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Google mash-up I'd like to see

 
 
Ilya Zakharevich
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      12-20-2007
[A complimentary Cc of this posting was sent to
David Bernier
<(E-Mail Removed)>], who wrote in article <T_kaj.6427$(E-Mail Removed)>:
> Currently, effects from general relativity are included by JPL and
> others. Trying to understand solar dynamics formulated
> in general relativity is beyond me.


I'm very sure that (maybe with an exception of Mercury; but I think
even for it) the main term of the effects of GR can be expressed as
minor additions to Newton inverse square law (a term of degree not
-2, + a term depending on relative velocity). (I do not have a
reference at hand, but I think it is in the beginning of any book on GR...)

Of course, this assumes the observer far away from the system, and not
hopping from one body to another one. Which reminds me (an urban
legend?):

When first launched, GPS satellites had a (software) switch. In one
position, they would take into account the effects of GR; in the
other, they would not.

Engineers being naturally suspicious of "high brow" calculations,
the at-launch position was OFF. During the first day of testing,
the errors accumulated so much, that they grudgingly agreed to turn
it ON.

Yours,
Ilya
 
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acl
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      12-20-2007
On Dec 20, 8:55 am, Ilya Zakharevich <(E-Mail Removed)> wrote:
> [A complimentary Cc of this posting was sent to
> David Bernier
> <(E-Mail Removed)>], who wrote in article <T_kaj.6427$(E-Mail Removed)>:
>
> > Currently, effects from general relativity are included by JPL and
> > others. Trying to understand solar dynamics formulated
> > in general relativity is beyond me.

>
> I'm very sure that (maybe with an exception of Mercury; but I think
> even for it) the main term of the effects of GR can be expressed as
> minor additions to Newton inverse square law (a term of degree not
> -2, + a term depending on relative velocity). (I do not have a
> reference at hand, but I think it is in the beginning of any book on GR...)


I am pretty sure that the advance of the perihelion of mercury can be
accurately calculated from an eqn of motion that differs from the
Newtonian one only by a term (or 2) like the ones you describe. The
reason I'm so sure is that the last written exam I ever took was GR,
and that was one of the questions
 
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Chris Malcolm
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      12-22-2007
Ilya Zakharevich <(E-Mail Removed)> wrote:
> [A complimentary Cc of this posting was sent to
> David Bernier
> <(E-Mail Removed)>], who wrote in article <T_kaj.6427$(E-Mail Removed)>:
>> Currently, effects from general relativity are included by JPL and
>> others. Trying to understand solar dynamics formulated
>> in general relativity is beyond me.


> I'm very sure that (maybe with an exception of Mercury; but I think
> even for it) the main term of the effects of GR can be expressed as
> minor additions to Newton inverse square law (a term of degree not
> -2, + a term depending on relative velocity). (I do not have a
> reference at hand, but I think it is in the beginning of any book on GR...)


> Of course, this assumes the observer far away from the system, and not
> hopping from one body to another one. Which reminds me (an urban
> legend?):


> When first launched, GPS satellites had a (software) switch. In one
> position, they would take into account the effects of GR; in the
> other, they would not.


> Engineers being naturally suspicious of "high brow" calculations,
> the at-launch position was OFF. During the first day of testing,
> the errors accumulated so much, that they grudgingly agreed to turn
> it ON.


That's a geat story! I hope it's true!

I'm still very awed by the fact that only 250 years after Harrison
made a clockwork clock accurate enough to determine longitude for ship
navigation by means of time and celestial observations, you can now
buy for $200 a urban street satellite navigation device which times
its observations to 10 nanoseconds and requires relativistic time
corrections.

--
Chris Malcolm http://www.velocityreviews.com/forums/(E-Mail Removed) DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

 
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