In general relativity it is assumed that all forms of energy
are associated with a gravitational field.However, given that quantum
mechanics says there should be 10^120 Joules per cubic metre in the
universe,
and that no-one can see anything wrong with this calculation (even
though experimental evidence suggests it is wrong), shouldn't we
look at the possibility that some forms of energy do not curve
space-time?

alistair wrote:

[...]
shouldn't we
look at the possibility that some forms of energy do not curve
space-time?

Of course we should. This is a *major* experimental program,
with easily a dozen groups investigating the question of whether
composition affects gravitational fields.

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.

Did you have some other kind of energy in mind?

Steve Carlip

In article ,
writes:

Did you have some other kind of energy in mind?

I think he was referring to the cosmological constant, vacuum zero-point
energy etc.

wrote in message
...

alistair wrote:

[...]
shouldn't we
look at the possibility that some forms of energy do not curve
space-time?

Of course we should. This is a *major* experimental program,
with easily a dozen groups investigating the question of whether
composition affects gravitational fields.

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,

Reference, please.

strong interaction energy,

Reference, please.

and gravitational binding energy,

Reference, please.

with somewhat weaker limits on kinetic energy and the
energy of the parity-conserving part of the weak interactions.

Reference, please.

For these, we have experimentally ruled out the possibility
that they don't gravitate.

Did you have some other kind of energy in mind?

How about thermal energy? The last reference you gave for this (Will,
section 2.4) did not contain anything on the subject.
http://www.google.com/groups?selm=vg....supernews.com

Hmmm, I missed your response where you abandoned Will, and went to your own
1988 paper, where you note:
"Surprisingly, the observational evidence for this prediction does not seem
to be discussed in the literature."

But this paper is still not available online to nonsubscribers. So, another
trip to the library will be needed to see if there is actually any support
for your conclusion. "Reanalysis" of "existing experiments" is always a
tricky effort.

--
greywolf42
ubi dubium ibi libertas
{remove planet for e-mail}

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

On Tue, 16 Nov 2004 wrote:


alistair wrote:

[...]
shouldn't we
look at the possibility that some forms of energy do not curve
space-time?

So far, though, not one speck of evidence has been found to
suggest that ``some forms of energy do not curve space-time.''

Did you have some other kind of energy in mind?


I'm glad that researcher like you asked this kind of question. Whether
there is some form of energy that doesn't curve spacetime or not is not
very important to me. Of course, it is important because it is about the
concept of equivalence of mass and energy and the dynamics curving
spacetime and to what extent this concept holds.

I incline to ask question like whether a quantized composition field with
gravity significant enough in it will non-linearize other kind of forces.
For example, might it be possible that EM waves will be amplified in some
quantum gravity system?
Or the EM waves shares some sort of tidal wave effect? Right now, I don't
think we have observed or demonstrated any effect like I asked. The main
reason is we don't have a full-fledged quantum gravity theory, and
this makes researcher hard to formulate a scientific statement, then hard
to verify any statement.

In the past, I tried to ask this kind of question and I was toasted by
John Baez in some private emails. So I hope this time I have had asked
in a more acceptable way.

In order to make it short I stop asking here.



"I always wish everyday I woke up, I would ride a high tide of love
gliding through the Universe."------Charles Hui

wrote in message ...
alistair wrote:

[...]
shouldn't we
look at the possibility that some forms of energy do not curve
space-time?

Of course we should. This is a *major* experimental program,
with easily a dozen groups investigating the question of whether
composition affects gravitational fields.

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.

Did you have some other kind of energy in mind?

Steve Carlip

I didn't have some other kind of energy in mind.I do think though,
that given how successful quantum mechanics has been over the
years,the
likelihood of there being 10^120 Joules/m^3 is high.If this energy
doesn't gravitate then perhaps this is because of the unusually high
energy density.
In other words,at very high energy densities space-time might not be
highly curved - good news if you want to stop a singularity from
forming at the beginning of the universe.

greywolf42 wrote:

wrote in message
...

alistair wrote:

[...]
shouldn't we
look at the possibility that some forms of energy do not curve
space-time?

Of course we should. This is a *major* experimental program,
with easily a dozen groups investigating the question of whether
composition affects gravitational fields.

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,

Reference, please.

At high enough electrostatic fields the vacuum sparks. An atomic
nucleus with Z approaching 1/(Fine Structure constant) would cause
pair production at its surface via vacuum decay and spontaneously
lower its atomic number via inverse beta-decay. Magnetic fields have
no such apparent limits.

strong interaction energy,

Reference, please.

Res ipsa loquiter given the mechanism and the Standard Model.

and gravitational binding energy,

Reference, please.

Black holes.

with somewhat weaker limits on kinetic energy and the
energy of the parity-conserving part of the weak interactions.

Reference, please.

How can you hope to converse upon a topic for which you have no
knowledge? Haul your butt over to arXiv.org and look up the basics.

[snip]


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

(alistair) wrote in message . com...
wrote in message ...
alistair wrote:

[...]
shouldn't we
look at the possibility that some forms of energy do not curve
space-time?

Of course we should. This is a *major* experimental program,
with easily a dozen groups investigating the question of whether
composition affects gravitational fields.

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.

Did you have some other kind of energy in mind?

Steve Carlip

I didn't have some other kind of energy in mind.I do think though,
that given how successful quantum mechanics has been over the
years,the
likelihood of there being 10^120 Joules/m^3 is high.If this energy
doesn't gravitate then perhaps this is because of the unusually high
energy density.
In other words,at very high energy densities space-time might not be
highly curved - good news if you want to stop a singularity from
forming at the beginning of the universe.

An energy density of 10^120 Joules per cubic metre (using m = E/c^2
this is 10^103 kg) corresponds to 10^52 kg (approximately the rest
mass of the universe as a whole) in a sphere of radius 10^-17
metres.So if space-time is curved very little, or not at all,at this
energy density,and given that the universe was extremely hot at the
outset,and so would probably have been able to expand with gravity so
weak,I conjecture that a classical calculation - not involving general
relativity - would show that our universe never got smaller than
10^-17 metres, and that such a calculation is valid.

An energy density of 10^120 Joules per cubic metre (using m = E/c^2
this is 10^103 kg) corresponds to 10^52 kg (approximately the rest
mass of the universe as a whole) in a sphere of radius 10^-17
metres.So if space-time is curved very little, or not at all,at this
energy density,and given that the universe was extremely hot at the
outset,and so would probably have been able to expand with gravity so
weak,I conjecture that a classical calculation - not involving general
relativity - would show that our universe never got smaller than
10^-17 metres, and that such a calculation is valid.

Actually, this reasoning is incorrect, for the following 2 reasons
(which are connected).
Firstly, as is laid out in the FAQ, there is no universal definition
of energy in GR, such that it is conserved in integral form. That is,
locally energy is conserved in terms of flows, but integrated over the
universe where the curvature is global, it is not.

Secondly, when the Universe expands by scale factor L, the matter
density falls as L^-3, but the radiation density is Doppler-shifted,
so the radiation energy density scales as L^-4. The result is that in
the early Universe, it was dominated by the radiation energy density.
Which means that the total energy in the universe was much greater
than it is now.

The second argument suggests that it would be a closer approximation
taking the 3K microwave background, converting to an energy density,
and then scaling by L^4 to see when it hits the Planck energy density.
But I don't know whether detailed calculations would actually support
that either. Because the microwave background tells you what happened
when the radiation decoupled from matter as it de-ionised, and it is
much further still to a radiation-dominated universe