Tom Roberts alle ore 05:20:38 del 06/08/2017 ha scritto:
>> The "surprising causal effect" (real not apparent) [...]
>
> This is NOT "real" in the sense that it is part of a valid model
> of the world. Causality is not involved, as at the instant the
> traveling twin measures (or computes) the home twin's age they are
> separated by a spacelike interval.
>
> Consider how the traveling twin would measure the home twin's age:
> there would have to be an assistant at rest in the traveling twin's
> inertial frame pre- positioned to be co-located with the home twin
> at the instant of the measurement, who observes the home twin's
> clock; this assistant would then send the measurement data to the
> traveling twin. Do this immediately before and immediately after
> the traveling twin turns around, and the assistants are located and
> moving very differently -- it's no surprise that their measurements
> are very different, as the assistants' clocks are synchronized very
> differently with the traveling twin's clock. It is, of course, that
> change in clock synchronization that is the underlying effect.
>
> The home twin, of course, is completely unaffected and notices
> nothing (except the traveling twin's assistants, who pass by in
> opposite directions many years apart).
>
> The whole notion of "what does the traveling twin measure" is highly
> artificial, requiring outrageously impractical assistants; Fontenot's
> "CADO frame" is merely a way to compute the highly artificial value
> that such assistants would measure. As "all physics is local"
> [Einstein and others], this is not part of any valid model of the
> world; it is a measurement over a spacelike interval. The aspect
> of this that proves its artificiality is the fact that it is
> coordinate dependent -- coordinates are arbitrary human constructs
> which Nature does not use, and no natural phenomenon can possibly
> depend on such an arbitrary human choice....
>
> What is real (i.e. unambiguous) is the comparison of the twins'
> ages when they reunite. That is both independent of coordinates and
> very non-local.
>
> Tom Roberts
La distanza TS tra la Terra T e la stazione spaziale S è
perfettamente misurabile senza che ci sia bisogno di assistenti e
quant'altro.
Dalla terra basta inviare segnali elettromagnetici e aspettare il
ritorno.
Il gemello (o chi per lui) l'ha già fatto e quindi sa che la "misura"
della distanza TS è di quasi 40 anni-luce.
Poi il gemello parte e arriva alla stazione spaziale S dove esegue
un'altra misura col suo orologio che segna il tempo di 5 anni.
Quest'altra misura gli garantisce che il viaggio è durato 5 anni e
quindi l'effettiva distanza reale percorsa è stata di quasi 5 anni-luce
(non potrebbe essere altrimenti perché in 5 anni non si possono
percorrere 40 anni-luce!).
Le due "misure" (prima e dopo l'accelerazione) documentano
inequivocabilmente che la distanza Terra-StazioneSpaziale era di quasi
40 anni-luce prima dell'accelerazione e s'è ridotta a quasi 5 anni-luce
dopo l'accelerazione.
Nessuna apparenza, nessun "modello" e nessuna necessità di
assistenti, solo "misure reali" e nient'altro.
Ed è solo l'accelerazione che fa la differenza tra il gemello che
parte e quello che resta, perché uno ce l'ha e l'altro no.
Invece la velocità non discrimina alcunché perché nessuno dei due
gemelli ha una velocità più legittima dall'altro.
E' quindi l'accelerazione (e non la velocità) che contrae lo spazio
e, conseguentemente, dilata il tempo.
Luigi.
(The TS distance between Earth T and Space Station S is perfectly
measurable without the need for assistants and more. From the ground
just send electromagnetic signals and wait for the return. The twin (or
who for him) has already done so and knows that the "measurement" of
the TS distance is almost 40 years-light. Then the twin starts and
arrives at Space Station S where he does another measure with his watch
marking the 5-year time. This other measure guarantees that the journey
lasted 5 years and therefore the actual real distance traveled was
almost 5 years-light (it could not be otherwise because in 5 years you
can not travel 40 light years!). The two "measurements" (before and
after acceleration) unambiguously document that the
Earth-StazioneSpaziale distance was close to 40 years-light before
acceleration and reduced to nearly five years-light after
acceleration. No appearance, no "model" and no need for assistants,
only "real measures" and nothing else. And it is just the acceleration
that makes the difference between the twin part that left and what
remains, because one has it and the other does not. But speed does not
discriminate anything because neither of the two twins has a more
legitimate speed on the other. It is therefore the acceleration (and
not the speed) that contracts the space and consequently expands the
time).
--
Luigi Fortunati
Credere e' piu' facile che pensare
Believing is easier than thinking
Received on Mon Aug 07 2017 - 09:10:35 CEST