When two (or more) relativistic observers intersect, they are all
observing the same universe.
It is in this that the notion of simultaneity is invariant by change of
frame of reference.
What varies, by change of frame of reference, is chronotropy. That is to
say the way that beat
reciprocally the watches (each sees the other beating less quickly). But
not the notion of simultaneity.
We have to give things very precise definitions.
The notion of simultaneity is defined by the set of events which occur at
the same instant.
We note this with a time. It is said that the event occurred at five
o'clock.
The notion of chronotropy is a notion of duration. It is said that such an
event occurred for fifteen years, but that in another frame of reference,
it occurred for nine years.
Simultaneity and chronotropy are not the same thing.
By an abuse of language, one says: "Two watches placed in different
inertial frames of reference, have different notions of simultaneity".
I have always found these terms improper, and confusing to the student.
The student will then start to believe that if two (or more) observers
cross each other in space,
each will see a different universe, at different times. That's not what it
means.
From there will be born the famous paradox of the "war of Andromeda".
This may also give rise to misunderstandings in the description of the
evolutions of Langevin's traveler.
I take this opportunity to put back here the correct transformation for
the effective crossing of several relativistic interveners AT THE MOMENT
of their crossing.
I specify well, at the time of their crossing.
I thus try to avoid the criticisms of people very prompt and very eager to
criticize an opinion which they did not only include / understand, or
worse, and there, it is much more dramatic, which they have, at least in
part, fully understood.

<http://news2.nemoweb.net/jntp?2Ke7DpA1B8BE1bgGB_cBqZxMS1E@jntp/Data.Media:1>

R.H.

--
Clic here to full screen ---> <http://news2.nemoweb.net/?DataID=2Ke7DpA1B8BE1bgGB_cBqZxMS1E@jntp>

On 26-Dec-21 1:54 pm, Richard Hachel wrote:
> When two (or more) relativistic observers intersect, they are all

> I have always found these terms improper, and confusing to the student.

Whereas taking a word from a completely different field, and then giving
it a different meaning, won't confuse students at all.

Sylvia.

Le 26/12/2021 à 04:20, Sylvia Else a écrit :
> Whereas taking a word from a completely different field, and then giving
> it a different meaning, won't confuse students at all.

The important thing to understand in science is that sometimes ideas or
concepts are not clear.
If we add the fog of words, things get even more difficult.
I have seen that many people think, for example, that there is a possible
"time-gap" in the Langevin (which would mean that when the brother turns
around, he sees the watch of the earthly brother jump from several years,
others think that there is a contraction of the distances and that it
should be quantified at l'= l.sqrt(1-v²/c²) and therefore that if I
move, at 0.8c to go replay a star close to 12 light years, I will travel
7.2 light years,
others think, finally, that the notion of simultaneity is relative when
observers cross paths, and that we can calculate a time lag, see the
preparations for a war which has already taken place observed (paradox of
the Andromeda war) and thus, perhaps, prevent it.
If there are these things, if there are cranks, it is because the bases of
the theory are poorly understood, and that some reasoning is not quite
right, even if, of course, I am not thinking to reconsider the theory of
relativity. Just refine the basics so that everyone can better understand
and accept it.

R.H.

Richard Hachel wrote:

> When two (or more) relativistic observers intersect, they are all
> observing the same universe.

8 more points for you:

,-<https://math.ucr.edu/home/baez/crackpot.html>
|
| The Crackpot Index
|
| […]
|
| 4. 3 points for every statement that is logically inconsistent.
|
| 5. 5 points for each such statement that is adhered to despite careful
| correction.

PointedEars
--
Q: What happens when electrons lose their energy?
A: They get Bohr'ed.

(from: WolframAlpha)

Le 26/12/2021 à 14:53, Thomas 'PointedEars' Lahn a écrit :
> Richard Hachel wrote:
>
>> When two (or more) relativistic observers intersect, they are all
>> observing the same universe.
> 8 more points for you

Aucun intérêt.

Vous n'avez rien d'autre à faire?

Essayez au moins, si vous voulez intervenir, de répondre aux questions,
ou d'apporter une contribution à la phrase.

Ici, la question posée est nécessite une réponse claire : "c'est vrai
ou c'est pas vrai"?

Quand j'écris cela : C'EST VRAI OU C'EST PAS VRAI?

> PointedEars

R.H.

Richard Hachel wrote:

> Le 26/12/2021 à 14:53, Thomas 'PointedEars' Lahn a écrit :
>> Richard Hachel wrote:
>>> When two (or more) relativistic observers intersect, they are all
>>> observing the same universe.
>
>> 8 more points for you
>
> Aucun intérêt.

Did you notice that despite you are fully capable to write understandable
English, you are switching to French when you have run out of arguments?

It is a pathological behavior of you, a desperate attempt to have the final
word.

Tough luck.

PointedEars
--
Q: Where are offenders sentenced for light crimes?
A: To a prism.

(from: WolframAlpha)

Thomas 'PointedEars' Lahn wrote:
> Richard Hachel wrote:
>
>> Le 26/12/2021 à 14:53, Thomas 'PointedEars' Lahn a écrit :
>>> Richard Hachel wrote:
>>>> When two (or more) relativistic observers intersect, they are all
>>>> observing the same universe.
>>
>>> 8 more points for you
>>
>> Aucun intérêt.
>
> Did you notice that despite you are fully capable to write understandable
> English, you are switching to French when you have run out of arguments?
>
> It is a pathological behavior of you, a desperate attempt to have the final
> word.

When out of arguments, on fr.sci.*, Richard "Hachel" Lengrand (M.D.)
switches from French to Latin. Same psychopathology.