wrote:
=20
alistair wrote:
=20
[...]
shouldn't we
look at the possibility that some forms of energy do not curve
space-time?
=20
Of course we should. This is a *major* experimental program,
with easily a dozen groups investigating the question of whether
composition affects gravitational fields.
=20
So far, though, not one speck of evidence has been found to
suggest that ``some forms of energy do not curve space-time.''
There are strong limits for electrostatic and magnetstatic
energy, strong interaction energy, and gravitational binding
energy, with somewhat weaker limits on kinetic energy and the
energy of the parity-conserving part of the weak interactions.
For these, we have experimentally ruled out the possibility
that they don't gravitate.
=20
Did you have some other kind of energy in mind?
=20
Steve Carlip

http://www.mazepath.com/uncleal/eotvos.htm#b21
The number of "different" observables for gravitational interactions
is strongly constrained by the symmetries of physics. Conversely, the
interested reader is invited to propose an observable outside the box.

http://wugrav.wustl.edu/people/CMW/update98.pdf
http://www.astro.northwestern.edu/AspenW04/Papers/lorimer1.pdf
Equivalence Principle testing

http://www.npl.washington.edu/eotwash/pdf/prl83-3585.pdf
http://arXiv.org/abs/gr-qc/0301024
Nordtvedt Effect

Science 303(5661) 1143;1153 (2004)
http://arXiv.org/abs/astro-ph/0401086
http://arxiv.org/abs/astro-ph/0312071
Deeply relativistic neutron star binaries

http://relativity.livingreviews.org/Articles/lrr-2003-1/
http://arXiv.org/abs/gr-qc/0311039
http://www.weburbia.demon.co.uk/physics/experiments.html
Experimental constraints on General Relativity

There is no Equivalence Principle violation, weak or strong field,
tested to one part in ten trillion difference/average in some cases.=20
Further,

http://fsweb.berry.edu/academic/mans/clane/
http://physicsweb.org/articles/world/17/3/7
No Lorentz violation

http://physics.indiana.edu/~kostelec/faq.html
V.A. Kostelecky, Phys. Rev. D 69, 105009 (2004)

Google
L=E4mmerzahl lorentz 166 hits
Laemmerzahl lorentz 103 hits

However, one can empirically falsify both the Equivalence Principle
and Lorentz invariance by demonstrating that gravitation includes a
parity violation as does the Weak Interaction. Gravitation parity
violation has never been examined until recently,

http://www.mazepath.com/uncleal/qz.pdf
In progress, Huazhong University. P3(2)21 quartz vs. fused silica is
running. P3(1)21 vs. P3(2)21 quartz to commence January 2005.=20
P3(1)21 quartz vs. fused silica to finish Summer 2005. Then, we will
know.

http://www.mazepath.com/uncleal/qzdense.png
Current calculation of P3(1)21 vs. P3(2)21 quartz parity divergence
to a 0.22 mm diameter single crystal test mass. Enantiomorphic single
crystals of quartz with convex shapes to possess all equal moments of
inertia are among the most parity divergent solids obtainable.

There are strong arguments constraining ay gravitation parity
violation to less than ten parts-per-trillon difference/average. The
effect, even existing at full throttle, is not macroscopically
manifest. It would heavily impact all theories of gravitation (metric
vs. affine gravitation; M-theory, lattice qauatum gravitation, etc.)
as well as quantum mechanics (that postulates Lorentz invariance).

--=20
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf