Dark Matter/Energy? Just leaky gravity?

[colinha]

According to some variants of String Theory, we are living on a 4 dimensional membrane in a 10 dimensional bulk space.
Gravity appears weak because it is the only force that leaks out of our membrane ( and presumably can interact with other "branes").
Is it therefore possible that the gravitational effects that we put down to dark matter effects are due to another cause.
Could they be due to gravity leaking from nearby multidimensional membranes in the bulk multispace?
Could anyone knowledgeable about string theory please debunk this idea for me?

[jake-the-peg]

I think the problem is that this is a theory based on a speculation.

Any prediction you might care to make to determine whether it is true or false can easily be met with the answer "Well perhaps when gravity permeates and leaks from these other dimensions it doesn't do so like that"

There's therefore no way to test it so it's a bit of a dead end, much like string theory has been so far for much the same reasons.

The computer simulations so far seem to suggest WIMPs (Weakly interacting massive particles) things like neutrinos (which we now know have some very tiny mass). If these models are right the Fermi satellite should be able to show that this is the case.

[fo3nix]

To add to Jake's answer, our understanding of dark matter only comes from requirements from General Relativity anyway; this itself may not be entirely correct.

[another-view]

"According to some variants of String Theory, we are living on a 4 dimensional membrane in a 10 dimensional bulk space. "


I'll have whatever they are smoking please.

[jake-the-peg]

Well I'm not that sure fo3nix.

The dark matter stuff comes from observation not fitting the model sure, but the observations point to a great deal of lumpiness in the distribution of the "dark matter".

I'm sure our understanding of gravity is incomplete but if that lack of understanding were responsible for this I'd not expect to see that, I'd expect to see a smoother supposed distribution.

Now dark energy is another point entirely - that might well show us stuff we don't know about gravity

[rov1200]

As our universe is said to be the shape of a torus or ringed doughnut the dark matter is probably a form of cream.

[fo3nix]

Jake: I agree on the dark energy matter.

My point is simply that String theory tries to predict things after making certain assumptions which have yet to be shown to be true, or close to it.

String theory makes for some good pop science books though :)

[colinha]

I understand that string theory has some problems making testable predictions. However are there any differences that could be observed between "leaky gravity" and dark matter effects?
What will the Fermi satellite observe and will it clarify this?

[jake-the-peg]

Well this is the difficulty gravity leaking into other dimensions is speculative so leaking out again more so.

You can simply make the theory fit any observations because it's not contrained bby any facts.

Simply put there's no way of proving it wrong.

Generally speaking Dark matter theories fall into WIMPS and MACHOs

Wimps are Weakly interacting Massive particles, sub atomic particles like neutrinos that only interact with the weak force so are hard to observe but have a small mass.

MACHOs are MAssive Compact Halo Objects. Things like dead and dying neutron stars and brown dwarfs, things made of normal matter that we just can't see

Most of the smart money seems to be heading towards WIMPs right now.


Fermi is a Gamma ray telescope stuff on it here: http://www.independent.co.uk/news/science/at-l ast-light-is-shed-on-secrets-of-dark-matter-99 8210.html

[WaldoMcFroog]

Have you followed the recent discovery which may suggest the universe is actually a hologram, meaning we're 2D..?

http://www.newscientist.com/article/mg20126911 .300-our-world-may-be-a-giant-hologram.html?fu ll=true

Fascinating stuff, though I won't pretend I quite grasp it all!