Matti Pitkanen (matpitka@pcu.helsinki.fi)
Wed, 7 Jul 1999 10:03:43 +0300 (EET DST)
On Wed, 7 Jul 1999 WDEshleman@aol.com wrote:
> Time Group,
>
> This, my first post, was inspired by the discussion of "dissipation". I
> enjoyed reading a great many posts after being away from my computer for a
> time.
>
> My question is: Since Einstein tells us that all of the orbits around our
> Sun loose about 28 kilometers (6*pi*G*M/c^2) of orbit per orbit due to GR,
> then could this loss of length be interpreted as "dissipation" of orbital
> angular momentum.
I am not sure what you mean with the effect the loss of
orbit... Mass point in Schwartscildt metric has stationary orbit.
If orbits are shrinking with this velocity and we assume that
Earth has orbited for at least 10^9 years one would have
that the reduction of orbit, if constant in time, would have been
about 10^11 km. This would be larger than the recent radius of
Earth's orbit! Something goes wrong!
Could you give some detail on what you mean.
In any case, all dissipative effects enter as modifications
of the basic field equations and involve parameters like coefficient
of viscosity, friction, various conductivities, etc... In General
Relativity this would mean that one adds dissipative terms into energy
momentum tensor T_ij. From my Landau-Lifcshitz I remember that in
nonrelativistic limit simplest dissipative term is something like
eta*( partial_jv_i+partial_jv_i)
for fluid. Dissipative terms are typically linear in velocity
since this is simplest term leading to the breaking of time reversal
invariance.
The covariant generalization of this term would enters to the
the energy momentum tensor and affect the geometry of spacetime
replacing it with effective 'almost envelope' for the sequence
of nondissipative spacetimes .
>
> Sincerely,
>
> Bill Eshleman
> http://members.tripod.com.EshlemanW/
>
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