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  • Bruce Griffing
    replied
    Evan-
    The paper suggests exactly what you would expect - that clocks moving in circular motion slow down. A fact that has been experimentally confirmed. Much of the discussion in that paper is related to the acceleration part of the process, which as discussed before, requires GR. The corrections for GR are small, but it is instructive to look at the acceleration process to understand the sign of the correction. The key question is this - does the acceleration make the object go faster WRT the "rest" frame or slower. This is important because as a practical matter, we do not really have a rest frame here on earth. If it goes faster, the clocks slow down. If if goes slower, the clocks speed up. But for the rotor experiment originally discussed, this does not matter. The rotor experiment can be treated as if we are at rest. Done correctly, the clocks on the moving rotor will slow down.

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  • Fasttrack
    replied
    Incidently, Penrose has some very fascinating books published. I've just started The Road to Reality - its a nice review of my theoretical class.

    I've been pretty busy lately and have not been able to do much work on my idea or, indeed, follow this thread too closely. I'm headed to NM tomorrow to pick up some machinery that I purchased, but after that excitement is over hopefully I can get up to date on whats been going on

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  • Evan
    replied
    Here is a very interesting paper that describes what happens to the clocks in the "fly around the Earth" experiment. The result is the opposite of what would be expected in a simple case of SR time dilation and illustrates why we cannot determine what is actually happening in the accelerated frame from the non-accelerated frame.

    As with the comparison of a clock brought into a gravitational field from far away to that of a clock constructed within the field, the result of equation (9) is the same one we get if we construct a clock in an inertial reference frame and then impart the circular motion to it. We can determine the rate of slowing due to (9) in the same manner we used for a clock placed in motion from its rest frame. This is done in equation (4), and we arrive at the result that the accumulated time on a clock undergoing circular motion is less than that accumulated on a stationary clock and is given by t’ = tg-1
    A clock constructed in the lab frame, and then placed on the edge of a rotor, will slow down due to the acquired energy. When removed from the rotor and placed again in the lab frame, the clock will speed up to its original, inertial rate. Similarly, a clock constructed on the moving rotor would run at the same lower rate as the lab frame clock placed on the rotor. When removed from the rotor, both clocks will speed up by the same amount, reflecting the more inertial, lower energy environment. In the case of the west-bound flying clock, we are taking a clock that has been constructed on a rotor (the rotating earth), and then moved to a more inertial frame. Thus the clock speeds up as compared to an earth bound clock. We allow the west-bound clock to circumnavigate the globe until it is again at the same location on the earth as the earthbound clock. The west-bound clock will have accumulated more time than the earthbound clock. Being in a more inertial state, the clock rate speeds up as it approaches metaphysical time.
    Imagine that we were to place a clock on a rocket, and launch it into space at the point of earth’s perihelion in its orbit around the sun. We keep powerful rockets pushing on this clock so that it remains at this point in space as the earth pulls away in its year-long journey. From the earth’s reference frame, this clock will have been accelerated mightily, and will have attained a tremendous velocity (30 km/sec) with respect to the earth. After a year has elapsed, and the earth is approaching perihelion and the space clock once again, we read the elapsed time on the space clock and compare it to one of our earth-bound clocks. We find that, even though the space clock was accelerated to a high velocity as measured with respect to us, it has recorded more time since we’ve been gone, not less as would be expected of a clock placed in motion.
    Even after we adjust the time recorded on the earthbound clock for the slowing due to the earth’s rotation and the presence of the clock in the earth’s gravitational field, we still have accounted for less time than recorded on the space clock. The reason is that a clock stationary at the point of earth’s perihelion is in a more inertial reference frame than a similar clock in orbit around the sun. Thus this clock runs closer to metaphysical time, and, therefore, runs faster than the earthbound clock. The same would be true if we could set a clock in space and wait for the entire Milky Way to complete one revolution. As the solar system drags back around after millions of years, the space clock will have recorded much more time than a clock kept on the earth for the duration. Again, we have neglected or pre-corrected for all gravitational effects. The space clock, set free of the rotational grasp and effects of the Milky Way, will have been one step closer to fully inertial, metaphysical time.



    http://renshaw.teleinc.com/papers/london1/london1.stm


    It also deals with some of the more esoteric concepts such as abberation which is closely related to the Penrose rotation.



    BTW, the paper obviously does support the concept that rotation does produce time dilation, but not necessarily in the expected sense.

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  • Bruce Griffing
    replied
    Evan-
    On your point about orbital motion - A satellite does undergo acceleration because its vector velocity changes. But it is a special kind of acceleration in which the force is always perpendicular to the direction of motion. The net result is a changing velocity vector, but a constant velocity magnitude. It is the magnitude of the velocity that is traded against progress in the time dimension in SR, so there is time dilation (however small in real cases).
    As to the problems involving general relativity, any problem involving acceleration will need GR to understand completely. But the case of an clock accelerating to a velocity, traveling at that velocity and returning can, in most cases, be delt with using SR. Most of the effect on the flying atomic clocks is due to SR. That part is just the velocity part discussed above.

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  • Bruce Griffing
    replied
    Alan-
    I am recently retired here. I am trained as a physicist and had a career in technology development in the electronics industry. Temple is indeed a quiet town. I enjoy the warm weather at least 9-10 months a year. The other months are quite hot - thank God for air conditioning. I have a nice shop attached to the house and enjoy working there. I did work in the Phoenix area for about 16 months and owned a house in Chandler. I sold it about two years ago.

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  • aostling
    replied
    Bruce,

    While Evan is pounding posts (instead of posting them) may I ask what your background is? I've visited 252 of the 254 counties of Texas, including your Bell County. Temple struck me as a quiet place, fortunately bypassed by I-35. It has a nice courthouse square and church, a big VA complex, but no college of higher learning where I might expect you to be on the faculty. Are you retired there?

    Leave a comment:


  • Evan
    replied
    You mention gravitation. Acceleration, due to gravity or otherwise is the source of the time difference. It is the acceleration that makes the twins in the twin paradox different.
    What makes them different is what makes it a general relativity problem. The traveling twin occupies two different non inertial frames of reference, one going away and one coming back. As soon as we add a third frame of reference the situation changes since we have two frames to compare to a third. That still doesn't permit us to

    A satellite orbiting the Earth is in an inertial frame of reference as it is falling through an equipotential path in curved space. It undergoes no acceleration as it orbits. A rotating mass on a stick, which is what this thread is about, is a non inertial frame of reference and and the signal sent from the mass will be equally red and blue shifted resulting in a null difference.

    There is more but I have to pound some fence posts for a neighbor.

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  • Bruce Griffing
    replied
    Evan-
    My point is that is is not necessary for the moving clock to stop to observe time dilation. Consider the following example -

    A spaceship passes earth at high speed. As it passes on the outgoing leg, it transmits a time signal. It continues to travel at high speed but after a long flight, it turns around and comes back at the same speed. The same protocol is used to transmit a time signal as the ship passes earth (judged from the moving frame). In each case, the time signal will be received. The trip is planned so that roughly 100 years of time difference build up. Now, there is an error associated with the "drive by" SR effects, but it is tiny compared to 100 years. If the protocol is carried out correctly, that error will cancel between the first and last signals. But the cancellation is not important. The point is that time dilation is observable without the moving clock coming to rest. The case of orbital motion - which is the original point of this thread - is even more special in that the distance to the moving clock is constant. This creates lots of simplifications.

    You mention gravitation. Acceleration, due to gravity or otherwise is the source of the time difference. It is the acceleration that makes the twins in the twin paradox different.

    Leave a comment:


  • Evan
    replied
    As to your point on the speed of light - of course the speed of light introduces a delay. To the extent that the distance is known, this can be corrected. For real situations, like clock calibration, it is of course easier to avoid the correction by putting the clocks together. Again, this does not prove anything.
    In the case of clocks stationed on the earth or flying around it the delay is unknown and cannot be accurately characterized. We can only set upper and lower bounds on it. The velocity of light is only constant in a vacuum. As soon as the electromagnetic wave must travel through the atmosphere the travel time becomes unpredictable. Not only does the density of the atmosphere vary but the path the radio signal takes varies as well. The only solution is to bring the clocks together which is why the clocks at the LORAN station are calibrated to another clock in the room. The same applies to a gravity well although that is at least easier to characterize. In fact, the gravity well effect completely overwhelms the time dilation due to velocity of the clocks on GPS satellites. They run slower because of their relative velocity but since they are further out of the Earth's gravity well the net result is that they run fast.

    Even if the distance is known and we attempt to compensate we cannot distinguish the nature of the curvature of space as caused by gravity. We do not know and cannot know what the gravipotential difference is between two arbitrary points in space. These are not nitpicks as the discovery of numerous "Einstein rings" caused by gravitational lensing demonstrates.

    Even in the case of a fly by as you suggest, the Penrose rotation prevents us from viewing the clock in the contracted frame. All we will see is the frame rotated rather than contracted. The same will apply to any signal with the equivalent of rotation being a doppler shift.

    The rules of simultaneity clearly make it impossible to observe another frame of reference and see what someone in that frame sees. We will see something but what we see is unique to our frame of reference relative to the other and an absolute determination of what is visible in the other frame cannot be made.

    No two locations in space/time share the same frame of reference.

    Also, for any two frames of reference that have intersecting world lines there is a third frame that will see both of the first two as being identical even while both see each other as different.

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  • Bruce Griffing
    replied
    Evan-
    The reference you list is of course correct - for the case of linear motion. In that case, it is not possible to detect the time dilation without the moving clock turning around and coming back toward the fixed observer. It does not have to stop however, to observe the effects of time dilation if the clock does make a return pass. In short - your example is correct for the "fly by" case, but that is not the case being discussed. The fact that it is impossible for this case to detect time dilation does not prove the general case impossible.
    As to your point on the speed of light - of course the speed of light introduces a delay. To the extent that the distance is known, this can be corrected. For real situations, like clock calibration, it is of course easier to avoid the correction by putting the clocks together. Again, this does not prove anything.

    Leave a comment:


  • Evan
    replied
    I assure you that I am not speculating on this matter.
    Neither am I. It isn't a matter of the size of the error or inaccuracies in transmission of a signal.

    Here is an explanation of why it is impossible.

    http://galileo.phys.virginia.edu/cla.../time_dil.html

    I should point out that while you can observe a difference in the clocks you have no way of determining which clock is correct or time dilated.

    [more]

    As for the LORAN station clocks, they are held to a maximum error of 20 nanoseconds per year. That's the amount of time it takes for light to travel about 20 feet. In order to calibrate those clocks the reference clock must then be within that distance to be considered as being in the same frame. In fact, the exact length of the cable used to connect the reference to the triple clocks matters since it also causes a delay in transmission.

    The basic fact is that time is different for different locations, even if they are only a few feet apart. Since you can't be in two places at the !exact same time! there is no way to make a comparison of times in two different locations that is any more accurate that 2X the speed of light delay between those places even if there is no relative motion. If there is relative motion all that can be observed in reality is the doppler effect of any received signal. While this is proportional to the dilation amount it isn't an observation of the actual dilation effect.
    Last edited by Evan; 05-25-2008, 08:13 AM.

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  • Bruce Griffing
    replied
    Evan-
    I have a high opinion of your work on many things - but in this case we just disagree. It is simply not necessary for the an object to return to the rest frame in order to observe time dilation. Consider the airplane already discussed. I do agree that it is much more practical to land to do comparison measurements. Think about it a different way. Do an Einstein style thought experiment. Imagine a flight that goes on for a very long time. The time differential would build up to a point where it the errors associated with transmission would not drown out the effect. So I stand by my statement that it is not necessary for the object to return to the rest frame to observe time dilation. I assure you that I am not speculating on this matter.

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  • Evan
    replied
    Not so. Consider atmospheric muon decay. The muon does not slow down until it decays - thus sending a signal to the observer. In the case of the flying atomic clocks, the clock was returned to land only for convenience - with proper equipment it could have been still flying. Consider Thomas precession - another example of the object not returning to the observers reference frame.
    In the case of the muon we don't even know it exists until it decays. That is when it enters our frame of reference. Prior to that it's world line does not intersect ours. We then can infer what it's lifetime must be to decay at that altitude but we cannot do so by direct measurement.

    We cannot send a signal from the flying clocks for the purpose of comparison. It will be subject to the same relativistic effects as the clocks themselves making comparison impossible. It is for that exact reason that every year a portable atomic clock is flown here to Williams Lake in order to calibrate the triple atomic clock stack at the Loran C station. There is no way to send a signal from Boulder Colorado to Williams lake for that purpose. The two locations are in different frames of reference. This is all a matter of simultaneity at work.

    I am considering the Thomas precession but am not sure what the applicability is to other aspects of relativity, yet.

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  • dp
    replied
    36,000 inches per minute is 3000 feet per minute. 1 mile per minute is 5,280 feet per minute, or 60 mph. 36,000 inches per minute is 34.090 mph.

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  • Paul Alciatore
    replied
    Originally posted by knucklehead
    special relativity?
    why didn't you say so...
    36000ipm is only about 35mph.

    can you run your experiment in a car?

    how long do you plan to run for?

    -Tony
    That's funny, I get 375 MPH. A bit of a different ball game as regards using a car. But I guess there a few out there. And finding a stretch of road may be just as big of a challenge.

    Leave a comment:

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