Re: Wacky new theory about dark matter
Sat, 20 Nov 1999 16:39:50 -0800

Robereski J. Bradbury,, writes:
> Mitch Porter wrote re:
> >
> > 1) There are extra dimensions whose radius is only a bit less
> > than a millimeter.
> > 2) The reason we don't observe atoms leaking out into the
> > extra space is because ... [snip of things not worth repeating...]
> I believe, I'm paraphrasing Eliezer on another topic, when I say
> [...]
> There is also the problem that there is more dark matter in galactic
> clusters (derived from galactic velocities) than in the galaxies
> themselves (including the galactic dark matter). There is some
> recent evidence that some of the dark matter may be neutral hydrogen,
> but I haven't seen anyone suggest that this explains away the entire problem.

On reading the paper in more detail, it is necessary for them to assume that conditions in the adjacent "brane(s)" are very different from here. Specifically the matter density must be lower, so that galaxies and clusters have not yet formed. If they did, we would expect to see see missing mass within globular clusters, and it is not present there.

On the other hand the density can't be too low or there wouldn't be enough to explain the missing mass.

There is a magic value of about 1/4 the local density that looks like it would work, but it is pretty ad hoc to start juggling parameters like that. It's much simpler to assume that the universe is much the same everywhere.