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Subject: Re: [SR and synchronization] Cognitive Dissonances and Mental Blockage
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From: Richard Hachel <r.hachel@wanadou.fr>
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Le 01/09/2024 à 08:46, Thomas Heger a écrit :
> No, not really...
> 
> Many textbooks about relativity use the picture of a train with one 
> observer on the banks of the track and one within the train.
> 
> These observers are usually placed in the middle between two 
> simultaneous events at both ends of the train.
> 
> Now the man on the bank has kind of special mirror, which allow him to 
> see both flashes at the same time.
> 
> Then relativity of simultaneity is explained as different observations 
> on the bank and in the train.
> 
> But I would require to remove the delay, caused by the finite speed of 
> light, what would make both observations equal.
> 
> And as far as I call tell, Einstein used the picture from above, because 
> he made no attempts to remove the delay.
> 
> His concept would allow to synchronize clocks, too, but only two clocks 
> at a time.
> 
> In contrast I would use a different concept and use a hypothetical 
> signal with infinite velocity to define simultaneity.
> 
> To make light usuable I would measure the delay and add that to the 
> observed time value (seen at the remote clock).
> 
> This would allow a time measure, which is valid for the entire frame of 
> reference.
> 
> 
> TH

No, that is the relativity of chronotropy, not of simultaneity.

If two men are in the same place, we call that a joint event; and we will 
take the example of a man sitting in a train (or a rocket) and who passes 
in front of a man on the platform (or on the earth).

In this very specific case, the two men, even in relative speed of Uo=0.6c 
or Vo=0.8c, have EXACTLY the same simultaneity of universes. It is 
extremely simple to understand, but extremely difficult to teach.

For example, one observes the explosion of a supernova and receives a 
burst of neutrinos and photons; the other will observe it and receive them 
too.

It is so obvious that any attempt to deny the fact will quickly drift into 
the grotesque and the absurd.

This means that, for both observers, the visible universe is simultaneous 
(with Lorentz deformations on x).

x'=(x+Vo.To)/sqrt(1-Vo²/c²)
y'=y
z'=z
t'=t
To'=(To+x.Vo/c²)/sqrt(1-Vo²/c²)

We therefore have a relativity of the internal chronotropy of the watches 
of the two observers (they do not beat at the same speed, and each one 
turns faster than the other, which is not a paradox once the theory is 
understood and the notion of anisochrony integrated into the whole 
description), but at this very precise moment, they mark the same time (it 
will not last long), exist in the same present moment, and observe an 
absolutely identical present universe.

R.H.