Thread: Is time universal? NO (and its proof)

  1. #621
    Valued Senior Member Neddy Bate's Avatar
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    Quote Originally Posted by 2inquisitive
    </em>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.
    All of this talk of Sagnac has made me curious again. Unlike relativity, I have never heard of the (linear) Sagnac effect becomming null when observed in its own reference frame.

    Using GPS or space vehicles, has any experiment ever been performed which demonstrates that the "event" is dragged along with the reference frame? For example, using 2inquisitive's centrally located 'event' above, is there documented evidence that the light reaches the bombs simultaneously in their own reference frame? I know of M&M, but are there any experiments which are more modern?

    Note: By definition, an event is of infinitessimal duration, and therefore cannot be 'dragged' per se. For lack of a better term, I am just trying to describe how, in the bombs' reference frame, the event does not move one way or the other, and therefore the distances between the bombs and the event are held constant in this frame only.
    Last edited by Neddy Bate; 01-13-06 at 01:03 AM.

  2. #622
    Quote Originally Posted by 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?

    Light will always tie in a race where one pulse is emitted from a moving frame the other frame a stationary frame. The independence of the speed of light postulate (SOL independent of the motion of the source of light) tells us that the light will move equal distances in equal times. If the end points are stationary, i.e the points represent the "vacua" discussed by AE in "Relativity" Section 7, then the lights will arrive at the end points simultaneously, at the same instant.
    Geistkiesel

  3. #623
    Quote Originally Posted by 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.
    So if the bombs are stationary (train frame), they explode simultaneously.
    If the bombs are moving (embankment frame), they do not.

    What's your point?

  4. #624
    Please use Sugar Cane Alcohol Billy T's Avatar
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    Quote Originally Posted by MacM
    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.
    You can be 100 light years away but in the same frame as observers on the train (I.e. wrt you train has zero velocity.) and you will not know about the explosions for at least 100 years. This does not change when they occurred. All clocks in each frame are mutually sychronized but not with the one in another frame that are mutually synchronized. The one next to explosion, and stopped by the explosion gives the time of the explosion event, not your delayed perception or knowledge of it.

    Your claim otherwise (Made bold by me in your text above) is stupid. If the adjacent clock stopped at 13:07 GMT on 13 Jan 2006 and you only learn of it on 13 Jan 2107 13:09, do you really think that is when it occurred? What about the woman who was 50 light years away? Is her view that the event occurs on 13 Jan 2055 at 13:08 less valid than yours is? LOL

    The time shown on the stopped stopwatch adjacent to the explosion, and only it, is the event time. I must congratulate you however, as you have found a new "duck and weave." By my count, you now have at least a dozen different ones to drag out instead of accepting the simple facts, clearly demonstrated without any SR calculations that:

    Events simultaneous in one frame are not simultaneous in any other.

  5. #625
    Please use Sugar Cane Alcohol Billy T's Avatar
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    Quote Originally Posted by Pete
    ...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...
    Yes that is what I would mean if I were discussing with one who could think clearly and who accepted SR or agreed on how the calculated corrections should be made.
    Mach can think clearly but not when he has made up his mind he is correct and most physicists are wrong. He just "ducks and weaves" to confuse the question. That is why I have adjacent clocks, stopped by the explosions on both the ground and on the train so that no corrections for propagation delays are required.

    MacM will not admit that the time shown on these stopped stop-watch clocks is the time of the event, but now he is claiming the time the event OCCURED (His very word - see his text I made bold in my reply to him below) is when he sees the event. Even that he can change the order of the events by moving from rear of train to front. (That would be nice if true, as then the effect could preceed the cause! - MacM is in Alice and Wonderland. - as the queen said: "Sentence first, then the trail." If sentence is "not guilty" think of all the legal expense we could save by cancelling the trial!)This is a new low in his list of "duck and weaves" but a new one, none the less.

  6. #626
    Please use Sugar Cane Alcohol Billy T's Avatar
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    Quote Originally Posted by Pete
    ...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...
    Yes that is what I would mean if I were discussing with one who could think clearly and who accepted SR or agreed on how the calculated corrections should be made.
    Mach can think clearly but not when he has made up his mind he is correct and most physicists are wrong. He just "ducks and weaves" to confuse the question. That is why I have adjacent clocks, stopped by the explosions on both the ground and on the train so that no corrections for propagation delays are required.

    MacM will not admit thqt the time shown on these stopped stop-watch clocks is the time of the event, but now he is claiming the time the event OCCURED (His very word - see his text I made bold in my reply to him below) is when he sees the event. Even that he can change the order of the events by moving from rear of train to front. (That would be nice if true, as than the effect could precced the cause! - MacM is in Alice and Wonderland - as the queen said: "Sentence first, then the trail." If sentence is "not guilty" think of all the legal expense we could save by cancelling the trial!))This is a new low in his list of "duck and weaves" but a new one, none the less.

  7. #627
    Please use Sugar Cane Alcohol Billy T's Avatar
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    Quote Originally Posted by Neddy Bate
    ...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,...
    You did not say where or what is reflecting the light back. I will assume four mirrors two on fixed to the wall of the moving train and equally distant form the flash source also fixed to the train wall. Then yes the beams reflected by the two train fixed mirrors return to it the source point simultaneously.

    If the other two mirrors are mounted on posts in the ground equally distant from "Post M" (called "M" as it is exactly Midway between the two mirror posts) and post M has battery and pair of wires extending towards the passing train etc. which trigger the flash exactly when the train mounted flash unit is passing post M, then again yes the ground post mirror reflected light does return to post M from both the ground post mirrors simultaneously. What is strange?

    You surely do not think, like geistkiesel, that neither set of mirror will reflect the light simultaneously back to the point (different in the two frame, except at the instant of the flash) from which it originated as both the train and the Earth are moving wrt to "absolute rest" do you?

    BTW geistkiesel, welcome back. I have missed you.

    Unfortunately, I could not understand hardly anything in you long post of 13 after the hour. I do want to thank you for taking the trouble to read my post that started this thread, long ago. (Perhaps you were on a fast rocket so time lapsed for you was much less?)

    I have found that my speaking of “shoulder-to-shoulder” men standing along the track with noses "just grazed" by the passing bomb has confused some (Others are concerned for their health, and do not think men should die for science etc. )

    I do not understand why these concerns, but the men have been replaced by zillions of stop watches, all synchronized and running. They too are very close together, mutually, and all are only "microns" from the passing bombs, which are now better called "tiny firecrackers," just powerful enough to stop a pair of stop watches. (One nearest to the end of train firecracker and the other is the one nearest to the front of train fire cracker.) The stopped pair of watches were less than one micron from the exploding firecrackers. (Propagation delay effects, are entirely negligible as the train is very very long - it takes the central flash form source mounted on the train several weeks to reach the equally distant firecrackers at the two ends of the train and stop the train's co-located stop watches simultaneous!

    Also the train is very fast. I do not want to discuss how long "several weeks” of train time are on the ground clocks, so I only note that during the correspond ground time period, the speed of the train is such that the advance of the firecracker at rear of the train towards the oncoming light and the attempt of the firecracker at the front of the train to escape the light rushing forward to it cause the ground-based stopwatch, stopped by the rear firecracker to stop showing five minutes less time that the ground stopwatch stopped by the front of the train firecracker. That is why, compared to five minutes difference between these ground recorded times, I neglect the propagation delay for light (or explosion gasses) to travel less than one micron. Both tiny propagation delays should have been identical anyway, but I like to be sure that the two ground stopped stop watches show very non simultaneous event times for the two firecracker explosions.

  8. #628
    Valued Senior Member Neddy Bate's Avatar
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    Quote Originally Posted by Billy T
    </em>You did not say where or what is reflecting the light back. I will assume four mirrors two on fixed to the wall of the moving train and equally distant form the flash source also fixed to the train wall. Then yes the beams reflected by the two train fixed mirrors return to it the source point simultaneously.

    If the other two mirrors are mounted on posts in the ground equally distant from "Post M" (called "M" as it is exactly Midway between the two mirror posts) and post M has battery and pair of wires extending towards the passing train etc. which trigger the flash exactly when the train mounted flash unit is passing post M, then again yes the ground post mirror reflected light does return to post M from both the ground post mirrors simultaneously. What is strange?

    You surely do not think, like geistkiesel, that neither set of mirror will reflect the light simultaneously back to the point (different in the two frame, except at the instant of the flash) from which it originated as both the train and the Earth are moving wrt to "absolute rest" do you?
    I agree with your description of the locations of the mirrors, and the simultaneous arrival of the light pulses back to the midpoint in both frames. Of course these mirrors are not necessary for your original thought-experiment in which the firecrackers burst simultaneously in the train frame, yet they burst sequentially in the embankment frame. I only considered the addition of the mirrors because Geistkeisel's long post at 13 after-the-hour considered the idea that if the firecrackers were mirrors, there light would arrive simultaneously back at the midpoint.

    The only reason this struck me as strange is because at first it seems to imply that there might be some way to synchronize the two different clock systems in the two different frames. The light is emitted simultaneously in both frames, and after reflecting off the mirrors, the light arrives back at the midpoint simultaneously in both frames. At first, it seems to offer a glimmer of false hope for synchronizing all of the clocks, but apparently it does not work after all.

    This is how I picture the train and embankment clocks at the time of the firecrackers going off:


    <table border=1 cellpadding=4 align=center><tr><td>Train(Rear)</td><td>Train(Front)</td></tr><tr><td>2:30</td><td>2:30</td></tr><tr><td>FirecrackerA</td><td>FirecrackerB</td></tr><tr><td>0:00</td><td>5:00</td></tr><tr><td>Embankment(Front)</td><td>Embankment(Rear)</td></tr></table>

    In thie above example, there is a five minute delay between the firecrackers according to the embankment clocks, yet they are simultaneous according to the train clocks. Of course, at any given time, all clocks read identical in their own frame, so according to the embankment observers, their own clocks are synchronized while the train clocks are out-of-synch as follows:

    <table border=1 cellpadding=4 align=center><tr><td>Train(Rear)</td><td>Train(Front)</td></tr><tr><td>5:00</td><td>0:00</td></tr><tr><td>2:30</td><td>2:30</td></tr><tr><td>Embankment(Front)</td><td>Embankment(Rear)</td></tr></table>

    In the above example, FirecrackerA has already gone off 2:30 minutes ago, and FirecrackerB will go off 2:30 minutes from now. I am just not sure what is supposed to happen when the relative motion between the train and the embankment comes to a stop. Certainly time is not expected to move backwards, so I imagine that some clocks shift ahead greatly, while others only shift ahead slightly, until they are all in synchronization together in the same rest frame.

  9. #629
    Registered Senior Member MacM's Avatar
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    Quote Originally Posted by Billy T
    Is her view that the event occurs on 13 Jan 2055 at 13:08 less valid than yours is? LOL

    It is time you stopped being a smuck. In past conversations the propagation delay was thrown in to dispute my claim of simultaneous events. The arguement has been the events only exist when you experienced it. My arguement was that the event occured in its frame and observers in other frames do not alter the event timing.

    The claim to the contrary shows the falicy of the interpretation of the measured invariance of light problem. It is the best arguement for strong consideration of the RCM or Extinction Emission Shift Theories of light.

  10. #630
    Quote Originally Posted by MacM
    The arguement has been the events only exist when you experienced it.
    Not from anyone who knew what they were talking about.

    I suspect you misunderstood.

  11. #631
    Registered Senior Member MacM's Avatar
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    Quote Originally Posted by Pete
    Not from anyone who knew what they were talking about.

    I suspect you misunderstood.
    Not quite. I did not misunderstand and I know they knew better but it was their arguement at the time since they simply would not agree with anything I had to say.

  12. #632
    Please use Sugar Cane Alcohol Billy T's Avatar
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    On 13 January 06 at 26 past hour MacM posted:
    Quote Originally Posted by MacM
    ... In past conversations the propagation delay was thrown in to dispute my claim of simultaneous events. The arguement has been the events only exist when you experienced it. My arguement was that the event occured in its frame and observers in other frames do not alter the event timing....
    In above MacM is correct, but these “conversations” about “propagation delay" were not with me or Pete.* MacM must have been talking to himself, because

    On 12 January 06 at 55 past hour MacM posted:
    Quote Originally Posted by MacM
    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.
    And here MacM is arguing that one does not even need to change frames to change when an event occurred - just change seats in a train!

    On the 13th MacM makes “claim of simultaneous {nature of} events…and observers in other frames do not alter the event timing.”

    On the 6th MacM makes claim that he can change "event timing" (even the order in which two events occurred!) just by changing seats on a train.

    As I have noted several time before, it is hard to be consistent when you are making it up as you go along without any accepted theory to guide you.

    Any one want to bet how long it is before he switches positions again?
    (Hint: it is usually at least a month - this switch in 7 days is quickest reversal I know of.)
    ___________________________________
    *We even agree that ST equations are the correct way to correct for "propagation delays", but MacM disputes SR and uses some thing related to their "velocity history" or which was accelerated, or speed relative to the absolute reference frame, (which he admits to believe exists, but can not demonstrate it.) How to make corrections for "propagation delays" has been one area where MacM has switcted positions many times. I have no idea what his current view is, perhpas none of these three approaches is still popular with hm, but I suspect it uses (erroneously) the constancy of "tick rates" in all frames which as far as I know, MacM has been consistent (wrong) about. He alway disputes the "twin paradox" truth with something about "reciprocity" and believes that if events are simulatneous in one frame they are simultaneous in all. (For example, the twins must have their 15th birthday "simulatnaeously etc.)
    Last edited by Billy T; 01-14-06 at 05:47 AM.

  13. #633
    Maxwell's demon Kron's Avatar
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    What exactly is the argument in this thread? I believe that time itself is universal, but WHEN we observe it (and therefore WHEN we think it happened) is not. What does this have to do with relativity? This concept can be demonstrated with sound, or electricity or any other type of communication that is propagated at a finite speed.

    (Note: If I am totally of the topic and babbling like a depraved lunatic, can anyone please explain what the argument is about in one post? Thanks.)

  14. #634
    Please use Sugar Cane Alcohol Billy T's Avatar
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    Quote Originally Posted by Kron
    What exactly is the argument in this thread? I believe that time itself is universal, but WHEN we observe it (and therefore WHEN we think it happened) is not. What does this have to do with relativity? This concept can be demonstrated with sound, or electricity or any other type of communication that is propagated at a finite speed.

    (Note: If I am totally of the topic and babbling like a depraved lunatic, can anyone please explain what the argument is about in one post? Thanks.)
    Hi Kron. I will try, but I am “long winded” to be clear (and I hope convincing.).
    All people initially, until they learn sometimes that their normal experiences are not always true for comparisons between reference frames moving rapidly wrt each other believe, as you that "I believe that time itself is universal." and that it is only "propagation delays" that make it seem not true.

    Usually the first hint that this extension or ordinary experience is faulty comes with velocity addition. For example, if car speed is Vc and bullet speed is Vb the speed of bullet fired from the car is Vc+Vb, but if big rocket "a" going away from Earth at 60% of speed of light (or Va = 0.6c) when it fires little rocket “b” with 70% of speed of light (Vb =0.7c) going away from rocket "a" then the common experience would say that the little rocket b is receding from Earth at 130% of the speed of light. - Not only does modern physics say this is impossible, but common sense makes it strange (I.e. self conflicting with common sense): - If you could travel faster away from Earth faster than light and had a very big telescope with you, then could watch your mother give birth to you! or see her birth! or see the gas cloud forming the sun! or the Big Bang forming the universe, etc.

    One of the consequences of a correct (Special Relativity theory) understanding of how events in different frames should be compared is that universal time does not exist. Both frames find that all events in the other frame are proceeding more slowly. (when their duration is timed by the clocks of the frame which the event is NOT taking place.)

    From a common sense point of view this is silly. How can clocks in both frames each be going slower than the other? The answer is not too hard, and several have explained it in detail, but it is too long to repeat now. The essential part of the explanation is that time intervals to be compared must be measured between the same "start event" and "stop event." (All agree with this requirement.)

    It is easy to get clocks in both frames set to zero simultaneously by a “start event“- just flash a "reset light" when pair of clocks, one in each frame, are passing "side by side." The problem comes later when they are very distant and you need "simultaneous stop events." People, like MacM, think that this is also easy as identical clocks must have the same "tick rates" so just use 10,000 ticks as the stop events etc in both frames. Unfortunately, it is not true that identical clocks in different tick simultaneously together, or that is time is universal for all frames as MacM and most without formal training in physics believe. (MacM knows all the SR equations etc, but disputes that they are true.)

    Usually this simple fact gets lost in comlex math arguments or discussions of how to correct for “propagations delays” etc. That is why I designed a "thought experiment" where not only are the two "start event" clocks (one on ground and one on fast moving train) adjacent to the firecracker explosion when it occurs, but also the second ("second" on the ground only, as it is simultaneous on the train.) firecracker event or "stop event" is also timed by two adjacent clocks, one on the ground and one on the train. To do this, I postulate "zillions" of very closely spaced clocks, which are in a long line beside the train track and only "a micron" from the passing firecrackers which are mounted on the outside of the train at the two train ends, and equally distant from the flash source, also mounted on the outside of the passing train. Only the four clocks, two on ground, two on train, which are closest to the two explosions are stopped by the explosions, and record the time of he explosions.

    Thought Experiment Conclusions:

    (1)Clearly in the train frame, the flash which sets off the equally distant firecrackers causes "simultaneous explosions." (Same time shown on the two stopped train clocks.) (As someone noted, I could be tricking you and the train is really at rest, but the train station is in rapid motion. Surely then you would agree that firecrackers triggered by light flash equally distant from them explode simultaneously on the non moving train.)

    (2)Clearly the rear of the train is advancing towards the on coming light and the front of the train is moving farther down the track as the light flash races towards it. Thus, on the ground, the light travels less distance to trigger the rear explosion (which occurs first) than the distance it travels to set off the front explosion (which is second, not simultaneous).

    SUMMARY:
    Without any assumption that the SR math is correct, without any assumption about clock "tick rates," without any human observers (until weeks later when they find the two stopped stop watches among the "zillions" that are still accumulating time, unstopped), without any "propagation delays“, without leaving any reasonable "duck and weave" confusion rebuttal possible to avoid the facts; we know that:
    Events simultaneous in one frame are not simultaneous in another frame moving wrt the first frame.

    If you think just a little about it this implies that time is not universal. With slightly more thought, you can understand the twin paradox. Put twin "B" on the train when both are born. (If you worry how this is possible, use frozen embryos collected years earlier with train standing in another station and use cesarean delivery just as the two mothers are passing, etc.) When twin B has his 1-year birthday, at that very instant, SIMULTANEOUSLY FOR HIM, twin A is only 6 months old. Likewise, when twin A has his 1-year birthday, at that very instant, SIMULTANEOUSLY FOR HIM, twin B is only 6 months old. This is possible (and true) because the time in frame A which is simultaneous for twin B on his 1year birthday is not the same time in frame A that twin A has his 1year birthday. (Converse also true.) That is, the two "SIMULTANEOUSLY FOR HIM" times are different, not the same., because the concept of "simultaneity" change as you change frames. To try to express this contra intuitive fact again, using the train /firecracker example:

    There are two different times on the train that for the ground clocks were "simultaneous" with the ground time for each of the two sequential explosions, but these two different times are not the same times as the train clocks record for the two explosions (The train times of the explosions were the same time, not different, as they were "simultaneous.")

    When one twin has his 1year birthday the other does not. Both even correcting for perception delays correctly, find the other is not yet one year old. Time is not universal. The small rocket "b" is not going at speed 1.3c. Lots of totally unreasonable to common sense things are true.

    For example the muons that passed thur your body while you read this, were formed high above you in the atmosphere and even if they travel at c (and they essentially do) they can only descend a few thousand feet before decaying as they have a very short half life. Yet many traveled 100,000 feet to pass thru you. How? You are measuring the period of their existence with your clocks. The clock that they decay by is THEIR clock and it is running very slow as your clock measures time. Same reason why the fast moving twin also ages slowing.

    Note the "fast moving twin" is always the "other twin" from the point of view of the one who regards himself at "rest" - all motion is relative. Everyone regards the frame they are in as "being at rest". You do this on an air plane as you pour your coffee, on the earth as you pour your coffee, in the solar system as you pour your coffee, in the local group of galaxy all accelerating towards the "great attractor" as you pour your coffee, moving thru the cosmic back ground radiations as you pour your coffee. - all frames with very different speed wrt to each other.

    Hope that helped.

  15. #635
    Quote Originally Posted by Billy T
    Hi Kron. I will try, but I am “long winded” to be clear (and I hope convincing.).
    "Brevity is the soul of wit." William Shakespear

    "I have made this letter longer than usual, only because I have not had the time to make it shorter." Blaise Pascal

  16. #636
    Quote Originally Posted by Kron
    What exactly is the argument in this thread?
    Although this thread tends to obfuscate it, the real issue is the constancy of the speed of light. If all observers always measure the same c, then relativity is logically necessary and simultaneity is not universal.

    -Dale

  17. #637
    Registered Senior Member MacM's Avatar
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    Quote Originally Posted by Kron
    What exactly is the argument in this thread? I believe that time itself is universal, but WHEN we observe it (and therefore WHEN we think it happened) is not. What does this have to do with relativity? This concept can be demonstrated with sound, or electricity or any other type of communication that is propagated at a finite speed.

    (Note: If I am totally of the topic and babbling like a depraved lunatic, can anyone please explain what the argument is about in one post? Thanks.)
    You are quite correct. Unfortunately neither side has actual proof of what is going on here and the general opinion has a majority view agreeing with relativity.

    But it is important to understand that that view has not been specifically tested as to the type of gendankin we are argueing.

    I am awaiting a reply from a NASA, Phd, Physicist as to the acceptability of my view before I respond to Billy T. But I will respond.

  18. #638
    Quote Originally Posted by Billy T
    It is easy get clocks in both frames set to zero simultaneously by a “start event“- just flash a "reset light" when pair of clocks, one in each frame, are passing "side by side." The problem comes later when they are very distant and you need "simultaneous stop events." People, like MacM, think that this is also easy as identical clocks must have the same "tick rates" so just use 10,000 ticks as the stop events etc in both frames. Unfortunately, it is not true that identical clocks in different tick simultaneously together, or that is time is universal for all frames as MacM and most without formal training in physics believe. (MacM knows all the SR equations etc, but disputes that they are true.)
    Billy T,
    Assume that the two clocks on two inertial frames are zeroed at the same instant as you described. Then have the two ships make slow wide turns until the shps are approaching each other. If we assume the two clocks will eject a piece of paper with the current time on each clock at the instant of head on impact of the frame, then A moving at .2c and moving at .6c, both velocitites wrt their origin on earth, then the two pieces of paper will indicate different elapsed times from each other the instant they were synchronized, correct?

    Now it does seem bizaar for anyone to claim that the times printed on both pieces of paper will both show elapsed times less than the other. I understand that this is a statement consistent with SRT, and if so how can this be if both clocks were actiually ticking the same total length of time as measured wrt the earth frame clock that also was zeroed (no acceleration measured on the earth clock), at the time and place the A and B frames were zeroed.

    Howe can this be?

    Geistkiesel

  19. #639
    Quote Originally Posted by DaleSpam
    Although this thread tends to obfuscate it, the real issue is the constancy of the speed of light. If all observers always measure the same c, then relativity is logically necessary and simultaneity is not universal.

    -Dale
    DaleSpam, Your "If" statement has a possible ambiguity. If we substitute a duck flying at .999999c and measure the relative velocity of duck and earth frame and then measure the relative velocity of duck, Vd, and inertial frame, Vf, that had accelerated to .1c wrt the earth, Vc - Vf = Vdf, then we would measure a relative velocity of Vd - Vf = Vdf = .999999c - .1c = .899999c and each frame would determine the same speed of the duck.
    Yet if we measure the relative velocity of frame and photon, and here make the same measurement, Vc - Vf = Vcf = 1c - .1c = .9c, whch SRT tells us is wrong, and that the Vcf = Vc - 0 = Vc is the true measured SOL.

    The ambiguity is, in use of the words, measuring the SOL or measuing the relative speed of frame and photon. In both cases the SOL, wrt the vacua, is the same in both uses of the words that could mean either the SOL wrt thge vacua , or relative speed of light and frame, though the latter measurment should be 1c - .1c = .9c, where the .9c is not a measurment of a dimished measured SOL, rather it is merely a statement of how much faster the SOL is wrt the speed of the frame.

    If we use as a standard ambiguity strainer, the description of the measured SOL wrt the vacua and a train published by AE in 1916, "Relativity", Sections 7 and 6, then we must conclude that the relative velocity of the frame and photon, as measured by the embankment observer, is Vc - Vf > 0, where Vf > 0 and that the description does not describe c - v = w as measured wrt the train as the coordinate frame of reference.

    Geistkiesel

  20. #640
    Quote Originally Posted by Neddy Bate
    Discussing the post from Billy T above) I agree with your description of the locations of the mirrors, and the simultaneous arrival of the light pulses back to the midpoint in both frames. Of course these mirrors are not necessary for your original thought-experiment in which the firecrackers burst simultaneously in the train frame, yet they burst sequentially in the embankment frame. I only considered the addition of the mirrors because Geistkeisel's long post at 13 after-the-hour considered the idea that if the firecrackers were mirrors, there light would arrive simultaneously back at the midpoint.

    The only reason this struck me as strange is because at first it seems to imply that there might be some way to synchronize the two different clock systems in the two different frames. The light is emitted simultaneously in both frames, and after reflecting off the mirrors, the light arrives back at the midpoint simultaneously in both frames. At first, it seems to offer a glimmer of false hope for synchronizing all of the clocks, but apparently it does not work after all.

    This is how I picture the train and embankment clocks at the time of the firecrackers going off:


    <table border=1 cellpadding=4 align=center><tr><td>Train(Rear)</td><td>Train(Front)</td></tr><tr><td>2:30</td><td>2:30</td></tr><tr><td>FirecrackerA</td><td>FirecrackerB</td></tr><tr><td>0:00</td><td>5:00</td></tr><tr><td>Embankment(Front)</td><td>Embankment(Rear)</td></tr></table>

    In thie above example, there is a five minute delay between the firecrackers according to the embankment clocks, yet they are simultaneous according to the train clocks. Of course, at any given time, all clocks read identical in their own frame, so according to the embankment observers, their own clocks are synchronized while the train clocks are out-of-synch as follows:

    <table border=1 cellpadding=4 align=center><tr><td>Train(Rear)</td><td>Train(Front)</td></tr><tr><td>5:00</td><td>0:00</td></tr><tr><td>2:30</td><td>2:30</td></tr><tr><td>Embankment(Front)</td><td>Embankment(Rear)</td></tr></table>

    In the above example, FirecrackerA has already gone off 2:30 minutes ago, and FirecrackerB will go off 2:30 minutes from now. I am just not sure what is supposed to happen when the relative motion between the train and the embankment comes to a stop. Certainly time is not expected to move backwards, so I imagine that some clocks shift ahead greatly, while others only shift ahead slightly, until they are all in synchronization together in the same rest frame.


    Very Important: Yes the lights both arrive at the midpoint simultaneously in both frames, but they wioll not arrive back at the respective midpoints at the same instant with respect to each other.The moving frame round trip time is longer in the moving frame.
    Neddy Bates,
    Consider this simple description. The light moving from the midpoint of both frames will arrive simultaneously at A and B in the embankment frame, will then reflect and arrive back at the physical midpoint of the A and B mirrors simultaneously.

    In the m,oving frame the light will strike the oncoming A mirror (from the rear of the train) and at this instant the right moviong light is still a distance 2vt from the B mirror on the moving frame. Even though these two lights arrive sequentially at A and B they will necessarily arrive back at the physical midpoint of A and B simultaneously on the moving frame that has moved away from the midpoint of A and B on the embankment.

    There is no synchronization problem here. However, notice that for a brief period both lights are moving in the same direction to the right just as the light reflects off of A and is moving parallel to the right moving photon as it catches up to the B mirror in the front of the train.

    This period of time when both lights are moving in the same direction is a short period of asymmetrical motion.

    This time period where the light moving right covers the 2vt distance, plus the time distance the light moves in the interim while travelling through the 2vt distance as ct' = 2vt + vt' and then,
    t' = t(2v)/(c - v), which is the difference in round trip times of the lights wrt the stationary frame and moving frame conditions where the longer time s-pan is in the moving frame of reference.
    Geistkiesel

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