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Re: electromagnetic literacy



On Sat, 13 Sep 2003, Jack Uretsky wrote:

Kopeikin's more recent paper (2/03) is also available on Spires. Checking
citations, I found only 2:

On the Speed of Gravity and the v/c Corrections to the Shapiro Time Delay
Stuart Samuel (LBL)
Phys. Rev. Lett. 90, 231101 (2003)
and


Here is a partial list of the many errors in Samuel's paper,
which I have presented elsewhere.

1) Samuel is not careful enough in specifying his time and space
coordinates. For example, it is not clear if his Eq. 1 is
derived in the Earth-based frame, the Jupiter-based frame, or the
barycentric frame of the solar system.

2) The unit vector n (see page 2, 3rd line from top) is
orthogonal to vector K at the point of the closest approach
_only_ in the Jupiter-based frame. In all other frames this is
not true. Samuel ignores this property.

3) Samuel defines the observed angle, theta_obs, for an observer
at rest with respect to the Jupiter-based frame. But the VLBI is
located on the Earth which, obviously, is moving with respect to
Jupiter. Hence, the angle theta_obs as defined by Samuel cannot
in fact be what is observed.

4) Samuel's transformation of Eq. 5 from the static frame of
Jupiter to the moving frame (see eq. 8) is completely erroneous,
due to the mathematically incorrect transformations (6) and (7).
As a matter of fact, Eq. 6 is correct only in the static frame.
Blindly substituting Eq. (7) into (6) does not represent a
complete transformation because the time coordinate should be
transformed as well. Samuel ignores this obvious relativistic
property of space and TIME coordinates.

5) As a consequence of the previous criticisms, Eq. 8 for the
VLBI time delay is wrong, and it is missing terms of order
1/theta^2. Also, Samuel adds even further confusion in that Eq. 8
is a mixture of quantities related to the static frame of Jupiter
and the moving frame of observer. The VLBI makes measurement in
the frame of the observer who is moving with respect to Jupiter.
Hence, in order to use Eq. 8 for real measurements, all quantities
must be expressed in terms of quantities related to the moving
frame.

6) Samuel claims that Kopeikin et al. used Eq. (10) for
measurement of the effect, which is totally incorrect. Kopeikin
instead used Eq. (11) without any expansion of it with respect to
time t_1. Samuel is, at best, confused about this issue.

7) Samuel claims that the speed of gravity appears only if the
acceleration-dependent terms are measured. This is wrong. The
speed of gravity relates to the gravitomagnetic
(velocity-dependent) effects which are equal to zero if the speed
of gravity is infinite. In other words, the speed of gravity
always appears when the first time derivatives of the metric
tensor are involved in calculations and/or measurements. Samuel
seems confused and has associated the speed of gravity only with
gravitational waves, while the speed of gravity is a constant
parameter in the left side of Einstein's equations and it can be
measured in stationary processes at which gravitational waves are
not emitted.

All in all, it is unfortunate that Samuel's paper made it into
publication, since his wrong assertions only add new confusions
to what is already confusing to some who do not follow the
inexorable logic of Kopeikin's brilliant theoretical formulations
and experimental results.


From: Joshua A. Faber <jaf184@lulu.it.northwestern.edu>
Date: Fri, 14 Mar 2003 22:50:26 GMT (8kb)
The speed of gravity has not been measured from time delays
Authors: Joshua A. Faber


Samuel says that the v/c correction is too small to be measured,
where v is the planet speed, so he seems to be in agreement with Faber.


I'm not sure why the "Submitted to Astrophys.J." was left out of
the description above, but Faber's paper was rejected by ApJL and,
as far as I know, has not been accepted by any other Journal to
which it was submitted.

--
Stephen
speicher@caltech.edu

Ignorance is just a placeholder for knowledge.

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