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From: "Paul.B.Andersen" <relativity@paulba.no>
Newsgroups: sci.physics.relativity
Subject: Re: Space-time interval (2)
Date: Thu, 15 Aug 2024 21:22:23 +0200
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Den 14.08.2024 15:24, skrev Richard Hachel:
> I'm talking about the initial 
> synchronization. At some point you have to synchronize all the watches 
> in all the capitals with each other.
> However, this is by nature impossible.

"you have to synchronize all the watches
  in all the capitals with each other."

Good grief! 😂


> The notion of universal anisochrony means that each watch will lag 
> behind the other with an anisochrony Et=x/c, a reciprocal phenomenon 
> that will affect all the watches in the universe.

How naive is it possible to be?

You don't sync two clocks to each other, you sync one clock
to another clock.

A clock showing precise UTC can send a signal with the time
to another clock, which can be set to the received time.
This way, the clock will obviously lag on UTC, because of
the transit time of the signal.
If the master clock is, say 1000 km away, the clock
will lag on the UTC by ~ 3.3 ms, which will be adequate
for most purposes.
If better precision i needed, and the distance is known
to be, e.g. 1000km, the clock can be set to the received
time - 3.336 ms, and its precision is in the order of
microseconds.

--------

Richard, I have a question for you.

I suppose that you, like all  people in France, have
a clock which is set to show the time GMT+2h.

How did you do that?


> So, to start the watches at t=0, you'll need a point in the universe 
> placed at an equal distance from all the others, and only an abstract 
> point placed in an imaginary, perpendicular dimension, at an equal 
> distance from all the points in the local universe will be able to do this.
> It's not hard to understand.


That you find this nonsensical babble easy to understand
is rather alarming for your mental health. 😂

But how it was started in the real word is easy to understand,
since it is historical facts.

Here is how you start:
You are at Greenwich in the 19th century, and you say:
I herby define our pendulum clock to show GMT,
which is 12.00.00 when the medium sun is in the meridian.
All other clocks in the world must be synchronised from this
clock. We will lower a flag at 12.00.00 so all the ships
in the harbour can synchronise their clocks to show GMT.
When the radio is invented, we will send a signal to make
it possible to sync the clocks in all the UK and the rest of the world.
The clocks can now be synced to within a second, which will
be acceptable for all practical purposes (like celestial navigation).

In 1960 GMT was renamed to UTC (Coordinate Universal Time)
and the second was based on the Cs atom in stead of the Sun.
The standard clock was now an atomic clock (actually many atomic
clocks),and advances in radio communication made it possible to sync
the clocks all over the world very precisely.
In the 1978 came GPS, which was fully operational in 1993.
Now anybody can have his clock synced to within few ns.
(If he has the right equipment.)

---------

I will be otherwise occupied for a few days, and will
not post to this forum for some time.

-- 
Paul

https://paulba.no/