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Subject: Re: Sync two clocks
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Date: Tue, 20 Aug 24 14:45:49 +0000
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From:  Richard Hachel   <r.hachel@jesauspu.fr>
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Le 20/08/2024 à 13:13, Mikko a écrit :
> On 2024-08-19 23:15:28 +0000, Richard Hachel said:
> 
>> Le 19/08/2024 à 22:32, "Paul.B.Andersen" a écrit :
>>> Below I show how two real clocks in the real world can be
>>> synchronised, strictly according to Einstein's method.
>>> 
>>> We have to equal clocks C_A and C_B. They are not synced in any way,
>>> but they are using the same time unit, let's call it second.
>>> The clocks run at the same rate.
>>> 
>>> In our very big, inertial lab, we have two points A and B which are
>>> separated by some distance. Let's call the transit time for light
>>> to go from A to B is x seconds. We will _define_ that the transit time
>>> is the same from B to A. (This follows from Einstein's definition
>>> of simultaneity).
>>> 
>>> At point A we have:
>>> Clock C_A, a light-detector, a flash-light and a computer.
>>> The computer can register the time shown by C_A when
>>> the flash-light is flashing, and when the light-detector
>>> registers a light-flash.
>>> 
>>> At point B we have:
>>> Clock C_B, a light-detector, a mirror and a computer.
>>> The computer can register the time shown by C_B when
>>> the light-detector registers a light-flash.
>>> 
>>> In the following we will synchronise clock C_B to clock C_A.
>>> That is, we will adjust clock C_B so it become synchronous
>>> with clock C_A.
>>> 
>>> Now we let the flash-light at point A flash.
>>> At this instant, C_A is showing tA = n seconds.
>>> tA is measured by C_A at A.
>>> 
>>> When the flash hits the light-detector at B,
>>> Clock C_B shows tB = m seconds.
>>> tB is measured by C_B at B.
>>> 
>>> A short time later the light detector at A registers
>>> the light reflected by the mirror at B.
>>> At this instant Clock C_A shows t'A = n + 2x seconds.
>>> t'A is measured by C_A at A.
>>> 
>>> Einstein:
>>> "The two clocks synchronise if  tB − tA = t'A − tB."
>>> 
>>> Or: tB = (tA + t'A)/2 = (n+n+2x)/2 = (n + x)
>>> 
>>> That is, to be synchronous clock C_B must show a time midway
>>> between tA and t'A when the light is reflected by the mirror.
>>> So  tB should show (n + x) seconds when the light is reflected
>>> by the mirror.
>>> But at that instant tB is showing m seconds, so to make the two
>>> clocks synchronous, we must adjust clock C_B by:
>>> δ = (n-m) + x seconds.
>>> 
>>> 
>>> After this correction, we have:
>>> 
>>> tB  − tA = (m - n) seconds +  δ     = x seconds
>>> t'A − tB = (n + 2x - m) seconds - δ = x seconds
>>> 
>>> The clocks are now synchronised.
>>> 
>>> Please explain what in the above you find impossible
>>> to do in your lab.
>> 
>> I have explained these things a hundred times.
>> It is impossible to synchronize two watches A and B located in 
>> different places.
> 
> So you agree that Paul B. Andersen's prodedure is doable and achieves
> what you call "impssible".

It's much more complicated than that.
We can accept it for a Galilean frame of reference,
for example the Earth frame of reference.
But for an accelerated frame of reference, for example, it doesn't work 
anymore.
If we ask a relativistic physicist, for example Paul who is still an 
educated and intelligent person (compared to Python the clown) to give me 
the time taken by Bella to reach Tau Ceti (12 ly; a=1.052 ly/y²) he will 
answer me correctly and set To=(x/c).sqrt(1+2c²/ax)=12.9156 years.
The problem is, if I ask him for Bella's proper time, everything will sink 
into horror, because he will give me an incredibly low proper time, by 
performing an abstract integration adding abstract times. And there, it is 
unworthy of a relativistic science, and I think that in the decades to 
come we will understand the enormous blunder which consists in taking 
"reflections of reality" as real.

R.H.