Is time universal? NO (and its proof)

[Pete]

Mac, you're not equating the time an observer sees the explosion with the time the explosion occurred for that observer, are you?

Yes, because Billy T had said all on board train observers see the explosions as being simultaneous and that is false.

Mac, regardless of what Billy said, it is wrong to equate the time an observer sees the explosion with the time the explosion occurred for that observer.

Do you think that this is what Billy thinks? If so, I suggest that you misunderstand him, and you should honestly try to clear it up before proceeding.

Billy said:

for all train observers, the two bombs (always equally distant from the light flash source) are exploding simultaneously

It's seems clear to me that he does not mean "All train observers see the explosions simultaneously."

I think he means "When the train observers accurately determine the time of the explosions, they all see that the two explosions were simultaneous".

Do you agree?

 

[MacM]

Mac, regardless of what Billy said, it is wrong to equate the time an observer sees the explosion with the time the explosion occurred for that observer.

I think what you meant to say was:

"Mac, regardless of what Billy said, it is wrong to equate the time an observer sees the explosion with the time the explosion occurred."

If so we agree.

I think he means "When the train observers accurately determine the time of the explosions, they all see that the two explosions were simultaneous".

Do you agree?

Most likely but then he needs to be more careful since he would have jumped on me with both feet for such an error.

 

[Billy T]

... Billy T had said all on board train observers see the explosions as being simultaneous and that is false.

No I did not. I said for all train observers the time of the explosions occur is the same, simultaneous. (even blind ones. Nothing to do with perception, seeing etc.)

The whole point of having the observers "with noses grazed by the passing bombs" in some version of the experiment and in other, differently described, versions of the same experimental arrangement described as "stop buttons of the stopwatches microns from the passing bombs" is to eliminate "signal delays" perception effects etc. In second version I usually state that no human even looks at the stopped stop watches for a week to further remove your favorite “objections” such as: “perception,” “signal delays,” “time dilation,” “tick rates,” “length contractions,” “reciprocity,” “GR, & SR calculations” etc.

This thought experiment was designed to make your customary "duck and weave" objections, totally ridiculous.

Feel honored. I think you intelligent enough to be worth my designing a thread to show you the error of you ways, but I was overly optimistic. You prefer to “duck and weave” rather than learn. I guess old habits are hard to break.

From my post of 7 Jan 06 at 34 past the hour:

"I.e. for all train observers, the two bombs (always equally distant from the light flash source) are exploding simultaneously, but the ground clock /stopwatch that happened to be adjacent to the rear bomb when it exploded records the explosion as earlier than the ground stop watch adjacent to the front of train bomb when it explodes (Not simultaneous explosions for ground clocks.)"

I alway say "for all train observers" - they need not have eyes. I have never seen an electron but have done several experiments* where I have observed their motion thru electric fields. For me, one can make observations using instruments. Clearly observing the simultaneity or not is done with clocks, preferably co-located with the event so no need to correct for signal delays. One can read the recorded time years later, You have even suggested this when disputing SR and suggesting that a video camera be used to record the moving clock for later viewing on Earth.
________________________________________
* I was about 10 years old when I did my first. Playing with a magnet next to an old Black and white TV. I was a amateur radio operator so I knew about the dangers of high voltage. I would not recommend this with a Color TV. Some shoot the electrons thru a very fine array of holes to hit only one of the three phosphors at a time. The residual magnetism may cause the TV to have false color effect permanently - I do not know but think it likely.

 

[MacM]

No I did not. I said for all train observers the time of the explosions occur is the same, simultaneous. (even blind ones. Nothing to do with perception, seeing etc.)

Thanks for clearing that up. So now it is even more clear that your are in error. You refuse to accept my statements regarding universal event times but now you invoke it?? :bugeye:

You either agree that events have a universal standard or they do not. The passengers on the train are distributed all along the train some are near the front and some are near the back. When the explosions occur (according to you) has varied as to location of the observer but now you say that doesn't matter that the explosions are simultaneous regardless of when observed?.

If not then we agree that the explosion can be simultaneous but appear nonsimultaneous based on location and relative velocity of the observer to the events.

 

[Pete]

You refuse to accept my statements regarding universal event times but now you invoke it??

No, Mac... for all train observers (ie observers on the train) the time of the explosions is the same.
They're all at rest in the same reference frame, so there's no difference in simultaneity for them.

For different reference frames (eg for ground observers), there is a difference in simultaneity according to SR.

The passengers on the train are distributed all along the train some are near the front and some are near the back. When the explosions occur (according to you) has varied as to location of the observer but now you say that doesn't matter that the explosions are simultaneous regardless of when observed?.

Of course... you don't think that SR says differently, do you?

 

[2inquisitive]

Here is a statement by Dr. Dowdye on his website concerning transmission times of data signals travelling with, vs. against, Earth's rotation. I have not been able to verify the difference in signal travel times by using Google so far. Does anyone know if the statement is correct?

"Taking the rotational rate of the Earth of (2x3.14159 / (24x3600sec)) = 7.27E-5 radians per sec, the radius of Earth, 6.37E+6 meters, the area A = 1.275E+14 sq meters enclosed by a signal that would circle the globe around the equator, the Sagnac effect (4A/c2) x angular rate of Earth yields 412 ns, which represents the difference in transit times of the signals in opposite directions. Taking a projection of the area enclosed by New York, Los Angeles and the Earth center onto the plane of the equator, one gets approximately 28 ns for the difference between signals in opposite directions between New York and Los Angeles. This time difference is routinely observed in the extremely high data rate communication systems where, the pulse rates are more than sufficiently high enough to resolve the time differences between the transit times of the opposing directions.

Note, this effect is clearly due to emissions and re-emissions of electromagnetic signals on a rectilinear path by N point emitters rigidly attached in a rotating frame. The expanding spherical wave front made up of the constituent photons responsible for the effect does not rotate or move along any curved path or along any path deviating from that of a purely rectilinear path, between points of re-emission!"
http://www.extinctionshift.com/topic_01.htm

Another point concerning the constancy of the speed of light comes from the observation of short duration GRB's (gamma-ray bursts). Short duration bursts only last a few seconds, quickly fading away. The observation is that 2 TeV (terra electron volt) photons arrived 280 seconds before 1 TeV photons, from the same source. The source was Markarian 421, a blazar located at a redshift of Z = 0.03. At very high energies, physics doesn't seem to follow the same rules as in our low energy world.

Another point that seems to support the varying speed of light at different energies is the detection of Cerenkov radiation being emitted from Ultra High energy NEUTRINOS while in the vacuum of space. Seems the neutrinos can travel at speeds very near the Ultra High energy photons, which is faster than low energy visible photons, thus emitting the Cerenkov radiation. In fact, the very low rest mass neutrinos are now thought to be the particles producing the Ultra High energy cosmic rays we observe hitting our atmosphere.

 

[MacM]

No, Mac... for all train observers (ie observers on the train) the time of the explosions is the same.
They're all at rest in the same reference frame, so there's no difference in simultaneity for them.

For different reference frames (eg for ground observers), there is a difference in simultaneity according to SR.


Of course... you don't think that SR says differently, do you?

Take a deep breath and have another cup of java Pete. If I am setting at the back of the train the aft explosion occurs first and vice versa if I am setting at the front of the train.

 

[geistkiesel]

Assume a train is moving past a line of men who are standing extremely close to the passing train. Assume two small bombs have been placed on the outside of the train and they just graze the noses of the men standing along the track as they pass. The bombs will explode when light from a flash bulb, placed on the train’s side, equally distant between the bombs, reaches them. An observer on the train standing midway between the bombs observes simultaneous explosions shortly after setting off the flash bulb.

I cannot agree with your conclusion here. For this to be a correct statement, the men seen from the train frame of reference(at the ends of the train) must have died at the same time, but this cannot be true as they died sequentially. One cannot have it both ways, because in the moving frame the light arrives at the end of the frame simultaneously, or so the claim. The light flashes seen from the ground will be identical to the light flashes seen on the train. In other words, if the light emitted on the train also was split in two parallel paths, the embankment observers would see each light pulse moving at the same speed. Yes, the forward light would arrive at the forward end of the train before arriving at the rear of the train, Likewise, the observers on the train would see the same thing.
We do not need clocks here to describe the event, we only need to see if the events of the explosions killed the men sequrntially or at the same instant.

The clocks synchronized on the train would record the sequential arrival of the lights as did the observer's clocks on the embankment. There is no way the observer at the midpoint between the ends can "see" the end points in a different context from the clocks located there. The lights will reflect back to the moving observer, and will arrive there simultaneously, but will arrive at the end points sequentially as these points are moving away from and townrd the two oncoming lights. The observer who is moving along with the physical device that emitted the light might think he is stationary, but he is in fact moving. Both endpoints are moving wrt the point of the emitted light (which coincidentally, cam be recorded in the embankment).

Look at chapter 7 of Einsteins, "Relativity". He has two conditions. First he has a man walking on the moving train. AE wri8tes the expression for the man's velocity seen from the embankment frame of reference as,
Vme = Vte + Vmt,
or, the velocity of the man wrt to the embankment is the sum of the velocity of the train wrt thew embankment plus the velocity of the man wrt the train. Actuall y AE wrote the expression as, W = v + w.

In the beginning of chapter 7 AE reminds the reader of the independence postulate of light, that the velocity of light is independent of the motion (the speed) of the soure of the light. However, he makes a curious statement stating that it is obvious that the light seen from the embankment can be replaced by c, while the man walking on the can be replaced y the light moving inside the train. However, this clearly violates the independence postulate. AE looks at the expression as c - v = w, which is less than c and he complains. He started talking about the light seen in the embankment frame and would have us believe that the rearranged expression is seen from the train as the coordinate frame. The c-v = w statement, or Vle - Vte = Vlt is an accurate statement for the relative motion of light seen from the embankment frame of reference. If we recognize this statement then when writing Vlt = Vte + V'le (where the prime is the light speed in the train same as the vacua) then Vle = Vte + Vlt,
Vle = Vte + V'le - Vte, then the Vte cancel and we have as expected Vle = V'le. One must subtract out the velocity of the moving train in order to maintain the independence postulate and to remove the problem from the man walking on the train.

Two of the thousands of men, who were standing on the ground right next to each other and right next to the passing train are killed by the exploding bombs. The man near the end of the train dies before the one near the front. They do not die simultaneously because in the line of men’s reference frame, the light flash moving towards the rear of the train explodes its bomb before the bomb at the front of the train explodes. (During the transit of the light towards the bombs, the bomb at the rear of the train has been moving towards the on coming light, while the one at the front of the train was trying to race away from the on coming flash of light.)

Note that their “non-simultaneous deaths” is not due to the time for light to travel to any observer - I had the two (now dead) stationary observers stand right next to the bombs when they exploded. If a third stationary observer, is standing mid way between the two that get killed, that third observer would observer them die at different times. (The two delays for him to see them die, due to finite speed of light, are equal.)

One must understand that AE made an arbitrary derfinition of "simultaneous". Lights emitted at A and B are simultaneously emitted if they arrive at their common midpoint. So, using AE's model slighty different from your own, lights can never be simultaneously emitted in a moving frame, as the mispoint moves from wher that midpoint was in space when the lights were emitted. In AE's gedanken he uses the sequential arrival of lights from the forward emitter than from the rearward emitter as proof of loss of simultaneity, but the test is for the emission of the lights, not when they arrive at the observer. Lights emitted in the embankment will always arrive at their midpoint simultaneously, there is no need to measure that point. Likewise, lights emitted at the A and B point on the train simultaneously, as determined from the clock measurements on the train, will always arrive at the observer sequentially.

Using your scenario, the lights will also arrive at the A and B points on the train sequentially whether the physical emitter is on the moving frame or the embankment, yet will reflect back to the moving observer and arrivie there simultaneously.

CONCLUSION: Simultaneous event in one frame are not simultaneous in one moving wrt to it. This is real effect of SRT. It is not due to any delay of light traveling to an “observer” waiting to sees the events.

The disagreement cvontinues. It is not the effect of SRT that the moving observer sees something different than the stationary observer, it is because of the "definition" that AE imposed that simultaneity is lost. In AE's definition he starts out with simultaneous question bening whether the lightning flashes striking A qand B on the train and the embankment are seen as simultaneous, yet he uses the moving observer and his, AE's, defintion of simultaneous to determine what he thinks is the physics of the matter.

People who dispute SRT often claim that the events are “really” simultaneous in all frames, but only “seen to be non simultaneous.” Events (or clocks) synchronous in one frame are not synchronous in a different frame and “seeing delays” are not the reason for their lack of simultaneity as most opponents of SRT claim. Thus clocks that strike noonday chimes simultaneously in one frame can not strike them at the same time as synchronized clocks are striking noon day chimes in another frame. That is, synchronized clocks distributed about in one frame can not be synchronous with many in another frame which are correctly keeping time in that frame.

The lights arrive at the endpoints at the same instant as observed by both, without recourse to looking at clocks or comparing synchronicity. If the moving observer looked at his clocks he wouild see the lights arriving there sequentially, from his own frame of reference.

If the time dilation of SRT is computed and used to adjust the rate of clocks in one frame, it is possible to synchronize any pair of clocks in two different frames, but not all of them, if they are to correctly keep time in their own frame. The reason is simple. A set of clocks that are separated only by space in one frame are separated by a mixture of space and time in the other. Thus clocks at different locations can not be both synchronous with each others in the same frame (keep time correctly) and yet synchronized with all synchronous clocks in another frame. Take your pick, (but only one of the following two):

Without going into time dilation, both sets of clocks would maintain synchronicity in their respectivie frames. Therefore the moving observer can check his own clocks and see the lights arrived at the end point s sequentially.

(1)You can have all clocks in two different frames all show the same time (Each has a unique SRT correction to it rate, which depends on the clock‘s location.) but they do not show the same time as clocks that are synchronous in their own frame. (I.e. they are not keeping correct time in their own frame.) OR
(2) You can have all clocks in both of two different frames synchronized with others in their same frame, (Keeping correct time in their own frame.) but the clocks in one frame will not be synchronous with the clocks in the other frame.

You cannot determine loss of simultaneity in each frame using this statement as the clocks are symentriacal in each frame for rate etc.

Any comments from people who claim that all clocks in two different frames can both keep time correctly in their own frame and yet be synchronized with clocks in another frame that are all also showing the correct time in their frame? I.e. people who think time is universal for all frames and thus SRT must be wrong.

Remember, this thread says that the men will die at different times as seen in both frames, meaning that, the embankment observer will see them die seqeuntially, the moving observer sees them dying at the same instant. This is not a condition where the embankment sees them dying sequentially and the moving observer seeing them dying sequentially but at different instances.
In laws of testacy, or the transfer of propery upon death of an ancestor is determined often from which ancestor died first, the wife or the husband. How do you argue your case in a court of law when the man and wife were standing at opposite ends of the train or the embankment?​

Geistkiesel

 

[Neddy Bate]

Using your scenario, the lights will also arrive at the A and B points on the train sequentially whether the physical emitter is on the moving frame or the embankment, yet will reflect back to the moving observer and arrivie there simultaneously.

Unless you are assigning 'absolute motion' to the train, there is no reason to assume that the light pulses will arrive sequentially rather than simultaneously, in the reference frame of the train. For all we know, BillyT is tricking us and the train is actually at rest while the embankment is moving past it. This would not change the outcome of the experiment, would it?

There is also no reason to consider the light reflecting back to the centrally located emitter. The firecrackers go off when the light reaches them, and that is all that is required for this thought-experiment gendanken to work.

However, I do tend to agree with you that the two light beams would reflect back and arrive at the emitter simultaneously in both reference frames. I find this to be a strange result, but I am not sure if there is any significance to it with respect to "absolute time". It would be useful if it allowed for synchronizing the two clocks systems in the two different inertial frames. However, I do not see how it would help us do this.

 

[2inquisitive]

Let me restate Billy T's gedanken a little.

This time, place the bombs on the embankment, not the train. Keep the flash that triggers the bomb explosion on the train. The flash is ignited as it passes a trigger located midway between the bombs, the trigger also located on the embankment.

The bombs will not explode simultaneously in the reference frame of the train, because the bombs are moving toward/away relative to the point of the emitted flash. This is the Sagnac effect, it does not only apply to rotating frames.

Now, in the reference frame of the embankment, will the bombs explode simultaneously?

 

[Pete]

If I am setting at the back of the train the aft explosion occurs first and vice versa if I am setting at the front of the train.

Is that your own opinion, or what you think SR says?

Wrong in either case.
Both SR and Newtonian mechanics say that if the explosions occur simultaneously according to one observer on the train, then they occur simultaneously for all observers on the train.




Yes, the light from the rear explosions will reach the rear observer before light from the from explosion does, and vice versa for the front observer... but so what? That doesn't tell the observer anything about when the explosions occurred unless they also figure out how long the light took to arrive.

 

[Pete]

Now, in the reference frame of the embankment, will the bombs explode simultaneously?

Yes they will

 

[MacM]

Is that your own opinion, or what you think SR says?

Wrong in either case.
Both SR and Newtonian mechanics say that if the explosions occur simultaneously according to one observer on the train, then they occur simultaneously for all observers on the train.

Somebody stop this merry go round. Damn it we are either talking time in a universal sense or time as experienced by observers located different distances from the explosions.

Information propagation delays about such explosions makes them seen to occur at differrent times by all observers on the train except those located midway between such simultaneous explosions.

Yes, the light from the rear explosions will reach the rear observer before light from the from explosion does, and vice versa for the front observer... but so what? That doesn't tell the observer anything about when the explosions occurred unless they also figure out how long the light took to arrive.

Now you want to talk about the explosion in terms of calculated time based on computing the simultaneity shift. I have commented on this many times. You and Billy T seem to be talking about different times.

 

[Pete]

Somebody stop this merry go round.

Damn it we are either talking time in a universal sense or time as experienced by observers located different distances from the explosions.

Neither one, Mac.

We are talking time as experienced by observers in different reference frames. The location of an observer in a reference frame is irrelevant.

SR says that observers in different reference frames (ie observers moving relative to each other) experience time differently, and that neither can tell which (if either) has the "true" experience.

SR says that all observers in the same reference frame all experience the same time, regardless of their location in that frame.

Information propagation delays about such explosions makes them seem to occur at differrent times by all observers on the train except those located midway between such simultaneous explosions.

That is true... but so what?
When we talk about the time an event occurred for some observer, we're talking about the time that the event occurred, not the time they found out about it.

 

[Pete]

Now you want to talk about the explosion in terms of calculated time based on computing the simultaneity shift. I have commented on this many times. You and Billy T seem to be talking about different times.

Mac, I don't know what you mean when you say "simultaneity shift". Do you mean "propogation delay"?

I think that when Billy mentioned the time of an event, he is always talking about calculated times, ie the time that light from an event reached an observer less the time taken for the light to get there.

This is standard practice... it usually needs no explanation. When we talk about the time an event occurred for some observer, we're talking about the time that the event occurred, not the time they found out about it.

 

[geistkiesel]

Unless you are assigning 'absolute motion' to the train, there is no reason to assume that the light pulses will arrive sequentially rather than simultaneously, in the reference frame of the train. For all we know, BillyT is tricking us and the train is actually at rest while the embankment is moving past it. This would not change the outcome of the experiment, would it?

No, Billy T is no trickster. However, like the resolution to the "Twin Paradox" where the the space ship twin was the one that acctually accelerated and moved, onloy yhe train accelerates and moves wrt the embankment, the ever faithful at rest frame wrt to earth borne objects moving relative to the embankment.

There is also no reason to consider the light reflecting back to the centrally located emitter. The firecrackers go off when the light reaches them, and that is all that is required for this thought-experiment gendanken to work.

There is a reason if you trace the relative motion of frame and photon wrt the "vacua" as AE put it. There is a slightrly longer time for the round trip of photons emitted at the midpoint to equally spaced reflectors and back to the physical midpoint. This is fairly simple to determine. Comparing the roundtrip for the embankment at rest condtions both light pulses are perfectly symetrical as I describe the motion: Each pulse is always moving oppositely to the other and both reflect simultaneously. However, when the frame is moving to the right the photon moving left initially meets the oncoming mirror before the right moving photon has arrived at the right mirror. For this brief instant the pulses are a symetrical in motion as both are moving in the same direction. It is this time difference that SRT is really discussing, but I fear they might deny the suggestion.

The instant the left photon has reached the left mirror the frame has moved a distance vt. The right moving photon is, at this instant, 2vt from the right mirror. To cross the 2vt distance plus a tad more the frame moves in the interim, vt', the light must move ct', or ct' = 2vt + vt' and t' = t(2v)/(c - v). For t' = zero the frame is at rest, for t' > 0 the frame is in motion.​

I do tend to agree with you that the two light beams would reflect back and arrive at the emitter simultaneously in both reference frames. I find this to be a strange result, but I am not sure if there is any significance to it with respect to "absolute time". It would be useful if it allowed for synchronizing the two clocks systems in the two different inertial frames. However, I do not see how it would help us do this.

Me either, however, there is the problem, in the two roundtrip times that may fortuitously approach the SRT time difference that is interpreted by SRT as time dilation. The calculations are not identical and the t' calculation kicks in earlier than SRT, meainiung it can be detected earlier. Synchreonization of clocks doensn't appear to me to offer much in the way of useful ness here as our concern wrt to simultaneity is onoly whether the lights arrive at the ends of the moving frame at the same instant, or whether they arrive sequentially, so even if there is a time dilation in the moving frame this doesn't explain simultaneous vs sequential arrival times.
I have struggled to see how SRT csn provide a reasonable argument or thesis for the light to reach both ends simultaneously when the frame is moving. I recongize that if one considers that an observer will always measure the speed of light as the relative velocity of all moving frames and photons, as if the frames were actually at rest wrt the embankment then this hypothesis would result as SRT says. This makes little headway to me. SLAC can acceolerate electrons to .999999c as I have been informed. If a duck were flying at .9999999c the measured relative velocity would be.0000009c, but if we do the same measurment with light we are supposeed to measure the relative velocity of c.
Einstein describes this question thus: :The motion of light should be measured by the same laws of physics in all mioving frames of reference. He then supposes that light moving along a train at c wrt the embankment would be measured the sam way as a man was walking on the train and concludes that the velocity of light on the train is less than c. Hw anbts us toi bekieve that he hasc onc=structed the problem that he gets c -v = w ( where W = c + w in the man walking scenario and W is the velocity of the man wrt the embankment, and w the velocity of theman wrt the train). He substitues light on th etrain for w and c for W, but his is clrearly in error as this assumes the motion of light is not undependent of the movtion of the train. and tha it is identical to the man walking.
To me the words, "The measured speed of light in all frames of reference is c" is ambiguous. Of course the speed of light is always c, but the relative motion of frame and photon is c - v for parallel moving light and frame. This statement only says that c moves faster than the frame by the amount c - v. This statement to me says nothing of a diminished measurement of the speed of light. Likewise, to assert that the laws of physics for light should be th esame in all inertial frames is no more than saying the laws of motion of ducks should be the same in all moving frmaes also. The l;aws of motion for light and ducks do not require we treat them differently as suggested by SRT and AE who, to my reading, changes the meani8ng of the laws of physics should be the same for the mtoion of light in all frames of reference to meaning that we must alweays measure the relative motion of frame and photon the same in all frames of reference.

I have looked at section 7 of "Relativity" in as many convoluted interpretations as my fading gray cells allow. The third or fourth paragraph reminds us of De Sitter's experoiments and the independence postuilate of light motion: The speed of light is independent of the speed of the frame of the source of the light. AE even says then that "obviously" light takes the place of the man walking on the train and makes no reference to the independence postulate of light. He then substitutes the speed of light c for W and w he interprets as the light moving on the train as if the train, all of a sudden was now the coordinate system, which should result in the same measurement as the speed of light relative to the embankment.

Finally, in looking for the clearest and least obtuse meaning of the words "the measured relative velocity of frame and photon will always be c" places a vertain certain dependence of the speed of light on the motion of frame and photon.

This picture may not be convincing to the SRT crowd, but conspder a cylinder 3000 meters long by 300 meters in radius. At the rear of the cylinder moving at v in the center of the cylinder radius a light source attached to the embankment emits a pulse of light. Then light and cylinder are moving independent of each other and are not in any special relationship to each other. Using the words of SRT there is a very definite nonindependent relationship which makes no sense to me.[/indent]
Geistkiesel

 

[2inquisitive]

Yes they will

Thanks Pete. I don't want to detract from your current discussion with others, other than to state I do understand what you are discussing in Billy T's example.

From my example, however, can you agree that there is no 'time shift'. The explaination for the difference in the reference frames is due to the Sagnac effect. The 'bombs' are approaching/retreating from the flash signal in the train frame, but the point of emission of the flash does not move with reference to the bombs in the embankment frame, even though the apparatus that emitts the flash is moving. No need for 'contracted distances' nor slower ticking clocks. Time remains universal with regard to velocity.

Now in Billy T's example, IF the train observer considers himself moving and the embankment stationary, the flash will be emitted at a certain point, unmoving with regard to the stationary embankment. While the signal is propagating from that point, the train observer and bombs will be moving relative to that emission point which does not move. IF the train observer lets his frame move instead of the embankment frame, the results will be the same as in my example. The explosions will not be simultaneous in the train frame, but will be simultaneous in the embankment frame. That is the difference that happens when an observer always considering his frame as the one at rest.

 

[Neddy Bate]

</em>No, Billy T is no trickster. However, like the resolution to the "Twin Paradox" where the the space ship twin was the one that acctually accelerated and moved, onloy yhe train accelerates and moves wrt the embankment, the ever faithful at rest frame wrt to earth borne objects moving relative to the embankment.​

You are too quick to assume this. I know BillyT would not deliberately trick us, but regardless, the fact remains that it makes no difference in his thought-experiment if we assume the train is at rest and the embankment is moving.

In the above 'reversed case', I suppose Geistkiesel would say that the light pulses would arrive at the firecrackers simultaneously in both the train's and the embankment's frame of reference. The reason this cannot be correct is because it would require that one of the light beams propagate at faster-than-light-speed in one of the reference frames (you are free to figure out which beam, and which frame, if you wish).

<em> There is a reason if you trace the relative motion of frame and photon wrt the "vacua" as AE put it. There is a slightrly longer time for the round trip of photons emitted at the midpoint to equally spaced reflectors and back to the physical midpoint. This is fairly simple to determine. Comparing the roundtrip for the embankment at rest condtions both light pulses are perfectly symetrical as I describe the motion: Each pulse is always moving oppositely to the other and both reflect simultaneously. However, when the frame is moving to the right the photon moving left initially meets the oncoming mirror before the right moving photon has arrived at the right mirror. For this brief instant the pulses are a symetrical in motion as both are moving in the same direction. It is this time difference that SRT is really discussing, but I fear they might deny the suggestion.

The instant the left photon has reached the left mirror the frame has moved a distance vt. The right moving photon is, at this instant, 2vt from the right mirror. To cross the 2vt distance plus a tad more the frame moves in the interim, vt', the light must move ct', or ct' = 2vt + vt' and t' = t(2v)/(c - v). For t' = zero the frame is at rest, for t' > 0 the frame is in motion.​

All of the above pertains to the embankment frame, where the train is considered to be moving. In the train's own frame, the firecracker at the rear of the train does not close-in on an oncoming light beam. The distance between emission event and firecracker remains constant. Likewise, in the train's own frame, the forward light beam does not chase after the firecracker at the front of the train. Again, the distance between emission event and firecracker remains constant in this frame (according to SR).

</em>...Synchreonization of clocks doensn't appear to me to offer much in the way of useful ness here as our concern wrt to simultaneity is onoly whether the lights arrive at the ends of the moving frame at the same instant, or whether they arrive sequentially...​

Quite to the contrary. The explanation for the two different frame's experiencing two different results (sequential versus simultaneous) is the fact that all of the clocks in one frame are synchronized only with respect to their own reference frame. They are not synchronized with respect to 'the other frame'. If we could synchronize both clock systems, we could end the disagreement between frames about firecrackers bursting sequentially versus simultaneously.

</em>... so even if there is a time dilation in the moving frame this doesn't explain simultaneous vs sequential arrival times.​

You are correct that it has nothing to do with time dilation.

</em>I have struggled to see how SRT csn provide a reasonable argument or thesis for the light to reach both ends simultaneously when the frame is moving. I recongize that if one considers that an observer will always measure the speed of light as the relative velocity of all moving frames and photons, as if the frames were actually at rest wrt the embankment then this hypothesis would result as SRT says.​

Yes. Pursue that line of reasoning, and you will begin to understand.

</em> ... SLAC can acceolerate electrons to .999999c as I have been informed. If a duck were flying at .9999999c the measured relative velocity would be.0000009c, but if we do the same measurment with light we are supposeed to measure the relative velocity of c.​

Yes. Pursue that line of reasoning, and you will begin to understand.

If you accept that light propagates at c relative to an observer, regardless of any relative motion between that observer and the source, then you will need something like SR to keep everything in order.

If you could show that the speed of light varies according to the relative motion between the observer and the source, then I believe you would be free to discard SR.

 

[Pete]

From my example, however, can you agree that there is no 'time shift'.

What do you mean by 'time shift'?
If the bombs are stationary on the embankment, then the explosions are simultaneous in the embankment frame, but not in the train frame, right?

The explaination for the difference in the reference frames is due to the Sagnac effect.

I think you misunderstand the Sagnac effect. You appears to think it provides an alternative explanation that doesn't rely on relativity? Think again.
All the Sagnac effect tells us in your example is that the explosions are not simultnaeous in the train frame - Special relativity explains how the explosions are simultaneous in one frame but not the other.

Now in Billy T's example, IF the train observer considers himself moving and the embankment stationary, the flash will be emitted at a certain point, unmoving with regard to the stationary embankment.

The emission of the flash is an event. It can be considered to be stationary in any frame without making any difference to anything.

While the signal is propagating from that point, the train observer and bombs will be moving relative to that emission point which does not move. IF the train observer lets his frame move instead of the embankment frame, the results will be the same as in my example. The explosions will not be simultaneous in the train frame, but will be simultaneous in the embankment frame. That is the difference that happens when an observer always considering his frame as the one at rest.

Hi 2inquisitive,
I'm not sure what you're thinking. You may be reading to much into the notion of an observer. An "observer in frame X" is really shorthand for "measure using rulers and clocks that are at rest in frame X".

It is actually irrelevant whether an observer thinks that they are moving or not... the relevant question is what is measured on rulers and clocks in the observer's frame.

 

[2inquisitive]

OK Pete, let's remove the observer. The emission of the photons from the flash propagate at the speed of light from the event. This event does not move in spacetime. If there is no relative velocity between the event and the bombs at the ends of the train, they will explode simultaneously. Notice I said the 'event', not the device that emitts the photons. Now let the bombs be moving while the 'event' takes place. The event does not move in spacetime, but the bombs do in this case. The rear bomb is approaching the event while the photons propagate, reducing the flight time needed for the photons to reach the bomb. The forward bomb is retreating from the event while the photons are propagating, increasing the flight time of the photons. This IS the Sagnac effect, used in GPS and NASA's deep space network where space vehicles are at great distances from the Earth.