Einstien . . .wrong ??

[system]

please look at the actual article that TAS was referring to (I posted the link in my first message). It actually makes data-based claims which should be able to be analyzed directly

Remember, you asked … I’ll be pretty complete about the beginning of the paper, and just hit the points I find interesting at the end. Since the end is a mixture of the history of relativity and conclusions based on the erroneous beginning of the paper, I think this is reasonable. But you’ll have to get down the the end of this post somehow to get my comments on the GPS question. {grin}

As I believe I said in another post, the overall problem with Mr. Van Flanden’s post is that he tries to mix Newtonian mechanics and General Relativy and comes up with an inconsistent mish-mosh.

Newtonian mechanics give the correct answers if the gravitational “field” strength is low and we asssume infinite propagation time for gravity. If you try to use Newtonian mechanics with a finite gravitational propagation speed you will get the wrong answers. If you try to use any field-based analysis without verifying that it is a reasonable approximation, you may get the wrong answers.

General relativity gives the correct answers for low and high “field” strengths (although, strictly speaking, GR does not include the concept of a field) using gravitational effects propagating at the speed of light in a vacuum.

Further quotes are from his paper:

The effect of aberration on orbits is not seen … If gravity were a simple force that propagated outward from the Sun at the speed of light, as radiation pressure does, its mostly radial effect would also have a small transverse component because of the motion of the target … There can be no doubt from astronomical observations that no such force is acting.

Indeed, there is no doubt that there is no such force. However, he is assuming both a finite propagation velocity for gravity (GR) and a force field directed towards the center of gravity of the body (Newton). Not kosher. If the field strength is low enough to approximate the GR solution by a force field (which it is, for the case of the Earth and the Sun), then the force vector does not point towards the center of gravity by an amount that just cancels the effect of the finite propagation speed. Again, see Does Gravity Travel at the Speed of Light?

Gravity and light do not act in parallel directions … the acceleration now is toward the true, instantaneous direction of the Sun now, and is not parallel to the direction of the arriving solar photons now.

Basically the same comment as on the first quote. Yes, the force vector (whether measured or derived from an approximation of the GR solution) points toward the current position of the Sun and does not point toward where the center of gravity of the Sun was when the “gravity left the Sun”. This is predicted by the GR solution. It seems weird, but it is because there is no force vector; force vectors are convenient visualizations, and are often close enough to correct as to make no difference, but they are only approximations to the true situation.

The solar eclipse test … Since the observed times of eclipses of the Sun by the Moon agree with predicted times to within a couple of seconds, we can use the orbits of the Sun and the Moon near times of maximum solar eclipse to compare the time of predicted gravitational maximum with the time of visible maximum eclipse. … In practice, the maximum gravitational perturbation by the Sun on the orbit of the Moon near eclipses may be taken as the time when the lunar and solar longitudes are equal. … We find that maximum eclipse occurs roughly 381.9 seconds of time, on average, before the time of gravity maximum.

Sorry, when attempting to analyze on as accurate a level as this, we may not assume that the maximum gravitational perturbation occurs when the longitudes are equal. We have to calculate the GR solution and predict when the maximum gravitational perturbation occurs. I haven’t done the calculation, but I strongly suspect that the answer would be that the maximum perturbation is not expected when the longitudes are equal, just as the "force vector’ is not centrally directed.

Myth: Gravity from an accelerating source experiences light-time delay … However, a finite speed of propagation of gravitational force must add angular momentum to orbits.

This is the same argument as the first point to which I responded, dressed up with more mathematics. He is still assuming a central force field (Newtonian) and a finite gravitational propagation speed (relativistic), and getting the wrong answer.

Myth: Gravitational waves contribute to gravitational force …

This entire section appears to be an introduction to the rest of the paper. It is strange that he never mentions curvature of space-time, or changes in that curvature propagating.

Is gravity caused by a curvature of space and time … rubber sheet analogy … The reasoning in the analogy further suggests that target bodies simply respond instantly to the local curvature of the underlying spacetime medium

Yes. But the local curvature changes would change only as fast as a disturbance could propagate (as an elastic wave) along the sheet. In this respect the rubber sheet analogy is pretty good. But not in other respects …

A target body sitting on the side of an indentation would stay in place, with no tendency to roll downhill, unless there were already a force such as gravity underneath the rubber sheet pulling everything downhill

Yes. This is a failure of the analogy, not a failure of the theory on which the analogy is based. He is trying to analyze based on an analogy, which doesn’t work. First you calculate using the real theory, then and only then can you try to create or validate an analogy.

And this failure of the analogy helps us identify the precise problem with the curved space-time description of gravity - the lack of causality. Without consideration of why a target body is induced to accelerate through space, and how quickly it receives updates of information about how to accelerate through space, neither the space-time curvature explanation nor the rubber sheet analogy can help us understand why gravity appears to act so much faster than light.

GR is a model. It includes an explicit speed-of-light-in-vacuum propagation velocity for gravitational effects, so it does say “how quickly it receives updates of information …”. However, it does not include a meta-explanation of why Nature acts as she does. We can certainly calculate using the model without knowing why (although why is certainly an interesting question).

And there is no evidence for gravity propagating faster than the speed of light. The examples presented earlier in the paper are flawed, as I explained above. Since gravity does not appear to act faster than the speed of light, there is no point in asking why it does.

[quote]
contrary to what the rubber sheet analogy implies, an orbiting body such as a spacecraft orbiting the Earth is not following the curvatu

[douglips]

Thanks, JonF! That was totally what I needed. I just have one piece of the puzzle left.

Why doesn’t the SR correction work the opposite way for the satellite? That is, if we had to advance the clock by 7200 ns/day to make us think the satellite’s clock was running at our rate, shouldn’t the satellite see earth’s clock as running at 14400 ns/day too slow? After six years (see above post) wouldn’t the satellite say “You may think our clocks are synchronized, but I think you are 14 milliseconds slow.” Does the acceleration of the orbit cancel this out or something?

[JonF]

Why doesn’t the SR correction work the opposite way for the satellite?

That one makes my head hurt. I’ll have to think about that for a while, and hope somebody else jumps in soon {grin}.

One way of looking at it may be the way suggested in GPS Time in Orbot; since GR includes SR, you don’t need to calculate the two effects separately. The overall relativistic difference is that the GPS satellite’s proper time ticks about 38,700 ns/day fast relative to a clock on Earth, so they slow the clocks down by that amount. Because things don’t depend on your frame of reference, a clock on Earth will tick 38,700 ns/day slow relative to the satellite’s frame (even if you calculate in the satellite’s frame), and therefore will keep pace with the slowed clock on the satellite (while the satellite’s proper time clock pulls steadily ahead). However, I admit that I haven’t done the calculations and I can’t come up with a better hand-waving argument off the top of my head.

Two comments on my previous post; I referred to Mr. van Flanden as Mr. Flanders. Sorry 'bout that. I just noticed that What the Global Positioning System Tells Us About Relativity is also by Mr. van Flanden!!! Reconciling the two articles is beyond my abilities … but I don’t agree with his analysis of the twin “paradox”.

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jrf

[RM_Mentock]

Originally posted by JonF:
Reconciling the two articles is beyond my abilities … but I don’t agree with his analysis of the twin “paradox”.

Part of the discrepancy is from where you quoted him as saying “No … corrections … were needed.” In context, the meaning is a bit different. In his article he says:

No “relativity of simultaneity” corrections, as required by SR, were needed. This too seemed initially to falsify SR. But on further inspection, continually changing synchronization corrections for each clock exist such that the predictions of SR are fulfilled for any local co-moving frame. To avoid the embarrassment of that complexity, GPS analysis is now done exclusively in the Earth-centered inertial frame (the local gravity field). And the pre-launch adjustment of clock rates to compensate for relativistic effects then hides the fact that all orbiting satellite clocks would be seen to tick slower than ground clocks if not rate-compensated for their orbital motion, and that no reciprocity would exist when satellites view ground clocks.

That’s his version. My take on that: it means that any frame of reference is valid in GR, rotating or no. Might as well use the easy one, the Earth-centered inertial frame. If you were to analyze the complex relationships when you slap a co-moving frame on a single GPS satellite–analyzing the rest of the system from that frame–you still get the same answer, it’s just more complicated. That sounds a lot like what Einstein was getting at.
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[JonF]

Why doesn’t the SR correction work the opposite way for the satellite?

OK, I’ve thought about it some, and I pretty much give up. However, I did find another link with some interesting explanations and simpler math: The Global Positioning System (warning - lots of typos). In there, they discuss the issue of what goes on in the satellite’s frame of reference, by looking at a world-line diagram.

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jrf