Re: Fw: more controversy

[Leigh Palmer <palmer@SFU.CA>]

At 4:04 PM -0800 1/31/00, Jack Uretsky wrote:
> Hi all-
>
> On Mon, 31 Jan 2000, Leigh Palmer wrote:
>
> > > There are papers and proposed experiments on dark matter in the solar
> > > system.  They are easy enough to find.  Has Hewitt done his library
> > > research before proposing his "new" idea?
> >
> > He doesn't realize that any "dark matter" which is attached to light
> > (or lit) matter is no longer dark. "Dark" really means "unobserved".
> > Any matter that sinkes to the center of the Sun or a planet is already
> > accounted for as part of the mass of the object in question. Dark
> > matter isn't necessarily unobservable; it just hasn't been observed
> > yet.
> ______________________snip_________________________
>        I think it's more complicated than that, depending upon the
> distribution and temperature of the dark matter.  If the solar system
> is immersed in a sea of dark matter then the sea correlates only
> roughly with the observed distribution of ordinary hadronic matter.
>        Nucleosynthesis arguments, based on big-bang theory, seem to
> indicate that dark (non-hadronic matter) predominates almost everywhere
> (possibly excepting Kansas).

But there is no dark matter problem in the solar system. It runs quite
nicely on the ephemerides (timetables) that Newtonian physics says it
should, and where it doesn't, GR fixes up the tiny problems*. The best
models take into account all of the known planets and the Sun. Nothing
more is needed, nor has been since the discovery of Neptune, the next
to last dark matter problem the solar system had.

The Galaxy, on the other hand, has a dark matter problem. The speed of
revolution of stars about the galactic center as a function of radial
distance is not well modeled by the gravitational attraction of the
observed stellar population. It would be understandable if a population
of unseen massive objects is present in the halo of the Galaxy. That is
one of the outstanding dark matter problems. There are (at least) two
more on a larger scale, and the largest one is currently in a state of
confusion because of recent (two+ years ago) measurements of galactic
recession velocities and distances using Type Ia supernovae. Many feel
that the largest scale "problem" is no longer a problem because the
slowing, expanding universe picture the dark matter was meant to
explain seems not to be observed!

Of course if the solar system were immersed in a very homogeneous part
of a very, very large sea of nonhadronic matter with which it did not
interact except gravitationally that would be difficult to detect.
Indeed Occam's razor would suggest that we ignore it completely since
it is inconsequential. In any event concentrations of the stuff which
varied over time (as it settles into the centers of planets) would
work against the ideal homogeneity of the medium which is required so
that it should be unobservable, and unless there is a secular drift in
the universal gravitational constant which just cancels the effect,
the planets should speed up!

Solar system mechanics is an arena of high precision observation. The
nonexistence of observable anomalies is very strong evidence that all
significant masses in the system have been identified.

Leigh

*One of these, the anomalous precession of the perihelion of Mercury,
was at first attributed to dark matter, an unseen (but not unnamed)
planet between Mercury and the Sun.

Leigh