Re: black holes




Happy Hippy wrote:
> Mark Martin wrote:
> > Happy Hippy wrote:
> >
> >
> >>Where does the energy come from?
> >
> >
> > The energy for what?
> >
> > -Mark Martin
> >
> gravity

Well first, gravity doesn't "use up" energy. Gravitation is between
pairs of bodies. What work is apparently done on one is balanced by
that done on the other. The total energy in the Universe remains
unchanged.

But let's cut you some slack and play it by your rules for just a
minute. You say that gravity uses up energy, so you ask where a black
hole could possibly get that energy. Well... asking where a black hole
gets such energy is like asking where *any* gravitating object gets
that energy. You've no doubt that Earth has a gravity field do you? Or
the Moon? Or anything? You may insist that gravity is a consumer of
energy and that we don't know the origin of that energy. But that
doesn't change the fact that masses DO gravitate, observably,
measurably, and that the kinematics of objects subject to gravitation
is well understood. Eclipses are rountinely and reliably forecast by
using such well understood kinematics. The behavior of spacecraft are
similarly very precisely understood in the same way. So regardless that
you insist that gravity is a one-way eater of energy, the implications
of gravity are established facts. And by extension, the properties of
black holes can be consistently extrapolated.

-Mark Martin

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