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Einstein's clock synchronization live

Auteur :Max Born

Definition

Definition
S. 894: "Wir haben bisher nur eine "-Zeit" und eine "-Zeit", aber keine für und gemeinsame "Zeit" definiert. Die letztere Zeit kann nun definiert werden, indem man durch Definition festsetzt, dass die "Zeit", welche das Licht braucht, um von nach zu gelangen, gleich ist mit der "Zeit", welche es braucht, um von nach zu gelangen." We have not defined a common “time” for  and , for the latter cannot be defined at all unless we establish by definition  that the “time” required by light to travel from to equals the “time” it requires to travel from to . Let a ray of light start at the “A time” from towards , let it at the “B time” be reflected at B in the direction of , and arrive again at at the “A time” . In accordance with definition the two clocks synchronize if . We assume that this definition of synchronism is free from contradictions, and possible for any number of points; and that the following relations are universally valid. In agreement with experience we further assume the quantity , to be a universal constant—the velocity of light in empty space. We imagine further that at the two ends A and B of the rod, clocks are placed which synchronize with the clocks of the stationary system, that is to say that their indications correspond at any instant to the “time of the stationary system” at the places where they happen to be. These clocks are therefore “synchronous in the stationary system.” We imagine further that with each clock there is a moving observer, and that these observers apply to both clocks the criterion established in § 1 for the synchronization of two clocks. Let a ray of light depart from A at the time , let it be reflected at B at the time , and reach A again at the time . Taking into consideration the principle of the constancy of the velocity of light we find that  and where denotes the length of the moving rod—measured in the stationary system. Observers moving with the moving rod would thus find that the two clocks were not synchronous, while observers in the stationary system would declare the clocks to be synchronous. In order to understand the durations  and   just look at http://ggbtu.be/m2418133
Wenn man die Nummer des Hauses nicht kennt, an das man eine Pizza liefern soll, nutzt es nichts, wenn man durch Definition festsetzt, dass es das Haus in der Mitte der Straße sein solle.
If you don't know the number of the house to that you have to deliver some pizza, it will be nothing to establish by definition that the house in the middle of the street is that one. 
Jeder mag definieren, was ihm gefällt. Was als ableitbar behauptet wird, muss auch ohne Definition ableitbar sein (Merke: Nicht-Kreativität, Eliminierbarkeit und Nominalität sind die Kennzeichen von Definitionen). Kann man mit Hilfe einer Definition eine Bedeutung ‚erschaffen‘, die ohne sie nicht existiert hätte? Can we give reference by definitions which was not there before? Note: You cannot give reference if you don't have some. Man kann mit Definitionen keine Erkenntnisse gewinnen. You cannot gain insights by definitions.

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