Re: Wacky new theory about dark matter
Fri, 19 Nov 1999 10:50:48 -0800

Mitchell Porter, <>, writes:
> [...]
> The new twist is:
> 3) The brane we inhabit is folded back on itself in the
> extra dimensions. Electromagnetic and other 'gauge'
> interactions are confined to the interior of the brane,
> but gravity can travel through the 'bulk', the external
> space in which the brane is embedded. The dark matter
> whose gravitational influence we observe in astronomy is
> just ordinary matter in a neighboring fold of the brane:
> less than a millimeter away through the bulk, but perhaps
> trillions of light-years away through the brane!

(I don't have time to read the article right now, some quick comments...)

As far as I know, all galaxies have dark matter, hence this would imply that all galaxies have colocated other-brane partners. Furthermore they all have about the same amount of dark matter, so the colocated partners must be equal in size to the galaxies, despite the fact that galaxies vary considerably in size. Also, either there is only one other brane in the local space, or there are multiple branes but all of them have colocated galaxies.

I wonder if this theory would predict stars would happen to form near each other in the adjacent branes. You start off with a diffuse cloud of gas, and in one brane it gets compressed, perhaps due to a shock wave from a supernova. Now gas in the adjacent brane should be drawn in as well due to the increased gravitational attraction from the other brane. It doesn't feel the shock wave but it does feel the gravitational compression. If the star formed in the first brane were big enough then it might collect enough gas to form a colocated star in the other brane.

Or maybe you could have planets in one brane orbiting an unseen star in the other brane, with perhaps only a very small dwarf in their own brane, far from massive enough to hold the planets.

The two colocated stars would probably have some relative motion, so they would actually be in orbit around each other. This would mean that many stars would be moving in small circles, depending on the mass of their invisible companion. Presumably we could put an upper bounds on the mass of any dark companion of our own sun because of the absence of an unknown component of its motion.

It all seems a little too pat.