On Thu, 5 Aug 2010, Shane Mage wrote:
> Just to point out that the "dark matter" is not observed, merely a
> computer-generated artefact reflecting an arbitrary mathematical
> construction to which nothing in physical reality corresponds.
Not nothing. It corresponds to very larage discrepencies that shouldn't be there in the pure big bang model. Adding "inflation" -- an extra booster stage in the first second of the universe's existence -- fixed some of it. Then we added dark matter. Then dark energy.
So it fills a need. But there is something to be said for the vague feeling that these first second add-ons are beginning to accumulate like pre-copernican circles and maybe there's something fundamentally wrong at the bottom. Which perhaps is what you are getting at with the arbitrariness idea.
FWIW, there is an alternative theory, called the endless universe theory, that gets rid of dark matter:
http://www.amazon.com/Endless-Universe-Beyond-Big-Bang/dp/0385509642
It posits that big bangs happen over and over, each time creating a new membrane between the old and new universes through which nothing can pass except gravity. And that what is now attributed to dark matter and energy is actually the gravitational pull of stuff on the other side of the brane.
Michael