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From: "Paul.B.Andersen" <relativity@paulba.no>
Newsgroups: sci.physics.relativity
Subject: Re: Sync two clocks
Date: Tue, 20 Aug 2024 15:08:28 +0200
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Den 20.08.2024 01:15, skrev Richard Hachel:
> It is impossible to synchronize two watches A and B located in different 
> places.
> It is not a technical problem, it is not a problem of intelligence, it 
> is simply that it is as impossible as finding a round square, or a 
> natural number between 5 and 6.
> Because nature is not made like that.
> Anyone who wants to synchronize watches with each other does not realize 
> that he is looking for rabbit horns.

--------------------

> The only thing we can do is to find a kind of abstract, imaginary 
> synchronization procedure, called the Einstein procedure where tAB is 
> supposed to be equal to tBA not only for the point M which is the only 
> real origin of the synchronization, but for everyone.

So the only thing we can do is to do what Einstein did,
namely to define a synchronisation procedure which
makes it possible to synchronise two clocks at different
places in an inertial frame of reference.

So why did you say: "It is impossible to synchronize two
watches A and B located in different places." ?

If we have two stationary clocks in an inertial frame,
  and clock A shows t1 when it emits light,
  and clock B shows t1 + td when light hits it,
  and clock B shows t2 when it emits light,
  and clock A shows t2 + td when the light hits it,

then t1, (t1+td), t2 and (t2+td) are all proper times
which are frame independent (invariants) and the same for all,
so of course the transit time td is the same in both directions
and the same for all, which means that the clocks according
to Einstein's _definition_ are synchronous in the inertial frame.
For all!

What is "imaginary" about this?
Where is your mysterious point M?

> We then have a useful procedure, but false.

Einstein did define a very useful procedure which works
in the real world, so why is it "false"? :-D

-------------------------

> There is no global synchronization, but a synchronization of type M, as 
> I have explained.
> A and B, as I explained, will never "live" in the same global, real, and 
> reciprocal present moment.

What an awkward way to express something which is correct;
"there is no absolute simultaneity."

And you believe it is YOU that have discovered that? :-D

Before 1905 everybody believed it was a "universal, present now",
that simultaneity was absolute, and that clocks could be absolutely 
synchronised. Newton took it for granted!

But Einstein showed that there is no absolute simultaneity,
and clocks can't be absolutely synchronised.

https://paulba.no/paper/Electrodynamics.pdf
See: § 1. Definition of Simultaneity

Did you really not know that it was Einstein who discovered this? :-D

But we can _define_ what we mean by "simultaneity" in
an inertial frame of reference.
That is what Einstein did.
And with this _definition_, we can make two clocks at different
locations in the inertial frame simultaneously show the same;
the clocks are synchronous _in said frame of reference_.
But they are NOT synchronous in a frame of reference which
is moving relative to the first frame of reference.

Note that clocks showing UTC are synchronous in the non-rotating
Earth centred frame of reference (ECI-frame), but they are NOT
synchronous in the ground frame.
Note the rather peculiar phenomenon that the UTC clocks
are synchronous in the frame were they are moving, but
not synchronous in the frame where they are stationary.

Of course "simultaneity" and "synchronism" are man made,
theoretical notions, but they are very practical, and
the world would be even more chaotic than it is without it.
Think if it was no way to tell you when your train or
aeroplane would go, and there was no way to tell you
when you would arrive at the destination. The world
is _very_ dependent on synchronous clocks.

Don't you think that a man made theoretical entity
can be real?

Why do you call the man made theoretical entity
"synchronism" for "imaginary"?

Why do you call the man made theoretical entity
"synchronism" for "false"?

------------------

It is interesting to see that you now have realised  that it
is indeed possible to synchronise clocks in an inertial frame.
It doesn't help if you call Einstein's procedure
"a kind of abstract, imaginary synchronization procedure"
and "We then have a useful procedure, but false.".

You know that clocks at different places in an inertial frame of 
reference can be synchronised. So now you know that your clock
an my clock are synchronous in the ECI-frame, since they both
show UTC + 2h. Don't you? :-D


But you will of course repeat your tirade where you explain
that we are stupid because we didn't understand that you didn't
say what you said.

-- 
Paul

https://paulba.no/