Re: The problem of relativistic synchronisation

Le 30/08/2024 à 15:20, Paul.B.Andersen a écrit :

Den 30.08.2024 00:15, skrev Richard Hachel:
 Let's analyse Richard's post.

>
Speaking of that, personally, I give up a little, even if I am convinced of the usefulness of a short article of a few lines on the notion of simultaneity
and synchronization (the basis of RR).
I think that on average (too bad if it hurts them) the regulars are too stupid, I especially mean too stupid aside from the dick, the dick, always the dick.
It's very unfortunate, but we don't come out any more here on the Anglo-Saxon forums than on the French-speaking forums. It will be about who is the stupidest with the biggest dick.

 I have never seen anybody but Richard Hachel boast of his big dick,
so who are the "regulars" he is accusing of doing so?
 

>
It's a shame, there is nevertheless food for thought, and certain reflections are sometimes interesting,
like the posts on relativistic synchronization between two points A and B.

 So Richard is talking about Einstein's synchronisations method.
 

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It sometimes goes well (like your explanations of events e1, e2, e3) and the fact that we can already
offer CAREFUL evidence before going any further.

 "You" is probably Python. Richard never quote what he is
referring to, and he doesn't define the events e1, e2, e3.
But we know:
e1 is the event that light is emitted from A
e2 is the event that light is reflected from B
e3 is the event that the reflected light hits A
 Note e1 and e3 are happening at A, e2 is happening at B.
 

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We can then pose without fear: tA(e3)-tA(e1)=2AB/c

 tA(e3) is the reading of a clock at A at the event e3
tA(e1) is the reading of a clock at A at the event e1
 Einstein says:
"We assume the quantity 2AB/(tA(e3)-tA(e1)) = c
  to be a universal constant—the velocity of light in empty space."
 It is a postulate in SR that say the speed of light
in vacuum is constant and invariant, and his paper is about
the consequence of the postulates, so of course he assumes that.
 It is thoroughly experimentally verified that the speed
of light indeed is constant and invariant.
So we _know_ that tA(e3)-tA(e1)= 2AB/c
 

Then, admitting that A warns of e1 and e3, either with photons or with slugs of the same speed, any point M of the stationary frame of reference, we have yet another tautology:

 This statement doesn't parse.
 

>
tM(e3)-tM(e1)= tA(e3)-tA(e1) = 2AB/c

 tM can only be the reading of a clock at the point M,
which is an arbitrary stationary point in the frame where
A and B are stationary.
 But the events e1 and e3 happen at A, and not on M,
so tM(e3)-tM(e1) is meaningless.
 Richard doesn't seem to know what an event is.
 

For the moment we cannot say more about the speed of light between A and B in the direction AB,
nor in the BA sense.

 Above Richard say the posts on relativistic synchronization
between two points A and B are interesting, but so far he
has said nothing about synchronization.
 The equation:
   tB(e2) - tA(e1) = tA(e3) - tB(e2)
is Einstein's _definition_ of synchronism and simultaneity.
If this equation is true, then the clocks are synchronous
in the frame where A and B are stationary.
 

>
On this, we breathe we breathe, Einstein does not seem to agree with Hachel. For Einstein, the question does not arise, and it seems certain that t(AB)=t(BA).

 What are you saying? :-D
 Einstein says:
"We have not defined a common “time” for A and B, for the latter
  cannot be defined at all unless we establish _by definition_
  that the “time” required by light to travel from A to B equals
  the “time” it requires to travel from B to A."
 And:
  "In accordance with definition the two clocks synchronize if
      tB(e2) - tA(e1) = tA(e3) - tB(e2)"
   tB(e2) - tA(e1) is the time the light uses to go from A to B
  tA(e3) - tB(e2) is the time the light uses to go from B to A
 Einstein _defines_ that the clocks simultaneously show
the same (are synchronous in the stationary system)
if the time the light uses to go from A to B equals
the time the light uses to go from B to A.
 

>
Except that this is no longer true in an anisochronous environment, and that our universe is not "a 4D hyperplane of absolute simultaneity, even for a simple inertial frame of reference".
We can then propose A synchronization based on A hyperplane of simultaneity, but we must propose THE appropriate candidate, and it can obviously be neither A nor B.
So we continue from there.
We can then propose a synchronization of A and B by M (and we will have a synchronization of type M).

 SR doesn't depend on the definition of simultaneity
(but everything would be very awkward without it)
so another definition is possible.
 But in the real world no other than Einstein's definition
would work, so no one would use your alternative definition.

This is exactly what I tried to explain him on fr.sci.physique.
In vain.