Exact Solutions and Scalar Fields in Gravity - Instituto Avanzado de ...

On the experimental foundation of Maxwell’s equations 307
5.4. CHARGE CONSERVATION
If we again associate the time dependence of the fine structure constant
with charge–nonconservation, then astrophysical estimates on
can be interpreted as test of charge conservation. In a recent paper
[44] the cosmological constraint on a time dependence of is given by
5.5. MAGNETIC FIELDS
Since macroscopic objects like stars in general are neutral, there is
no way to observe the potential of a charged astrophysical object. However,
most astrophysical objects possess a magnetic moment so that there
is a magnetic field around. Accordingly, the measurement or observation
of the magnetic field of the earth, of our galaxy or of a cluster of
galaxies gives very good restrictions on deviations from the usual Maxell
equations. The best founded estimate in the framework of a scalar
photon mass of this kind is of Goldhaber and Nieto [45, 24] and gives
There are better estimates from the consideration of
galactic or intergalactic magnetic fields but these are loaded with more
assumptions and uncertainties.
5.6. TESTS FOR SPECIAL RELATIVITY
While it is not possible to test the isotropy of light propagation because
we cannot send light in different directions, it is possible to analyze
the motion of stars in order to get results about whether the velocity of
light depends on the motion of the source or not. Such an analysis has
been carried through by K. Brecher [46]. If the velocity of light depends
on the velocity of the source, then the light which we observe
should possess different velocities according to the velocity the star had
during emission. This in general should lead to multiple images of the
same star e.g. during evolution around a binary compagnion. This has
never been observed. In the case of small velocities we may expand
where is the velocity of the star and the velocity of
light if the star is at rest, the observation of Hercules X1 place a limit
If we analyze the short events of pulses in the same
way, one may reach
6. CONCLUSION
Collecting the above listed experiments and observations, one arrives
in terms of the parameters defined in the generalized Maxwell equations
(17) at the following rough estimates