Den 21.07.2024 22:34, skrev Richard Hachel:
Le 21/07/2024 à 21:26, "Paul.B.Andersen" a écrit :
You have said strange statements about synchronisation of clocks.
Clock synchronization.
I have already told you hundreds of times over the past 40 years that it is impossible to synchronize two clocks placed in different places.
Please address what I wrote:
You know of course that all clocks in the same time zone
are synchronous. In France and Norway clocks are currently
showing GMT + 2 hour, so my clock and your clock are actually
synchronous.
Please explain why our clocks are NOT synchronous.
(To within few seconds)
If I place a very precise atomic clock, one on this bench, one on this table, the other on the mantelpiece, I could never synchronize them absolutely, because it is impossible and an abstract representation of the notion of simultaneity of present time.
What do you call the phenomenon that when you look at the clocks
on your table and on your mantelpiece, they always show the same?
(to within the precision with which you have set the clocks.)
In the best case of my synchronization, each watch will delay the other by t=x/c unavoidable, universal, physical delay.
It is obviously impossible to make two clocks side by side show
the same with infinite precision, there will always be a difference.
For atomic clocks this difference may be less than 1 ns,
for say - wristwatches it will be less than 1 second.
As long as the difference is less than the precision of your
measurements, the clocks can be considered to be synchronous.
Practical examples:
100 m sprint:
Two synchronous clocks at start and finish line.
The precision of the measurements is 0.01 second
So the clocks must be synchronous to within 10 ms.
Tour de France.
Start and finish line may be ~200 km from each other.
The precision of the measurement is 1 second.
So the clocks at the start and the finish must
be synchronous to within 1 second.
Do you accept this, or are you still insisting that it
is impossible to have clocks synchronous to within
the precision of the actual measurement?
We will say: “How does GPS work?”
GPS works on the idea of an abstract point, located outside our universe, and placed orthogonally and ideally almost to infinity, such that an impulse coming from it will be returned to it at the same time by all the components of our universe.
It is on such an “ideal and abstract” point that GPS works, giving the illusion of a real universal present time.
:-D
All the clocks in the the GPS system (satellite clocks, ground clocks)
are synchronous with the UTC (Coordinated Universal Time)
to within ~1 ns.
Your clock on your table is synchronous with the UTC+2 hours,
to within the precision you have set the clock.
The UTC is universal in the sense that it covers the whole Earth
and the space in its vicinity.
It is coordinated in the sense that it is defined at any point
on the Earth and in the space in Earth's vicinity.
It is real even if it is defined by man. It is no illusion.
All clocks on Earth and in the GPS-, GLONASS- and Galileo-satellites
are synchronous to the UTC or UTC+n hours.
It is a fact that you can synchronise clocks via the GPS.
The GPS receiver determines four entities, the time, altitude,
latitude and longitude. If the spatial position is within 1 m,
the time must be the UTC to within ~2 ns.
Yes, your GPS receiver does indeed determine the time to within few ns
of the UTC, it must do that to determine the position to few metres.
It is obviously no point in displaying the time with this precision
on the screen.
-- Paulhttps://paulba.no/
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