Re: Space-time interval (2)

Den 14.08.2024 00:42, skrev Richard Hachel:

 I just explained to you the synchronization used by GPS.

You have no idea of how the GPS SV-clocks are kept synchronous.

Abstract synchronization, but interesting to be able to use a universal present time plan (which does not exist in nature).

Quite.
The "universal present time plan", namely
the "Coordinated Universal Time" or "Temps Universel Coordonné",
short UTC (not CUT or TUC - a compromise)
is indeed a theoretical time defined by humans.
("It does not exist in nature", Good grief! :-D)
That it is coordinated simply means that UTC is the same at any point
in the non rotating Earth centred frame of reference (ECI-frame).
UTC's rate is defined by stationary clocks (as defined by SI) on
the geoid. UTC is 12.00 when the mean sun is in the meridian
at Greenwich.
You seem to think that what you call "a universal present time plan"
has something to do with GPS. But UTC was created January 1, 1960,
before the GPS.
The UTC was nothing new, before that was Greenwich Mean Time, GMT.
GMT was the time shown by the pendulum clock at Greenwich,
which was kept in sync with the mean solar day, and the second
was defined by the mean solar day.
The GMT was used from the 19th century. The word "coordinated"
was not used, but at the time of Newton's absolute time, everyone
thought it obvious that GMT was the same everywhere.
The only way to navigate across the oceans at that time (and until
recently) was by celestial navigation. That is, by measuring the angular
height of a celestial body, usually the sun, with a sextant, and
via tables (made by the British Admiralty) and the time determine
the position. And the time in the tables is GMT. So the navigator
had to have a clock synchronous with GMT. Since the sun moves
1 minute of arc in 15 seconds, an error of 15 seconds from GMT
will give an error of 1 minute of arc on the Earth, which is one nautical mile. If the clock was 1 minute off GMT, the error would
be 4 nautical miles, which would be acceptable in most cases.
To be in the middle of the Pacific at the 19th century and have
a clock synchronous with GMT within few minutes was no simple task,
but that's another (and long) story.
The point is:
Universal time and synchronous clocks have been used for centuries!
And you claim that clock's in Oslo and Paris can't be synchronous!
In 2024!
--
Paul
https://paulba.no/