The discussion centers on the complexities of understanding how light from two sources reaches a passenger on a moving train, particularly in relation to the principles of relativity. It highlights that while light travels at the same speed for all observers, the timing of when it reaches the passenger can differ based on the frame of reference used for synchronization. When synchronized with the train's frame, both light pulses can appear to hit the passenger simultaneously, whereas in the ground frame, they arrive at different times due to the train's motion. The conversation also touches on the mathematical representations of four-velocities and the implications of spacetime geometry on the perception of simultaneity. Ultimately, the discussion illustrates the nuanced nature of light propagation and observer-dependent effects in relativistic contexts.
#241
solarflare
177
0
if they hit the platform and not the train then by the time the flashes move to where the train observer will see them - she will no longer be equidistant from the flashes- therefore she will see them separately.
and instead of having the targets on middle ship have them on the stationary one
the big ship fires its lasers when the middle ship is in the centre - but by the time the flashes hit the stationary ship and move to meet the small ship - the small ship will no longer be equidistant from each flash.
#243
solarflare
177
0
Again, it is not important that the strikes actually hit the train (instead of, say, two adjacent points on the ground or two points on another passing train). All that matter are the position and time that the light from these lightning strikes originates from--the sources of these light rays are single points in spacetime.
So yes, I am trying to avoid the situation because you keep attributing false meaning to both strikes hitting the train. So, to further probe this point, perhaps you can clarify for me what the difference between the following three scenarios would be in your opinion:
------------------------------------------------------------------------------------------------------------------the things you say are not important - are
this is what i was saying about picking and choosing data - you can not decide what parts are and what are not important
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#244
solarflare
177
0
Doc Al said:
Not true. (Unless those strikes are simultaneous in the platform frame.)
The strikes occur simultaneously in the platform frame.
Don't keep flipping back and forth between the two physically different scenarios:
(1) The lightning strikes are simultaneous in the platform frame.
(2) The lightning strikes are simultaneous in the train frame.
They cannot both be true. Stick to scenario 1 (as in the video) until you understand it.
my ship scenario shows just one physical scenario - but seen by two different observers
my ship scenario shows just one physical scenario - but seen by two different observers
Even though I think it's a waste of time, I will ask you to describe your ship scenario in words. Your diagram is not self-explanatory.
Why do I think it's a waste of time? Because the train scenario is very easy to analyze yet you resist it. And it illustrates the relativity of simultaneity nicely.
And even after progress is made (if it ever is) with your ship scenario, you'll still have to go back and understand the Einstein train scenario.
#246
solarflare
177
0
Doc Al said:
You should take that quote to heart. You've been repeatedly proven wrong in this thread.
1) it was you that said the video was accurate - then you admitted it wasnt
2) george now says he believes the video is wrong
3) when the video was shown to have flaws you wanted to move the discussion away from
the video
if they hit the platform and not the train then by the time the flashes move to where the train observer will see them - she will no longer be equidistant from the flashes- therefore she will see them separately.
Again you miss the point.
From the viewpoint of the platform frame, the light flashes reach her at different times because she is moving. This has nothing to do with the lightning hitting the train instead of the platform.
From her train frame viewpoint she is always equidistant from the flashes. The speed of light with respect to her is constant. Yet she agrees that the light flashes reach her at different times.
1) it was you that said the video was accurate - then you admitted it wasnt
2) george now says he believes the video is wrong
3) when the video was shown to have flaws you wanted to move the discussion away from
the video
i would say it was the other way around
How about we deal the the actual Einstein train experiment, which has been described very clearly--and repeatedly--in this thread. (Forget the poor attempts in the video.)
(So far, most of the problems with the video were pointed out by George, not you. Most of your objections seem based on your misunderstandings of relativity. Unfortunately, the video's sloppiness doesn't help.)
3) when the video was shown to have flaws you wanted to move the discussion away from
the video
You're right about that! I wanted to discuss Einstein's thought experiment, not someone's mistaken description of it. And I thought that's what you were interested in also. Most of the statements you made were independent of the video.
Alas, it seems that you were attempting to learn relativity from that (admittedly sloppy) video, which is unfortunate. (Perhaps that explains the misconceptions that you've posted.)
If you want to discuss the flaws of the video, first demonstrate that you understand the real Einstein thought experiment and the relativity of simultaneity. (Your statements in this thread show that you do not.) Then you are free to pick apart the video, like George did.
Several folks have gone to great lengths in this thread to describe the (real) Einstein train scenario and point out your errors. I strongly suggest you take advantage of that. It's easy! (But subtle.)
#250
solarflare
177
0
Doc Al said:
How about we deal the the actual Einstein train experiment, which has been described very clearly--and repeatedly--in this thread. (Forget the poor attempts in the video.)
(So far, most of the problems with the video were pointed out by George, not you. Most of your objections seem based on your misunderstandings of relativity. Unfortunately, the video's sloppiness doesn't help.)
so let me get this right - i say the video is wrong
george says I am wrong - along with many others
i explain why i think the video is wrong - you say I am wrong the video is accurate -
george then quotes me - and then says - now i understand what you mean -
george then goes on to explain what is wrong with the video
( admittedly beter then me )
you then agree the video in not accurate ( agreeing with what i said at the beggining )
you then want to move away from the wrong video - and make a different scenario
if i did not understand RoS then i would not have seen the flaws.
If you understood RoS then you would not have made most of the statements you've made in this thread. You have not demonstrated any such understanding, at least as far as I could make out. Most of your statements are independent of the video.
How about this: Forget the video. Just describe Einstein's train experiment correctly. Show how the two frames disagree about the lightning strikes being simultaneous (and how that follows from the invariance of the speed of light).
I recommend that you start with the events that I have outlined in post #155.
#253
solarflare
177
0
mathematics is like building a house - the scenario is like the foundation
you can build a perfect - strong house
but if you build it on the wrong foundation it will still collapse
mathematics is like building a house - the scenario is like the foundation
you can build a perfect - strong house
but if you build it on the wrong foundation it will still collapse
And your point is?
#255
solarflare
177
0
look at my ship scenario
the middle ships targets have just been hit and send out light from the explosions
the ships pilot reports that the two targets were destroyed simultaneously because they occurred on his ship
but what does the stationary observer see
#256
solarflare
177
0
This diagram is in the frame of the stationary other ship. At some time t=0 in the stationary ship's frame, the stationary ship detects two flashes from the targets being obliterated by the laser cannons. The stationary ship knows, based on the sizes of these explosions, that it was equidistant from both explosions, so it concludes that the targets were obliterated at t=−30.15 units.
the middle ships targets have just been hit and send out light from the explosions
the ships pilot reports that the two targets were destroyed simultaneously because they occurred on his ship
but what does the stationary observer see
Please describe your ship scenario clearly. I don't understand your diagram. (Where are the ships? Where are the targets? How are they moving?)
#258
solarflare
177
0
the event occurs in the frame of the moving ship
the stationary observer see the flashes from that event
#259
solarflare
177
0
the middle ship is moving in a direction from south to north as you look at it
the lasers are fired from west to east as you look at it
the targets are the 0 at the front of the ship and the 0 at the rear
if you look at the diagram it looks like this --------0----------- the target is the 0
-----------------------------------------------/
----------------------------------------------I ------- this is the position of the pilot
the ship is moving at 500 m/s from south to north
the two targets are hit simultaneously in the little ships frame
#260
solarflare
177
0
the stationary ship is equidistant from the explosions when they happen
Events don't occur in a specific frame, they occur in all frames.
I don't understand your ship scenario, but if the events in question are separated along the x-axis and the moving ship moves along the y-axis, then there's no issue. Both frames will view them as simultaneous.
i could see the flaws in the video - and you could not -
if i did not understand RoS then i would not have seen the flaws.
I am going to call BS on this one. Nothing that you said above indicates that you were aware of any of the actual flaws in the video. Your mistakes appear to be entirely your own and not an identification nor a repetition of any flaws in the video.
mathematics is like building a house - the scenario is like the foundation
you can build a perfect - strong house
but if you build it on the wrong foundation it will still collapse
I am still waiting for you to provide a mathematical proof of any of your points or to identify a specific flaw in the math that I have presented or the assumptions I used. If the house is weak or the foundation wrong then you should be able to identify the specific flaw, particularly since you are so much more amazingly perceptive than all of the rest of us . If you cannot prove your own point, then you at least need to directly address the disproof.
Doc Al already mentioned that events occur in all frames. To expand on that, an event occurs in all frames, but each frame assigns that same event to different time and space coordinates. The equation which relates the coordinates assigned to any arbitrary event in one frame to the coordinates of the same event in another frame are given by the Lorentz transform:
if they hit the platform and not the train then by the time the flashes move to where the train observer will see them - she will no longer be equidistant from the flashes- therefore she will see them separately.
Can you confirm your agreement or explain why you don't agree even though your recent comments seem to indicate agreement?
#266
Muphrid
834
2
solarflare said:
the point is that the stationary observer is seeing an event where the ship ACTUALLY was hit simultaneously in that frame.
if your saying it doesn't matter then you are sayin reality has nothing to do with it - and if you say that then you also say relativity has nothing to do with reality
The stationary other ship is seeing two events that happen to be simultaneous in the reference frame that he is stationary.
As yet, I haven't posted the complete conclusions. I just want to make sure we agree on the math. Read what I posted again (which I'm quoting so you don't need to flip back and forth). The stationary ship believes both targets were destroyed at the same time t = -30.15. It also believes that the flashes from those two events will reach the moving ship at different times. I have yet to calculate whether the moving ship will calculate that the two events took place at the same time in its frame because I want us to agree on these very basic principles first.
If you believe that connecting the two targets to the moving ship makes a difference, how does it make a difference to what has been calculated so far? Do you think that means the moving ship will receive the flashes at times other than I have calculated (times in the stationary other ship's frame)?
Muphrid said:
Code:
30 units
|==============================|
Laser cannon
|--- 0 Target
| \
| |
| | #
| | Small -># +Y-velocity beta = 0.9 #<-Stationary other ship
| | Ship ] #
| | |-3 units
| / ]
|--- 0 Target
Laser cannon
|====================|
20 units
This diagram is in the frame of the stationary other ship. At some time t=0 in the stationary ship's frame, the stationary ship detects two flashes from the targets being obliterated by the laser cannons. The stationary ship knows, based on the sizes of these explosions, that it was equidistant from both explosions, so it concludes that the targets were obliterated at t = -30.15 units.
The small ship is traveling at \beta = 0.9 between the targets, which are confined to a line but otherwise have thrusters that allow them to move in an arbitrary manner along that line. The stationary ship monitors the small ship's trajectory and believes that the small ship was equidistant from the targets at t = -30.15, the time both targets were obliterated. If the stationary other ship is at y = 0, then it believes the light from the upper target will reach the small moving ship at t = -30.15 + 1.58, or 1.58 units of time after the explosion, and at y = 1.42. It also believes that the flash from the lower target will reach the small moving ship at t = -30.15 + 30, a full 30 units of time after the targets were obliterated, at y = 27.
Let's stop here before we go any further. Do you agree with the conclusions I have reached so far?
#267
Muphrid
834
2
solarflare said:
if they hit the platform and not the train then by the time the flashes move to where the train observer will see them - she will no longer be equidistant from the flashes- therefore she will see them separately.
No, no, absolutely not. The sources of the flashes do not "move with" the object the lightning/lasers hit. The sources are points in space and time. They do not move. They do not have worldlines. When the train observer sees the flashes, she is looking into the past, to the places and times the strikes hit, not to where the point of impact actually has moved to. That is why we keep saying it does not matter if the strikes hit the train or the platform.
In other words, it is only the platform observer who thinks the train observer has caught up to the forward flash and was closer to it. As long as the platform observer and the train observer were right beside each other and the events were equidistant from the platform observer, the events must be equidistant from the train observer (in her frame) whether or not the platform or the train was actually struck.
So this is the chain of reasoning:
a) The train observer must believe herself to be equidistant from the sources of the flashes (yes, even if the sources were lightning strikes that hit the platform, not the train)
b) The platform observer sees that the train observer must detect the forward flash before the rear flash; this sequencing of events is something all observers must agree upon because it's the difference between two points in space and time
c) Because of (b), we know the train observer detects the forward flash before the rear flash. Because of (a), she can't attribute the difference in times to a difference in distance of the sources. Therefore, she attributes the difference in times to an actual difference of simultaneity, saying the forward strike happened before the rear strike.
No, no, absolutely not. The sources of the flashes do not "move with" the object the lightning/lasers hit. The sources are points in space and time. They do not move. They do not have worldlines. When the train observer sees the flashes, she is looking into the past, to the places and times the strikes hit, not to where the point of impact actually has moved to. That is why we keep saying it does not matter if the strikes hit the train or the platform.
In other words, it is only the platform observer who thinks the train observer has caught up to the forward flash and was closer to it. As long as the platform observer and the train observer were right beside each other and the events were equidistant from the platform observer, the events must be equidistant from the train observer (in her frame) whether or not the platform or the train was actually struck.
So this is the chain of reasoning:
a) The train observer must believe herself to be equidistant from the sources of the flashes (yes, even if the sources were lightning strikes that hit the platform, not the train)
b) The platform observer sees that the train observer must detect the forward flash before the rear flash; this sequencing of events is something all observers must agree upon because it's the difference between two points in space and time
c) Because of (b), we know the train observer detects the forward flash before the rear flash. Because of (a), she can't attribute the difference in times to a difference in distance of the sources. Therefore, she attributes the difference in times to an actual difference of simultaneity, saying the forward strike happened before the rear strike.
This is to elaborate on Muphrid's answer for solarflare.
If there were additional train observers on board, not just at the center of the train, but also at the actual locations and times at which the lightning strikes occurred, and if these observers had clocks that were synchronized with the clock of the woman at the center of the train, then the time displayed on the clock of the forward observer when the forward strike occurred would be earlier than the time displayed on the clock of the rear observer when the rear strike occurred. So, as far as everyone on the train is concerned, the forward strike occurred first, and then the rear strike (according to all the synchronized clocks on the train). If the woman is half way between the forward and rear observers, she will receive the flash from the forward strike first, followed by the flash from the rear strike. This describes what is observed on the train whenever a similar set of 3 platform observers note using their synchronized clocks (i.e., synchronized within their frame of reference) that the two lightning strikes occurred simultaneously. This is a reality of special relativity, of the Lorentz Transformation, and an experimentally confirmed reality of our actual universe.
#269
bahamagreen
1,015
52
Just some thoughts that might help (assuming I'm not in error)...
The train itself is not the same as the frame of the train, nor is an observer on the train necessarily in the frame of the train.
The platform itself is not the same as the frame of the platform, nor is a platform observer necessarily in the frame of the platform.
The train may be observed from the platform in either the frame of the platform or the frame of the train (if the platform observer is moving wrt the platform so to be at rest wrt to the train).
Likewise, the platform may be observed from the train in either the frame of the train or the frame of the platform (if the train observer is moving wrt the train so to be at rest wrt to the platform).
In fact, any observer might be in any arbitrary frame whatsoever. It all depends on precisely how the experiment is stated.
I think part of what is going on is that folks are saying that because the platform observer in the platform frame observes the two strikes at the same time in his frame, he will conclude that the train observer in relative motion wrt the platform MUST see the forward strike before the rear strike... and since she is in the center of the train, she must conclude that the strikes were separated in time.
This might be misunderstood as giving the platform observer the "correct" view of events, and the train observer observing an "illusion"; especially if the reasoning is that her mistake is a natural one because of her motion which intercepts the forward flash prior to the rear flash... as if the train strikes really were together in time, but the motion of the train forward causes the difference in arrival.
So a possible confusion might stem from assuming that the strikes at the same time in the platform frame entail that the train itself received strikes at the same time in the train frame. The reasoning for this would be that the light propagates at constant speed independent of the motion of the source... as if it did not matter that the train was moving wrt the platform observer or not. This is a confusion between the train and its frame... if the train was not in motion relative to the platform then the train frame and platform frame would be the same. The frames are separate as a result of the relative motion between them.
The effect of relative motion between frames shows in the relationship between the source location of a light flash and the center of its subsequent sphere of expansion... observed from within one's own frame, all observers will observe spheres of the same time radius to contain the flash source's original location of the flash at the center of the sphere. This is the same as saying that all observers agree on c... but it may help to see why observers in different frames disagree about other observations.
The platform observer will see the flash source locations hold still in his frame... the forward and rear ends of the train just happen to be at these locations as it moves by... and it keeps on moving past them. This makes him conclude that the train observer will see one flash before the other.
The train observer in her frame will see the flash source locations hold still in her frame, too... the same forward and rear ends of the same train itself, but for her these source locations ARE the ends of the train and continue to be so even as it continues to roll along because she is at rest wrt the train.
So, the two frames disagree about the flash source locations and those source positions with respect to the subsequent flash sphere centers.
Just some thoughts that might help (assuming I'm not in error)...
The train itself is not the same as the frame of the train, nor is an observer on the train necessarily in the frame of the train.
The platform itself is not the same as the frame of the platform, nor is a platform observer necessarily in the frame of the platform.
What we're defining as the "train reference frame" is the *rest frame* of the train. In other words, it's the inertial reference frame in which the train is stationary.Therefore, any observer who is NOT moving relative to the train is in the "train frame" (i.e. that observer's rest frame is the same as the train's). This obviously includes the observer on the train in our scenario.
EDIT: Likewise for the platform. When we say that an observer is "in the platform frame", we mean that that observer is at rest relative to the platform. So both the platform and the "platform observer" are "in the platform frame" by definition.
. If you cannot prove your own point, then you at least need to directly address the disproof.