# Branes and Worlds

Although I read many pop-sci books (Elegant Universe, Warped Passages, etc.). Imagining branes is still a bit over my head. Some questions to confirm what I know.

1. I know that in a 3-brane, it just represents the 3 dimension as flat for purposes of giving better illustrations in a limited 3d paper, right or is a brane really flat?

2. In a 3-Brane, is there only 3 spatial dimension or does it include the 6 compactified dimension too? If so, then a 3 brane is actually 10 dimension (3 extended, 6 compactified)?

3. Before M-theory. All particles only exhibit 10D (9 dimensions + 1D time). After M-theory with the addition of another dimension. Brane worlds begin to exist. Is the 11th dimension compactified too or infinite in extent? But the only way you can put 2 branes side by side is by an infinite 11th dimension. It's like our 3D world. Supposed we are only 2D and flat with only up-down and left-time movement. When the third dimension of depth occurs and we are still trap in 2D (signifying the strings trapped on a brane), we can have endless stack of 2D planes in the 3D world. Is this the case with 11th dimension too such that you can put an endless branes stack on it? Does each stack occupy the entire plane or can you put two stack side by side, for example.. one inch away from you.. you can see two branes side by side or must one of them always be more or less than 1 inch? Btw.. all this only occurs if the 11th dimension is infinite, or is it compactified?

4. In Brian Green PBS Elegant Universe. He showed Manhattan curving into U shape and a wormhole connecting the opposite ends. Can you bend a brane this way too? Supposed you can bend a brane and the gravitons pass from one end to end (say the brane is one light year distant). Then doesn't it violate special relativity because the gravitons can reach it before light use the usual brane path? Maybe quantum entanglement or Bell's Theorem at 1 light year distance use such massless bosons and brane wormless to convey the information?

5. In the concept of where our 3-brane is floating in larger multidimensional universe. Is 11 dimensions still the limit or could there be more than 11 dimensions of M-theory? But how could this be when M-theory dimensions is only 11. Also this assume the 11th dimension is infinite in extent? Also could you add more than 11 dimension and still make the theory consistent?

That's all for now. Thanks!

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bapowell
2. In a 3-Brane, is there only 3 spatial dimension or does it include the 6 compactified dimension too? If so, then a 3 brane is actually 10 dimension (3 extended, 6 compactified)?
A p-brane is a p-dimensional object. Some of the p-dimensions could be compactified. For example, our universe could be a 9-brane, with 3 non-compact dimensions and 6 of the branes dimensions 'wrapped' around the compact dimensions.

3. Before M-theory. All particles only exhibit 10D (9 dimensions + 1D time). After M-theory with the addition of another dimension. Brane worlds begin to exist. Is the 11th dimension compactified too or infinite in extent?
Branes exist even in 10D string theory. In the original Horava-Witten formulation of M-theory, the 11th dimension is compactified on an orbifold (essentially a line segment.) Two branes exist at the orbifold fixed points (the ends of the line segment). This setup motivated some of the first cosmological brane world models (like the ekpyrotic scenario), but other brane world models exist happily in 10D string theory.

But the only way you can put 2 branes side by side is by an infinite 11th dimension. It's like our 3D world. Supposed we are only 2D and flat with only up-down and left-time movement. When the third dimension of depth occurs and we are still trap in 2D (signifying the strings trapped on a brane), we can have endless stack of 2D planes in the 3D world. Is this the case with 11th dimension too such that you can put an endless branes stack on it?
D-branes do have some thickness, typically set by the Planck scale or so.

Does each stack occupy the entire plane or can you put two stack side by side, for example.. one inch away from you.. you can see two branes side by side or must one of them always be more or less than 1 inch?
That depends on the geometry. The branes could not be side-by-side along the non-compact dimensions, because in these directions the branes extend to infinity.

Then doesn't it violate special relativity because the gravitons can reach it before light use the usual brane path?
Wormholes are general relativistic phenomena....you should not be mixing special relativity and wormholes. That's dangerous!

5. In the concept of where our 3-brane is floating in larger multidimensional universe. Is 11 dimensions still the limit or could there be more than 11 dimensions of M-theory? But how could this be when M-theory dimensions is only 11. Also this assume the 11th dimension is infinite in extent? Also could you add more than 11 dimension and still make the theory consistent?
M-theory is only consistent in 11-D, although there are so-called 'non-critical' formulations that can exist in other dimensions. F-theory is a 12-D construction (with two time dimensions) that has also been studied extensively.

A p-brane is a p-dimensional object. Some of the p-dimensions could be compactified. For example, our universe could be a 9-brane, with 3 non-compact dimensions and 6 of the branes dimensions 'wrapped' around the compact dimensions.
Familiar with Lisa Randall Warped Passages? She used in her modelling the 5th dimension as the bulk while the brane is 4D. Does this illustration encompass the compact dimensions already? If not, how could she demonstrate the string confined to the brane when compact dimensions are not even used. I thought 6D compact dimensions are a requirement in string theory.

Branes exist even in 10D string theory. In the original Horava-Witten formulation of M-theory, the 11th dimension is compactified on an orbifold (essentially a line segment.) Two branes exist at the orbifold fixed points (the ends of the line segment). This setup motivated some of the first cosmological brane world models (like the ekpyrotic scenario), but other brane world models exist happily in 10D string theory.
I don't know what video or audio I heard it. The speaker said Branes can exist without string theory. That is. Branes are independent. Are they talking about p-brane or D-brane as possible to exist without String theory? If true. How then is matter stick to the brain if there are no strings involved. What else can replace strings?

Wormholes are general relativistic phenomena....you should not be mixing special relativity and wormholes. That's dangerous!
Why dangerous? What would happen mixing them. But the mere existence of wormholes can create a situation where information that travel "virtual faster" (via wormholes) than light can produce a frame of reference where things can appear to go backward in time. Hope you are familiar with what I'm talking about. How do they handle this seeming conflict?

bapowell
Familiar with Lisa Randall Warped Passages? She used in her modelling the 5th dimension as the bulk while the brane is 4D. Does this illustration encompass the compact dimensions already? If not, how could she demonstrate the string confined to the brane when compact dimensions are not even used. I thought 6D compact dimensions are a requirement in string theory.
Yes, you are referring to the Randall-Sundrum models, of which there are two types. They are both 5-dimensional models and are therefore inconsistent with string theory. I suppose it is possible for the remaining dimensions to be compactified, but this was not considered in the original papers. The first type, RS1, involves two (3+1)-branes bounding a compactified 5th dimensions. The second type, RS2, involves just a single (3+1) brane and an infinite 5th dimension. Gravity is confined to the brane (on which we live) due to the high warping of the 5th spatial dimension.

Compact dimensions are not needed to confine strings to branes. Strings attach to D-branes as a result of boundary conditions.

Why dangerous? What would happen mixing them. But the mere existence of wormholes can create a situation where information that travel "virtual faster" (via wormholes) than light can produce a frame of reference where things can appear to go backward in time. Hope you are familiar with what I'm talking about. How do they handle this seeming conflict?
I just mean that special relativity is not applicable to wormholes. It makes no sense to apply it. Wormholes are general relativistic solutions, so you must use general, not special, relativity to analyze and study them.

Yes, you are referring to the Randall-Sundrum models, of which there are two types. They are both 5-dimensional models and are therefore inconsistent with string theory. I suppose it is possible for the remaining dimensions to be compactified, but this was not considered in the original papers. The first type, RS1, involves two (3+1)-branes bounding a compactified 5th dimensions. The second type, RS2, involves just a single (3+1) brane and an infinite 5th dimension. Gravity is confined to the brane (on which we live) due to the high warping of the 5th spatial dimension.

Compact dimensions are not needed to confine strings to branes. Strings attach to D-branes as a result of boundary conditions.
In Lisa Randall RS2. The 5th dimensional is infinite in extent or as large as our 3 dimension. Well. If this was real. There would be strange phenomena at least reported. But don't we have just this strange phenomena where unknown aerial objects were sighted by thousands? But it's ironic that scientists just completely ignored them and expected only to find evidence for normal 3D spatial phenomenon. But if the 5th dimensional higher infinite brane is true, how could scientists expect to see it when they just ignored it at will and instead gave excuses they are not real because they are not part of 3D spatial world. I can't understand this illogic. Pls. explain this. Thanks.

bapowell
In Lisa Randall RS2. The 5th dimensional is infinite in extent or as large as our 3 dimension. Well. If this was real. There would be strange phenomena at least reported. But don't we have just this strange phenomena where unknown aerial objects were sighted by thousands? But it's ironic that scientists just completely ignored them and expected only to find evidence for normal 3D spatial phenomenon. But if the 5th dimensional higher infinite brane is true, how could scientists expect to see it when they just ignored it at will and instead gave excuses they are not real because they are not part of 3D spatial world. I can't understand this illogic. Pls. explain this. Thanks.
The theory underlying RS2 is understood and with it, one can make predictions. In fact, RS2 was devised to explain the relative weakness of gravity wrt the other known forces. In RS2, gravity is confined to the 3-brane but some of it still 'leaks out' into the 5th dimension, weakening it. I'm not sure why you presume that scientists are ignoring things. The theory makes predictions, and one can do experiments or make cosmological observations to look for these things. But it's only really a hypothesis at this point, and some might say not even that -- it's a model, meant to emulate, but not fully represent, reality.

The theory underlying RS2 is understood and with it, one can make predictions. In fact, RS2 was devised to explain the relative weakness of gravity wrt the other known forces. In RS2, gravity is confined to the 3-brane but some of it still 'leaks out' into the 5th dimension, weakening it. I'm not sure why you presume that scientists are ignoring things. The theory makes predictions, and one can do experiments or make cosmological observations to look for these things. But it's only really a hypothesis at this point, and some might say not even that -- it's a model, meant to emulate, but not fully represent, reality.
Oh. You don't get the context of what I'm saying. I don't know if mentioning this taboo word can get message erased, but this is in the best interests of science. I'm referring to UFOs. What if they came from another brane that uses the infinite bulk 5th dimension to travel. We have thousands of reports and many even seen by pilots and by nuclear facilities personnel.. so you can't discount them as rantings of gullible public. But physicists totally ignore this. Again this is the context of what I mean that (let me repeat) in Lisa Randall RS2. The 5th dimensional is infinite in extent or as large as our 3 dimension. Well. If this was real. There would be strange phenomena at least reported. But don't we have just this strange phenomena where unknown aerial objects were sighted by thousands? (that is UFOs). But it's ironic that scientists just completely ignored them and expected only to find evidence for normal 3D spatial phenomenon. But if the 5th dimensional higher infinite brane is true, how could scientists expect to see it when they just ignored it at will and instead gave excuses they are not real because they are not part of 3D spatial world. I can't understand this illogic. Pls. explain this. Thanks.

Lisa Randall said in her book that when she first proposed the idea of RS2. Physicists don't believe her. But slowly they started to believe her. And now they believe her. As you know ideas come in stages before they get integrated into world view. I guess evidences of off brane realities would also come in stages. I wonder how I can get in touch with Randall. I want to ask her the above question too. She believes in RS2. And when there seems to be many indications we are being visited by entities that live off-brane. We ignore them and insist it can't be real because it doesn't fall within 3D+1 reality. This is double standard. Don't you agree guys?

I just found out that Randall 5D bulk is an anti de Sitter space. I read in wikipedia:

"In physics, Randall–Sundrum models (also called 5-dimensional warped geometry theory) imagine that the real world is a higher-dimensional Universe described by warped geometry. More concretely, our Universe is a five-dimensional anti de Sitter space and the elementary particles except for the graviton are localized on a (3 + 1)-dimensional brane or branes."

From reading Lisa Randall Warped Passages it wasn't mentioned whether he got the idea totally from AdS/CFT correspondence but according to wikipedia. She does. But since AdS/CFT correspondence is not totally proven yet. Then it means Randall conjecture about RS2 can fall into thin air?

What does it mean the 5th dimensional bulk is an anti de Sitter space. I was thinking that other branes can exist in Randall RS2. If it can't. What models can accomodate many branes like ours existing in a higher dimensional space? Even Randall Local Localized Gravity model doesn't offer such flexibility because the other dimensions are beyond the horizon of this universe. I'm looking for a model where one can open up another space (5 dimension) right here on earth. Can't Randall anti de Sitter space do that? Is it a real space or just some odd duality theory like Juan Maldacena and only dependent if the AdS/CFT correspondence were true?