From: Brett Holman <b.holman.nul>
Date: Thu, 22 Jul 2004 23:12:34 +1000
Fwd Date: Thu, 22 Jul 2004 10:21:21 -0400
Subject: Re: Could We Really Be At The Center of The


>From: Terry W. Colvin <fortean1.nul>
>To: UFO UpDates - Toronto <ufoupdates.nul>
>Date: Mon, 12 Jul 2004 19:57:34 -0700
>Subject: Could We Really Be At The Center of The Universe?

>Could We _Really_ Be At The Center of The Universe?

>Newly published data from the Sloan Digital Sky Survey (SDSS),
>led by Max Tegmark of the University of Pennsylvania, shows that
>our galaxy is centered on a great concentric distribution of
>galaxies.

>The foregoing quotation is based upon an ambitious astronomical
>survey effort involving more than 200 astronomers at 13
>institutions. So far, over 200,000 galaxies have been mapped.
>The accompanying figure is a two-dimensional, wedge-shaped slice
>of this cosmic map. It pinpoints approximately 33,500
>galaxies. ...Note the rough concentricity about the earth.

>Source: http://www.sdss.org/news/releases/galaxy_zoom.jpg

>The roughly concentric distribution of galaxies about the point
>of the wedge, which is earth, is inescapable. Also readily
>apparent is a decrease in galaxy density with increasing
>distance from the earth.

The latter is easily explained: the further out you look, the
fainter the galaxies will be. So for any given sensitivity (ie
limiting magnitude), and all else being equal, a redshift survey
will see a lower space density of galaxies at greater distances.

Incidentally, selection effects like these are why one shouldn't
attempt to overturn established cosmologies based upon a single
redshift survey map of a very limited slice of the Universe in a
single plane.

>The implications of the SDSS work so far is highly unsettling
>for two reasons:

>1 - The Cosmological Principle, which demands that the universe
>be homogeneous with no favored center, is violated.

This is to misunderstand the point of the cosmological principle
- it's not intended to be an iron law - that's why it's a
"principle". It's always been clear that the principle applies
only on very large scales, if at all (otherwise all the matter
in the universe would be evenly smeared out across the Universe,
and you wouldn't get little clumps like planets and people) -
 and even then it is only an approximation. We have been aware
of clusters and superclusters of galaxies for many decades, and
of bigger structures (walls, etc) for one or two. The point is
that these should average out on the largest scales. But if
there _is_ significant inhomogeneity or anisotropy, then that's
very interesting too, because it allows us to test different
cosmologies which make predictions about these sorts of things.
That the cosmological principle's "demands" are not met simply
means that simplistic cosmologies won't do, not that we have
misunderstood redshifts etc.

And, for what it's worth, the SDSS data taken as a whole and in
conjunction with other survey results _does_ tend to confirm the
cosmological principle. The following page is the press release
which included the galaxy map in question:

http://www.sdss.org/news/releases/20031028.powerspectrum.html

It also includes a plot of density fluctuations versus scale,
and the SDSS data clearly indicates that the Universe gets
smoother at larger scales.

>2 - The earth _does_ seem to be at center of the observable
>universe contrary to the adamant philosophical declaration of
>science that the earth and its cargo are insignificant in the
>Grand Scheme of Things - whatever _that_ is!

Of course we are at the the center of the _observable_ Universe.
Where else would we be? But the observable Universe is not the
entire Universe, nor do we see everything clearly even within
the observable Universe. That's why astronomers assume our
position within the Universe is unprivileged; we've learnt the
value of this the hard way (Ptolemy onwards).

As for this supposed "declaration of science that the earth and
its cargo are insignificant in the Grand Scheme of Things", I'm
not sure why being at some supposed center of the Universe would
make us any more important. Does the value of Hamlet decrease
with our distance from the center of the Universe?

One other point.....

>(Hartnett, John; "New Evidence: We Really Are at the Centre of
>the Universe," _TJ_, 18:9, no. 1, 2004. TJ = Technical Journal.)

"Technical Journal" sounds innocent enough, but the unwary should
note that this is a creationist magazine.

http://www.answersingenesis.org/home/area/magazines/technical.asp

http://www.answersingenesis.org/home/area/magazines/tj/TJ_v18n1.asp
--
________________________________________________________________

Brett Holman            	         b.holman.nul
IT Manager, School of Earth Sciences _ IT Support, Astrophysics Group
The University of Melbourne, Victoria 3010, AUSTRALIA _ +61 3 8344 7307
http://astro.ph.unimelb.edu.au/~bholman/ _ Remember: KLAATU BARADA NIKTO