Assumptions on M-Theory Membranes

[rrw4rusty]

Hi,

 

On many of the videos I've watched they show waving sheets hanging next to each other or, slices of bread, or spheres to represent branes. They also show different people or worlds or universes on each 'slice of bread' or 'wavy sheet' brane. In and around all of this there is talk of 'higher dimensions'. Also 'wavy sheets' branes clash together and bingo, big bang. I have come away with certain assumptions about brane theory I wish to confirm and some confusion I wish to clarify.

 

I hate to do a post with multiple questions, just quote this and confirm or refute what you know or believe.

 

* All the things we can detect or interact with are on the same brane, yes?

 

* The videos also say that branes can be very large... as large as universes, but also, very thin... is this correct (I realized that there are many types)?

 

* The 'higher' dimensions are the extra 7 believed to be curled up at the string level and have nothing to do with branes (this is, a brane is not considered a 'dimension')?

 

 

* The videos seem to imply that a brane equals a universe... in fact a 'parallel universe' (all those parallel wavy sheets, a world on each one). But the phrase 'parallel universe', which is also used in the Many Worlds Interpretation of Quantum Mechanics, does not seem to be used with branes. Confusion... what are branes? Just... branes?

 

* If a brane is a universe and two branes clashing together create big bangs (i.e. another universe) does this mean that another brane is created????

 

Thanks for any help you can offer this stumbling old county sci-fi writer!

 

Rusty

[ajb]

 

* All the things we can detect or interact with are on the same brane, yes?

 

Strings do not need to start and end on the same brane. I think realistic models require a stack of branes. Or at least, in order to build gauge theories you need stacks of branes.

 

You also have the possibility of things on different branes interacting gravitationally. Closed strings can propagate in the bulk.

 

* The videos also say that branes can be very large... as large as universes, but also, very thin... is this correct (I realized that there are many types)?

 

Branes can be infinite in size and are of various dimensions depending on the exact theory you are studying.

 

* The 'higher' dimensions are the extra 7 believed to be curled up at the string level and have nothing to do with branes (this is, a brane is not considered a 'dimension')?

 

In superstring theory we have 10 dimensions. The question is why do we see only 4?

 

One possibility is that the other 6 are curled up very tightly (plus some technical conditions).

 

The other is that our world is "stuck on a brane". The Randall–Sundrum models.

 

I do not see that these two ideas are necessarily mutually exclusive. That is, why can't some be curled up and we still live on a brane. I am not an expert in this field, so I doubt I can say much more on "hybrid models".

 

 

* The videos seem to imply that a brane equals a universe... in fact a 'parallel universe' (all those parallel wavy sheets, a world on each one). But the phrase 'parallel universe', which is also used in the Many Worlds Interpretation of Quantum Mechanics, does not seem to be used with branes. Confusion... what are branes? Just... branes?

 

I would view the idea of many branes in the bulk as a slightly different notion as the many-worlds in quantum mechanics.

 

I do not see how the two are directly related.

 

* If a brane is a universe and two branes clashing together create big bangs (i.e. another universe) does this mean that another brane is created????

 

As far as I can tell we pretty much know everything about a classical non-interacting brane.

 

The problems start when we consider interactions and quantisation. Right now these are research topics. Some deep mathematics such as higher categories are being applied to these questions.

 

I doubt I have answered all your questions very well, but I hope I have been of some help.

[rrw4rusty]

Hi ajb!

 

Thank you for replying! As always, it was helpful!

 

Strings do not need to start and end on the same brane. I think realistic models require a stack of branes. Or at least, in order to build gauge theories you need stacks of branes.

For myself and for the purpose of my book, string theory has become M-Theory. There are many theories and I wish I had time to read them all but I don't right now. Yes to ‘a stack of branes’.

 

You also have the possibility of things on different branes interacting gravitationally. Closed strings can propagate in the bulk.

I very much depend on this element.

 

Branes can be infinite in size and are of various dimensions depending on the exact theory you are studying.

Agreed… I think. When you say dimensions, do you mean like the basic 4 we see; up, down, side to side, etc.

 

In superstring theory we have 10 dimensions. The question is why do we see only 4?

As mentioned, I'm using M-Theory which has 11 dimensions (I'm pretty sure anyway). I'm making an assumption that all the extras beyond the basic 4 are thought to be of the type that are tightly curled up at the string level (size). I know that this is just one idea about where they are, I guess I mean that the 11th one M-Theory adds is no different from the other extras.

 

I do not see that these two ideas are necessarily mutually exclusive. That is, why can't some be curled up and we still live on a brane. I am not an expert in this field, so I doubt I can say much more on "hybrid models".

Absolutely agreed. Furthermore I view the ‘Many Worlds’ theory as being at the ‘particle level’ and branes to be at the string level. That is to say that parallel universes (of many worlds) are a super set of branes (which are a subset of particle level items such as parallel universes). Each parallel universe would contain its own set of branes, strings, closed loop strings, etc.

 

I would view the idea of many branes in the bulk as a slightly different notion as the many-worlds in quantum mechanics. I do not see how the two are directly related.

Agreed.

 

As far as I can tell we pretty much know everything about a classical non-interacting brane.

That's a bold statement but then I only know of branes from M-Theory and I really don't know what a classical non-interacting brane is. It may not be important to my book.

 

I doubt I have answered all your questions very well, but I hope I have been of some help.

Definitely. The way I'm using certain areas of M-Theory (as well as quantum mechanics and, relationships to dark matter and energy) is summarized in the post located here:

 

http://www.scienceforums.net/forum/showthread.php?t=45594

 

I'm still banging it into shape (pun intended) but my deadline looms so I'm trying to get feedback on this. Perhaps, lol, it is maddening or distasteful for you to read sci-fi 'made up' ideas. I (of course) believe that mine are pretty... logical, even good. However, my quantum mechanics is about 15 years old and I've only been cramming on string/m-theory for a few months. Anyway, if you can provide feedback it would be greatly appreciated. Just keep in mind that this has an M-Theory focus and a light weighted, 'every reader' target and... that its sci-fi.

 

BTW, as far as I can tell, among other things, M-Theory involves: combining the 5 string theories; and, (not perhaps not exclusively) branes, open and closed loop strings, the idea that open strings are (or, maybe) attached to branes, that gravitons ‘wonder’ between branes, when branes collide = big bang.

 

Thanks!

Rusty

[ajb]

There are 5 string theories, [math]\textnormal{Type I}[/math], [math]\textnormal{Type IIA}[/math], [math]\textnormal{Type IIB}[/math], [math]\textnormal{SO(32)}[/math] and [math]\textnormal{E}_{8}\times \textnormal{E}_{8}[/math].

 

The importance of branes in string theory is that they allow for explicit realisations of nonperturbative string dualities. That is there are transformations that relate the five 10-dimensional string theories to each other.

 

The 5 string theories are then understood to be perturbative expansions of some underlying theory around 5 different vacua. This theory is called M-theory.

 

What is known about M-theory is that it is 11 dimensional and as well as string it admits other nonpurterbative extended excitations, these are the p-branes.

 

It is also known that the low energy limit of M-theory is an 11 dimensional supergravity theory (with some branes).

 

Amongst these branes, the D-branes are the very important. That is branes whose quantum dynamics is governed by the theory of open stings that are constrained to start and end on them.

 

Right now, not very much is really known about M-theory. It is difficult to understand how p-branes interact.

 

I believe quite a lot is known about M2 branes. There is a very interesting field theory description of coincident M2 branes in which the fields take there values in a Filippov 3-algebra. That is a generalisation of a Lie algebra, but this time the bracket takes 3 elements not 2. This is the Bagger-Lambert-Gustavsson theory. This is very interesting to me as I am currently working with another generalisation of a Lie algebra, which can find an application in string field theory and point particle quantum field theory.

[Tugrul]

As mentioned, I'm using M-Theory which has 11 dimensions (I'm pretty sure anyway). I'm making an assumption that all the extras beyond the basic 4 are thought to be of the type that are tightly curled up at the string level (size). I know that this is just one idea about where they are, I guess I mean that the 11th one M-Theory adds is no different from the other extras.

 

There is a video on you tube incorparating paralell universes and describing the 10 dimensions with pictures and stuff i will give a link, it might not be correct.

 

[ajb]

As mentioned, I'm using M-Theory which has 11 dimensions (I'm pretty sure anyway)...

 

What are you trying to do in M-theory?

[rrw4rusty]

As mentioned, I'm using M-Theory which has 11 dimensions (I'm pretty sure anyway). I'm making an assumption that all the extras beyond the basic 4 are thought to be of the type that are tightly curled up at the string level (size). I know that this is just one idea about where they are, I guess I mean that the 11th one M-Theory adds is no different from the other extras.

 

There is a video on you tube incorparating paralell universes and describing the 10 dimensions with pictures and stuff i will give a link, it might not be correct.

 

 

This is not how I imagined the extra dimensions to be and this is the first time I've heard anything like this. If correct, it begs the question, what is the 11th dimension of M-Theory for the video shows how we run out of dimensions at 10?

 

Thanks,

Rusty

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What are you trying to do in M-theory?

 

 

I meant that the questions in my OP are related to M-Theory. I'm trying to understand M-Theory a little better without involving the 'math'. I understand that it is possible that some aspects of the theory need the 'math' for understanding. Also that understanding other theories is needed in order to understand M-Theory. And finally, that almost no one completely understands M-Theory.

 

I just want progress as far as possible.

 

r

[ajb]

And finally, that almost no one completely understands M-Theory.

 

I do not think anyone knows what M-theory is. Apart from the sting theories and 11-d supergravity not much more is known.

 

For example there has not yet been found the Lagrangian for M-theory, if it exists. The closest thing I know of is the work of Bagger-Lambert-Gustavsson.

[rrw4rusty]

I do not think anyone knows what M-theory is. Apart from the sting theories and 11-d supergravity not much more is known.

 

For example there has not yet been found the Lagrangian for M-theory, if it exists. The closest thing I know of is the work of Bagger-Lambert-Gustavsson.

 

Not even Edward Witten?

[ajb]

Not even Edward Witten?

 

Not even Witten.

 

I get the impression as progress in M-theory was slow interest slowed down. But with the relatively recent results of Bagger-Lambert-Gustavsson (and now many others) interest will increase again.