# [time 437] Re: [time 436] Re: [time 434] Re: [time 406] Dissipation

Matti Pitkanen (matpitka@pcu.helsinki.fi)
Thu, 8 Jul 1999 08:09:16 +0300 (EET DST)

On Wed, 7 Jul 1999 WDEshleman@aol.com wrote:

>
> > 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. (Mati)
> >
>
> Mati,
>
> The loss to which I refer causes Mercury's perihelion to advance, but is
> present in all of the orbits around our Sun. I don't fully grasp why the
> entire orbit does not decay except that it is relativistic and makes the
> orbit itself orbit. Thus my question.

OK. I think that the orbit does not shrink. One can say the the
approximately ellipse shaped orbit rotates. Therefore dissipation
is not in question: for instance, one can assign conserved energy
and angular momentum to the orbit in the approximation that motion occurs
in spherically symmetric stationary metric.

I thought that the dissipation you were referring to might be from
gravitational radiation and indeed cause gradual decrease of the orbit
radius but this effect must be extremely small.

>
> Calculations have indicated to me that near a black hole, the advance can be
> the entire orbit.

Best,
MP
>
> Sincerely,
>
> Bill Eshleman
> http://members.tripod.com/EshlemanW/
>

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