How does Einstein define simultaneity in his 1905 paper?

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Discussion Overview

The discussion revolves around Einstein's definition of simultaneity as presented in his 1905 paper "On the Electrodynamics of Moving Bodies." Participants explore the clarity and implications of Einstein's treatment of clocks and time, addressing both theoretical and conceptual aspects of relativity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express admiration for Einstein's paper but note that it may not be entirely clear, particularly regarding his definitions of time and simultaneity.
  • One participant emphasizes that Einstein's clocks serve as idealized constructs for measuring time, suggesting that the discussion of ideal clocks is crucial for understanding the paper.
  • Another participant highlights the importance of additional assumptions required for synchronizing clocks beyond immediate proximity, indicating that this is a significant aspect of special relativity.
  • Concerns are raised about the interpretation of "immediate neighborhood" in relation to clock synchronization, with a participant providing a quantitative perspective on tolerable timing errors.
  • Some participants question whether Einstein's mention of clocks with hands is relevant to the concept of time measurement, suggesting that the existence of an ideal clock is more important than the physical characteristics of actual clocks.
  • There is a discussion about the potential confusion arising from the idea that different types of clocks might keep different kinds of time, with a participant cautioning against this line of reasoning as a distraction.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the clarity of Einstein's definitions or the implications of his treatment of clocks. Multiple competing views remain regarding the interpretation of simultaneity and the role of ideal clocks in the discussion.

Contextual Notes

Some participants note that Einstein's initial presentation of relativity has been refined over the decades, suggesting that the 1905 paper may not represent the final understanding of his theories. Additionally, there are unresolved questions about the assumptions underlying clock synchronization and the nature of time measurement.

  • #61
Aufbauwerk 2045,

Also, in OEMB Section 1 when Einstein talks about an observer "in the neighborhood" of the clock, or the clock "in the neighborhood" of the event, he's only minimizing the light travel time (delay) from event to clock, and/or clock to observer('s eyes). An observer (A) at a train station with clock in hand, knows the train arrived at 7pm ... little hand at 7 and train at station. If an observer (B) 20 light seconds away (say also at rest with the train station) awaits light signals from that distant event, the received light image shows the clock arrived at the station at 7, by the clock on the wrist of he at the station. However, this distant observer's own clock then reads 7:00:20, not 7 ... because light takes 20 sec to traverse a 20 light-sec separation. If that observer (B) used his own clock to define the event, he'd say the train arrived at 20 sec after 7. So this is what Einstein is pointing out in Section 1, when he talks about "in the neighborhood of". As stated in the thread already, he's defining the situation whereby the light's flight time from event to clock, or clock to eyes, is "negligible enough for all intents and purposes". As such, your own clock's time readout that you see "is essentially" the time the event occurred (train at station). The observer, his clock, and the event, are essentially in-the-same-place-at-the-same-time.

Best Regards,
GrayGhost
 
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  • #62
Sorry, I have a type-O correction in my prior ...

I wrote ... ", the received light image shows the clock arrived at the station at 7, by the clock on the wrist of he at the station."

I should have written ... ", the received light image shows the train arrived at the station at 7, by the clock on the wrist of he at the station."

The paper reference being ... http://www.fourmilab.ch/etexts/einstein/specrel/www/

Best Regards,
GrayGhost
 
  • #63
EDoMb Section 1 is called Definition of Simultaneity.

It does not define simultaneity of separated clocks. It defines synchrony of separated clocks.

EDoMB Section 2, in connection with "discovered length" makes reference to "definite time." Definite time is simultaneity at separate locations, the endpoints of a rigid body.

Section 2 ultimately uses synchrony and not simultaneity for discovered length, synchrony having been plausibly defined in Section 1.

Einstein's article in The 14th Encyclopedia Britannica ( title: Space-Time ) roughly 1930, says "there is no such thing as absolute simultaneity."

Algebraically, simultaneity at separate locations A and B is: tA = tB. No such equation appears in EDoMB and is very hard to find anywhere on the web. It is not in the EB article.
 
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