Today Special Relativity dies

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Discussion Overview

The discussion revolves around the concept of simultaneity in the context of special relativity, specifically examining thought experiments involving a man on a movable platform and photon emitters. Participants explore different cases to analyze how simultaneity is perceived from various reference frames, addressing theoretical implications and interpretations of special relativity.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants assert that in Case #1, photons emitted from two synchronized clocks will be detected simultaneously by an observer at the midpoint, assuming a single reference frame.
  • In Case #2, there is contention regarding whether the photons are emitted simultaneously in the moving platform frame versus the stationary background frame, leading to differing conclusions about detection simultaneity.
  • Participants note that in Case #3, the moving observer will not detect the photons simultaneously due to their motion towards one emitter, which raises questions about the relativity of simultaneity.
  • Some argue that thought experiments cannot definitively prove or disprove theories, emphasizing the need for physical experiments to validate the implications of special relativity.
  • There is a call for clarity regarding which reference frame is being used to define simultaneity, as ambiguity in frame specification leads to confusion in the conclusions drawn.
  • Several participants highlight that simultaneity can fail at distance, suggesting that if photons are detected simultaneously in one frame, they should be detected simultaneously in all frames, although this is contested.

Areas of Agreement / Disagreement

Participants express disagreement particularly regarding Case #2, with differing interpretations of simultaneity based on the chosen reference frames. There is no consensus on the conclusions drawn from the thought experiments, and the discussion remains unresolved.

Contextual Notes

Participants note the importance of specifying reference frames when discussing simultaneity, as assumptions about which frame is being referenced can significantly alter the conclusions. The discussion also reflects the complexities of applying special relativity to thought experiments.

ram1024
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Mark it on your calendars, people. Let us begin.
Case #1:
Code: 
[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:
Code: 
[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:
Code: 
[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.
 
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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.
 
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.
 
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.
 
We've had this discussion before: you can't prove/disprove a theory with a thought experiment, only with evidence.
 
jcsd said:
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.
 
wespe said:
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
 
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jcsd said:
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.
 
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.
 
  • #10
(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.
 
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  • #11
wespe said:
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.
 
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  • #12
Hurkyl said:
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
 
  • #13
Good catch; it's been fixed.
 
  • #14
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.
 
  • #15
ram1024 said:
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?
 
  • #16
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
 
  • #17
ram1024 said:
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


ram1024 said:
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.
 
  • #18
so do we have (True, True, True) yet?

need couple more opinions/verifications then we can move to the next stage
 
  • #19
editting main post to include the clock bit, since it confuses you guys. I thought it was self explanatory, my bad.
 
  • #20
ram1024 said:
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?
 
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  • #21
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.
 
  • #22
ram1024 said:
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.
 
  • #23
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) ?
 
  • #24
ram1024 said:
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.
 
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  • #25
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.
 
  • #26
ram1024 said:
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...
 
  • #27
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
 
  • #28
ram1024 said:
nah they'll probably just reprogram the service. should be simple enough to do with all the computers they have

:rolleyes:

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.
 
  • #29
ram1024 said:
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.
 
  • #30
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
 

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