THE RELATIVITY OF SIMULTANEITY:- Help me physics nerds (1 Viewer)

[student.hsc]

ok, this is a question i posed in class and my teacher, didnt know.

This is a standard model:

A flash of light is given off at the center of the train just when the two observers pass each other. The observer on the train sees the front and back of the train at fixed distances away from the source of the light flash. Assuming (stipulating) that the speed of light is a constant relative to the train, according to that observer the light flashes will reach the front and back of the train at precisely the same instant of time — simultaneously.
On the other hand, the observer on the platform sees the back of the train moving toward the point at which the flash was given off, and the front of the train moving away from it. This means that the light flash going toward the back of the train will have less distance to cover than the light flash going to the front. Assuming that the speed of light is the same in both directions relative to the platform, the flashes will not strike the ends of the train simultaneously.


My Question:

If the doors ONLY open if the light strikes them simultaneously, and the experiment is carried out, and the train subsequentially stopped, what will both observsers see? The same thing? (if so what- open or closed doors?) Or different?

This kinda reminds me of a relation (wherby one x value yields >1 y values). And it tends to make me think about parrelel universes.

PS: Although i dont like the HSC deffinition of a relation...:mad1:

 

[jest]

why would the doors be opening?

 

[student.hsc]

Q: "why would the doors be opening?"

A:

"according to that observer (the one on the inside) the light flashes will reach the front and back of the train at precisely the same instant of time — simultaneously."

" My Question:

If the doors ONLY open if the light strikes them simultaneously"



"although I'm not sure what you're saying about slowing the train to a stop."

I mean after the experiment was conducted, after the flash of light and to the guy on the inside the doors are open, and to the guy on the outside the doors are closed, the train is stopped


"I'm not entirely sure if I've got what you mean, but I'd say that both observers would see the doors open as the doors are in the frame of reference where the light strikes them simultaneously."

but then the only explanation is that there is no space/time dilation...


This question confuses the hell out of me...


BTW: Awesome response rate guys! 2 mins, thats so cool...

 

[student.hsc]

No, I'm pretty sure the doors would appear open to both of them while the train is still travelling at the high speed. Even though to the observer on the outside the light doesn't appear to strike simultaneously, the doors will still appear to open (as in fact they have). The doors are in the frame of reference that the light strikes simultaneously in, so they will open.

That's my take on it, anyway.

hmmm, I can see what your saying and I aggree, it seems that the doors are observers yes. But, einstein reckoned they did, I'm really just assuming that part about the difference in observation.

http://en.wikipedia.org/wiki/Relativity_of_simultaneity

And this leads me to the conclusion that:

a. Einstein and Lorentz were wrong

or

b. this creates a parrelel-universe type scenario...

 

[xiao1985]

re: the train subsequently stops...

it depends when does it stop, does it stop when the photon is already in motion?! or before it's ejected?!

also, if the train are to stop, it would involve an acceleration of the train, which would make the train non-inertial frame of reference, which eistien's special theory of relativity (what is being learnt in hsc) no longer applies...

 

[milton]

the train can't just stop instantaneously, the train has momentum and it takes time to decelerate. but once you include acceleration into the scenario, the whole thing changes and becomes GENERAL relativity

with your idea of parallel universes- there is an interpretation of quantum mechanics which proposes that at each moment in time, the universe splits into several alternate parallel universes each time a decision is made. i don't think you need parallel universes to understand special relativity, its perfectly plausible, alas a bit counterintuitive, that different people in different frames of reference have different versions of events i.e. there is no such thing as "absolute truth"

 

[student.hsc]

I wasn't saying that the doors are observers, just that they will appear to open to the observer on the outside as well - it is an event that occurs within the frame of reference of the train. The outside has no impact on whether the doors open - the doors are assumedly opening due to some mechanism on the train which causes them to open when it detects the light hitting each end of the train simultaneously. It will detect the light hitting each end of the train simultaneously and open the doors. The outside observer has no impact on whether the doors open and therefore sees them open despite not seeing the light hitting the end of the train simultaneously. This observer will see the mechanism to be faulty as despite the light not striking each end at the same time, the doors still open. I hope that makes sense?

That does make sense, thanks . My reference to the doors as observers makes sense too, because they observe a stimulus. I think my problem was that I wasn't distinguishing between the door's role as observers/reactors (if that makes sense?)

 

[bboundy]

This is ironic because a kid in my class asked the teacher almost that exact same question 2 days ago. Got us all stumped.