A special point in special relativity

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Discussion Overview

The discussion revolves around a scenario in special relativity involving a moving train and the synchronization of clocks between different reference frames. Participants explore the implications of Lorentz transformations, the relativity of simultaneity, and the observer's perspective on time measurement in different frames. The focus is on understanding the significance of a specific point in time and space where the observer's clock matches that of a car on the train.

Discussion Character

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

Main Points Raised

  • Some participants describe a scenario where an observer sees a train moving at speed v=sqrt(3/4)*c and calculates that the clock in a car shows the same time as the observer's clock at a specific moment.
  • Others argue that the simultaneity of clocks in different frames is not guaranteed, emphasizing the relativity of simultaneity and that events simultaneous in one frame may not be in another.
  • A participant introduces Lorentz transformation equations and proposes a method to find a point where the observer's clock matches that of a car, suggesting that this point can be calculated and is significant.
  • Some express skepticism about the special nature of this point, questioning the arbitrary nature of the coordinate and time settings used in the calculations.
  • Concerns are raised regarding the observer's ability to actually see the time on a remote clock, noting that light travel time affects what the observer perceives.
  • Participants discuss the implications of time dilation and how different observers may perceive time and distance differently due to their relative motion.

Areas of Agreement / Disagreement

Participants express differing views on the significance of the calculated point where the observer's clock matches that of a car. While some see it as a meaningful consequence of the Lorentz transformations, others question its importance and highlight the arbitrary nature of the definitions involved. The discussion remains unresolved regarding the special nature of this point.

Contextual Notes

Limitations include the dependence on specific definitions of time and distance, the effects of light travel time on observations, and the unresolved nature of the implications of the Lorentz transformations in different reference frames.

  • #31
n_ktt said:
All clocks should show the same time, or I’m wrong.
You are wrong. See post 24.

The key is understanding the relativity of simultaneity.
 
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  • #32
When the train is at rest with respect to the ground (prior to its initial acceleration), its clocks can be synchronized with one another and with the clocks on the ground. But, during the acceleration of the train, the clocks on the train will fall out of synchronization with one another (and with the clocks on the ground). This is analogous to the gravitational time dilation effect.

After the acceleration is complete, and the train is now traveling at constant speed, its clocks can be resynchronized with one another. At this point, the locations on the train and the clock times on the train can be related to those on the ground by the Lorentz transformation. But, when the train next decelerates down to zero speed relative to the ground, its clocks will again fall out of synchronization, so that when it stops, they will again have to be resynchronized with one another and, if desired, with those on the ground. If, after the initial acceleration, the clocks on the train are not resynchronized with one another, then my guess is that, after the final deceleration down to zero speed, the clocks on the train will again be in synchronization with one another and with those on the ground. However, I am not sure of this, since I have not analyzed the problem in detail. Maybe another responder with more experience than I could address this.

Chet
 

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