Trying to Understand Light in Motion: A Frustrating Puzzle

[Doc Al]

that is true

but A and B are still the source for what both frames see

and C is the position of the observer when they see it - they do not see it at A and B

C is at the position of the train observer. C represents the event of the light from each end reaching the train observer.

So what?

 

[solarflare]

C is at the position of the train observer. C represents the event of the light from each end reaching the train observer.

So what?

so that means that A and B are the source of the light

 

[solarflare]

and as the sources are both at t = 0

then they must be simultaneous

 

[Doc Al]

and as the sources are both at t = 0

then they must be simultaneous

Simultaneous according to whom?

 

[solarflare]

I made this spacetime diagram a while ago, and I *think* it corresponds to the original scenario that is being discussed here. Maybe it will help. The "worldline" of the train (which is its path through spacetime) is clearly indicated, and it of course coincides with the t' axis:

The worldline of the photon that is coming in from the front (i.e. from the positive side) clearly intercepts the worldline of the train before (i.e. at a smaller value of t') the worldline of photon that is coming in from the rear (negative side) does.

The coordinate grid I've drawn is for the train observer, in the primed (t',x') coordinate system.

this was posted to show the videos worldline

the strikes are along the X axis both at t = 0

as they occur on the train - they must be simultaneous

the light then travels from the sources to the platform observer at t = 4

the lines also cross the t prime line but the x prime line is not used to show where they cross on the t prime line

if the x-axis used to show the strikes for both frames then t = 0 is where they originated from for the t prime line

this means that they struck the train simultaneously in the trains frame also but the train moves forward to meet the front strike and away from the rear

 

[Doc Al]

this was posted to show the videos worldline

Once again, you have switched scenarios. This diagram is for the standard scenario in which the lightning strikes are simultaneous in the platform frame.

the strikes are along the X axis both at t = 0

Yes, in the platform frame.

as they occur on the train - they must be simultaneous

The fact that they occur 'on the train' is irrelevant. They are simultaneous in the platform frame, not the train frame.

the light then travels from the sources to the platform observer at t = 4

Sure, it takes time for the light to travel to the platform observer.

the lines also cross the t prime axis but the x prime line is not used to show where they cross on the t prime line

You should be able to draw in the lines to see where and when the events (the lightning strikes) happen in the train frame.

 

[solarflare]

it is not irrelevant when the graph says they occur on the train simultaneously

and again the lines cross t prime from the source on the x-axis

if you want to say that t prime is relevant then the source of the lines that cross t prime must also be relevant

 

[Doc Al]

This thread is obviously going nowhere (and very slowly at that). So it's time to shut it down.

Solarflare: All your questions have been answered several times over. Repeating the same thing isn't going to help. If you're serious, I suggest getting an intro book on relativity. (Or you can read Einstein's own words--see George's link.) Then you can go back and read through this thread again.

Thanks to everyone who contributed their time and effort to this thread.