Relativity of simultaneity question

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Discussion Overview

The discussion revolves around the concept of the relativity of simultaneity as presented in a specific chapter of a physics textbook. Participants explore the implications of Mavis's movement within a train and how it affects her perception of light flashes from different sources, raising questions about the consistency of light speed across different frames of reference.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Meta-discussion

Main Points Raised

  • One participant questions the interpretation of light reaching Mavis at different times, suggesting it implies that the flashes occurred at different times in her frame.
  • Another participant confirms that while the speed of light is constant in all frames, Mavis's movement leads her to conclude that the flashes were not simultaneous in her frame.
  • A participant acknowledges a misunderstanding related to the diagrams, indicating that they initially focused on the wrong elements and later realized their mistake.
  • There is a discussion about potential errors in the diagrams, with participants noting inconsistencies in the placement of points A' and B' across different images.
  • Some participants express agreement that the errors in the diagrams may have contributed to confusion regarding the relativity of simultaneity.

Areas of Agreement / Disagreement

Participants generally agree on the interpretation that Mavis perceives the light flashes at different times due to her movement. However, there is some disagreement regarding the clarity and accuracy of the diagrams presented in the textbook, with no consensus on whether these errors are significant to the overall understanding of the concept.

Contextual Notes

Participants note that the diagrams may have printing errors, leading to confusion about the positions of A' and B' in relation to Mavis's movement. This highlights potential limitations in the visual representation of the concepts discussed.

laurub
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i have a question about chapter 37.2 relativity of simultaneity (pearsons international edition university physics, 12th edition) .

the text besides image b sais: inside the train, mavis moves toward the light coming from the front of the train and away from the light coming from the back of train.

then image c shows the light from the front of the train reaching her first, in my understanding, this implies mavis sees the flashes at different times because she is moving towards the origin of one of the flashes.

this is very confusing to me, because what i learned in the previous chapter tells me that cA' = cB' no matter how the train moves.

Above statement is correct right?!

if it is, then why does it look like the images are trying to tell me cA' < cB' in mavis' frame.
 
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laurub said:
then image c shows the light from the front of the train reaching her first, in my understanding, this implies mavis sees the flashes at different times because she is moving towards the origin of one of the flashes.
The light reaches her at different times (everyone agrees with this) and she concludes that the light flashes must have happened at different times in her frame.

this is very confusing to me, because what i learned in the previous chapter tells me that cA' = cB' no matter how the train moves.
Yes, the speed of light is the same in every frame. This is what forces her to conclude that the flashes were not simultaneous in her frame.

if it is, then why does it look like the images are trying to tell me cA' < cB' in mavis' frame.
Please explain why you think that.
 
thank you, your response led me to seeing my mistake, i focussed so much on the arrows and waves from A' and B' that i did not see the arrows and waves from A and B, and this somehow led to my mistake.

I no longer think the images are confusing.

EDIT
I got confused because A' and B' in image a are on the corners of the train, in image b they aren't, and in image c they are again on the corners of the train.
is this a printing error?
 
Last edited:
laurub said:
thank you, your response led me to seeing my mistake, i focussed so much on the arrows and waves from A' and B' that i did not see the arrows and waves from A and B, and this somehow led to my mistake.

I no longer think the images are confusing.
Good. :approve:

EDIT
I got confused because A' and B' in image a are on the corners of the train, in image b they aren't, and in image c they are again on the corners of the train.
is this a printing error?
Looks like they were a bit sloppy with the diagrams. A' and B' are the ends of the train; they should move with the train.

I see that Mavis has moved to a different seat in diagram b. More sloppiness!
 
Doc Al said:
I see that Mavis has moved to a different seat in diagram b. More sloppiness!

yes, A' and B' are incorrectly moved the same amount of distance as mavis is.
they are probably caused by the same printing error since they both only occur in diagram b.
 
laurub said:
yes, A' and B' are incorrectly moved the same amount of distance as mavis is.
they are probably caused by the same printing error since they both only occur in diagram b.
I'll bet you are right.
 

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