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Is the relativity postulate of simultaneity reasonable?

  1. May 11, 2004 #1
    Is the relativity theory postulate of simultaneity reasonable?

    M is half way between light sources A and B. Simultaneous pulses from A and B arrive at M at the same instant a moving observes heading from A to B arrives. Does the moving observer see the lights turn on simultaneous in his frame? According to relativity theory O’ observes the pulses starting at different times in his frame. Let us see if this is a valid conclusion. While O’ is still heading to M the light pulse from A leaves the source at A. When O’ arrives at M at the same time as the sources from A and B, O’ concludes from the constancy of the speed of light that both wave fronts must necessarily be located equidistant from M. Any divergence from this conclusion would be observed as contradiction of the observed simultaneous arrival of the pulses at M.

    Therefore, O’ concludes that the while the sources of the pulses need not necessarily start at the same time, the wave fronts must be located equidistant from M at all times during their mutual journey to M. Suppose that as O’ passes A on the way to M he zeroes his clock and later the A source emits a pulse. When the pulses and O’ arrive simultaneously at M, O’ can determine when the pulse left A. From the argument above, if B had been pulsed earlier than A then its location is farther from M than A in the O’ frame. However, the wave front from B must emain equidistant from M at all times as the time of flight of both wave fronts are identical in order that they arrive at M simultaneously.

    B. If both A and B emits a series of simultaneous pulses before O’ arrives at M and the pulses are recorded by O’ while still approaching M, O’ has no justification in saying the pulses were not simultaneously emitted by A and B, even though he pulse from B could have preceded the pulse emitted from A. As O,’ approaches M the time difference between pulses from A and B will approach zero as O’ approaches M and will be zero at the instant of the simultaneous arrival of the pulses at M. If the series of pulses were emitted at regular intervals, say one per second, then if O’ analyzes the time difference in the arrival of these pulses he could synchronize his clocks to the rate of the stationary time of A and B.

    In both cases discussed above, once O’ learns from O that A and B are equidistant from M in the stationary frame then O’ must also conclude the pulses wee emitted simultaneously in the O’ frame.

    These measurements do not guarantee that O’ knows the pulses were emitted simultaneously, but the wave fronts from B must be such as to guarantee their simultaneous arrival at M with the A pulses. When O’ learns from O, the stationary observer, that the A and B sources are equidistant in his frame then O’ must unambiguously agree the pulses left A and B simultaneously.

    C. We have a space ship with clocks located in the forward and rear locations. The O’ observe then sends a pulse of light to both clocks, but knowing he had accelerated at some time in the past to reach his current velocity O’ would know the clocks are not synchronized. O’ then rotates the clocks 90 degrees so they are extending to the left and right side of the ship. O’ now sends a synchronizing signal to both clocks transverse to the direction of travel. When O’ slowly reorients the clocks to the forward and rear locations of the space ships the clocks are synchronized within the O’ ability to measure any differences.

    It appears to this writer that simultaneity is a concept confined to the psychological state of mind of the state of information of the human observer and has nothing to do with any universal physical principals. There is no physical process that denies any observer a measurement allowing him to accurately synchronize clocks.

    Experiments that are purported to support relativity theory require reevaluation in light of the loss of an essential element of RT, to wit, the postulate of simultaneity. An essential element ignored in theoretical discussions of RT is that all ‘moving’ platforms have undergone acceleration. Hence. the ability of the mass vibrational energy state of these accelerated masses to exchange energy with the surroundings and intrinsically have been unambiguously affected. The energy exchange efficiency is decreased with acceleration and increased velocity. Deceleration reverses this process. Likewise, from Doppler analysis the absolute velocity of moving platforms may be measured. In experiments like A and B above the moving platform will observe blue/red shifts of the rear and forward approaching wave fronts and hence determine absolute velocity measurements.

    One can make a series of ‘Hubble’ measurements from a space ship and locate a ‘best position’ at rest with the surrounding stellar masses. While not guaranteeing the discovery of the center of the universe, an effective local approximation to a universal center is possible.

    As stated above simultaneity postulate follows from the different arrival times of pulses arriving at a moving platform at O’ which is not equidistant from the sources, or from the wave fronts of sources. These same conclusions of simultaneity will follow measurement of any set of signals by a moving platform, where the signals, of whatever nature they happen to be, including racing snails, are moving with equal and constant velocity.
  2. jcsd
  3. May 11, 2004 #2


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    I am not sure what your point is. Most people would agree with most of this statement anyway. Relativity explains HOW certain of these effects occur and can be measured. The measurement of the speed of light as a constant is an important consequence of SR. Are you denying this to be a real physical effect?
  4. May 11, 2004 #3
    Are the bells tolling taps for the simultaneity postulate of relativity?

    No, I am not denying that the measurment of the speed of light being constant from whatver frame mesured.. In fact I assme this in the post you responded to (or thought I did by inference anyway). I am denying the 'simultaneity postulate' of relativithy as originally outlined by Einstein. Please see the following where the often discussed moving train gedunken of Albert's is anallyzed. This is slightly different than the problem you responded to in the original post, but the analysis is straight forward.

    I appreciate your response here. Thank you.

    Einstein’s original simultaneity experiment, “Relativity”, pages 25-27, has a moving observer, O’ moving toward a light source B, from a light source A, behind. As O’ passes, M at velocity v = 1 at t = t0 = 0, the midpoint between A and B in the stationary frame, the lights are pulsed on at A and B. Sometime t1 later, the light from B is recorded by O’ and at t2 later, the light from A is recorded.

    This example is a definition of simultaneity, or the lack of, the simultaneous occurrence of events between inertial frames moving wrt each other.

    A t0|→----------------------------------|--------------------------------------------←|t0 B
    ---------------------------t1|-----------|t0---------- |t1-----|t2---------------------------->

    According to theoretical postulates, that O’ measures the light from A and B at different times, O’ must conclude the lights are pulsed on at different times as O’ has no way of knowing he is moving wrt the sources at A and B.

    Is this the only valid interpretation?

    First, O’ can conclude he does not know if he is moving or not. If he is moving wrt to the sources of the light then the different times of recording do not leave the simultaneity postulate as the only conclusion. Therefore, O’ makes an effort to determine any O' motion wrt to a stationary frame. When he records the pulse from B, he notes the wavelength and time of arrival. Sure enough, at t2 the light from A arrives. Immediately O’ notices the blue/red shift of the light pulses and concludes there is a possibility of the pulses measured with blue/red shifts are from sources with identical light characteristics, hence O’ determines v = 1. From the measured time between pulses, Δt ═ t2 – t1 = 1, he calculates the distance O’ traveled from the measured velocity, v = 1, as d’ = vΔt = 1.

    Now O’ asks, if the pulses were simultaneous emitted in a stationary frame, where is t1 located wrt to the midpoint. Of course O’ is starting from an assumption he crossed M at t0 in the stationary O frame. This is just the first of many assumptions he can make.

    O’ is moving at v ═ 1 for a time t1 when the pulse from B arrives at t1. The distance B-M = D = ct1 + t1 = t1(c + 1). During ∆t = 1 the light from A would travel from -t1 to t2 or a distance 2t1 + v∆t = 2t1 + 1 during ∆t = 1. This assumes the lights were pulsed simultaneously. So O’ waits and measures Δt = 1.

    O’ having recorded the time for the arrival at t2, calculates backwards a distance dA = cΔt, and obtains the distance traveled by A from –t1 to t2. This distance is 2t1 + vΔt, or 2t1 + 1. This confirms the lucky guess. If O’ hadn’t passed the midpoint of A-B at to = 0, then the measured ∆t would be greater or less than 1 if the assumption that O’ was moving is correct.

    Because he problem is framed as it is O’ correctly determines his relative motion and velocity and the fact that the pulses started at t0 in the stationary frame and the moving frame. Whatever the frame used, the result is the same. In other words O’ can make the calculations using a symbolic reasoning with the Δt and v measurements only. The measured Δt, the measured v gives the same result in analysis of the problem. The difference in numbers using the stationary frame numbers, as calculated by O, for instance, gives the same result. However, O has the advantage that he knows that O’ is the moving frame and that the conditions are as outlined in the definition of the problem. O’, knowledgeable in time dilation phenomena of clocks, does not fall into a dogmatic trap of assuming the relativity postulate of simultaneity without question.

    The O’ observer, therefore determines the significant events as simultaneous, notwithstanding his measured values of t and v differ from those made by the stationary O observer.

    I trust that the use of empirical data, the blue/red shift velocity determination, does not rasp harshly on theoretical purists. :smile:
  5. May 12, 2004 #4
    Forgive this premature addition and please excuse the "graphics " in the previous post. I meant it -t1 t0 t1 t2 on the moving platform with t0 at M, the midpoint between A and B and thought I had it all worked out when editing.

    It is rather clear that Einstein has mixed the meanings of simultaneity. From one angle he is referring to the state of mind of the observer as the defining parameter of simultaneity. The other, not so clear, is the suggestion that simultaneity operates as a postulate of physics, independent of the observers’ correct or incorrect reading. This means (my definition) a natural process of a person detecting the sequence of events should not pose any simultaneity constraints on the moving platform observers as a matter of physical principal. At t0 as the train passed through the midpoint of A-B the event of the simultaneous pulsing of light occurred in “both frames” at t0 = 0 for both. Then this event evolved into events of measurement during recognizable positions of the moving platform and embankment when these events occurred. See my previous post where the observer is seen to be able to determine whether the pulses were simultaneous to him.

    The embankment observers are peeking at the moving observer from an x-ray wavelength from the measuring apparatus of the moving observer and sees the same events the same time and place as the moving observer, to wit, the arrival of a pulse of one complete wavelength of light. However, there is nothing of a physical nature concerned with simultaneity that should draw one’s attention to the series of events following the emitted pulses from A and B. Even assuming a Lorentz contraction and time dilation of the moving clocks, the different numbers each observer come up with when comparing notes is unrelated to the physical occurrence of the simultaneity of the events. Each observer can easily determine that the simultaneity of events is unrelated to their calculations that assume “simultaneity” as a principal determining physical reality, the events. If the observer starts with the postulate that different measuring events means non-simultaneity of the event then that is as far as the discussion goes and this is what their reality is, simply what they believe. Einstein says on page 26 of “Relativity” in reference to the moving platform:

    “Now in reality (considered with reference to the railway embankment) he is hastening towards the beam of light coming from B, whilst he is riding on ahead of the beam of light coming from A. Hence the observer will see the beam of light emitted from B earlier than he will see that emitted from A. Observers who take the railway train as their reference-body must therefore come to the conclusion that the lightening flash B took place earlier than the lightening flash A. We thus arrive at the important result:

    Events, which are simultaneous with respect to the embankment, are not simultaneous with respect to the train, and vice versa (relativity of simultaneity). Every reference-body (coordinate system) has its own particular time; unless we are told the reference-body to which the statement of time refers, there is no meaning is a statement of the time of an event.”
  6. May 17, 2004 #5
    No. You can build an ether model that shows an event as having absolute simultaneity for all observers and all distances being invariant - with regard to absolute time measurements.
    However, observers that move relative to absolute frames measure things with relative time, because of time dilation effects, etc, and so their perception of simultaneity is affected.
  7. May 21, 2004 #6
    With no reference to "aether", models, relativity, theory, or even physics, the question is. Are events simultaneous in different grames of reference? For instance a moving platform with reflecting mirrors extending forward and rearward reflect a pulse of light at the midpoint of the platform. For a stationary platform the light refleacts back to the midpoint - no problem here. Now, for the moving platform, will the observer see the event of a single pulse which was the source of the pulses being reflected back to her as simultaneous? I say there is no other rational conclusion.

    An excellent animation of this situation is seen in the first link.


    http://frontiernet.net/~geistkiesel/ [Broken]

    The analysis proves that the moving observer may not accurately conclude there were more than one pulse at the origin. She must conclude there was one and only one pulse of light at the origin the instant the moving platform's midpoint coincided with the source of the pulse. If her "perceptions" differ, must the laws of physics then politely conform to what the observer perceives?

    AN interesting observation here is the simultaneous location of the midpoint of the platform. Would you suggest that an instantaneous measurement of the locations of the reflecors not coincide with the locations of the stationary platform? If some shrinking of the moving platform occurs, doesn't the observer still see the original pulse source as a single pulse of light?

    In other words, are there two actual pulses as sources of the reflected light in the moving platform, or is this a mere "perception" ?

    Finally, are any "ether models" you referred to in your reply shown here? :smile:
    Last edited by a moderator: May 1, 2017
  8. May 23, 2004 #7
    It is an assumption of special relativity that the stationary and moving observers both record the pulse of light as meeting at the moving car's centre point. There has never been any experimental evidence to support this (Michelson-Morley type experiments do not prove a single pulse of light meets back at the centre and no moving clock experiments have been done to test this). With lack of experimental support it's hard to accept this as being true. If a test is done and the results are not as the model predicts then the argument for length contraction may not be needed.

    An ether model that shows relativistic effects but doesn't support the model is given at http://www.kevin.harkess.btinternet.co.uk


    "particles of nothingness"
    Last edited by a moderator: Apr 20, 2017
  9. May 23, 2004 #8

    Taking the tack that if all physical measurements are such that all events are recorded as simultaneous in any frame, I say this seriously undermines the derived "loss of simultaneity" element of relativity theory. So who cares what the "oberservers calculate" using relativity theory if all measuremnts show simultaneity of physiocal events, what else is there too discuss?

    The moving platform meets at thje midpoint of the pulses as they are emitted. This event marks a common zero point. Measuring all other arrivals of the light
    simultaneously by the stationary and moving observer, again sets a common time for all events and all events are simultaneous. There is no need for watches or clocks or shrinking platforms. .Why come along later with a calculation to indicate other than experimentally established?

    http://frontiernet.net/~geistkiesel/index_files/ [Broken]
    The enemies of truth. Convictions are more dangerpous enemies of truth thn lies. :smile:
    Last edited by a moderator: May 1, 2017
  10. May 23, 2004 #9
    Recently I've been somewhat obsessed with simultaneity, so I think we can discuss this. First, as far as I know, there can be no disagreement of simultaneity, for any observer, if the two events in question are occuring at the same point. Disagreement on simultaneity is applicable only for events seperated by a distance.

    Are we talking about this? :

    Your description above is different, so I continue with that. The two pulses meet at the same point, so if M sees them at the same time, so must O'. But O' cannot be the judge to determine simultaneity in his frame, because he was not at the mid point when the pulses were emitted.

    The experiment at the link above is different. M and M' are initially at the same point, but M' moves a bit to the right so the pulses from the lightenings hit him at different times. In train frame, M' was at the mid point when the lightenings stroke, and if speed of light is constant, the only variable you can tweak is their simultaneity. But as a consequence, faster than light travel means going back in time, because a person at B could then, after seeing the lightening, travel to A before the lightening would strike at A.
  11. May 24, 2004 #10

    I too am laboring uinder the same simultaneity obsession syndrome (SOS). It must be going around.

    In order to accelerate the stagnated inertia of the subject I propose the following:

    Please do not take this personally Wespe, nor a challenge to yout expertise as a physicist, however, I challenge yourself, or any others, to disprove the assertions made in the short and concise link below. You might agree with the conclusions, hence you would take up the call. The thread is open.

    http://frontiernet.net/~geistkiesel/index_files/index.html [Broken]

    The link cannot be challenged by mere reference to relativity theory.

    Loss of simultaneity of events as measured in different inertial frames as a consequence of relativity theory is incompetent. If the derivation of the simultaneiity construct from relativity postulates was properly made then relativity itself is fatally flawed. In any event, no pun intended, I suggest a serious look at the now instinctive assumptions underlying the postulates of relativity theory.
    Last edited by a moderator: May 1, 2017
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