Theory of Everything Channel 4 last night (Sunday)

There seemed to me to be one rather obvious cosmological implication
that didn't get mentioned in this week's programme.

[For those that didn't see the programme, one of the things that they
postulated is that our universe might be a 4-dimensional "membrane" in
an 11-dimensional space. They said that gravity could be so weak
compared to the other fundamental forces because the particles that
carry gravity are closed loops of string and can travel off the
membrane, whereas the other force carriers are open-ended strings with
their ends caught in the membrane. They also suggested the idea the it
might be possible to communicate with beings in a parallel membrane
universe via gravity waves.]

But if gravitons can travel between parallel universes, that surely
gives a really neat explanation for dark matter. It's just that there
are other membranes close to ours which contain matter. We feel the
gravity from those universes and they feel the gravity from ours, so
matter in all the nearby universes tends to pool in corresponding
locations. Their equivalents of galaxies are in the same places as our
galaxies, just offset somewhat in the higher dimensions. As far as we
are concerned the matter in adjacent universes is dark because photons
are unable to cross from their membrane to ours.

The laws of physics in these adjacent membranes could be somewhat
different from our own, with slightly different values for the 20-odd
fundamental constants that define how things work. This could lead to
the matter in their galaxies tending to gather into slightly different
shapes than our own, which would be why dark matter appears to be
concentrated in the halo regions of our galaxies. Or perhaps there's
just lots of such universes and the planes of their spiral galaxies just
have different orientations, so that much of the extra mass is off our
galactic plane.

If the parallel membranes were very close, and their laws of physics
allowed their matter to form into stars, then our attempts to detect
MACHO type dark matter would have observed gravitational lensing caused
by such off-membrane objects. So the membranes would have to be
displaced from ours by a few light years in some dimension so that the
gravitational lensing effect is smudged out, or it could be that a
slight difference in their value of, say, the charge on the electron
prevents star formation in their universe.

--
Mike Williams
Gentleman of Leisure

"Mike Williams" wrote in message
...

Snip
But if gravitons can travel between parallel universes, that surely
gives a really neat explanation for dark matter.
Snip

--
Mike Williams
Gentleman of Leisure

I remember the same idea postulated in the issue of Scientific American in
which I first read the theory of gravitons not being bound to the 'brane
like the other force particles. Can't remember which issue, but memory seems
to place it about 2-3 years ago. It was certainly after I read "The Elegant
Universe" because I don't recall seeing it suggested in there.

"Iain A. Sutherland" wrote in
message ...

"Mike Williams" wrote in message
...

Snip
But if gravitons can travel between parallel universes, that surely
gives a really neat explanation for dark matter.
Snip

--
Mike Williams
Gentleman of Leisure

I remember the same idea postulated in the issue of Scientific American in
which I first read the theory of gravitons not being bound to the 'brane
like the other force particles. Can't remember which issue, but memory
seems
to place it about 2-3 years ago. It was certainly after I read "The
Elegant
Universe" because I don't recall seeing it suggested in there.


After a search on the Scientific American website I think that this is the
article I remember, but can't confirm since I can't find the issue, probably
lent it to someone :-(

The Universe's Unseen Dimensions; August 2000; by Nima Arkani-Hamed, Savas
Dimopoulos, Georgi Dvali, side bar by Graham P. Collins; 8 page(s)
The visible universe could lie on a membrane floating within a
higher-dimensional space. The extra dimensions would help unify the forces
of nature and could contain parallel universes

Wasn't it Iain A. Sutherland who wrote:

"Mike Williams" wrote in message
...

Snip
But if gravitons can travel between parallel universes, that surely
gives a really neat explanation for dark matter.
Snip

--
Mike Williams
Gentleman of Leisure

I remember the same idea postulated in the issue of Scientific American in
which I first read the theory of gravitons not being bound to the 'brane
like the other force particles. Can't remember which issue, but memory seems
to place it about 2-3 years ago. It was certainly after I read "The Elegant
Universe" because I don't recall seeing it suggested in there.

I'd never heard of the idea. Cosmologists only seem to talk about the
WIMP, MACHO and dark-energy theories, never about leaky m-brane theory.

--
Mike Williams
Gentleman of Leisure

"Mike Williams" wrote in message
...

I'd never heard of the idea. Cosmologists only seem to talk about the
WIMP, MACHO and dark-energy theories, never about leaky m-brane theory.

It was also mentioned on Horizon: Parallel Universes (14/02/2002) in which
Michio Kaku revealed himself to be a skating puff.

On Tue, 18 Nov 2003 19:16:26 GMT, "Iain A. Sutherland"
wrote:


"Mike Williams" wrote in message
...

Snip
But if gravitons can travel between parallel universes, that surely
gives a really neat explanation for dark matter.
Snip

--
Mike Williams
Gentleman of Leisure

I remember the same idea postulated in the issue of Scientific American in
which I first read the theory of gravitons not being bound to the 'brane
like the other force particles. Can't remember which issue, but memory seems
to place it about 2-3 years ago. It was certainly after I read "The Elegant
Universe" because I don't recall seeing it suggested in there.

I can't recall it either, but the idea certainly makes sense. Have there
been any relatively un-mathematical books published about cosmology /
string theory since Greene's, and Hawking's "Universe in a Nutshell"?

--

wrmst rgrds
Robin Bignall

Quiet part of Hertfordshire
England