Length contraction depends on the distance of the object?

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Discussion Overview

The discussion centers around the concept of length contraction in special relativity, particularly whether it depends on the distance of an object from an observer. Participants explore the implications of a scenario involving a train moving at a significant fraction of the speed of light and how this affects the perceived length of the train at different times.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that length contraction might vary based on the distance of the object from the observer, questioning if the length of the train would change at different times due to its distance.
  • Another participant argues that the problem pertains to the visual appearance of length contraction as perceived by an observer, clarifying that actual measured length contraction does not depend on the observer's distance.
  • A participant seeks to visualize the situation through a diagram, asking for feedback on whether it accurately represents the scenario of length contraction.
  • Another participant advises to redraw the diagram to include the worldlines of the train, indicating a need for a more precise representation of the situation.

Areas of Agreement / Disagreement

Participants express differing views on whether length contraction is influenced by the distance from the observer, indicating that multiple competing perspectives remain in the discussion.

Contextual Notes

The discussion highlights potential confusion between visual perception and actual measurements of length contraction, as well as the importance of accurately representing relativistic effects in diagrams.

Who May Find This Useful

Individuals interested in special relativity, particularly those exploring concepts of length contraction and its implications in different observational contexts.

Shukie
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http://home.orange.nl/kuip3148/phys1.JPG

Not exactly homework, but a problem I found in my lecture notes. The train is moving at a constant speed 0.5c. Question b asks what the length of the train will be then at t = -1. From what I understand, this suggests that length contraction depends on the distance the object is away from an observer? So at t = -5 the length contraction would be different?
 
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It seems that this problem is asking about the visual appearance of length contraction as seen by a particular observer, not the actual measured length contraction--which is obtained after accounting for light travel time and is the same for all observers within a frame. The actual measured--not just "seen"--length contraction does not depend on distance from any particular observer, since it's not a simple visual effect.
 
Thanks for your answer. I'm just trying to visualize what is going on and so I made a drawing. Can you tell me if this is in any way resembles what is actually going on?

http://home.orange.nl/kuip3148/phys2.GIF

The green line would be the length Bob observes, while the black thingy denotes the actual length of the train.
 
Last edited by a moderator:
Redraw your diagram to show the worldlines of the front and rear of the train. They should be parallel, but not overlapping.
 

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