Today Special Relativity dies

[ram1024]

it SHOULD not be moving. which means MOTION of the train should bring the train closer to it.

it IS a contradition, because in picture 1, the train is without a doubt making relative motion towards it.

in the second image the train and the two sources/centerpoints move together. why are the centerpoints moving? they shouldn't be.

 

[wespe]

poke your pen in the centers of the expanding spheres.
picture 1 = movement towards expanding sphere to the right

I don't see center of spheres moving in any pictures.

If the author of the animation is the same person who posted the link, maybe he can create a version showing the center of spheres in the second picture.

 

[Hurkyl]

it SHOULD not be moving. which means MOTION of the train should bring the train closer to it.

And if the train is NOT MOVING (as in the second picture), then the train should not get closer.

in the second image the train and the two sources/centerpoints move together.

The train is not moving. The sources are. The centerpoints are not.

 

[ram1024]

not moving relative to the picture frame, I'm talking about moving relative to the tracks, just like the train is moving.

 

[Hurkyl]

i'm talking about moving relative to the tracks, just like the train is moving.

Yet the train is not moving in picture #2; the tracks are.

 

[ram1024]

no no no hurkyl. the second picture is not the train stationary, it's supposed to be the vantage point from the train IF the train was stationary.

what would be the point of comparing a moving train to a stationary one?

they both move in both pictures, that's the exercise, they're both supposed to get relative views of "what happens" to the same even viewed from two vantages.

the problem is. in picture 1, the train makes definate relative movement towards the emitter to the right.

in picture 2 there is no movement towards it.

i can only conclude that the picture is somehow interpretting the data incorrectly OR, someone fudged the calculations intentionally.

 

[Hurkyl]

no no no hurkyl. the second picture is not the train stationary

Sure it is; it remains at exactly the same point in the picture at all times, right? That is the very definition of stationary.

what would be the point of comparing a moving train to a stationary one?

It's the same train; the appropriate choice adjective "moving" or "stationary" depends on which reference frame you are using.

they both move in both pictures,

No they don't; the train remains at exactly the same point in picture #2. It's velocity is zero. It's stationary.

they're both supposed to get relative views of "what happens"

And, by golly, the train is stationary relative to itself.

the problem is. in picture 1, the train makes definate relative movement towards the emitter to the right.

in picture 2 there is no movement towards it.

In both pictures, the distance between the train and the emitter is very clearly decreasing.

I point out, once again, that if the emitter is moving, then it does not remain at the center of the sphere light.

i can only conclude that the picture is somehow interpretting the data incorrectly OR, someone fudged the calculations intentionally.

That person is you. You are mentally converting picture #2 back into picture #1 before you do any interpretation.

 

[russ_watters]

see that's the thing, if simultaneity can be real at a single point, then simultaneity MUST be able to be real at a distance. not "according to an observer" but according to "reality".

to say it doesn't happen is like saying "no two things in the universe EVER happen at the same time"

whether or not they happen "at the same time to you" is merely a matter of perception and is NOT reality

Well here's the thing, and its a catch-22 for you: your definitions of words like "simultaneous," "reality," and "perception" aren't the definitions science uses. So even if you are correct that perception does not equal reality (you're not), you still have to stipulate to it for the purpose of examining what the theory says. Otherwise, you're arguing that the sky is orange and defining orange to be the color between green and indigo. You won't get very far in science with that approach.

Regarding perception vs reality: what is perception? Its measurements, observations, data collected from an observer's reality. If these perceptions aren't reality, then there is no way to know what reality is and no use for science. Science has no choice but to assume that our perceptions are real. Otherwise, there isn't anything that science can "know."

Basically (not surprisingly), your objections to science are philosophical in nature. And I'm sorry, but you can't ever hope to understand science if you can't accept its philosophy.

From my thought experiment, ram - what if you don't know your distance between the two distant clocks. In that case, if the signals reach you at different times, how can you figure out if the signals are simultaneous in another reference frame? (Hint: you can't.)

 

[ram1024]

what if you don't know your distance between the two distant clocks. In that case, if the signals reach you at different times, how can you figure out if the signals are simultaneous in another reference frame? (Hint: you can't.)

but if you DO know the distance you CAN. and simultaneity would be the same to everyone else who did their own calculations.

i'll point out the problem in the pictures in detail as soon as i can figure out how to work my paint program :surprise:

 

[Janus]

no no no hurkyl. the second picture is not the train stationary, it's supposed to be the vantage point from the train IF the train was stationary.

what would be the point of comparing a moving train to a stationary one?

they both move in both pictures, that's the exercise, they're both supposed to get relative views of "what happens" to the same even viewed from two vantages.

the problem is. in picture 1, the train makes definate relative movement towards the emitter to the right.

in picture 2 there is no movement towards it.

i can only conclude that the picture is somehow interpretting the data incorrectly OR, someone fudged the calculations intentionally.

The emitters are the red dots, which it is assumed in this case emitted one brief flash, represented by the expanding rings. Once that flash is emitted, there is no reason for there to be any connection between the center of emission and the source that intially emitted it.

The point is that there is no preferred frame of reference. You can not absolutely say whether it is the train or tracks that are "moving". Both observers have equal claim that it is they that are stationary and that it is the other that is moving. Thus each observer will measure events as if they are the in stationary frame. In this case, the train observer sees the flash expand outward at the speed of light as a sphere from the point of emission. But the initial emitters move away from that point.

The observer beside the tracks has no motion relative to the emitters, thus for him, the center of expanision and the emitters remain together.

 

[Alkatran]

so speed is distance over time

left light travels 1 full distance in 1/2 the time the right light.

left light is comparatively twice as fast.

what happened to relatively constant?

I think I understand why you don't understand now. You REFUSE to believe that light can be at c for more than one observer at the same time. I am willing to accept there is a better solution than relativity out there, but it better pass all the tests relativity has before I accept it.

Consider this: In picture two the track is being shoved sideways by some massive force at a constant speed. The train is standing still because it is rolling on the track at just the right speed to be at 0. The light is emitted and you get what you're seeing!

Does that makes more sense to you?

 

[ram1024]

stupid paint program is worthless for animated gifs.

oh well now i have the file done but my webhosting is down

 

[ram1024]

http://www.imagedump.com/index.cgi?pick=get&tp=87816

temporary host :|

 

[Hurkyl]

You're still confusing "source of sphere of light" with "center of sphere of light".

The center is a geometric concept. Its definition depends on the (simultaneous!) measurement of the extent of the sphere of light at a given time in the given frame.

The source is a physical object. It is not required to remain at the center of the sphere of light in a given frame.

 

[ram1024]

that's why source is in "parenthesis"

in picture two we're NOT making relative motion towards "the source (geometric center"

in picture one we are.

let's assume that "the source" was an explosion and the physical source no longer exists.

how would you perform your calculations in picture 2?

 

[Doc Al]

that's why source is in "parenthesis"

in picture two we're NOT making relative motion towards "the source (geometric center"

in picture one we are.

The two animations are different views of the same thing. In both animations, the sources are fixed (attached) to the track. Animation #2 takes the view of someone on the train (thats why the train doesn't move). The sources (red dots) certainly move. The centers of the light spheres never move in either animation: that's what "invariant speed of light" means--any observer will see the light moving in a perfect sphere from wherever and whenever it started according to him. The speed of the light has nothing to do with the speed of the source.

let's assume that "the source" was an explosion and the physical source no longer exists.

how would you perform your calculations in picture 2?

I'm not sure what calculation you are trying to do. If you are calculating the speed of the light: remember the speed of light is constant relative to you the observer. The animation shows this pretty well.

 

[ram1024]

remember the speed of light is constant relative to you the observer. The animation shows this pretty well.

not if you take out the physical sources. basically you're saying that sources moving towards a stationary body and emitting photons simultaneously is exactly the same thing as sources stationary from a stationary body but emitting light non simultaneously.

the difference is where reality would agree with it. I didn't want to resort to it, but play the "where's the photon" game with both pictures. unless you're going to tell me the location of the photon is "relative" as well it's pretty closed case.

 

[Doc Al]

not if you take out the physical sources. basically you're saying that sources moving towards a stationary body and emitting photons simultaneously is exactly the same thing as sources stationary from a stationary body but emitting light non simultaneously.

Think of the source as emitting a single pulse of light and then shutting off. So, from an observer's view in describing how the light emanates from the source--all I care about is where the source was at the instant it flashed (according to me).

The "reality" is the fact that the photons from both sources arrive at the train together. That has nothing to do with who's viewpoint you take. The animations just show you that what one observer views as two simultaneous flashes of light, another observer views as two non-simultaneous flashes. But everyone agrees that the two pulses hit the train together.

the difference is where reality would agree with it. I didn't want to resort to it, but play the "where's the photon" game with both pictures. unless you're going to tell me the location of the photon is "relative" as well it's pretty closed case.

Please do play "where's the photon"! It's very instructive. Just be aware that relativity (and reality) insist that photons always travel at speed c with respect to the observer.

One trap to be wary of is that nothing prevents an observer from measuring that the apparent rate* at which light approaches another (moving) object may differ from c. For example in animation #1 the train is moving, so the rate at which the train and second light pulse come together is greater that the speed of light! But that's no problem. (But from the train's point of view (animation #2), the light speed is just c as usual.) It's tricky stuff.

* (I would refer to this rate as a "third party separation velocity" to distinguish it from a velocity with respect to the observer.)

You may be interested in checking out some of the other threads in TD. We've recently analyzed the crap out of this "train paradox" thing.

 

[Lama]

And what about Lorenz transformation?

 

[wespe]

the difference is where reality would agree with it. I didn't want to resort to it, but play the "where's the photon" game with both pictures. unless you're going to tell me the location of the photon is "relative" as well it's pretty closed case.

Ram, I understand what you mean: you want to run the two animations in parallel (you would have to move one of them manually to keep the trains aligned), then you want to see the egde of the spheres at the same positions all the time. But they won't be. If that was the case, there would be a common reality agreed in both frames. But, do you remember there was an animation I posted the link for. There were two frames skewed relative to each other in the time dimension. If we could run these animations skewed like that (instead of just parallel), you would see it makes sense. Maybe I could make such animations in flash.. But.. I'm not sure you would be convinced anyway.. In post#204, Hurkyl unbelievably bothered to make measurements on those animations for you, but you just ignored.. Nothing we say will convince you if you don't want to learn how this works..

 

[Alkatran]

Ram, I understand what you mean: you want to run the two animations in parallel (you would have to move one of them manually to keep the trains aligned), then you want to see the egde of the spheres at the same positions all the time. But they won't be. If that was the case, there would be a common reality agreed in both frames. But, do you remember there was an animation I posted the link for. There were two frames skewed relative to each other in the time dimension. If we could run these animations skewed like that (instead of just parallel), you would see it makes sense. Maybe I could make such animations in flash.. But.. I'm not sure you would be convinced anyway.. In post#204, Hurkyl unbelievably bothered to make measurements on those animations for you, but you just ignored.. Nothing we say will convince you if you don't want to learn how this works..

I agree completely. Any anyone bull-headed enough to go through 12 pages of people telling them basic things about relativity, such as the fact that c is relative, and still come out and say:

ot if you take out the physical sources. basically you're saying that sources moving towards a stationary body and emitting photons simultaneously is exactly the same thing as sources stationary from a stationary body but emitting light non simultaneously.

the difference is where reality would agree with it. I didn't want to resort to it, but play the "where's the photon" game with both pictures. unless you're going to tell me the location of the photon is "relative" as well it's pretty closed case.

is CLEARLY not listening to what we're saying. He's just glazing over the posts to find errors so he can get HIS point across. Then he wonders why all of our answers are different depending on the frame we are in!

 

[Alkatran]

Alright Ram, you disagree with the pictures because of the non-simultanity. But remember that picture with space distorted through time? (It was UP (ahead) in the direction of movement, and DOWN (back) the other way) Guess what that means? The train experiences certain "spaces" before an unmoving observer (the ones ahead of the train), but it also experiences certain ones AFTER (the events behind the train). Do you get how that can both perceive them as different YET??

 

[Hurkyl]

This hasn't been said... maybe it needs to be?

If the green fuzzy dots drawn in animation #2 are objects, then in animation #1 they would be moving to the right with the same speed as the train.

 

[Lama]

Where can we find Lorenz transformation in this thread?

I did not find it here.

 

[russ_watters]

but if you DO know the distance you CAN.

Yes! Now put the two together: the events are simultaneous when viewed from one frame, but are not simultaneous when viewed from another.
Again, "simultaneous" means "happening at the same time." If two signals reach you at different times, then you did not receive them simultaneously. Why is that such a difficult concept to accept?

...and simultaneity would be the same to everyone else who did their own calculations.

But only if they agreed on who'se frame would be considered the universal reference rame from which to do them. Remember, by any form of relativity, there isn't one. In fact, the top-down/outside-in reference frame we're using in our thought experiments does not exist in our hypothetical 2d universe. You could call it a virtual reference frame, one in which communication is instantaneous. But regardless, it still doesn't change the fact that you received the signals at different times.

Maybe something more physical: if two people throw baseballs at you and one hits you in the head a second before the second one hits you in the head, then they didn't hit you simultaneously.

 

[ram1024]

so answer case #6 already :|

 

[ram1024]

just in case you couldn't find the post here it is again

Case #6

[u](o)                    <-)|(->                    (o)[/u]

Same thing as case #5 except this time the two clocks use laser light and the distance between them to synchronize. They synchronize in such a way that the light from the center hits them both at what appears to them to be the same "time"

the train is them sped up FASTER in the direction it was traveling (let's say to the right) and another light is pulsed.

SR predicts they receive light non-simultaneous now (because of clocks getting messed up) even though nothing happened that changed clock synch relative to the other clock. (True / False)

explaining your answer in this case helps too. so try to :D

 

[jcsd]

Didn't I post an explanation of this a couple of pages back:

Or just imagine a device to sychronize them:

at the half way point we have a device that emits a photon to each clock, when that photon arives at the clocks they tick. This synchronises the clocks in the staionary frame, but in a moving frame one photon will have further to travel than the other so they CANNOT tick at the same time in the moving frame. As our photon device sychronises the clocks perfectly in the rest frame this must hold true for all clocks that are synchronised in their rest frame whether we use this device or not.

 

[Lama]

Let us add Lorenz transformation to our "story".

observer1
|(->__.__.__.__.__(o)__.__.__.__.__<-)|
   |(->__.__.__.__.__(o)__.__.__.__.__<-)|
      |(->__.__.__.__.__(o)__.__.__.__.__<-)|
         |(->__.__.__.__.__(o)__.__.__.__.__<-)|
 
observer2
|(->__.__.__.__.__(o)__.__.__.__.__<-)|
|(->___.___.___.___._(o)->.__.__.__<-)|
|(->____.____.____.____.(o)->_._._.<-)|
|(->______.______.______.__(o)->...<-)|

So there is no difference between observer1 and observer2 because space scale shrinks like a rubber sheet without losing its density ( exactly as (x/1)*(1/x) = 1 ) in the direction of the movement of observer2, and expends in the opposite side of observer2.

These opposite states can be observed as Doppler Effect.

So in both cases the speed of light is invariant in both directions.

 

[Doc Al]

case #6

just in case you couldn't find the post here it is again

Case #6

[u](o)                    <-)|(->                    (o)[/u]

Same thing as case #5 except this time the two clocks use laser light and the distance between them to synchronize. They synchronize in such a way that the light from the center hits them both at what appears to them to be the same "time"

Using the laser pulse to synchronized their clocks (call them A and B) in their own frame is a perfectly good method, as jcsd explained. No problem there.

the train is them sped up FASTER in the direction it was traveling (let's say to the right) and another light is pulsed.

Rather than introduce acceleration, and endless arguments about how it would affect the answer, just introduce another observer (call him Joe) who happens to be moving by. Now your once "stationary" arrangement of laser plus clocks A and B is moving according to this new observer Joe. No one will claim that anything was done to "mess up" those clocks--Joe does nothing but pass by. No one will claim that clocks A and B were accelerated: pure canonical SR. (Note that acceleration can certainly be handled, but why complicate matters?)

SR predicts they receive light non-simultaneous now (because of clocks getting messed up) even though nothing happened that changed clock synch relative to the other clock. (True / False)

In my version, it easy to see that SR predicts that clocks A and B will do exactly what they always did. Why shouldn't they? No one did anything to mess with them.

SR further predicts that measurements made by moving observer Joe will show that those laser pulses arrive at A and B at different times according to Joe.