# Two lightning bolts striking either end of train

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Simultaneity - Albert einstein and the theory of relativity. This video says that the person on the train will see lightning from front of the train first. But what if we take it that the train is stationary and the earth is moving below the train.

How could we tben explain the passenger on the train seeing the front bolt first

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Lord Antares    151

The speed of lights moves at a certain speed, however large. So of course it will be seen sooner by someone who is closer to the lightning bolt. Of course, this difference is imperceptable by humans and they would both agree to seeing it at the same time, but we are talking about technicalities, right?

Maybe I'm missing something because you haven't provided the video. There's not enough info to discuss more.

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Thanks heres the video

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swansont    6212

Simultaneity - Albert einstein and the theory of relativity. This video says that the person on the train will see lightning from front of the train first. But what if we take it that the train is stationary and the earth is moving below the train.

How could we tben explain the passenger on the train seeing the front bolt first

The conclusion from relativity is that strikes are not simultaneous in the train's frame if they are simultaneous in the earth's frame.

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The conclusion from relativity is that strikes are not simultaneous in the train's frame if they are simultaneous in the earth's frame.

Yest, but I think Tir21 wants to know how the thought experiment runs from the train passenger point of view. That's a different story.

I'll give it a try:

@Tir21

Very good question, Tir21.

-The embankment observer sees both bolts simultaneously. For him, in his frame of reference, both lightning bolts happened simultaneously( lights from the bolts travel same length).

-The train passenger does not see both bolts simultaneously.

Why does this mean for him both bolts didn't happen simultaneously?

If one would state (as is often the case) it is because he moves toward the front bolt, we could throw in maybe also for the train observer both bolts happened simultaneously, but he only SEES the light from the events at a different moment in time because he moves towards the light coming fron the front bolt and thus sees that one first... No relativity of simultaneity in that scenario!

But in fact he does't see them simultanously because when he meets the embankment observer no lighting bolt occurs:

1. first the front bolt occurs (before the train passenger meets the embankment observer), 2. then both observers meet. No lighting bolt occurs.

3. Finally the rear bolt occurs, after both observers separated a split second ago.

(Note: in train frame both light will travel dame distance to train passenger)

Look at it this way: when train passenger and embankment passenger meet, both bolts happen simultaneously for the embankent observer. Now, IF both bolts would ALSO happen simultaneously for the train passener when both observers meet, then the train passenger HAS to SEE both bolts also simultaneously, because in his frame the lights travelling from the simultaneous events also travel same distance (not necessarily same distance as in embankment frame, but that is irrellevent because only the front and rear distance in the train frame is important for the train observer analysis!), and hence would reach him simultaneously. But.... because the train observer sees both bolts not simultaneously he concludes: "For me (in my frame), lighting bolts occuring simultaneously when I and embankment observer meet can not be correct".

We know the train passenger indeed does not see the light from both bolts simultaneously, because that's what's experimentally observed bij the embankment observer. Receiving light from one bolt after recieving light from the other bolt are two different events. And that cannot change for the train passenger.

Now we get to your question: a thought experiment from the train passenger's point of view for simultaneous lighting bolts in the embakment frame.

Both bolts occur simultaneously in the embankment frame. Lights from the bolts do not reach the train passenger simultaneously (=two events). That's what he will physically experience and observe. Your question now is: how could the train passenger EXPLAIN seeing the front bolt first?

Train passenger knows the set up: in embankment frame both bolts occur when both observers meet. And lights hit embankment observer simultaneously (=one event).

Now train passenger he reasons as follows. "IF they ALSO occur simultaneously for me when I meet embankment observer, then they are also at same distance from me, hence both lights from bolts HAVE TO reach me simultaneously. But the lights from the bolts do NOT reach me simultanously. It can only be because for me (in my frame), lighting bolts occuring simultaneously when I and embankment observer meet can not be correct"

Is there another option?

The train observer might think for him both bolts DID occur simultaneously, but both lighning bolts were not at the same distance from him... hence both lights do not reach him simultaneously...

But that's not a valid option. Because it would mean

the three events

1/ front lightning bolt

2/ both observers meet

3/ rear lightning bolt

occur simultaneously in train AND embankment frame, but the embankment observer considers both observers halfway between the two simultaneous lightning bolts, whereas the train observer considers both observer NOT halfway between simultaneous bolts...

You might think it's a valid option, but there is no theory to explain it.

-------

Your question might be: if we consider the train at rest end the embankment moving, why does the train passenger knows he will not NOT see both bolts simultaneously (lights from the bolts not reaching him simultaneously)?

Or better formulated, why HAS IT to be that way (not seeing them simultaneously)?

The only 'thought experiment' reasoning we can make is: he and the embankment observer know it happens that way, because in the embankment frame the bolts reaching the train observer are two different events and they can not melt together into one event in the other frame.

And the best way to find out is doing the experiment. Both lights from bolts will and do not reach the train observer. But as a thought experiment one has also to wonder why ;-).

Edited by VandD

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swansont    6212

Yest, but I think Tir21 wants to know how the thought experiment runs from the train passenger point of view. That's a different story.

Perhaps a different story, but it had better end up with the same answer.

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geordief    53

My take on this is that simultaneity only occurs when two events are separated by zero space and zero time (a rare occurrence).

So, by my definition ,in this particular scenario neither observer can say that the 2 events are truly "simultaneous"

They can only claim they are simultaneous in so far as they respectively observe them as such,which is why they disagree.

If events are truly "simultaneous" according to my "higher" standard ,all observers will agree (perhaps trivially?)

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swansont    6212

My take on this is that simultaneity only occurs when two events are separated by zero space and zero time (a rare occurrence).

So, by my definition ,in this particular scenario neither observer can say that the 2 events are truly "simultaneous"

They can only claim they are simultaneous in so far as they respectively observe them as such,which is why they disagree.

If events are truly "simultaneous" according to my "higher" standard ,all observers will agree (perhaps trivially?)

That's not the relativity take on it. Same place and same time are required for an unambiguous determination. Same time depends on your frame if the events are not co-located. Hence the relativity of simultaneity.

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geordief    53

That's not the relativity take on it. Same place and same time are required for an unambiguous determination. Same time depends on your frame if the events are not co-located. Hence the relativity of simultaneity.

Well my take was no doubt simplistic and not particularly useful or helpful here (just a special case I guess)

Edited by geordief

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zztop    11

Well my take was no doubt simplistic and not particularly useful or helpful here (just a special case I guess)

Two events are separated by the amount of time $\Delta t$ and by the space $\Delta x$ in frame F.

In frame F', the two events are separated by the time interval $\Delta t'=\gamma(\Delta t -v \Delta x/c^2)$.

Now, if the events are simultaneous in F, it means that $\Delta t=0$.

This means that , in frame F', the events are separated by the time interval:

$\Delta t'=-\gamma v \Delta x/c^2$.

You can have $\Delta t'=0$ if $\Delta x=0$.

Another way of looking at it is : if $\Delta x=0$ then $\Delta t'=\gamma\Delta t$ , so, in this PARTICULAR case, simultaneity is preserved across frames of reference.

Edited by zztop

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My take on this is that simultaneity only occurs when two events are separated by zero space and zero time (a rare occurrence).

Two events separated by zero space and zero time are a contradiction in terms. Two events mean space separation and/or time separation. You cannot melt two events into one.

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geordief    53

Two events separated by zero space and zero time are a contradiction in terms. Two events mean space separation and/or time separation. You cannot melt two events into one.

Well ,we can as a limit and from an observer's frame of reference can't we?

But I have agreed it is of little consequence.

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Phi for All    4771

!

Moderator Note

Hijack and subsequent replies split off to their own thread in Speculations.

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swansont    6212

!

Moderator Note

Posts asking about the split have been moved to support, because really?

• 1

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Tir21.

Einstein in his 1905 article on relativity doesn't mention a train thought experiment, but he does analyse the same situation using imaginary rays of light & clocks & co-ordinate systems (with no paid observer as such), and somewhat later says .....

-- "It is clear that the same results hold good of bodies at rest in the stationary system, viewed from a system in uniform motion" --

although here he is talking moreso about his next idea down the line, & not forgetting that this is only an English translation of his German.

But i have never seen a detailed analysis confirming the same results when viewed as u say by the passenger in a carriage at rest & with the platform & embankment moving past.

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Tir21.

You probably missed (or didn't fully understand) my post #5

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VanD.

I think that the video showing a short bullet-train with observer on platform approx. L/2 from train & with a non-understandable explanation of events, indeed a misleading explanation, is impossible to analyse. Properly explained it would be possible, albeit having to use non-zero Y co-ordinate info (messy).

But if u move the platform-observer closer in so that he is kissing the window u now have Einstein's original thought experiment. Now its easy. U simply look at the whole thing in mirror-image, ie looking from the train-observer's point of view. In her frame she sees the 2 flashes simultaneously, & the platform-observer moving past, etc etc etc. Too easy.

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pzkpfw    164

My underline ...

VanD.

I think that the video showing a short bullet-train with observer on platform approx. L/2 from train & with a non-understandable explanation of events, indeed a misleading explanation, is impossible to analyse. Properly explained it would be possible, albeit having to use non-zero Y co-ordinate info (messy).

But if u move the platform-observer closer in so that he is kissing the window u now have Einstein's original thought experiment. Now its easy. U simply look at the whole thing in mirror-image, ie looking from the train-observer's point of view. In her frame she sees the 2 flashes simultaneously, & the platform-observer moving past, etc etc etc. Too easy.

No, she doesn't. Her experience (of whether the flashes reach her at the same time) can't contradict the platform observers experience (of whether the flashes reach her at the same time). Given the setup, the events were not simultaneous, for her.

Based on http://www.bartleby.com/173/9.html , it boils down to:

(warning : in the past I've found the bartleby website to do "dodgy" things; found a better source once but lost it).

1. Both observers are entitled to consider themselves as at rest (and the other observer moving).

2. Both observers, given the initial setup, are entitled to consider themselves as located between the two events.

3. Either observer, seeing the flashes at the same time, will then consider the events to be simultaneous.

4. The flashes are seen at the same time by the embankment observer, so the events happen to be simultaneous for them.

5. As shown from the embankment observers point of view, the flashes don't reach the train observer at the same time.

6. The flashes can't reach the train observer at the same time and also not reach the train observer at the same time.

7. So, the train observers experience can't contradict the embankment observers experience.

8. So the events were not simultaneous for the train observer.

9. Vice versa, two different events, which happen to be simultaneous for the train observer, won't be for the embankment observer.

Notes on the above

1. In the original thought experiment Einstein is clear to say "Then every event which takes place along the line also takes place at a particular point of the train." Note the lines for A and B drawn across both the track and the embankment. People sometimes think events happen in some frame of reference. That's not right, events happen in all frames. The event of an ice cream hitting the footpath occurs whether I'm standing still next to the person who dropped it, or I'm riding by on my motorcycle. However, Einstein tries to remove that confusion here.

6. The most common way to show this, is with the train observer holding a bomb that goes off if two detectors facing forward and back detect the flashes at the same time. The bomb will either explode or not. From the embankment observers point of view it's clear the flashes can't reach the bomb at the same time, so it won't explode. There's no alternate Universe where the flashes from the same two events reach the bomb at the same time and it does explode.

Another way is for the train observer to be holding two more mirrors, to reflect both flashes to the embankment observer. Consider whether the embankment observer would see those reflected flashes at the same time or not.

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pzkpfw.

I don't follow.

If one takes Einstein's exact description of his train thought experiment, then u or i should be able to describe the events from the train-passengers viewpoint, simply by changing Einstein's wording, eg replacing embankment with train, & train with embankment, etc etc, & u reach the same conclusions.

In this mirror-image sort of analysis the main player becomes the train-passenger, & she (its a she in the video) sees the flashes of any simultaneous lightning strikes simultaneously if she is midway (which she is). And of course here it doesn't make any difference whether the strikes hit the embankment (Einstein) or the train (video)(not that anyone said that it did, but just saying).

The bomb paradox sort of thing never comes up in my mind, it only comes up if one believes that Einstein's time dilation & length dilation are real, which they are not.

I almost remember the words of a Phd who is a solid Einsteinian & who believes that the M&M result was null etc etc (yes, the whole catastrophe), an expert at math, but wrote one of the most profound things about SR that i have seen, saying --

SR is merely a code for deciphering non-local information.

These are my words, i don't remember the exact words & i cant find the article.

The tricks & contortions in Einstein's code are there to give correct information, not to describe reality.

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pzkpfw    164

pzkpfw.

I don't follow.

If one takes Einstein's exact description of his train thought experiment, then u or i should be able to describe the events from the train-passengers viewpoint, simply by changing Einstein's wording, eg replacing embankment with train, & train with embankment, etc etc, & u reach the same conclusions.

For two different flashes, sure. He makes that clear. That's what he means by the "vice versa" at the end of that section.

In the experiment, it's stipulated that the two events were simultaneous for the embankment observer, then asks if they were also simultaneous for the train observer.

You could equally stipulate two events that are simultaneous for the train observer and ask if they are also simultaneous for the embankment observer.

Either way ... it's shown that the same two events can't be simultaneous for both observers.

In this mirror-image sort of analysis the main player becomes the train-passenger, & she (its a she in the video) sees the flashes of any simultaneous lightning strikes simultaneously if she is midway (which she is).

You are making the mistake of assuming that if the two events simultaneous for anyone, that they are simultaneous for everyone. That'd be a common (pre-relativity) assumption, but it's exactly what the experiment disproves. That two events are simultaneous of not depends on the point of view of the observer. Simultaneity is relative.

Two different events may be simultaneous for the train observer - but they won't be the same two events that were simultaneous for the embankment observer.

The point is: simultaneity is relative.

Not: simultaneity is absolute, but people have different views.

And of course here it doesn't make any difference whether the strikes hit the embankment (Einstein) or the train (video)(not that anyone said that it did, but just saying).

Good, then you're not confused by something that misleads a lot of people.

The bomb paradox sort of thing never comes up in my mind, it only comes up if one believes that Einstein's time dilation & length dilation are real, which they are not.

What?? Time dilation & length dilation are irrelevant here.

It simply shows that if, according to the embankment observer, the flashes reach the train observer at different times, then also according to the train observer the flashes reach them (the train observer) at different times.

I remember the words of a Phd who is a solid Einsteinian & who believes that the M&M result was null etc etc, & he is expert at math, yet he wrote one of the most profound things about SR that i have seen, he said that SR was merely a code for deciphering non-local information.

The tricks & contortions in the code are there to give the correct information, not to describe reality.

That's an incorrect interpretation. The effects of relativity are as real as anything.

No one can say that the view of the embankment observer or train observer is more correct or more real. Both of their views of the Universe are "real" - even though they get different answers for whether two events happen to be simultaenious or not.

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2. Both observers, given the initial setup, are entitled to consider themselves as located between the two events.

Be careful stating it this way.

Both observers are indeed together when for the platform observer both events simultaneously happen. But that's a statement that is not valid for the train observer. Because for the train observer when he (train observer) passes the platform passenger NONE of the two events occur for the train passenger! Hence stating the train passeger was in the middel of the two events is very miseading statement. Actually for the train passenger first the front flash occurs when the train passenger is not yet at the platform observer. And the second flash occurs when the train passenger has already passed the platform observer.

The reference text states that M1 moves relative to platform observer only to show/explain that the lightbeams definitely do not REACH the train observer. It is never stated that the two beams left the flashes (= the two events) when M1 is at platform observer. Why? Because for the simplle reason it's the purpose of the experiment to find out what actually happened (whether the two events occur simultaeously or not) for the train observer when he is at the platform observer!

The train observer has to reason as follows:

<< IF both flashes also occur simultaneously for me when (at the moment in time) I meet the platform observer, THEN both light beams HAVE TO reach me simultaneously. But.... the lights from the bolts DO NOT reach me simultanously, hence the two events DID NOT occur simultaneously for me.>>

Actually in the train thought experiment the train observer doesn't know when exactly the flashes occur. But that's not important. What is important for the experiment was to find out whether for the train observer the flashes happened simultanously or not. And the experiment gives the answer: they don't happen simultaneously for the train observer.

VanD.

I think that the video showing a short bullet-train with observer on platform approx. L/2 from train & with a non-understandable explanation of events,

...

Actually I do agree with you that the train thought experiment is not so easy to interpret correctly ... for the unitiated.

I seems piece of cake, but actually it takes some time to understand the analysis correcty.

Get to the bottom of it and you will love Einstein's genius thought experiment for the rest of your life

Edited by VandD

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pzkpfw    164

Be careful stating it this way.

Both observers are indeed together when for the platform observer both events simultaneously happen. But that's a statement that is not valid for the train observer. Because for the train observer when he (train observer) passes the platform passenger NONE of the two events occur for the train passenger!

You are way over complicating this, and that's not going to help madmac.

It's very clear from the original thought experiment, that both observers are able to consider themselves as between the (location of the) two events. For the train observer, the events are at the ends of the train, and she is in the middle. That's why, when she doesn't see the flashes at the same time, she knows the events were not simultaneous.

Your describing of what's going, in terms of when the events occur, from the point of view of the embankment observer, but for the train observer, is just going to confuse any onlookers.

Hence stating the train passeger was in the middel of the two events is very miseading statement. Actually for the train passenger first the front flash occurs when the train passenger is not yet at the platform observer. And the second flash occurs when the train passenger has already passed the platform observer.

Clearly, by "middle", this refers to the location of the events, not the when of the events.

After all, the "when" is then what the experiment then shows us something about (notably, that for the train observer, the "when" of these two events isn't the same.)

I'm summarising the actual thought experiment for madmac. Your after-the-fact "clarification" of what happened is not going to help him until he's got the basics right.

The reference text states that M1 moves relative to platform observer only to show/explain that the lightbeams definitely do not REACH the train observer.

You mean "... at the same time"?

It is never stated that the two beams left the flashes (= the two events) when M1 is at platform observer. Why? Because for the simplle reason it's the purpose of the experiment to find out what actually happened (whether the two events occur simultaeously or not) for the train observer when he is at the platform observer!

You're simply emphasising a different aspect of the proof than most would. From the ref I gave earlier (my two numbers added):

If an observer sitting in the position M’ in the train did not possess this velocity, (1) then he would remain permanently at M, and the light rays emitted by the flashes of lightning A and B would reach him simultaneously, i.e. they would meet just where he is situated. Now in reality (considered with reference to the railway embankment) (2) he is hastening towards the beam of light coming from B, whilst he is riding on ahead of the beam of light coming from A. Hence the observer will see the beam of light emitted from B earlier than he will see that emitted from A.

I've described (2), you're a bit hung up on (1). I think (2) is much clearer.

The train observer has to reason as follows:

<< IF both flashes also occur simultaneously for me when (at the moment in time) I meet the platform observer, THEN both light beams HAVE TO reach me simultaneously. But.... the lights from the bolts DO NOT reach me simultanously, hence the two events DID NOT occur simultaneously for me.>>

That's where your fixation on (1) goes astray. You complicate the reasoning for the train observer, and make it harder for someone to understand the experiment. Instead of simply knowing they are located between the events, but didn't see them at the same time, so they didn't occur at the same time; you have the train observer referring to the embankment observer. That's silly. (And, I think, raises the danger for some newbies that the embankment observer is seen as somehow "special".)

Actually in the train thought experiment the train observer doesn't know when exactly the flashes occur. But that's not important. What is important for the experiment was to find out whether for the train observer the flashes happened simultanously or not. And the experiment gives the answer: they don't happen simultaneously for the train observer.

No argument here; though it does seem to contradict your earlier insistence on how the train observer should consider the situation.

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pskpfw.

Yes events simultaneous for one cant be simultaneous for the other, no matter how u work it out. The train experiment (video) simply analyses what the platform-observer reckons that the train-observer sees. I said that Tir21 asked what does the train-observer see & reckon based on her assuming that the train was stationary & the earth moving. Are u suggesting that what Tir21 asked is what does she reckon that he sees & reckons?? If so then that question adds another layer of imagining that i think would send Einstein to a funny-farm.

But in any case that video proves that Einstein's law of simultaneity is wrong.

U will notice that initially he is standing at O1 a little over L/2 from the train (train length = L). Later he is standing at O2 a little less than L/2 from the train. The video says that in both cases he sees simultaneous flashes (they don't show O1 & O2, they are my invention)(& they don't actually refer to the two cases). They are correct, if he is standing still. But, he must have walked or run or jumped from O1 to O2, probably during the critical instant. In any case (3 cases in all), whether at O1 or at O2 or jumping in between (call this O12), he unquestionably (i think) sees simultaneous flashes. If so then the video is correct despite showing or inferring the 3 different cases.

However, this falsifies Einstein's law of simultaneity, because in O12 he is moving. The video falsifies what it wanted to prove.

Allow me to introduce madmac's imaginary train & ferris wheel (thought) experiment.

There is a ferris wheel on the platform, turning in the plane of M & O1 & O2 & O12.

Everyone on the ferris wheel will see that the two flashes are simultaneous if the wheel is stationary & if the wheel is turning.

Unquestionably any observer anywhere in that plane will see simultaneity whether stationary or not.

Einstein apparently ignored simultaneous events that have a plane of symmetry that splits the events, & every pair (2 events) has such a plane.

The problem with Einstein's law is that it is badly worded.

The wording should say that in some cases 2 relatively moving observers might both see simultaneity (of say flashes)(& of strikes), & they might see them flashes at the same time, but no such observers will deduce that their lightning strikes occurred at the same time as the other's.

Here i should remind that a lightning flash is the tip of a ray of light that hits the eye, a lightning strike is a vertical movement of charge that hits the embankment or platform or (in the video) the end of the train.

In this regard Einstein's explanation of events is sloppy, or at least the English translation is sloppy.

Alby mentions (two strokes of lightning)(the rays of light emitted)(where the lightning occurs)(when the flashes of lightning occur)(the light rays emitted by the flashes of lightning)(the beam of light coming from)(the beam of light emitted from)(the lightning flash B took place earlier than the lightning flash A).

This wording is not just sloppy, it is wrong.

Earlier in his book, Alby mentions (if a ray of light be sent along the embankment)(the tip of the ray)(lightning has struck the rails)(these two lightning flashes occurred simultaneously)(both the lightning strokes occurred simultaneously)(if the observer perceives the two flashes of lighting at the same time then they are simultaneous).

Is Alby trying to confuse us intentionally? Doesn't he know the difference tween a strike & a flash? It wouldn't be so bad if (having made the mistake of adopting the wrong word) he at least stuck to using it consistently throughout the book.

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You are way over complicating this, and that's not going to help madmac.

It's very clear from the original thought experiment, that both observers are able to consider themselves as between the (location of the) two events. For the train observer, the events are at the ends of the train, and she is in the middle. That's why, when she doesn't see the flashes at the same time, she knows the events were not simultaneous.

Your describing of what's going, in terms of when the events occur, from the point of view of the embankment observer,

No, I talked about the train observer.

but for the train observer, is just going to confuse any onlookers.

Clearly, by "middle", this refers to the location of the events, not the when of the events.

After all, the "when" is then what the experiment then shows us something about (notably, that for the train observer, the "when" of these two events isn't the same.)

I'm summarising the actual thought experiment for madmac. Your after-the-fact "clarification" of what happened is not going to help him until he's got the basics right.

You mean "... at the same time"?

yes

You're simply emphasising a different aspect of the proof than most would. From the ref I gave earlier (my two numbers added):

I've described (2), you're a bit hung up on (1).

The OP asks for the point of view of the train observer. He considers himself at rest and the platform moving.

That's exactly what I do.

I think (2) is much clearer.

It doesn't answer how the train observer has to reason. From the point of view of the train observer he (the train observer) DOES NOT move towards the beam of light. I.o.w. your <<Now in reality (considered with .... etc >> is not a reality for the train observer. He cannot use that.

That's the problem with focussing on location. People might think M1 moves from the midpoint towards (the location of) the first flash. It doesn't. The train observer doesn't consider himself moving toward the front beam, nor flash location.

That's where your fixation on (1) goes astray.

You complicate the reasoning for the train observer, and make it harder for someone to understand the experiment. Instead of simply knowing they are located between the events, but didn't see them at the same time, so they didn't occur at the same time; you have the train observer referring to the embankment observer. That's silly.

It's not silly, because you also have to refer to what the embankment observer experiences if both events occur simultaneously for the embankment observer. If you don't, why would you need an embankment observer in the thought experiment? If I read you correctly you would simply state: there are two events at same distance from an observer, the beams do not reach observers simultaneously, hence events didn't happen simultaneously for him. The whole purpose of the experiment is to find out whether the events occur simultaneously when both observers are together. From the train observer's perspective he (train observber) does not move toward the front beam, nor to location of flash.Hence what is left for the train oberver to know whether the events did happen simultaneously or not? All train obsever can think of is: <<IF both flash events also occur simultaneously for me when I and embankment observer are together, then both lightbeams should also reach me simultaneously. But I experiences they don't reach me simultaneously, hence flash events didn't happen simultaneously for me.>>

Edited by VandD

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pzkpfw    164

pzkpfw.

Yes events simultaneous for one cant be simultaneous for the other, no matter how u work it out.

Ah, you reverse this later in this post.

The train experiment (video) simply analyses what the platform-observer reckons that the train-observer sees. I said that Tir21 asked what does the train-observer see & reckon based on her assuming that the train was stationary & the earth moving. Are u suggesting that what Tir21 asked is what does she reckon that he sees & reckons?? If so then that question adds another layer of imagining that i think would send Einstein to a funny-farm.

Sorry. I really can't parse that. In any case, my replies to you, have been to you. You claimed in post #17 "In her frame she sees the 2 flashes simultaneously". That was wrong (at least, for the same two lightening strikes that the platform observer considers simultaneous.)

But in any case that video proves that Einstein's law of simultaneity is wrong.

But above you agree with the result?

U will notice that initially he is standing at O1 a little over L/2 from the train (train length = L). Later he is standing at O2 a little less than L/2 from the train. The video says that in both cases he sees simultaneous flashes (they don't show O1 & O2, they are my invention)(& they don't actually refer to the two cases). They are correct, if he is standing still. But, he must have walked or run or jumped from O1 to O2, probably during the critical instant. In any case (3 cases in all), whether at O1 or at O2 or jumping in between (call this O12), he unquestionably (i think) sees simultaneous flashes. If so then the video is correct despite showing or inferring the 3 different cases.

I'm not seeing your O1, or O2 at all in that video. You seem to be nitpicking artifacts of the the video. Maybe just stick with the written experiment, so you don't confuse yourself and so we can all agree on the setup.

However, this falsifies Einstein's law of simultaneity, because in O12 he is moving. The video falsifies what it wanted to prove.

The embankment observer is not moving, according to the embankment observer. If you think you're seeing such movement in the video, you're being misled by an artifact.

Allow me to introduce madmac's imaginary train & ferris wheel (thought) experiment.

There is a ferris wheel on the platform, turning in the plane of M & O1 & O2 & O12.

Everyone on the ferris wheel will see that the two flashes are simultaneous if the wheel is stationary & if the wheel is turning.

Unquestionably any observer anywhere in that plane will see simultaneity whether stationary or not.

Einstein apparently ignored simultaneous events that have a plane of symmetry that splits the events, & every pair (2 events) has such a plane.

While it is possible for an observer in relative motion with another observer to agree on simultaneity, this is a very specific case. It's not an exception that disproves the concept, as it doesn't explain all the other relative motions where simultaneity can't be agreed on.

Einstein didn't ignore this, it wasn't relevant.

The problem with Einstein's law is that it is badly worded.

The wording should say that in some cases 2 relatively moving observers might both see simultaneity (of say flashes)(& of strikes), & they might see them flashes at the same time, but no such observers will deduce that their lightning strikes occurred at the same time as the other's.

I'd say that's badly worded, as you lose the concept of simultaneity. Where you wrote "but no such observers will deduce that their lightning strikes occurred at the same time as the other's" you make it sounds like the events themselves are different events (e.g. four different lightening strikes?). Both the train observer and embankment observer here, have seen the same two lightening strikes.

Here i should remind that a lightning flash is the tip of a ray of light that hits the eye, a lightning strike is a vertical movement of charge that hits the embankment or platform or (in the video) the end of the train.

In this regard Einstein's explanation of events is sloppy, or at least the English translation is sloppy.

Alby mentions (two strokes of lightning)(the rays of light emitted)(where the lightning occurs)(when the flashes of lightning occur)(the light rays emitted by the flashes of lightning)(the beam of light coming from)(the beam of light emitted from)(the lightning flash B took place earlier than the lightning flash A).

This wording is not just sloppy, it is wrong.

No, again here you're nitpicking. By this stage of the original book, simple things like that ought not need to be explained over and over again. The difference between when an event occurs and when it is seen is well known.

Earlier in his book, Alby mentions (if a ray of light be sent along the embankment)(the tip of the ray)(lightning has struck the rails)(these two lightning flashes occurred simultaneously)(both the lightning strokes occurred simultaneously)(if the observer perceives the two flashes of lighting at the same time then they are simultaneous).

Is Alby trying to confuse us intentionally? Doesn't he know the difference tween a strike & a flash? It wouldn't be so bad if (having made the mistake of adopting the wrong word) he at least stuck to using it consistently throughout the book.

Oh rubbish. It's quite clear what's going on.

Focus on what's being explained in the experiment. Trying to find claimed "sloppiness" in the language doesn't change the result.

(Frankly, this seems to play into your iconoclasm. Your profile on this website says "I have come here to bury Einstein, not to praise him". That seems odd coming from someone who doesn't seem to have previously read or understood much of what Einstein wrote. That, and your silly attempt to show disdain by writing "Alby". Science isn't religion, and Einstein isn't some "prophet" that people "praise" (as you wrote). Bear in mind that there's been a fair number of years since Einstein. Relativity stands today not because of "praise", but because it remains valid - studied by untold scientists; who don't just read Einsteins work and recite it like a priest reciting scripture, but who do further work and actual experimentation. Science adjusts, corrects, and moves on. There is stuff known today that Einstein didn't know. Don't get lost in trying to cut down the tall poppy; nit picking the language is not going to overtrun relativity.)