the "flying clocks" when they are flown from Palo Alto to 
>>> Switzerland to compare time as maintained by the U.S. Naval Observatory in 
>>> Washington, D.C. to time at the Swiss Observatory in Neuchatel. The atomic 
>>> clock was designed to maintain accuracy for 3000 years with only one 
>>> second of error. The cesium-beam standard becomes the standard for 
>>> international time."
>>> I had wondered what accuracy was obtained - i.e. how far was each nation 
>>> out - and whether relativistic corrections had been needed for these 
>>> "flying clock" tests.
>> 1 sec/3000years is 1 part in 10^-11. The gravitational redshift is
>> gh/c^2 (g is gravity acceln on earth, h the height of the flight, and c
>> vel of light) which is 10^-12 -- ie below ( but not by much) the
>> accuracy of the clock. The velocity correction is 1/2 v^2/c^2 which is
>> again about 1 part in 10^12. Ie, both corrections are smaller (but not
>> much)  than the uncertainty in the clock rate. If the plane flew at Mach
>> 2, rather than well below Mach 1, you could get that velocity correction
>> up the accuracy and one would have to take special relativity into
>> account. 
>> Since the flight probably lasted say 10 hr, which is 100000 sec, th
> BUZZ!!!!!!!!
> Ten hours is HOW MANY seconds?
> I make that as 10*60*60 which is 36,000!

You are right which makes the relativistic corrections even smaller. 

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