# Relativity of simultaneity question

• laurub
In summary, Mavis observes that the light flashes from the front and back of the train reach her at different times, leading her to conclude that they were not simultaneous in her frame. This is confusing because it goes against what she learned in the previous chapter about the speed of light being the same in every frame. The images in the book may be misleading due to printing errors, such as A' and B' being incorrectly positioned in diagram b.
laurub
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.

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.

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.

## 1. What is the concept of relativity of simultaneity?

The relativity of simultaneity is a concept in Einstein's theory of special relativity that states that the simultaneity of two events is not absolute, but depends on the observer's frame of reference. This means that two events that appear simultaneous to one observer may not appear simultaneous to another observer in a different frame of reference.

## 2. How does time dilation affect the relativity of simultaneity?

Time dilation, another consequence of special relativity, also plays a role in the relativity of simultaneity. Time dilation states that time passes slower for objects moving at high speeds. This means that two events that appear simultaneous to a stationary observer may not appear simultaneous to an observer on a moving object due to differences in the passage of time.

## 3. What is the thought experiment used to explain the relativity of simultaneity?

The famous thought experiment used to explain the relativity of simultaneity is the "train and platform" scenario. In this scenario, a stationary observer on a platform sees two lightning strikes at the same time, but a person on a moving train sees the lightning strikes at different times due to their frame of reference.

## 4. How does the relativity of simultaneity challenge our understanding of time and space?

The relativity of simultaneity challenges the classical understanding of time and space as absolute and independent. It shows that time and space are not absolute, but are relative concepts that depend on the observer's frame of reference. This challenges our intuitive understanding of the world and requires a shift in thinking about the nature of time and space.

## 5. What evidence supports the relativity of simultaneity?

There have been numerous experiments and observations that support the relativity of simultaneity, including the famous Michelson-Morley experiment and the Hafele-Keating experiment. Additionally, the phenomenon of time dilation has been observed and confirmed through experiments, providing further evidence for the relativity of simultaneity.

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