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Posted by Ken S. Tucker on December 16, 2006, 2:28 pm
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Henry Spencer wrote:
> >>That's right. Relative to a stationary earth, the whole
> >>universe is in motion around us.
> >
> >...You can use that as a mathematical model, but there is observational
> >evidence that it isn't true.
> >The Earth is an oblate spheroid, so it is revolving, and the universe is
> >not rotating (relative to what? I don't begin to understand this :-)
>
> Unfortunately, if you dig deep enough into general relativity, all that
> observational evidence goes away -- a rotating universe would create a
> gravitodynamic force (one of several clumsy terms sometimes used to denote
> a type of force related to gravity but outside Newtonian physics) which
> would cause exactly the same oblateness.
>
> In fact, in general relativity there is no distinction between the two
> cases: relative rotation of the Earth and the (immensely more massive)
> universe is all that matters. Newtonian physics made all uniform linear
> motion relative, so one uniformly-moving reference frame was as good as
> another, but conceded that acceleration (including circular motion, which
> involves continuous acceleration toward a center) was somehow absolute.
> GR makes acceleration, too, strictly relative, with no preferred reference
> frame (but rather more complex math).
Studying piezo electrical effects
http://en.wikipedia.org/wiki/Piezoelectric
is interesting in GR and bridges to unified
field theory.
The mass and thus gravity of the deformed
crystal increases by either pressure or
electrical potential, our physical examples
are the electronic weigh scale and the
common audio alarm in smoke detectors.
For purposes of gravitation, the two are
combined in the "stress energy tensor" in
GR and can obviously oscillate.
The math is complicated because eventually
pressure is a quantum effect, like counting,
while classical GR theory is differential,
founded on a continuum evolved from Newton.
It's an easy "hands-on" apparatus to demo
that ominous and intimidating,
"Quantum Unified Field Theory".
When pressure is applied a current flows.
If the pressure oscillates so does the
output current.
When an oscillating current is applied
sound waves are outputted.
Regards
Ken S. Tucker
kxsxt
> --
> spsystems.net is temporarily off the air; | Henry Spencer
> mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net
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