[ntp:questions] Accuracy of NTP - Advice Needed

unruh unruh at invalid.ca
Wed Dec 28 19:24:07 UTC 2011


On 2011-12-28, Danny Mayer <mayer at ntp.org> wrote:
> On 12/27/2011 11:45 PM, Greg Hennessy wrote:
>> On 2011-12-28, Danny Mayer <mayer at ntp.org> wrote:
>>> On 12/27/2011 9:08 PM, John Hasler wrote:
>>>> Danny writes:
>>>>> GPS is not used for this kind of thing, they are too inaccurate, so it
>>>>> doesn't matter. They use atomic clocks.
>>>>
>>>> The requirement is for synchronization.  They use common view GPS.
>>>
>>> That's not good enough for experiments like this.
>> 
>> In what way is it not good enough? The neutrinos are apparently
>> arriving about 60 nanoseconds early, the distance is known, through
>> GPS to 10's of centimeters, and the time is synchronized, again
>> through GPS (although a second method is used as a double check) to
>> about 1 nanosecond. In what fashion is it 'not good enough'?
>
> No, they use synchronized Cesium atomic clocks for time accuracy. GPS is

And the clocks are synchronized by GPS. They also have some burbling
about using a truck with a portable atomic clock to check the
synchronization. 

> only used to get a fix on the location and I'm not sure that 10's of
> centimeters is good enough for what they are trying to prove. I'd have

10s of cm is good enough. The "error" in the speed of light is 20 m. 


> to look closely at the methods used and the data to even have a clue as
> to what is needed and I have touched that stuff in years.
>
> Danny



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