Today Special Relativity dies

[ram1024]

Mark it on your calendars, people. Let us begin.
Case #1:

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

man standing on a movable platform bed. at the EXACT center between two photon emitters. SR concludes that the simultaneously emitted photons from the two emitters will be detected by the observer at the same exact time.

ADDENDUM:the photon emitters are tied to precise atomic clocks

these clocks are perfectly aligned and synchronized and in all cases they move within the same inertial frame so they can stay calibrated.

(True / False) ?

Case #2:

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

Platform is moving. SR concludes the photons (still emitted simultaneously) will be detected by the observer at the exact same time.

(True / False) ?

Case #3:

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

Man is moving on platform towards an emitter. SR concludes that photons are NOT detected at the exact same time.

(True / False) ?

once we square these we'll move on to stage 2.

 

[wespe]

Simultaneously, but simultaneously in which frame? You cant' omit that.

Case #1 there is only frame, so assuming simultaneously in that frame, true.

Case #2 there is one frame (not counting the background), so assuming simultaneously in that one frame, true.

Case #3, there are two frames (man and emitters). So in which frame are the photons emitted simultaneously? If man frame, false (detected at the same time). If emitter frame, true (not detected at the same time).

That's my answer according to my understanding of SR.

 

[Chronos]

huh? if both frames are moving relative to each other, they must obey SR to measure one to the other. what is so difficult about that? it has been proven in particle accelerators many times.

 

[jcsd]

In all cases we have 2 refrence frames.

In case 1 these are the same so in both reference frames the phtons are emitted and detectd simultaneously

In case 2 these refrnce frames are different, in our reference frame i.e. the 'stationary' frame we conclude the phtons are emitted and detected simulatenously. In the refrence frame of the man THIS IS NOT THE CASE; the man does not think the phtons are emitted simultaneously, but he does conclude that they are detected simultaneously.

In case 3 in our refernce frame we conclude that the phtons are emitted but not detected simulatenously. In the refernce frame of the man, the photons are not emitted simulataneously and they are not detected simulataneously.

 

[russ_watters]

We've had this discussion before: you can't prove/disprove a theory with a thought experiment, only with evidence.

 

[wespe]

In case 2 these refrnce frames are different, in our reference frame i.e. the 'stationary' frame we conclude the phtons are emitted and detected simulatenously. In the refrence frame of the man THIS IS NOT THE CASE; the man does not think the phtons are emitted simultaneously, but he does conclude that they are detected simultaneously.

For Case#2 I didn't consider the stationary background frame in my reply. If the photons are emitted simultaneously in the stationary background frame, the photons are not emitted simultaneously in the moving platform frame, therefore the man does NOT detect them at the same time. There I disagree with jcsd.

ram, will you please specify the frames in which the photons are emitted simultaneously? Is it the stationary background frame in all cases? You can't expect too many replies for a poorly specified scenario.

 

[jcsd]

For Case#2 I didn't consider the stationary background frame in my reply. If the photons are emitted simultaneously in the stationary background frame, the photons are not emitted simultaneously in the moving platform frame, therefore the man does NOT detect them at the same time. There I disagree with jcsd.

ram, will you please specify the frames in which the photons are emitted simultaneously? Is it the stationary background frame in all cases? You can't expect too many replies for a poorly specified scenario.

There is ceratinly plenty of ambiguity as ram failed to define reference frames, I just assumed that ram's drawings refer to the point of view of the 'stationary frame' and hence it is in this frame that the photons are always emitted simulatenously.

However you are incorrect still as simulatenity fails only at distance, so if the photons are detected simulataneously in one frame, they're detected simulatenously in all frames.

edited for about 100 typos

 

[wespe]

However you are incorrect still as simulatenity fails only at distance, so if the photons are detected simulataneously in one frame, they're detected simulatenously in all frames.

Yes I know simultaneity fails only at distance. And, the photons cannot be detected at the same time by the man [for case#2, if photons are emitted simultaneously in background frame] They would be detected at the same time by a midpoint observer in the stationary frame. But the man does not remain at that midpoint, so he does not detect them at the same time.

 

[Janus]

Just to add my voice to what has already been said. You must state which frame the lights emit simultaneously in. Is it according to us, the background observer or is it according to the emitters themselves.

In the first case, they are one in the same.
In the second case they aren't
In the third case they are the same again.

Also, in the third case, it depends on where the man is on the platform when he detects the photons. If he is exactly between the two emitters when he does, he will detect the photons simultaneously. But this doe not mean that the photons were emitted at the same time in his frame (in fact, from his frame, they can't have been emitted simultaneously.) That is the whole point of Relativity of Simultaneity, that distance separated events that are simultaneous in one frame are not simultaneous in a frame moving relative to the first.

It is a consequence of the invarience of the speed of light for all observers.

And as also already pointed out, you can not kill a theory with a thought experiment. All a thought experiment can do is show you the consequences of any given postulates. It takes a physical experiment to show whether or not the results of the thought experiment agree with reality or not. So far, every physical experiment designed to test the predictions of Relativity has supported the conclusions of Relativity.

 

[Hurkyl]

(NOTE: This was in response to the original posting)

In all cases, I will assume by "simultaneously emitted photons" you mean that emission was simultaneous in the frame in which the picture is drawn.


Case #1: True.
Case #2: False.
Case #3: True.

Since there is some disagreement in case #2, so I'll explain my answers.



disagreement with wespe:
Given the presentation of the problem, I'm assuming that "simultaneous" means that they're simultaneous according to the "background". However, you are correct if we assume that ram2048 means that emission was simultaneous in the frame of the platform.

disagreement with jcsd:
In our frame, the guy is at the midpoint of the emitters when they flash, but he's moving towards the right emitter; thus he has to detect the right photon first. In the moving frame, they are indeed not emitted simultaneously, but the guy will still detect the right photon first.

 

[jcsd]

Yes I know simultaneity fails only at distance. And, the photons cannot be detected at the same time by the man [for case#2, if photons are emitted simultaneously in background frame] They would be detected at the same time by a midpoint observer in the stationary frame. But the man does not remain at that midpoint, so he does not detect them at the same time.

Yep, sorry you're correct. I what I incorrecty did was take the refernce frame of the platform which is the same as the staionary frame in the other two case.

 

[wespe]

In all cases, I will assume by "simultaneously emitted photons" you mean that emission was simultaneous in the frame in which the picture is drawn.

Case #1: True.
Case #2: False.
Case #3: False.

Hurkyl, by "Case #3: False.", do you mean "detected at the same time" or "not detected at the same time"?

Ram, look at the mess you put us in. Clean this up! LOL

 

[Hurkyl]

Good catch; it's been fixed.

 

[ram1024]

the clocks in all cases emit photon simultaneously RELATIVE TO EACH OTHER.

these clocks are perfectly aligned and synchronized and in all cases they move within the same inertial frame so they can stay calibrated.

 

[wespe]

the clocks in all cases emit photon simultaneously RELATIVE TO EACH OTHER.
these clocks are perfectly aligned and synchronized and in all cases they move within the same inertial frame so they can stay calibrated.

Do you realize you wasted people's time by not specifying this in the first place? OK, in that case, #1 and #2 are true.

But, as Janus says, #3 is still unclear: where is the man when he detects the photons?

 

[ram1024]

does it matter where the man is?

he's obviously NOT in the center...

you can put real values to it if you like and work it out from there. however you want to make it easier for you.

and as far as wasting people's time, we've got ALL DAY, you in a hurry? :D

 

[wespe]

does it matter where the man is?

he's obviously NOT in the center...

Then, he does not detect them at the same time. #3: true

and as far as wasting people's time, we've got ALL DAY, you in a hurry? :D

I might have better things to do if you'll excuse me

Take care.

 

[ram1024]

so do we have (True, True, True) yet?

need couple more opinions/verifications then we can move to the next stage

 

[ram1024]

editting main post to include the clock bit, since it confuses you guys. I thought it was self explanatory, my bad.

 

[jcsd]

editting main post to include the clock bit, since it confuses you guys. I thought it was self explanatory, my bad.

You need to define which refernce frame the [phtons are emitted simultaneously, the stationery observer's, the platform's or the man's.

edited to add so the clocks are in the rest frame of the platform?

 

[ram1024]

hehehe that's part of my hook.

what i can GIVE you, if the clocks are perfectly synchronized together in the stationary frame, they are locked onto the platform so they cannot move in relation to each other, and therefore cannot become unsynchronized, moving OR not.

they emit photons simultaneously in both the moving frame AND the stationary frame, basically.

 

[jcsd]

hehehe that's part of my hook.

what i can GIVE you, if the clocks are perfectly synchronized together in the stationary frame, they are locked onto the platform so they cannot move in relation to each other, and therefore cannot become unsynchronized, moving OR not.

they emit photons simultaneously in both the moving frame AND the stationary frame, basically.

No they're not, you see they 'don't become unsychronized they either are or aren't scynorised in a partcular inertial frame, as in method used to synchronize them in one partcular frame only makes them unscychronised in another frame.

 

[ram1024]

how so?

stationary they shoot light at the exact same moment. on the platform they shoot light at the exact same moment. MOVING the platform they STILL shoot light at the exact same moment.

they are never in a position where there exists ANY relative motion between them to "unsynch" them in respect to each other. these two clocks define a precise INSTANT in time where two events ARE perfectly simultaneous.

any unsimultaneity by the observers can only be concluded as perceptual errors.

(True / False) ?

 

[Janus]

does it matter where the man is?

he's obviously NOT in the center...

you can put real values to it if you like and work it out from there. however you want to make it easier for you.

and as far as wasting people's time, we've got ALL DAY, you in a hurry? :D

Yes it does matter, if he is at the midpoint he will detect both simultaneously, if he's not he won't.

Example: the two following gifs show what happens according to the frame the emitters are in and the frame the man is in for the same situation. (the actual animation deals with a railway car moving along a track, but we will just assume that the track represents the platform. In this situation we have to men, one that stays stationary to the platform and one that moves with it.

We further stipulate that the moving man is next to the stationary man when the light is first detected by either.

The first animation shows things from the perspective of the emitters and the stationary man:
http://home.teleport.com/~parvey/train1.gif

The photons expand at c in two spherical fronts that reach the mid point at the same time by the observation of both men (both men see the photons arrive at the same time.)

The second animation shows what happens according to the man movig relative to the platform/track.

Since the speed of light is invarient for all observers, he also must see photons exapand outward from the point of emmission as a sphere in his frame. But from his perspective, the emitters do not stay at the the point of emmission. Therefore, in order for him to detect the emissions from both emitters at the same time, and at the same time as the man stationary to the platform, in his frame, the emiiters do not emit simultaneously, but one emits after the other.

http://home.teleport.com/~parvey/train2.gif

The reason things have to be this way is that the two men, being at the same point at the same time according to both of them, and both seeing the flash from the emitters arrive simultaneously is a spacetime event that is invarient and must be agreed upon by everyone.

 

[jcsd]

They 'shoot light' simulateously only in their own rest frame, this is not the case in other rest frames. There is no perceptual error as there is nothing in particular that ties the photon to the rest frame of it's emitter.

 

[enigma]

Today Special Relativity dies...

Mark it on your calendars, people. Let us begin.

...

I guess I should throw out my GPS receiver then. Shame about that...

 

[ram1024]

Since the speed of light is invarient for all observers

that's an assumption. I'll elaborate when we get to the second stage. need hurkyl russ or tom to confirm (True, True, True) on the first 3 cases.

I guess I should throw out my GPS receiver then. Shame about that...

nah they'll probably just reprogram the service. should be simple enough to do with all the computers they have

 

[enigma]

nah they'll probably just reprogram the service. should be simple enough to do with all the computers they have

You are aware that GPS receivers use SR to determine their exact location relative to the satellites? That's why you need to have 4 sat's in view. You triangulate your position with three, but you need the fourth to solve for the SR clock bias.

 

[jcsd]

that's an assumption. I'll elaborate when we get to the second stage. need hurkyl russ or tom to confirm (True, True, True) on the first 3 cases.



nah they'll probably just reprogram the service. should be simple enough to do with all the computers they have

You won't get an answer until you specify which frame the clocks are synchronised in and whether the man is in the middle of the two emitters, otherwise there is no sensible answer.

 

[ram1024]

they are synchronized IN the rest frame and REMAIN synchronized in all inertial frames for the clocks and the platform

it's already been specified :D

 

[jcsd]

But they're not and that's whole point; you can't use the assumptions of Galilean relativity to disprove special relatvity.

 

[ram1024]

that's the point being made. by ANY standard used they are synchronized. if you can't accept that you can't get any further into the experiment.

if they're NOT simultaneous you MUST be able to explain why?

they're synchronized in the rest frame, and remain synchronized no matter what inertial frame they're in because THEY'RE THE SAME CLOCK. they're attached, see? :D

Tom decided not to join us. i think he already knows where I'm going with this...

 

[Janus]

that's an assumption. I'll elaborate when we get to the second stage. need hurkyl russ or tom to confirm (True, True, True) on the first 3 cases.

No, it is a postulate. A postulate that has been experimentally confirmed in numerous ways.

 

[quantumdude]

Tom decided not to join us. i think he already knows where I'm going with this...

I didn't say that, I said that the others were "kicking your butt just fine without me". Boy oh boy, talk about problems with reading comprehension!

The point that you aren't getting is that you can't simply declare[/color] that the clocks are synchronized in every frame. In fact, they won't be, because simultaneity is relative. That is, if the ticks from the two clocks are simultaneous in one frame, then if they are spatially separated then they cannot[/color] be simultaneous in any other frame.

they're synchronized in the rest frame, and remain synchronized no matter what inertial frame they're in because THEY'RE THE SAME CLOCK.

No, they aren't. You quite clearly stipulated that there are two different clocks. The fact that they are of identical construction and are perfectly synchronized in their own rest frame does not negate the fact that the two clocks are not one and the same.

 

[ram1024]

fine, the emitter/clocks are on a geared track with exactly the same amount of cogs.

they are synchronized together in the center of the platform then wheeled to their locations at either end across the cogged tracks at exactly the same rate.

at any given point in the experiment at ANY inertial frame, the emitters can be wheeled back to the center to verify they are still synchronized.

attacking the synch of the clocks gets you nowhere.

 

[jcsd]

a vbiew from one rest frame:

|>        o        <|

|-------->o<--------|

A view from another:

|>         0         |

----|-------->0<--------|

It should be clear that in the second rest frame in order for them to be detected simulatenously the two phtons cannot of been emitted simulateously.


lets do some maths for this

Let x^{\mu}_1 and x^{\mu}_2 (where x^0 = t)be the postion 4 -vector of the emitters as it emits the light where the orgin is half way between the emitters in the the rest frame of the emitters, where c is the speed of light and l the diatnce between the the two emitters:

x^{\nu}_1 = \left(\begin{array}{c}0\\{\frac{l}{2}}\\0\\0\end{array}\right)

x^{\nu}_2 = \left(\begin{array}{c}0\\{\frac{-l}{2}}\\0\\0\end{array}\right)

Let x'^{\mu}_1 and x'^{\mu}_2 be the postion 4 vectors of the emitters as they emit light in rest frame of someone who is moving with velocity u relative to the emitters:

the following realtionships apply:
x'^{\mu}_1 = {\Lambda^{\mu}}_{\nu}x^{\nu}_1

x'^{\mu}_2 = {\Lambda^{\mu}}_{\nu}x^{\nu}_2

therefore:

x'^{\mu}_1 = \left(\begin{array}{c}{\frac{-\gamma l\beta}{2c}}\\{\frac{\gamma l}{2}}\\0\\0\end{array}\right)

x'^{\mu}_2 = \left(\begin{array}{c}{\frac{\gamma l\beta}{2c}}\\{\frac{-\gamma l}{2}}\\0\\0\end{array}\right)

So in the first frame the photons are emitted both at t = 0

but in the second frame the're emitted at \frac{-\gamma l\beta}{2c} and \frac{\gamma l\beta}{2c} respectively which are only equal if u = 0.

They're not the same clock as they're not local.

 

[quantumdude]

fine, the emitter/clocks are on a geared track with exactly the same amount of cogs.

they are synchronized together in the center of the platform then wheeled to their locations at either end across the cogged tracks at exactly the same rate.

This doesn't address the point. You needn't specify the method of synchronization, you need to specify the (one!) frame in which they are synchronized, and you need to not assume[/color] that that condition holds in every other frame. From the context, it seems clear enough to me that you mean that the clocks are synchronized in their rest frame. Yes?

at any given point in the experiment at ANY inertial frame, the emitters can be wheeled back to the center to verify they are still synchronized.

On this basis, all you can say for certain is that the clocks will be in synch when they are at rest at the center of the track (provided of course that their motion to the center was perfectly symmetric).

attacking the synch of the clocks gets you nowhere.

No one is "attacking the synch of the clocks" (whatever the heck that means). People are trying to get you to explicitly state which frame the clocks are synchronized in, and to get you to stop insisting that the clocks will be synchronized according to all inertial observers. Unless you do that, you are posing a problem in Galilean relativity. That sort of problem is well-defined enough, but it has the unfortunate difficulty of not being descriptive of the actual universe.

 

[Janus]

that's the point being made. by ANY standard used they are synchronized. if you can't accept that you can't get any further into the experiment.

The problem is that you are trying to get people to accept something that they know isn't acceptable.

Your inability to grasp the concept of the Relativity of Simultanity can in no way be used as proof against SR. It is a failure on your part, not on the part of the theory.

The Relativity of simultaneity is a direct consequence of the two postulates of Relativity. To disprove it, you have to show one or both postulates to be in error by direct physical experiment.

All you are doing is showing that SR and Galilean relativity are incompatible. But we already know that. It takes a real physical experiment to determine which of the two is correct for our universe. And every real experiment performed to date has come down on the side of SR.

 

[ram1024]

you mean it doesn't work according to SR's universe

yes that's quite the point, since SR is what I'm disproving :D

in any case explain to me how they could POSSIBLY become unsynchronized.

what reason is there to assume they AREN'T synchronized, in other words.

do tell

 

[quantumdude]

you mean it doesn't work according to SR's universe

No, I meant what I said: It doesn't work according the real universe.

yes that's quite the point, since SR is what I'm disproving :D

No, you aren't disproving it. You are simply denying it. Try to understand the difference.

in any case explain to me how they could POSSIBLY become unsynchronized.

what reason is there to assume they AREN'T synchronized, in other words.

do tell

That question is equivalent to asking, "Why are the laws of physics the same in every frame, and why is the speed of light the same in every frame." It is equivalent because the relativity of simultaneity is derived from[/color] those premises.

And the answer to both sets of questions is the same: Because that's the way it is.[/color]

 

[jcsd]

you mean it doesn't work according to SR's universe

yes that's quite the point, since SR is what I'm disproving :D

in any case explain to me how they could POSSIBLY become unsynchronized.

what reason is there to assume they AREN'T synchronized, in other words.

do tell

They don't BECOME unscyhronised, they ARE unsychronised in different inertial reference frames.

 

[ram1024]

sure i can win any argument with "because i said so" too :|

that tells us nothing

 

[quantumdude]

sure i can win any argument with "because i said so" too :|

!

That's exactly what you are doing! You are simply declaring something about the universe that is known to be false, and then saying that it disproves SR.

that tells us nothing

You sure are a dense little fella.

I'm not saying that it's true "because I said so", I'm saying it's true "because the universe says so[/color]". It says so when we ask it, via experimientation.

 

[jcsd]

Relatvity shows that if the clocks are sychronised in all refrence frames you get results that cause irresovable paradoxes and/or do not fit in with empirical obsrevrations.

 

[ram1024]

lemme get this straight.

nothing in the known universe is being done to CAUSE the clocks to become unsynchronized, yet you want me to believe that they ARE because you say so.

don't give me this "the universe says so" because the universe didn't do anything to the clocks. we can discern NO universal change that would CAUSE them to be changed.

 

[Hurkyl]

the clocks in all cases emit photon simultaneously RELATIVE TO EACH OTHER.

In this case, then, indeed, (true, true, true).


However, I would like to comment on other things you have said:

what i can GIVE you, if the clocks are perfectly synchronized together in the stationary frame, they are locked onto the platform so they cannot move in relation to each other, and therefore cannot become unsynchronized, moving OR not.

This will not work. There is no such thing as a rigid body, so you cannot use that as a way to keep things in sync.

In fact, if you sync the clocks while they're stationary (in the background frame), then accelerate the platform, the clocks cannot be synchronized in their rest frame, nor in the background frame.

This is easy to see in the background frame; due to length contraction, one of the clocks must have been displaced more than the other.

they emit photons simultaneously in both the moving frame AND the stationary frame, basically.

Which cannot happen, according to SR, unless the situation is trivial; either the two clocks are at the same place, or two frames are the same.

(for simplicity, I'm speaking in one spatial dimension)


I'm lagging somewhat behind the course of the conversation (darned TV!) but I'm going to post this anyways.

 

[quantumdude]

nothing in the known universe is being done to CAUSE the clocks to become unsynchronized,

A better way to look at it is the way JCSD described. Nothing "causes" them to be unsynchronized in other frames, they simply are unsynchronized. There is no way that the postulates of SR can hold and for simultaneity to be absolute. So the question is, Do the postulates hold?

Experimentation has answered with an emphatic "YES".

yet you want me to believe that they ARE because you say so.

No, you are expected to accept it because the evidence[/color] says so. And even if you don't accept it, surely you must be able to accept that simply assuming that SR is false does not disprove it.

don't give me this "the universe says so"

And why not? Experimentation is the final court of appeals in science. If you aren't open to that, then there is no hope for you.

because the universe didn't do anything to the clocks.

That's correct, because nothing was "done" to the clocks, period. It's not as though some invisible agent resets the clocks so that they are out of synch when a moving observer passes by. It is just a simple consequence of the fact that, in our universe, the laws of physics and the speed of light are the same for everyone.

we can discern NO universal change that would CAUSE them to be changed.

But we can[/color] discern that the clocks don't tick at the same rate for all observers.

 

[ram1024]

which brings the final conclusion that perceptions are WRONG in moving frames. not that time/speed/measurement etc CHANGE <ludicrous i KNOW>.

let's move onto stage 2. i think i have enough of an idea of where we're at to continue now.

Case #4:

observer1
[u]|(->                    (o)                    <-)|[/u]
   [u]|(->                    (o)                    <-)|[/u]
      [u]|(->                    (o)                    <-)|[/u]
         [u]|(->                    (o)                    <-)|[/u]

observer2
[u]|(->                    (o)                    <-)|[/u]
[u]|(->                       (o)                 <-)|[/u]
[u]|(->                          (o)              <-)|[/u]
[u]|(->                             (o)           <-)|[/u]

Two trains side by side (4 clocks now, wheee!). both containing the exact same set up. in the first train, the whole train moves forward at 5ft/s. it starts moving the instant the photons are released. at the same moment on the other train, the platform is stationary and the OBSERVER runs ahead at 5ft/s.

who receives the photon from the right emitter first? who receives the photon from the left first? if they both receive photons at the SAME time, how can you justify previous responses that observer 2 on his own would receive photons NOT simultaneously but observer 1 WOULD.

please make answers detailed :D

we'll move to stage 3 <conclusion> soon

 

[ram1024]

stupid "code" screwing up my pretty trains

 

[quantumdude]

which brings the final conclusion that perceptions are WRONG in moving frames.

It has nothing to do with "perceptions". It is what his instruments would record. Sorry, but you can't argue with experimental evidence just because it doesn't fit your view of how the universe should work.

not that time/speed/measurement etc CHANGE <ludicrous i KNOW>.

It is ludicrous to the moving observer. You have absolutely no basis for telling him that what he measures isn't real.

who receives the photon from the right emitter first?

In which frame?

who receives the photon from the left first?

In which frame?

if they both receive photons at the SAME time,

In which frame?