That, I believe, would remain the same (at least at their centers).
Keep in mind that mass also dilates as a function of velocity, which would probably affect F=ma.
I remember having this discussion with others a while back. The consensus was that you also have to take into account when each part of the train reaches what point–the back, the middle, and the front–and because of the relativity of simultaneity, it’s not so cut and dry whether all points are where they are at the same time.
Well, if you agree that the train centers don’t change their relative positions, we can go from there. Some interpret your bible differently and would say that the distance between the centers contracts as well as the trains. I don’t really care one way or another, I just have to know which interpretation you prefer.
So okay, the train centers are still 20 meters apart when they pass by a station a long way up the track, right?
And that means that if the front train is 10 meters past the station, the rear train would be 10 meters before the station, right?
Yes, if you took the trains as one object.
Keep in mind, James, the relativity of simultaneity figures into this very question–where exactly does each part of the train (front, middle, back) exist along the track?–quite deeply. It says there is no fact of the matter.
A point on a train passing by a particular point on the track counts as an “event”. The back, the middle, and the front of the train passing by the same point on the track count as 3 “events”. When exactly each one is supposed to happen–at the same time, one after the other, one much longer after the other, etc.–is not absolutely determined. But if determined by an observer’s measurement (thereby making it only determined in that way relative to that observer’s reference frame), then that will determine the length of the train for that observer.
Sure, the centers of each train would be 10 meters from the center of the station.
Okay, since we are making progress, let’s add another feature to those trains. We have treated each of the identical trains identically and thus we can expect them to behave identically. Right?
So now let’s put a timer at the center of each train. We can synchronize these timers before any motion occurs and expect them to stay synchronized with each other throughout the journey as long as we continue to treat both trains identically. This is still in compliance with SR. Right?
And then let’s say that the timers were set to trigger at a set amount of time later when we knew (because we brilliantly calculated) the exact time reading on the front timer as it would reach the 10 meters past the station point. And of course, that means that the rear timer would be 10 meters before the station when its identical timer triggered. Right?
And when these timers trigger, they are designed to flash, much like a photon flash bulb. We want to do that because we want to test this theory concerning the speed of light and synchronicity at extreme speeds.
I have gone through this step by step, just to make sure everything is clear concerning what we are dealing with. So is it clear? Any questions so far concerning the trains, station, and timed flashers?
Let me introduce you to this picture, partially described above, just to help out with a visual. In this pictorial, there are additional clocks and an addition train being shown which have not yet been described. The upper portion of the pic signifies the Lorentz synchronizing process used in order to get the timers properly synchronized before the trains begin to move. The lower portion is a display of the trains arriving at the station and symmetric to it. “Xs” being the 10 meters that we have been discussing. And the blue dots indicate the location of the flash timers at the point they are set to flash.
Additionally you see two special extra clocks and a third, middle train. The middle train doesn’t really have to be a train. It could be merely a rubber band or plank stretched between the fore and aft trains that can carry the extra clock centered between the trains at all times.
The two clocks, one on the middle train and one at the station are special stop-clocks. Those stop clocks only stop if they each receive a flash from both sides at the exact same time. We want to verify the synchronicity, so rather than depend upon human observers, we can rig a clock to stop if, and only if, it experiences simultaneous flashing from its sides. There is no fooling the stop clock. If it stops, it can only be due to its experiencing of simultaneous flashing.
What is going to happen is that as the extremely fast trains pass the station, the two timers are going to simultaneously flash (from either perspective, station’s or trains) at equal distance from the centered stop-clocks, one at the station and one on the middle train. And then we are going to ask which, if either, of the stop-clocks will stop. We don’t really care at what time they stop. That is separate issue.
SR should provide us with the answer as to which stop-clocks stop and why.
Yes, I agree.
I can see where this is going.
At first, it seems there isn’t any question whether the stop-clock travelling with the trains mid-way between them will receive the flashes of light at the same time (and therefore stop). The question is: will the stop-clock at the station receive both flashes at the same time?
There is reason to believe it won’t: as you should know, time dilates as a function of velocity–the clocks on each train which we synchronized at the beginning will appear to run more slowly from the reference frame of someone standing at the station, which means that in our calculations of when we expected the flashes to go off, if we wanted them to flash at the exact moment when each was 10 meters from the center of the station, we would have to set them to go off before they reach the station from the point of view of someone on the train. If we didn’t take this time dilation into account, they would end up flash at some point past the station (or when the front train was more than 10 meters beyond the center of the station, and the rear train was less than 10 meters before the center of the station). If that happens, then the front flash would have a longer distance to travel in order to reach the stop-clock at the station than the rear flash. Thus, the stop-clock at the station wouldn’t stop.
But suppose we took this time dilation into account and set the flashes to go off right when they were each 10 meters from the center of the station (even though this would appear to be before the trains reached this spot relative to someone riding the train–but even then, the other stop-clock which is travelling with the trains mid-way between them would still go off). In that case, the stop-clock at the station would indeed stop, but then what do we say happens to the stop-clock travelling mid-way between the train? In this scenario, the latter stop-clock is just like the passenger riding the train in the video I posted above. From the perspective of someone at the station, it would receive the flash from the front before it receives the flash from the back, and thus it wouldn’t stop.
This is a paradox. As with most paradoxes, a good way to go about resolving them is to go back to our initial assumptions. I pick the assumption that the stop-clock travelling with the trains mid-way between them will receive the light flashes at the same time. ← This is wrong.
Yes, we did synchronize the clocks at the beginning, yes the trains are travelling at the same rates at all times, and yes they did begin the journey at the same time. But once again, the relativity of simultaneity allows us some leeway here–when exactly two events happen relative to each other is not all together determined. If relative to someone standing at the station, the stop-clock travelling between the two trains does not stop (because the flash from the front gets there before the flash from the back), then in order to preserve a consistent universe (where mutually exclusive events don’t both occur at the same time), we can say, thanks to the relativity of simultaneity, that relative to the stop-clock travelling between the trains, the stop-clock in the front train flashed before the stop-clock in the rear train.
This may be discomforting but it is not a paradox. We would like to say that synchronizing them at the beginning of the journey entails that they must be synchronized throughout the journey, but the relativity of simultaneity says that we have no right to posit this. That part way through the journey, one clock pointed to 10 after 12, and also that part way through the journey, the other clock also pointed to 10 after 12, is not grounds for concluding that they both pointed to 10 after 12 at the same time. The principle of the relativity of simultaneity says that when it comes to events which are supposed to occur at some point between a starting time and an ending time, there is no fact of the matter about when, relative to each other, they actually occur–only that the events in question must occur sometime between the start and the end of the given interval–but whether that’s at the same time as each other, one before the other, or the other before the first, there is no determined fact about.
The idea that the two clocks being synchronized at the beginning entails that they must remain synchronized thereafter is a habit of Newtonian physics and precisely what Einsteinian relativity debunks.
The point is this: it’s still true that you can’t have mutually exclusive events both occurring in the same universe–at least not at the same time in the same place–so if in one scenario the stop-clock stops and in another scenario, it doesn’t–we can reconcile that with the principle of the relativity of simultaneity, which always gives a certain window of leeway for when particular events are supposed to occur–we can no longer assume a perfectly Newtonian physics.
“Leeway”???
I’m afraid we cannot say that and preserve Science and logical thought. There is an issue of confirming the consequent and denying consistency of thought.
Everyone, on the train and off, knows that both timers were treated identically and thus must flash concurrently, else the laws of physics, and basically all of science in every field, cannot claim the consistency of “equal situation + equal treatment => equal result” and must abandon every notion of experimenting for sake of finding out what will happen at some future moment. It is not a matter of mere “discomfort”. You cannot arbitrarily say that one timer was time-dilated more than the other without giving a reason for such difference. We have intentionally ensured that there can be no difference.
The timers have no choice but to be predetermined to flash concurrently.
What someone observes later, giving the impression of simultaneity, is another issue involving the speed of the light and everyone’s motion. It is the ability to observe accurately that we are testing when we test SR, because SR was formulated under the presumption that every observer has the right to be right in his sight. We are testing to see if that presumption is right. But we cannot abandon all reasoning and demand that the relativity of simultaneity is right in order to make it right, else all of science becomes pointless; "If SR is right then it is right and all of scientific thought, including relativity, is wrong".
This isn’t about Newtonian physics. This is about formulae such as “F=ma” or “t’ = γ(x-vt)” being consistent each time it is applied. If it is true for one train and timer, why isn’t it true for another that was exactly like it?
The truth is that by definition, both timers flash concurrently. And to suggest that they do not, not only denies rational thought entirely, but also merely gives the right to the experimenter to say, “because my theory is right, nothing else matters.” You propose to negate thought in order to defend a theory based upon thought. That wouldn’t be much different than many of the pro-God arguments.
But now that you have changed your faith (as I suspected you might), realize that we could easily merely place trigger fingers at the 10 meter points, thus further guaranteeing both timers to flash concurrently. No concern for time dilation or timers would be required.
Such a choice would lead to this pictorial;
So again, which stop-clocks stop and why?
In the end, the clocks either stopped or they didn’t.
Simultaneity is not a subjective opinion any more.
Given up yet? 
Been busy. Hold on.
Okay, I have a bit more time now (had to work late last night–until 11:30).
Yes, it seemed this way to the scientific community too at the beginning of the twentieth century when Einstein first proposed (and then later proved) both SR and GR. But it is consistent and rational after all and certainly “preserves” science. You just gotta get used to it.
What result? The world presents us with events. These are the only results we need be concerned with. In the case of SR, we work backwards from the events with which we are presented, and deduce, based on the absolute velocity of light, what must be said for every other observer in every other reference frame. You, however, want to work forward, from the initial conditions of synchronizing the clocks to a set of events the world may or may not present us with, and dictate to the world what events ought to happen. This is classical thinking.
Any way you cut it, you will get consistent results: whatever event the world presents us with, that will be the result of the experiment for everyone–none of this clock stopping for you but not for me.
Why do you want to abandon anything? You just got a different result than you expected. You’d still get the same result if you repeated the experiment. The experiment simply forces us to adjust our assumptions and ways of thinking–we cater to it, it doesn’t cater to us.
More classical thinking.
This is not just dogmatically demanding that the relativity of simultaneity is right (come Hell or high water). The relativity of simultaneity is a consequence of hard objective real-world results–a mathematical conclusion drawn by Einstein and others based on prior experiments in the history of physics. Ever heard of the Michelson-Morley experiment? You should look it up. SR is built to resolve this. Also, you do know that both SR and GR have been experimentally proven based on astronauts returning home from space flight with their watches slightly behind stay-at-home observers, don’t you? If theory doesn’t debunk classical Newtonian mechanics, empirical findings such as these surely ought to, no?
Who said it wasn’t true? You do know that mass dilates with velocity, don’t you? And when you bring acceleration into the picture, you’re bringing in GR too.
F=ma applies to the trains–the force with which their masses are accelerated–what does that have to do with the time at which the stop-clocks go off?
What does that even mean: by definition? You mean the stop-watch is defined as something that flashes concurrently with another stop-watch? Well, if the relativity of simultaneity is true, your definition is incoherent.
Nice try, but you’re reaching. I’m all for entertaining alternative theories, but you will need to account for the Michelson-Morley experiment, the fact of astronauts’ watches falling behind, and all other evidence supporting SR and GR.
I agree that they either stop or they don’t–this is what I’m trying to say with regard to the world presenting us with events–but that doesn’t mean they happen simultaneously (and I never said simultaneity is a subjective opinion, I said it was indetermined).
To answer your question–which stop-clocks stop and why?–you have to answer my question: which event did the world present us with? You seem eager to settle on the stop-clock on the middle train having stopped, so let’s go with that. From the reference frame of the stop-clock on the middle train, you would have to conclude that the flashes went off at the same time–10 meters from the middle of the station center–but from the reference frame of the station stop-clock, the rear flash has to go off before the front one (in order to give the rear flash more time to catch up to the middle stop-clock), and the stop-clock at the station would not stop at all.
So how is this possible? How can the rear flash go off before the front flash if both the rear and the front trains both hit their triggers at the same time? The answer is: they don’t. Length contraction! You said it yourself: the entire system of trains can be treated as one object whose length contracts. Thus, the rear train will go over its trigger before the front train goes over its trigger. (I’ve since confirmed this, btw; the right way to think about this is to understand that it’s space that contracts, not the trains, and there is no center of contraction, just as there is no center of the universe. Again, it comes down to events: there are a limited set of events that are determined to happen–the trains start at the beginning of the track, they pass by the station, and they stop somewhere further down the track–these must happen; but someone standing at the station will measure their length to be less than someone riding on the train–this is simply a result of when they observe each event happening, when each part of the trains–front, middle, back–passing by a point on the track. They will measure the event of the rear of the train passing by a certain point on the track sooner than expected–that is, sooner after the front of the train passed by that point than expected according to Newtonian mechanics–and thus conclude that the train must have shrunk).
Most people who think they’ve found a hole in Einsteinian relativity are failing to make adjustments to one or more of all the variables that dilate–the faster an object moves, the more time and length, and mass, and I believe energy too dilate. Taking into account one of these but fail to do so for the others is a habit of Newtonian thinking (and very understandable). But you don’t just adjust them willy-nilly (to meet your expectations). The formulae of relativity tell us exactly by how much to adjust. For example, your question early about how much length would contract if the train were travelling at c/2 was: half the length. The formula is: l = l[size=50]O[/size] x sqrt(1 - v^2/c^2). I don’t get to set length to whatever I need in order to be right. The point is, you can be given a set of measurements–the “event” that the world presents us with–but you can make changes to any of those measurements so long as you make proportional changes to all the others (according to the formulae), and you will get results that you can consistently say someone else might experience in a different reference frame.
Gib, you will never be able to get around the necessary fact that if I have two identical timers that are synchronized and I treat them identically, they must still be identical and synchronized. To deny that is to revert to magic and superstition with inexplicable occurrences used to satisfy our pet theories. You might as well say, “The inexplicable God does it by mysterious ways.”
You think it was proven? No. It wasn’t. And even Einstein said that he couldn’t get GR to work out. Additionally, quantum physics disagrees with it. SR merely yielded better results than their prior theories had, understandably because Einstein merely reverse calculated from the measurements. But that doesn’t make it right, merely a better rule of thumb for those particular situations. And I admit that it comes close.
Oh really?
Perhaps you can explain to me which of the flashers goes off first and how that could possibly be since both were treated exactly alike and with the optional trigger fingers are triggered together. Relativity and QP require and demand magic in place of rational thought.
The result of the action or event. If I have two identical items (trains or timers) and treat them 100% exactly alike, how can they possibly become different?
Well, I’m sorry, but the point to Science is to project forward, not backward. If you cannot depend on the laws of physics moving in the forward direction, then they are useless.
You are suggesting that if I add 2 pennies to my pocket, later add another two, then calculate that I should have four pennies, but moments later discover that there are only 3 pennies now in my pocket, I MUST conclude that 2+2=3 because that is what I observed.
You are denying any possibility of potential observer error merely because such would invalidate the theory you are trying to defend. That is called being biased.
“Sometimes F=ma, depending on the results you get.”
Isn’t that a bit pointless?
That is the whole point of it, so which clocks stop according to SR?
And now you have changed your faith on another issue, Length Contraction. And as I said, that’s fine with me as long as you stay consistent (which isn’t proving to be the case so far). The reason it is fine with me is that the distance “Xs” can be precalculated to be anything, contracted or not. We can freely decide that Xs “really should have been” 7 meters rather than 10. We can then set the triggers at the proper locations and also preset the timers as we please to ensure that they flash squarely around the station.
That is why I gave you this pic;
But you didn’t treat them identically. You placed one at the front of the train and the other at the rear.
Digging a little deeper into this issue, I came up with this: in these kinds of scenarios, you do have to bring GR into it. You have to take into account the fact that the trains, in order to get up to speed, must begin by accelerating. That’s GR. Then, bring into the picture our good old friend: the relativity of simultaneity–what started accelerating first? The front or the rear? There is no fact of the matter. Any time differentiation between when the stop-clocks go off is accounted for by the front accelerating first (relative to whatever observer notices this time differentiation), thereby speeding the clock up (time speeds up in GR). This pushes the front clock ahead a bit. And yes, the rear clock does end up accelerating too–at the same rate, for the same amount of time–but this does not allow the rear clock to “catch up” to the front clock. While the front clock was accelerating, the rear clock ticked away at its usual resting rate. The front clock will tick away at a certain rate as well during the time when it has stopped accelerating and is waiting for the rear clock to finish accelerating, but since it is now in motion, its time is dilated and therefore it will tick away at a slower rate than the rear clock when it was ticking away at its resting rate while the front clock was accelerating. In other words, less time will go by for the front clock while it’s waiting than for the rear clock while it was waiting. Long story short, the rear clock ends up being ahead by a little bit.
Well, I’ll admit that proof is relative. One has to be convinced before something can be said to have been “proved,” but I don’t think the scientific community (or myself) will shed any tears over their failure to convince you. But there have been numerous experiments over the last century that have at least confirmed what SR and GR predict.
Which means we don’t understand everything… that’s it.
You still need a way of explaining all the actually measured and observed anomolies that, so far, only relativity explains–that is, if you’re going to persuade us to abandon relativity.
So then what hits it bang on?
Goes off first relative to whom? How many times do I have to reiterate this: there is no fact of the matter! If you want the stop-clock at the station to stop, then both the front and the rear stop clocks go off at the same time relative to someone standing at the station. But they won’t relative to someone riding the train. My explanation above about the simultaneity of when each clock started accelerating–the front and the rear–should be sufficient explanation for you. Now, if you want the middle stop-clock to stop, then they will not go off at the same time relative to someone at the station but they will for someone on the train. The simultaneity of when the front and the rear accelerate explains this for the observer at the station as well.
The point of science is to provide a methodology for acquiring knowledge. But it’s great for project forward or backward–even with relativity. Again, you’re just projecting the wrong results. Einsteinian relativity gives you a new paradigm to work with. Your predictions are based on the old Newtonian paradigm. Just because the latter fails you in your predictions doesn’t mean the world is chaotic and unpredictable.
You can depend on the laws of physics. You’re just depending on the wrong ones.
I’m saying nothing like that. The laws of mathematics don’t hang in the balance. I’m saying that the Newtonian rules which tell you that two clocks which are initially synchronized must remain synchronized is wrong. The correct rule to follow is that two clock which are initially synchronized will become unsynchonrized (in exactly the way that the formulae of relativity say) as velocity increases. ← This is still a rule, and it works perfectly well for making predictions. It’s a rule of physics, not mathematics. Rules of physics are based on observation and measurement. We come up with mathematical formulae to describe those rules. If one day science disproves those rules, it means we were wrong in coming up with those rules and we need new formulae to describe them, not that the original formulae now give different results even though we plug in the same initial values. The rules linking those initial values to the end result are mathematical rules and not subject to change. The rules of physics are the formulae themselves–as a whole–and when they prove to be wrong, we throw out the formulae all together for new ones.
Oh please, you’re now arguing that every result of every experiment which confirms relativity has been an observer error?
No, I’m pretty sure F=ma holds in all cases, and I never claimed otherwise.
You want to pull the triggers closer together in order for the front and rear of the train to hit them at the same time relative to someone at the station? Fine. In that case, the stop-clock at the station will stop. But then for someone riding the train (for whom there will be no length contraction of the train), the front of the train will hit its trigger before the rear. This is fine too. Remember: the station is moving back relative to the train. So the front flash will be emitted first and it will have to catch up to the station as it moves back. At some time later, the rear flash will go off and it too will have to catch the moving station, but note that it will start with the station coming towards it, and by the time it reaches the station, the front flash will have caught up with it, and they will both meet the station stop-clock at the same time.
You have made a variety of false claims in avoiding the question (as expected and will continue). Your responses are easily defeated. But to stay more focused on the most critical issue let’s stay at the beginning in the station’s time frame (despite your prior agreements on this issue). The train’s perspective would not be as you described, but we can get to that later.
So you are saying that if I have two identical trains on, let’s say an electric, track and I apply voltage to the track, one of the trains will necessarily out accelerating the other. And to ensure contraction between the trains, the back train must be the one out accelerating the front train. But the same voltage is being applied to both trains.
From the Station’s perspective/measurements/timeframe;
A) Which train didn’t follow the “F=ma” law (or which ever other law you wish to apply)?
B) How did the trains know which was in front?
C) What variation of “F=ma” does a train follow when there is not another train on the track?
D) If we start up a second train after the first train has already been accelerating, how does the first train know to alter its acceleration and if the second train is in front or behind so as to know whether to increase or decrease?
I’m not saying one train out accelerates the other, I’m saying that one train begins to accelerate before the other.
They both followed Newton’s second law. Like I said, they’re not accelerating at different rates, it’s just a question of when they started accelerating. t is not a variable in that equation.
The trains didn’t “know”–it happens to be a rule of relativity (you know, one of those things you think are completely lacking): things closer to the front of an accelerating system will temporally lag behind things closer to the rear. It’s the direction of travel that determines which part of the system will lag behind which other part.
Read my response to A).
I’m just glancing at this discussion… but did you really just say that!!!
That wouldn’t fit your argument and isn’t what you want to be saying. But if you are going to insist, which train is going to start first and why that one?
I think that you are misunderstanding your situation with SRT. If the front train merely delays before starting up, the gap between them will close, but the problem is that it will have closed even when the trains are going only 10 mph. That would have nothing at all to do with SRT. With SRT at 0.5c, they would be additionally contracted. The gap closes more at higher speeds, beginning with zero change at zero speed and very, very gradually decreasing the gap (according to your interpretation of SRT). SRT has nothing to do with delayed responses.
So you apply voltage to both trains, but you think that SRT says that because one train is in front of another, it will delay before starting???
Again, how does it being in front change “F=ma” or “a = F/m” into an “a = delay + F/m”.
It’s not even delay, it’s inversion.
It’s in my explanation:
Rear train.
You really are stuck in Newton land, aren’t you?
I’m going to make an acronym out of this so that I don’t have to keep repeating it: tinfotm, and it stands for (get ready) “there is no fact of the matter” (actually, I think I’ll call it tinfom–drop the “the” in order to make it more pronounceable). You’re still thinking as if there being a delay between when one train accelerates and when the other accelerates is an absolute fact. No! No, James, no! If an observer who saw the clocks being synchronized then sees that the middle clock stopped, then he would have to deduce that the rear train began accelerating before the front train. An observer on the train, however, wouldn’t have to conclude this. Who’s right, you ask. And you ask this because you and your tired old Newtonian understanding think there has to be an answer to this question, but… tinfom.
“a = delay + F/m” ← What kind of formula is this? You don’t even have your units right? You’re adding time to time^2/distance. Like I said already, there is no t in F = ma, so you can’t add “delay”.
The fact the matter is, F = ma has nothing to do with when the mass starts accelerating. That there is a delay for the rear train has no bearing on F = ma. When it starts accelerating, F = ma will be the appropriate formula to apply.
Yes… yes I did.
I am not stuck in any land other than simple logic. Your theory fails fundamental logic, before we can even get into any physics.
I’m not thinking it. YOU are telling me that one delays. I think you are nuts.
The question is not, “If the train clock stopped, then what happened?”
The question is, “Given the stated situation (both trains began simultaneously, being in the same frame as the station), which stop-clocks will stop?”
You don’t get to jump to the end and then deduce backward as to what you want the situation to have been.
“So what do we do to make sure our missile hits the target before theirs? Well sir, we wait to see which one hits first, then calculate back to see what we need to do to ensure that it’s ours.” 
The clocks either stop or they don’t. I am asking you WHICH CLOCKS STOP according to your understanding of SRT?
I thought you said there is no “fact of the matter”.
Well, I asked you what does determine when they begin. The stipulation was that they began together as the voltage is applied to both simultaneously. Why do you keep changing the scenario? What is causing a delay?
You can’t have logic unless you start with premises. Your premises are wrong.
Doesn’t matter. Your thinking that it’s an absolute fact that they both started to accelerate at the same time is wrong, for the same reason.
Now, now, James, you know that’s not what I meant.
The delay isn’t “caused”. ← This is more Newtonian thinking, the habit of thinking that a delay between events is absolute and the same for everyone. For the observer on the platform, there is a delay, not for other observers (like someone riding the train, for whom there is no delay). ← This is what you get with tinfom in regards to simultaneity.
Thank you James! You finally gave me something I can work with: if both trains begin simultaneously in the same frame as the station (which I interpret to mean relative to the observer at the station), then the answer to which clock goes off is… neither.
How’s that?
Well, at first I was with you thinking that surely one of two possibilities has to be the case: either a) the stop-clock in the middle of the train stops, or b) the stop-clock at the station stops… but my research into this puzzle (which has paralled this discussion) is now suggesting that the two clocks fall out of synch from each other for both observers–the traveller on the train and the person on the platform–such that neither clock goes off.
Here is a discussions I’ve been have with Janus, a moderator at thescienceforum.com/physics/ … post620576.
^^ This addresses exactly the question about why the acceleration phase of the train’s journey results in the clocks ending up out of synch with each other. It explains that this desynchronization happens for both the traveller on the train and the person at the station.