simple relativity question

two people are on a train, they will set their clock, on opposite ends of the train, to 12:00 when a flash is seen emitted from a bulb at the centre of the train, equidistant from each person. An observer watches from a platform, and says that the two events of setting the clock were NOT simultaneous while another observer says that they were. Since each viewpoint is equally valid, when the the people step off the train, what will their clocks actually read? is there a discrepancy or not?

From the outside observer's point of view, the clocks will re-synchronize as the train slows to a stop.

>>1

You should realize that the train would be very far away from the platform, and that both viewpoints are valid. Something that is 1 light year away from us is also 1 year in the past.

It's also a consequence of relativity that two simultaineous events in a particular inertial (0 acceleration) frame of reference are not neccesarily simultaneous in another inertial frame of reference. That is just how space-time works.

>>3
You should realize that the train would be very far away from the platform
What? Why? That doesn't make sense.

By the way OP, I'm only guessing in >>2. Ask a physicist (or break out the physics textbooks and work it out.)

The thing about these 'story form' questions is that they serve only to obfuscate what is usually a very simple problem. If you clearly reformulate the problem in terms of objects being accelerated, you'll easily see how everything works out.

>>2

The clocks won't resychronize because they will decelerate at the same rate.  Nothing to make time pass differently for either clock.

>>1

As for the main problem, yes, both viewpoints are equally valid, but since the clocks were both in the same reference frame, they will both read the same once the train stops.  The observer can swear up and down that the light hit the clocks at different times, and he'll be right in his reference frame, but the clocks record time from the train reference frame, so they will show the same time.

>>6
As for the main problem, yes, both viewpoints are equally valid, but since the clocks were both in the same reference frame, they will both read the same once the train stops.
This doesn't make sense. The observer on the platform sees them set the clocks to 12:00 at DIFFERENT times, hence the clocks will read different times from the observer's point of view. You say yourself that the clocks won't resynchronize, so how on earth will they read the same time when the train is stopped?

You basically just said the same as I said in >>2. But you're saying it's wrong?

For the observer to bring them both to himself to check the times, one (the one further away) must move for longer than the other. This is where the "correction" takes place.

>>7

Well I was assuming the observer saw the clocks get set, then didn't see them again until after the train was stopped.

I started to think about what would happen if the stationary observer watched the clocks the whole time, but the I realized; he can't!  He's supposed to be a stationary observer, which means the train has to move past him.  He can't keep up with the train to keep watching the clocks unless he moves with the train, in which case his reference frame is the same.  The observer will see the clocks get set at different times, but after the train stops and the clocks are brought to him, they read the same.

At least, I think that's the answer.  I could be quite wrong; maybe it does have something to do with time dilation due to the movement of the clocks.

I started to think about what would happen if the stationary observer watched the clocks the whole time, but the I realized; he can't!
Sure he can. The clocks can send out radio signals to indicate their current time, and he can correct the flight time of the signal to figure out what time they were showing when the signal was sent.

It's not a matter of when he SEES the clocks get set; it's a matter of when they ACTUALLY get set. This does not have to do with his observation; from his reference point, they get set at different times. It doesn't matter whether he ever sees them at all.

>>10

Okay, I understand your argument now.  But I think that the end result should be the same.  A clock is any device or process that records the passage of time.  The two clocks are in the same reference frame.  In that reference frame, the two clocks are set at the same time.  The clocks then begin to record the passage of time, and since they remain in the same reference frame for the remainder of the experiment, they will read the same time after the experiment is over, regardless of what the stationary observer saw.

I just have no idea what happens from the point of view of the observer during the experiment.  At the end, both clocks should read the same.

>>10
(cont from >>11)

Reading over your post again, this caught my eye:

>>it's a matter of when they ACTUALLY get set.

You're thinking about it wrong.  Once you introduce relativity and reference frames, you can't talk about "what actually happened."  You always have to state what your reference frame is.  Neither reference frame is "what actually happened," but both frames are "what actually happened" for observers in those frames.

>>12
You're thinking about it wrong.
No, no, no. When I say that, I mean in the platform observer's reference frame. I realize full well that what actually happens is different in each frame, and that both viewpoints are equally "right" and valid; what you need to realize is that this has nothing to do with when they SEE these things happen. It does NOT have to do with observation, with the time it takes for light to get from the watches to the observers' eyes. It's not just what they see happen; it's actually happening differently in each frame.

>>13

It is about observation.  Now, I agree, in the stationary reference frame, the clocks are actually set at different times.  But this means nothing for the clocks themselves, since they aren't in the stationary frame.  To the stationary observer, the clocks are set at different times, but to the clocks themselves, they are set at the same time.  So the clocks will always show the same time.

Again, I have no idea what would happen while the train slows to a stop so the clocks and the observer would be in the same frame.  But after it slows to a stop, the clocks still show the same time because both clocks are in the same reference frame the whole time.

>>14
To the stationary observer, the clocks are set at different times, but to the clocks themselves, they are set at the same time. So the clocks will always show the same time.
That doesn't make sense. They are set at different times in the stationary frame, so how could they possibly show the same time?

>>4

Guess what you have to do to get time dialation effects. You have to move VERY fast and for quite some time. Therefore, the observers would be very far from each other and certain events will occur at different "times" for each of them.

>>15

Because the clocks are not in the stationary frame.  They are in the moving train reference frame, and in that frame, the clocks are set at the same time.

>>17
Yes, but they aren't set at the same time in the stationary frame, so they won't SHOW the same time to the stationary frame.