Experiment to demonstrate mutual observed time dilation

Discussion in 'Physics & Math' started by superluminal, Apr 11, 2005.

  1. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I'll try to answer your questions, but think that you are assuming that it is possible to have events "a" and "b", which are seen in frame A as simultaneous, also always be seen as simultaneous in frame B and this is a great part of the reason why we disagree and have difficulty understanding/ communicating with each other. For example, when you speak of "accumulated time" recorded by a clock (I prefer on a chronometer, but don't insist on my term) the the accumulated time was between start event, "s" and termination event "t" which we can both agree were not simultaneous, at least in the frame of the chronometer recording the t-s interval. (To have a convent number for t-s, let me ignore the small transvers time dilation of SRT - not much of a problem for you as even the "inline" time dilation, I think you question.

    I suggest you will let me assume that the rockets A & B are symetrically moving perpendicularly away from the ecliptic. That is A & B can look back at the Earth orbiting the sun, and see when one year has past with little, if any, disagreement. So let t-s= 1 year, although I will drop "year" and just say t-s=1. I suggest this flight configuration so I don't need to argue with you about the general inability of A&B to agree on the temporal separation between s & t because one or both (according to SRT) may not be simultaneous with the corresponding event in the other frame. (I really am trying to avoid conflicts that can be avoided, even if it requires special geometry and both using the visible Earth orbit as their basic clock.) Because we have different concepts of physical reality (you anti, me pro SRT) you think there is no difficulty in "simultaneousness" betwen two differtent frames and I think there is, in general.
    On (1a)I would not call it an "error" for either to assume he is at rest and all the relative speed is due to the other guy moving, provided he understands that this is just a choice that is convenient for him.
    (1b) I don't understand concept "supported" as applied to "accumulated time." I think only safe way to compare ""accumulated time" is as I described in my "triplet paradox story" -I.e. bring the chronometers back to the dinner table of the reunion celibration, place them side by side with zero relative motion, and read their dials at the same time. I don't understand what other procedure you have in mind, but suspect that it is based on some ideas that I worried about at top of this post, where we have different ideas about "simultaneous measurements." If you care to be more clear about your terms and proceedures -I will try to respond, assuming I have time.
    (2) I think I can agree with you on this, at least if you are stating that the earth observer C, who is equally distant between A&B is doing the observations, but if he is not and the distance CA and CB are different, then the problem is more complex and again gets us into the simultanity questions.
    (3)N0 - trivial reason: by definition, chronometers are continuously accumulating time.
    SRT reason: Same problem, as in 2 , you mean / imply "at the same time." This is no problem if clocks could be sychronized in two different frames. ( I know you think that is possible and have tried to show it in many posts of a thread about a year ago "digital encoding of A's infromation sent to B etc.", "Just say four MacM", etc. and I don't want to reopen that can of worms.)
    (4)"Any theory...must be flawed" includes SRT, so of course my answer is NO, but again it is the same problem. If A & B's chronometer have a big led display on a post external that is orientated towards the other and each has a large telescope that can read the others display, I think that at t-s=2 for A locally, he reads B's t-s=1 via his telescope and likewise at t-s=2 for locally, B reads A's big chronometer display via his telescpe as showing t-s=1 also.

    I also think that if both flash a light on to the edge of the external display when locally it is t-s = 1 and two side by side observers on Earth (using two teloscopes) write down what they see when this "rim of display" light is flashed, they will record 1 as the display (almost by definition of when the light flashed) but on there earth clocks it shows that t-s - 1.109 years. See final note also.
    {5}If you mean all well made clocks moving together, show the same time, I agree. If you mean that when the chronometers are returned to the same place, side by side and locally simultaneously read, (event "t" ) then in general I expect them to show different accumulated time from the last time they were side by side (event "s"), but if there motion has been exactly in accord with the same round trip flight plan (except Va = -Vb at all times) then I Iexpect them to agree. It is also bossible that they might agree if one trveled only part of the journey faster than the other, but this would be a rare chance event (unless carefully done with SRT calculated flightplans designed to achieve this effect on total accumulated time

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    )

    Final comment, another suggestion for you to try to make some more of our conflict go away. Inaddition to "flying" at same flight plan speed (except for the minus sign) and directly perpendicular to the ecliptic, so visible Earth can be a clock for both, we agree to pick 12 bright stars, D1, D2...D12, all with zero declination (I.e. in the ecliptic) we can construct commonly viewed "months" with our "Earth orbit clock" - Imagine that rockets A&B can tell (measure) when the plane defined by star D7, for example, the sun and their own rocket ship is perpendicular to the ecliptic. When this occurs, month D8 is just starting. If both write down the time shown on their chronometers at the start of month D8 and D9 (and they always stick to thier "anti symeteric flight plans", always fly exactly pependicular to the eclipitic) you and I may be able to agree on more things. For example I think we agree that both show the same time difference between the start of month D8 and D9. I do't know if this helps you to communcate more clearly with me or not (I am trying).

    Please consider using concepts like this common viewed Earth-clock time to explain what you mean by things like (1b)'s "be supported by actual accumulated time on the clocks" I think the time accumulated on A&B's chronometers between start of months D8 abd D9 will be the same, not sure you agree because I think you suffer from the "absolute time" / "simultaneous in all frames" disease. And like the DR. I am, I want to cure you, free of charge!

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    - perhaps this common Earth clock medicine will help. Try to swallow it.
     
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  3. 2inquisitive The Devil is in the details Registered Senior Member

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    My take on this. Yes, Billy T, clocks CAN be synchronized in different reference frames.
    In GPS, all satellite clocks are synchronized with Earth clocks, without which GPS would not work. The satellite clocks are also synchronized with each other, all 24.
    It may be that the clocks are only synchronized in Earth's reference frame, but that has no bearing on the following example.
    That is the very basis by which accurate time-of-travel of the satellite signals are
    measured, usually from at least four satellites at one instant in time to calculate the
    position of the GPS reciever. For me, it is easier to think of clocks, or chronometers,
    as measuring time intervals, which definitely vary by gravitational potential and are
    predicted by STR to vary due to relative velocity. Calendars measure the accumulation
    of time intervals. So, what does this mean? The clocks of both travelers, A and B,
    can be preset to synchronize with the Earth-based clock of C while the travelers are
    in the inertial frames of their trip at .433c relative to Earth. During the inertial frames
    of the trip, all clocks will accumulate time (a calendar) equally. During the non-inertial
    frames of the travellers (A & B), the clocks will not count time at the same rate as the
    Earth-based clock of C. Yes, during the inertial frames, the Earth-synchronized clocks
    of A & B will both beat at the same rate and both beat at the same rate as the Earth
    clock. There is no 'telescope' large enough to 'see' the clock on a spaceship travelling
    away from the observer at .866c. That is only a faulty gedanken. The STR statement
    that A will 'see' B's clock beating at half the rate of his own, and B will 'see' A's clock
    beating at half the rate of his own because of .866c relative velocity is not upheld
    by actual experiments where tick rates are measured (GPS). Note that the clocks of
    A and B both have to be preset to beat relatively faster than the Earth clock of C by
    the exact same amount for all clocks to synchronize during the inertial frames of travel,
    if time dilation due to relative velocity is in fact true. What an observer is supposed
    to 'see' while in relative motion has no meaning in reality.
     
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  5. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    i don't agree withsome parts, agree with others and mostly am not sure what you are saying - same problem I have with MacM and anyone starting with concepts so differnent from mine. These concepts usuallyare ntoexplicitly stated, but implied in our statement or our statement are assuming them and this makes discussion tough.
    This is illustrated for exmple:
    On the ability to synchronize clocks. - if traveler at "time central" from which all clocks in the frame are contolled (no problem within the frame to get all frame clocks sychrionized we both agree on this) are equaly distant from a pulsar (It happens to in the plane that bisects their ground plane, so this is possible) have agreed that they will set their clocks to zero on the first pulse after a "glitch" (occasionally the pulse rate does change - at one time it was thought to be a suddend contraction of the neutron star with corresponding change in spin rate to conserve angular momentum, but not sure this is the current explanation for glitches.) an other fctor,if need be to make sure it is the same glitch, then yes, for a brief instant the clocks in the two frames will be synchronized. (I ignore the fact that the local reset to zero signal takes time to propigate in the frame to distant clocks of the frame - probably should just say that the main clock at time central of both frames can be synchronized at t=0.)

    Now is where the hidden presumptions (both of the anti-srt and pro srt people come to the surface) If you deny time dialtion, then for you the conclusion you stated at start of your post, "CAN be synchronized..." is obviously true, but for me it is obviously false - time dilation will make each think that the others clock is dropping out of sync as it runs too slowly to keep up with the time keep locally.

    I will not respond to you more, at leas tnot now, because:
    (1) this reason of different hidden presumptions causing confusion, miss understandings etc.
    (2) just trying to respond to your first claim, which I did understand, I am almost sure, took several paragraphs/ time and got no where for either of us - a waste of time.
    (3) I am not sure what you are saying/ asking in most places because nothing is said in detail about the proceedures to be use, how is "at the same time," often implied, operationionally confirmed etc.
    (4 ) I have a new plan for discussing the validity of SRT, bette than even the muons that I have tried to "beat MacM over the head" without success to show him the errors of his ways etc. (basic idea of it has been given in rececent post to Giestkeisel and copied in post to Chroot - not trying to hid it.)
    (5)I am tired and goig to bed.
     
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  7. MacM Registered Senior Member

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    Billy T,

    Unfortunately you tend to want to re-write the gendankins and create complex issues and interject simultaneity, etc, which really have nothing to do with the simple example I have provided.

    Suppose you address the simple issue.

    1 - What is the gamma function according to SRT for clocks A and B that have a relative velocity of 0.866c?

    Gamma = 2.0000 Yes or No?

    2 - Considering that A and B were launched from earth in opposite directions with equal acceleration and duration such that each has 0.433c relative velocity to earth (Ignoring velocity addition since it does not alter the conclusion and only complicates the example), then A and B would have a 0.866c relative velocity.

    Yes or No.

    3 - According to SRT clocks A and B will "Mutually Dilate" by a gamma = 1.109 relative to C (Earth clock) but have no systemic dilation between themselves even though they have a 0.866c relative velocity.

    Yes or No?

    4 - Since physically clocks WILL only accumulate time under conditions of #3 above, what is your excuse for the fact that the 0.866c relative velocity fails to produce a gamma of 2.000?

    5 - Does not this example demonstrate that relative velocity without knowldge of the velocity components of each clock which comprises the total relative velocity, is absolutely worthless information. Do you not require knowledge of component velocity, not just two points of referance to compute relavistic affects?

    Of course you do. It is most clear to anyone willing to actually look at the consequences of the example given and understand that thought gendankins prove nothing. The proof is in the emperical data and the fact that all such data fails to demonstrate any reciprocity and GPS demonstrates that component velocity, not relative velocity is the cause of relavistic affects.
     
  8. 2inquisitive The Devil is in the details Registered Senior Member

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    3,181
    Billy T, I am not challenging your knowledge of theory, I am stating that theory does
    not exactly reflect reality. Much is known about clock behaviour in orbiting satellites
    now-a-days. Atomic clocks, especially rubidium clocks, will be somewhat unstable
    for the first month or two in orbit, then start beating at a more reliable rate afterwards. After the initial corrections are made during two phases, the clocks will
    stay in synchronization for years withour further adjustment to the actual clock. The
    satellite clocks are turned on and adjusted from ground control. Here is an excerpt
    from a paper by one of the clock manufactors, ITT, as presented at a Precision Time
    and Time Interval Standards meeting for the USNO. The paper is an interesting read
    IF you truly want to know about measured data and reality, not just what theory predicts. I have links to other papers if you are interested.
    "In the start-up phase, a ‘‘cold injection” procedure is performed where the phase and frequency error of the
    clock are set to the vicinity of -100 microseconds and +15~10-’~, respectively, and no reduction is made to
    frequency drift. In this phase, the broadcast 10.23 MHz signal has the full frequency drift of the RAFS.
    Once the cold injection procedure is performed, there need be no further corrections of phase or frequency
    in the life of a nominal clock. If there is some major disturbance to the clock, such as a change of the clock
    phase, then corrective measures may be employed including changes in the phase and frequency.
    The initial operation phase starts when the cold injection procedure is completed and ends with the first
    frequency drift correction. In the initial operation phase, there are no corrections made to the clock, but
    there are changes in the phase, frequency, and frequency drift of the clock. The phase is driven from -100
    microseconds toward zero, because the frequency is positive, which causes the phase to increase
    algebraically. The frequency is driven from +15~10”~ to zero, because the frequency drift is negative,
    which causes the frequency to decrease algebraically. The clock frequency drift starts off with a very large
    value such as -20x10-I4/day and decays rapidly toward zero and, at the same time, stabilizes. The
    frequency error becomes a cue as to when to make the first frequency drift correction to begin the next
    phase. When the frequency error is in the vicinity of zero, a frequency drift correction is made to cancel
    out most of the frequency drift of the RAFS. This leaves the broadcast 10.23 MHz signal with a negative
    net frequency drift, but much reduced in magnitude from the frequency drift of the RAFS. The initial
    operation period is on the order of 6 months long. At the end of the initial operation period, the frequency
    error is essentially zero, the phase is close to zero and the frequency drift is much reduced in magnitude
    from its initial large negative value and is much more predictable. The initial operation period is clearly
    shown in Figure 3, where clocks start off with large positive frequency and decay toward zero.
    The normal operation phase starts off with the first frequency drift correction and continues for the rest of
    the life of the clock. During this time, frequency drift corrections are used to keep the clock frequency
    error between some limits such as k4~1O-l~. Because the frequency drift of the clock varies, it is not
    possible to have the clock frequency drift correction exactly cancel the clock frequency drift. If the net
    frequency drift is positive, then the clock frequency error will go toward +4~10-’~; if it is negative then the
    frequency error will go toward -4~10-’~. When the net frequency drift reaches a limit, a frequency drift
    adjustment is made so that the net frequency drift changes sign and the frequency error moves toward the
    other frequency limit. Typically, the frequency will have a zigzag curve between the frequency limits. It is
    expected that the average time between frequency drift corrections will be between 1 and 2 years."
    http://tycho.usno.navy.mil/ptti/ptti2001/paper49.pdf
     
  9. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    1 &2With the proviso that I don't check your numbers, I answer YES to both 1 & 2. I am breaking your 3 into its two componet parts, because if I understand you, first part's answer is YES, but second part's answer is NO.

    3a - MacM:"According to SRT clocks A and B will "Mutually Dilate" by a gamma = 1.109 relative to C (Earth clock)" Billy T: YES.
    3b - MacM:"but have no systemic dilation between themselves even though they have a 0.866c relative velocity." Billy T: NO, because I believe A & B each see dilation of all processes occuring in the other's frame, and certainly the movement or electronics of a clock is a "process," but you have not made it clear to me what is "systemic dilation." Is the type of "dilation" an Earthling sees the fast moving muon clock have "systemic dilation"? (Many muons are a clock - just like many c18? atoms are a clock commonly used to measure when ancient life died.)
    I know you don't like "sees" and I don't necessarily mean anything related to "looking" by that word, but I must use some verb (In earlier post I gave you a choice of about 10 alternative verbs, but you never selected one for me to use. I think "measures" may be better than "see", but tend to use "see" as it is less typing.)
    If "systemic dilation" differs from "dilation" as applied to the muons by the earthling, tell me how and I may be willing to change my "NO."

    4 - Here I don't understand you in the least. For me, a non-broken clock (I prefer chronometer if we are speaking of accumulating time) accumulates time under all conditions. Also, where did I agree to your "fact" = "... that the 0.866c relative velocity fails to produce a gamma of 2.000?" I think just the opposite, if I understand you. I.e relative velocity of 0.866 does correspond /produce (Your choice of verbs again) gamma = 2.

    I think if we are to communicate with any mutual understanding, you must spell out the operational proceedure that are to be used to make comparisons betwen chronometer A & B displays. I told you one proceedure I think is valid in my "triplet paradox story" - I.e. A & B departed from Earth and exactly followed anti-symetric flight plans that eventually brought them back to a dinner party on Earth. Then with their chronometers sitting side by side on the dinner table, I simultaneously read them and both they showed 3.2 years. My identical chronometer was also set to zero when I watched my two twin brother's rockets simultaneously separate from the launch pad. (Lets agree not to dicuss our disagrement about the twin and triplet paradox, but I note that when their chronometers both displayed 3.2, mine was showing that they had been gone for 7.4 years - I guess aging 4.2 years more than my twin brothers is the price I paid for lacking their courage to ride a rocket!)

    Please stop speaking of "time accumulated" unless you describe in some detail how the chronometers are set to show zero in one common instant and how the event that establishes the end of the accumulation period is operationally defined. Without clearly showing to one (Me) who does not shair your belief in "absolute time," simply referring to the "accumulated time" and asking if it is different or the same is nonsense. - The answer will depend on: (1) how they set the chronometers to zero (define the operational proceedure, where each was, what relative speed they had, if any. etc.) and (2)when (operational prceedure details) they turn the accumulators off.
    For example, A & B, with zero relative velocity, could both set chronometer to zero at dawn and turn turn them off at sun set and accumulate very different number of hours, on June 21, if one lives in southern hemisphere and other in NYC, but accumulate the same time if the are sitting all day, side-by side, on a bench in NYC's central park (assuming they did not get mugged.

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    )

    If they are in frames moving with respect to each other, avoiding nonsense is much tougher. - I tried to help you define an opertional proceedure for A&B to set zero and turn off accumulation by suggesting that in addtion to the exactly identical, but anti-symeteric flight, they always fly perpendicular to the ecliptic and both can see Earth in orbit (with same light propigation delays). I even explained how that 12 "months" could be defined (using zero declination distant stars, D1, D2...D12) to subdivide the "orbit year." - I was trying to make it easy for us to communicate by setting up a common clock both A & B could use, but you just complained that I

    "want to re-write the gendankins and create complex issues and interject simultaneity, etc, which really have nothing to do with the simple example I have provided."

    I certainly agree your example is "simple," too simple - the operational details have all been omitted and because of this one does not know what you are talking about or how to respond to your questions. Also please note that I am not "injecting simultanity problems." They are a problem for anyone who does not believe in "abslute time, equivalent in all frames" - If you are to successfully communicate and convence a beliver in SRT that he is wrong, then you must stop assuming there is no need to spell out how the start and stop events for turning on and off the chronometers are operationally defined.

    I understand that you believe this is needless because everyone can just turn them on at noon 25 december 2005 and off at noon 25 december 2007 since "clocks can be synchronized in all frames" but I don't believe this. If you are to persuade me on anything, you must only use facts I accept. If you base your arguments on "facts" I reject, then clearly you are wasting both our time.

    5 - No. Your example, which is based on many "facts" I think are false, is not persuasive for reasons just stated in some detail.
     
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  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Responding to 2inquisitive:
    Thanks for the offer of references to atomic clocks etc. When I worked at Applied Physics Lab of Johns Hopkins U., there was one on the floor above my office that contributed about 2 or 3% to the definition of the second. I went and looked at it afew times and was once vaguely aware of some of the problems you mention.

    Let me again state for one and all: I know so little about the way GPS makes corrections and about atomic clocks, that anyone spending an hour in web searching these subjects would be an "expert" relative to my knowledge. Furthermore, I plan to keep it that way and will not be drawn into discussions about how either atomic clocks or GPS can be used to either support or disprove SRT. I am too ignorate to participate in such discussions.

    I tend to think that even if GPS has not exactly followed even the orthodox SRT corrections, (as MacM has been telling me) that the "approximations" of the SRT rules and the selection of "wrong" reference frames used are not significant violations. I am sure that some physics effects most of agree are real have also been neglected because they are not important enough to include. For example, most of us (both pro and anti SRT) believe that as photons climb out of a deep gravity well, they are "red shifted." - have their frequency changed by a change in the gravitational field strength about them now compared to earlier. ("Change" always imples two different time).
    This "red shift effect" being true (commonly accepted by us all) then the frequency of the photons in an atomic clock will slightly change with the changing distance to Jupiter. I strongly doubt the corrections applied to GPS's clocks make any reference to where Jupiter is. Likewise if they use a reference frame in the center of the Earth or the top of the empire state building and have selected the "wrong one" from strict SRT theory, I assume (for reasons given in next two paragraphs) that "error" is also insignificant.

    I think most of the designers and 100% of those concerned with corrections for SRT effects related to the orbital speed of GPS, believe SRT is physically correct, not just some interesting math results that Einstein cooked up. I also bet 0% of the "orbit speed correction experts" believe in MacM's (or anyone else posting here their SRT alternative theories) have a better model than SRT for making the needed orbit speed corrections.

    The other reason why I think the application of SRT to GPS, even with the "approximations" that may slightly violate SRT, is valid is that it works. Very impressively. I have seen a classified film of a tomahawk missle, that was laucnched from a submerged sub and then flew more than one hour under GPS control, hit a small traget building that had been constructed just for this distructive fate. (The building's location in GPS coorinates was premeasured very well, I assume.) If there were any serious errors in the way these "believers in SRT" have applied "SRT corrections" (instead of those of MacM et. al.) to correct for orbital velocity effects, then this would not have happened!

    Sorry, but for reasons initially stated, I won't say more or get into details of either GPS or atomic clocks.
     
    Last edited by a moderator: Jun 18, 2005
  11. 2inquisitive The Devil is in the details Registered Senior Member

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    Sorry to confuse you, Billy T. You seem to be mixing me with MacM. I am not in
    agreement with MacM as you seem to think. I was addressing the following exchange
    between you and I.
    You, Billy T, initially stated that you did not believe clocks in two different frames of
    reference could be synchronized. I stated they CAN be synchronized as proven by
    GPS, otherwise GPS would not work. Synchronization of clocks is essential. The
    following is a cut and paste of your response to me, as I am the one who stated earlier
    that relatively moving clocks can be synchronized:
    =========================================================
    by Billy T:
    "Now is where the hidden presumptions (both of the anti-srt and pro srt people come to the surface) If you deny time dialtion, then for you the conclusion you stated at start of your post, "CAN be synchronized..." is obviously true, but for me it is obviously false - time dilation will make each think that the others clock is dropping out of sync as it runs too slowly to keep up with the time keep locally."
    ================================================================

    I responded that I was not challenging your knowledge of relativity theory, but that measured data does not always agree with relativity theory. I am speaking of clock
    synchronization in my comments, not agreeing with MacM's arguements. I posted
    the excerpt and link to actual data collection as to clock behaviour relative to an
    Earth-based clock in my next post. The relatively moving GPS satellite clocks can be
    synchronized both within the satellite constellation and with Earth clocks and STAY
    in synchronization for up to 1 to 2 years. That was what the link was about. Perhaps
    you would like another link to another paper where synchronization is two-way, time
    is read accurately between sat clock and Earth clock on both signals from Earth-to-
    satellite and from satellite-to-Earth? THAT is why I say actual data does not follow
    theory, but you have to read the data to understand this. One reason I differ from
    MacM is given in James R's cut & paste on GPS explanation in the thread he started.
    Frequency shifts in transmitted GPS signals can be explained by Newtonian effects,
    General Relativity effects (mostly gravitational) and Sagnac effects, as the author of
    James R's cut and paste stated. I totally agree. Neither STR nor ether theories are
    needed. MacM, of course, supports ether theories. I support field theories, field theories which could possibly explain the gravitational effects on clocks within a field
    and possibly clocks moving through a field. I do not have a particular theory to support, I only believe a good field theory is necessary to arrive at a better understanding of our universe. I believe a better understanding of gravity and gravitational fields holds the key to the universe. STR ignores gravity completely and
    GR mostly just models its effects on 'space-time'.
     
  12. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I don't know details of GPS, but am confident that the clocks on the satellites do run slightly slower than identical ones on Earth. Just to make up numbers, lets say when 1001 seconds have passed on Earth, only 1000 have past on the GPS satellite.

    This would not make GPS fail as you seem to think. If GPS needs to broadcast or know "Earth tme" it obviously must expand each of its clock's seconds by 0.1% -Simple adjustment, not a cause for GPS to fail. Thus your citing the fact that GPS does work (not fail) is no evidence that the satellite atomic clock is running in sych with those on Earth. All the fact that GPS works proves is that the guys (and gals) who make the correction calculations (and BTW, believe in SRT) know how to do it very well.

    To take a very simple example - about a year ago, before I finally threw it away, I had a cheap wrist watch that reliable gained 3 minutes each day. This did not make me miss buses etc, (fail / not work). I just had to remember how much to correct for the error (and about once a week reset it to correct time.) That, just because a clock is not keeping time the way others are, does not mean you can't use it. All the slow running clock in orbit still "work" - just if you want to compare with Earth clocks and appear to be in sync with them, you must make a correction, which is different (unique) for each different frame. I.e. the correction required to appear that GPS clocks were sychronized with clocks on Mars would be different.

    Summary: fact that GPS works does not, as you suggest, prove that GPS clocks must run at same rate as Earth clocks do, nor does it prove that moving clocks can be sychronized with Earth clocks. All it proves is that the believers in SRT, who compute the corrections required using SRT, or good approximations of it, know what they are doing. Fact that GPS works with these SRT corrections applied leads to just the opposite conclusion from your "proof" that it is possible to sync clocks in different frames. The need for clock corrections demonstrates that the clock are not in sync.
     
    Last edited by a moderator: Jun 19, 2005
  13. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    by Billy T:
    "Summary: fact that GPS works does not, as you suggest, prove that GPS clocks must run at same rate as Earth clocks do, nor does it prove that moving clocks can be sychronized with Earth clocks. All it proves is that the believers in SRT, who compute the corrections required using SRT, or good approximations of it, know what they are doing. Fact that GPS works with these SRT corrections applied leads to just the opposite conclusion from your "proof" that it is possible to sync clocks in different frames. The need for clock corrections demonstrates that the clock are not in sync."
    =============================================================
    I you are going to attribute remarks to me in the future, Billy T, I suggest you do a
    cut & paste or reply to my post. I never suggested that GPS clocks run at the same
    rate as Earth clocks without adjustment. Can you not read and comprehend what you have read or are
    you just building strawman arguments that you can tear down? The whole series of
    posts by me illustrates that GPS clocks CAN be synchronized with Earth clocks, I even
    gave links to how it was done. I NEVER said they would beat in unison without adjustments. AFTER THE ADJUSTMENTS ARE DONE, they are synchronized with Earth-
    based and other satellites clocks in the constellation. After they are initially synchronized, they will stay in synch for up to two years without needing resynchronizing. The SIGNALS broadcast by the satellites are adjusted more often
    than that because of other effects on their frequency, such as different amounts of
    charge in the ionosphere caused by changes in the intensity of the solar wind just to
    mention one cause for adjustment to frequency. And no, the satellite clocks DO NOT
    run slow according to Earth clocks, even before adjustment. They run FAST and must
    be adjusted prelaunch and after orbital insertion to correct for this and to synchronize
    with all the clocks in the GPS system. They beat FAST because the difference due to
    gravitational potential effects between Earth surface and orbit is greater than any theorized clock slowdown due to relative velocity effects (STR or aether). But the clocks CAN be, and
    ARE, synchronized. Synchronizing clocks presents no problem for General Relativity
    theory because time dilation due to gravitational potential is always one-way, with
    one clock always beating slower in the more intense gravity field. That is easily adjusted for in the synchronization process. Now, if you understand, I will quit talking
    of GPS in this thread.
     
  14. Quantum Quack Life's a tease... Valued Senior Member

    Messages:
    17,508
    BillyT if you feel that GPS functions as SRT predicts then I wonder how the GPS clock can synch with the earth clock if the earth clock is also running slower. Macms reciprication concept comes to play.

    so the GPS synchs with the Earth clock yet the GPS sees the Earth clock as slower and not faster so if SRT is applied how can the two clocks ever be in synch? [as each clock sees the other as slower. or symetrically inverse]

    the compensations are only made one way from what i understand as a two way tick rate compensation leaves the GPS clock chasing it's tail so to speak.
     
  15. James R Just this guy, you know? Staff Member

    Messages:
    30,358
    QQ:

    Which reference frame are you talking about?

    They can't be, in both frames. They can only synchronise in one frame. We use the GPS system on Earth, so we generally want synchronisation there.
     
  16. Quantum Quack Life's a tease... Valued Senior Member

    Messages:
    17,508
    so you are saying that in the Earth frame the Earth clock synchs with the GPS but the GPS doesn't synch with the Earth? [earth RF only]
     
  17. James R Just this guy, you know? Staff Member

    Messages:
    30,358
    I am saying that if the GPS clock is adjusted so that it ticks at the same rate as Earth clocks according to observers on Earth, then from the point of view of a GPS satellite, the Earth clocks will NOT be ticking at the same rate as the satellite clock.
     
  18. Quantum Quack Life's a tease... Valued Senior Member

    Messages:
    17,508
    so clearly the Earth frame observer aboard the satelite would see the clocks in synch but a satelite frame observer would see the clocks out of synch......interesting....hmmm
     
  19. Quantum Quack Life's a tease... Valued Senior Member

    Messages:
    17,508
    so as MacM might say, the question comes back to how does the GPS synch with earth? [given that the clock aboard the GPS is ticking in the GPS frame and not the earth Frame because of it's velocity]
     
  20. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    OK, I have read a little more about GPS from some different sources and have added
    a little to my limited understanding. When speaking of the whole system especially,
    GPS is complicated. James R, see if you agree with my somewhat simplified explaination
    of clock parameters.
    To begin with, the SV (satellite) clocks are preadjusted before launch, according to
    Dr. Ashby, to beat slower by about 38 microseconds per day. That offset is to compensate for the unadjusted fast beat of the orbital clock due to a lower gravitational potential in orbit. It is said that the slower beat due to satellite velocity
    relative to 0 velocity at the center of the Earth is compensated for in this adjustment
    also, deducted from a calculated total of about 45 microseconds.
    Once in orbit, the SV clock is turned on. An initial orbital adjustment is then performed on the clock in an effort to synchronize it closer to the beat of a hypothetical clock
    located at the center of the Earth. The rubidium clocks, especially, are not very stable
    for the first few months in orbit, then they begin to beat more consistently. A second
    adjustment is made to the beat rate of the clock, after which the clock usually does not to be readjusted again for 1 to 2 years. Note, this is the synchronization of the
    SV clock to the center of Earth clock, including the orbital velocity of the SV clock relative
    to a stationary clock located at the center of the Earth. All SV clocks, regardless of
    orbit, are at the same relative velocity wrt the Earth-centered clock. The surface of
    the Earth, represented by WGS-84 in the ECEF frame, has not come into play yet.
    The ECEF frame comes into play when the SV broadcast a signal to a GPS receiver
    on or near the Earth's SURFACE. The reciever first uses a coarse acquisition code from the satellite to get an initial lock and info from the sat. The receiver then uses a
    pseudo-random code, a seemingly broken and random noise, to match a similar code
    generated by the receiver itself. The receiver slides the two codes up and down beside each other, figuratively speaking, looking for a pattern of breaks that match. When the patterns match, the receiver clock is in synchronization with the satellite clock. By using the pseudo-
    random code to synch clocks, it doesn't matter whether the receiver is at the equator
    or the North Pole, it can eliminate any relative velocity effects due to Earth surface
    rotation that have yet to be accounted for. But the satellite clocks do have to be in
    synch with each other and with time at the Master Control Station at Schreiver AFB.
    Voila, the difference in Earth surface speed at different latitudes is not a factor. But,
    there IS a problem that I don't know the answer to. We just eliminated Earth surface
    speed as a factor in synchronization by this normally used method. The problem I don't
    know the answer to, is, this is not the only method that works. If someone, military
    or such, has their own highly accurate atomic clock, they can synchronize with the
    satellite clocks without using the pseudo-random code. If their clock is in perfect time
    with the master clock at Schreiver AFB, they are in synchronization with the GPS satellite clocks also, regardless of their location or latitude on the Earth. They can
    also get accurate position coordinates regardless of their latitude. If there is a time
    dilation due to relative velocity of satellite and receiver, how can this be? One millionth
    of a second error due to time dilation would amount to a 300 meter error. In this post,
    I am only speaking of clock synchronization errors, not effects due to the many other
    causes, like atmospheric delays, while the signal is in transit.
     
  21. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Messages:
    23,198
    Thanks for your information and comments. I was not setting up a "strawman" nor puting words in your mouth, but can understand why you thought I was.

    The basic cause of the "conflict" (which I now think does not exist - hence the quotes around the word) is we understand and use the term "synchronized" differently. For you (I am almost sure now) the definition, which I will call "sycn1", is that clocks that can be made to display the same time, even if a correction to its basics "tick rate" is required are said to be "sychronized." Sych2, my idea of "sychronization" is that clocks are in sync2 if and only if without any correction they have the same "tick rate"

    I granted that sycn1 is possible between any TWO different inertial frames in my prior posts, even illustrating that by my mental correction of the cheap wrist watch that gained 3 minutes each day, was in sycn1 with the bus station and other clocks, but it was not in sync2 with these clocks.

    I probably did "put words in your mouth" unintentionally as I am usually in this type of discussion with people unlike you (for example, MacM) who at least as I understand what they are saying believe that SRT is wrong and sycn2 is possible between clocks in different frames. Excuse me for responding to you the same way i respond to them and unconsiously assuming you were in their corner. I now think we agree totally.

    I also want to thank you for correcting me - I did not know (or at least failed to remember) that the weaker gravity field at the satellite distance "undid" more red shift that the orbit speed made. (net effect is that clocks satellite clocks run fast, not slow as I stated.)

    I think I should have known this as I participated in a thread where this was discussed (but more in terms of the " Escape velocity" as a function of distance from the gravitational center and how the gravitational and velocity time dilations compare). Forgive an old man whose memory may not always be what it should be.

    It is clear to me that you know much more than I do about GPS. At this stage in my life, I tend to apply general principles here and leave the details and calculations to others.

    As far as I can tell we agree, but I will asks specificly: Is there any part of SRT that you do not accept, or do you, like me, swallow it "hook line and sinker" ?
     
  22. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    Thanks, Billy T, no problem at all. I too, am retired, I have been for over three years.
    I did retire at 56 though, after a 30+ year career in the federal government. I think I
    misunderstood you also, about synchronization. All clear now.
     
  23. James R Just this guy, you know? Staff Member

    Messages:
    30,358
    2inquisitive:

    I don't have a good enough knowledge of the detailed workings of the GPS system to really respond to your question. For the purposes of the discussion we have been having, I can assure you that there are relative-velocity effects between the ground and the satellites. How these are compensated for in the GPS system, I am not an expert on.
     

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