Reference: Einstein’s 1920 Book
Section VIII (Part 1)
On the Idea of Time in Physics
Please see Section VIII at the link above.
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Summary
To define time properly, we require a definition of simultaneity such that this definition supplies us with the method by means of which two events can actually be observed to occur at the same time. This stipulation must be satisfied regardless of any other condition for two events to be considered simultaneous.
We place identical clocks at the position of the events. These clocks tick at the same rate, so their pointers are going to move simultaneously. By reading the position of the pointer when the event occurs, we can assign a time value to that event.
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Comments
The time value shall be read differently from different distances because of the finite velocity of light.
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