Re: Branes and gravity

George W Harris wrote:

On Mon, 20 Oct 2008 21:40:27 GMT, throopw@xxxxxxxxx (Wayne Throop)
wrote:
: Erik Max Francis <max@xxxxxxxxxxx>
: It seems to me that would give you the appearance of a uniform
: distribution of "dark matter" throughout your universe, not halos like
: we see.

Well, dark matter is still interacting with itself minimally via
gravity, but ... the fact that inter-brane stuff is attenuated so
sharply... I'm not sure that it would clump the way we see it. Hrm.

That question becomes how matter in a universe with only gravitation would behave. Would it clump? If so, so would dark matter (that is, matter in all branes would tend to clump in the same places).

Again, it seems to me this requires the branes be fixed relative to each other (another if) and that things are tweaked just such that the branes have significant influence to encourage clumping but not too much to cause everything to completely collapse on itself and not too little so that they don't interact (massively more ifs). The different branes have to encourage each other just so but not too much and they all have to do it in concert or it ends up being a muddle of uniform mass density everywhere which we don't observe. Guh?

In other words, it's another perfect example of the general problem with string theory -- it is very intriguing and has great promise in the imagination, but when it comes down to coming up with a testable theory, all these different tweakable parameters are a massive liability, not a benefit. The fact that it can explain pretty much anything you can imagine means, ironically, that it explains very little.

--
Erik Max Francis && max@xxxxxxxxxxx && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M erikmaxfrancis
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