Is it a universe or something?

Kind of. It's the extension of strings to a 3rd dimension, effectively making it a membrane. The theory does say that entire universes can be contained on a brane, but I'm not sure if it's necessary. M-theory certainly is whacky.

Branes are a generalization of strings in M-Theory, which is the superset of the different string theories.

While the string theories dealt with just, well, strings, M-Theory adds branes in all dimensions. A brane with m dimensions is called a m-brane. A 2-brane is a surface, a 3-brane is a volume and so on. 1-branes are the strings of the previous string theories.

Branes aren't universes as such, they are just the elementary components in M-Theory just as strings were before. However there were some features of open ended strings (i.e. not closed loops) found in the theory that make them stick to other branes with both ends. In the still rather hypothetical brane cosmology the universe is a 3-brane and everything in it is open ended strings that are stuck to it. That's why we don't experience the additional dimensions.

I think there is an explanation for the weakness of gravity using that model: Gravitons are closed strings, so they can escape our universe brane and spread in all dimensions unlike the other forces. Therefore we see only a tiny fraction of gravity and it appears very weak.

So it isnt a universe? or sometimes it might be and sometimes it might not be...are these so called "branes" what separates universes from each other?

As I understand it, branes are a dimensional boundary layer of sorts. Three-dimensional space is a three-brane moving through time. Branes can be described simply as boundary conditions in perturbative string theory.

Except, of course, since physicists don't take themselves too seriously, they usually use the variable p for the number of dimensions. So, yes, a brane with p dimensions really is usually called a p-brane.

don't take this the wrong way, but m theory doesn't seem a trivial enough area to give an answer to your question that non-physics types understand. Its easy enough to memorize a definition but understanding (if there is any) would surely not come until you'd become an expert in quantum physics and string theory.

Happy to stand corrected if anyone has a really easy succinct definition

Sometimes I wonder how much I really KNOW about physics ... i.e. when pressed could I model or solve some real life problem / reach meaningful answers using this knowledge

Like relativity for instance, I'm sure there's a few here, but generally I would consider it an extremely rare thing for somebody to actually understand general relativity enough to solve a problem using it.

Anyway, got carried off on my own little tangent there ..

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There are many theories – singularity, vacuum energy, membrane…All of them needs a special property of the space. The membrane came not from nothing – it came from the space structure. We know , our space is discrete with special structure – it is our existed space. This existed space allows to describe a particles by strings or waves. If there would be nothing we have no information at all.
The string theory describe the particles good, but do not shows how the particles come to being. We do not need such a miraculous beginning of our observable Universe. It exist just by the collection of the information in the eternal space.
A discussion about this problem – http://bencieszyn.w.interia.pl/antim...atter-ang.html

The amazing thing is that all these cosmological theories come about after a "bunch'a folks" (to quote a certain president) have spent years at their desks pouring though volumes of arcane and complex mathematical theory, tweaking a variable here, substituting a term there, extending and expanding as they go. They never look through a telescope or even go near an observatory -- it's all done with pen and paper (and PCs these days, I guess).

What *really* boggles my mind is that time and again from these backroom scribblings they have made predictions that have been verified by astronomers and physists once they have been told where to point their instruments.

Yes, we have a long way to go, but the future and frontiers of cosmology are as much buried in the dusty dishevelled offices of our brightest minds as they are out there in space.

Mike

I find Vaccuum Energy fascinating. Isn't it theorized that one could actually create a singularity using vaccuum Energy?

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by vacuum fluctuations?

so anyways...is our universe some kind of brane?

If I recall correctly, the universe was created by colliding branes. I think the universe is located within the brane (or on the surface of the brane?).

Platinum: here is something cool to look at which describes the process.

Note: you will need RealPlayer and PowerPoint to view the slides/presentation.

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"Imagination will often carry us to worlds that never were. But without it we go nowhere." - Carl Sagan

So in each brane there will be universes?

Well, I'm not entirely sure. When the branes collide, they don't do so uniformely. I'm not sure if this means that the universe comes into existence at different area's of the brane, or if the collisions each produce their own universe. In "brane" theory, there can be multiple universes, but they may be within different branes (an infinite number of branes--so infinite number of universes). We would never know this, of course, but the idea is interesting.

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"Imagination will often carry us to worlds that never were. But without it we go nowhere." - Carl Sagan

Yes it is, when people say branes they usually include multiple universes and dimensions

some good info, very strange and unique ideas... its very good and I like the details but its kind of nuts in a way that makes the madness Quantum-Mechanics look a lot more rational, this new theory is way out there. Perhaps it has some mistakes, any other links on these branes or M-theory strings or whatever you call them ?

Branes 8-[

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Astronomy is looking up... :)

Offical String Theory site.