What are higher dimensions for?

[Phi for All]

Are the higher spatial dimensions there simply to give perpective on each other or is there some other purpose for them?

[Tesseract]

The other dimensions are there for the same reason that the others are...I think you cansider the dimension in relation to humans...because they can be percieved dosnt mean they arent affecting each other, most of the unexplained things can be explained by other dimensions.

Hmm, can someone that knows somethingabout other dimensions answer better.

Until then look at this tesseract!!!http://pw1.netcom.com/~hjsmith/WireFrame4/tesseract.html

[jordan]

Believe me, Tesseract, nowhere in the rules is it stated replies are manditory. If you dont' have something that adds to the thread in a postive manner, don't reply.

 

Back on topic:

From what I understand, the higher dimensions come from the math used to describe the world. Most are from the new string theory which proposes 11 dimensions (at least the most common version of string theory). The scientist/mathmeticians will usually give an explanation as to what each dimension is, but they seem to know more about them from the math than actual tests and observations. The purpose seems to be to make the math fit the real world. Without them the math doesn't work. It always seemed that the dimensions were used to describe the math and not the other way around.

[alt_f13]

They are there only to allow for the mathematical explanation of our universe as per some theories.

 

Different theories need different ammounts of dimensions in order to work mathematically. For example, M Theory requires 3 spacial dimensions, one temporal dimension and 6 Calabi-Yau dimensions rolled up into tiny little balls, one per unit of space.

[alt_f13]

Damn you and your fast typing

 

:S

 

Oh yah... whats the last dimension in M Theory Jordan?

[Tesseract]

If anyone cares heres a really good site for M-theory and string theory:

http://www.damtp.cam.ac.uk/user/gr/public/qg_ss.html

[jordan]

Damn you and your fast typing

I always thought I was rather slow and mythodical at typicing. I try to make a few errors as possible so it ends up taking me 10 minutes to type that post. This one took four.

 

Oh yah... whats the last dimension in M Theory Jordan?

M Theory? Last dimension? How about we call it dimension X where X is denoted as the correct answer?

 

I have no idea, alt_f13. I've never heard of "M Theory".

[alt_f13]

M Theory is THE string theory. It's probably the same one you were talking about... anyway, I stopped typing and read for a moment during the post.

[Phi for All]

I'm familiar with Witten's M-Theory. Though the higher dimensions are needed for the maths involved in the whole string-based concept, I am asking if they merely give perspective on one another since they are all said to be spatial. I can wrap my mind around a fourth spatial dimension, giving perspective to the three we can see. But are the others just there to add perspective layers to what we perceive?

[alt_f13]

They are 6 spacial dimensions all wrapped up. They exist on a tiny level.

 

Look up calibi yau dimensions and check this out:

 

http://www.pbs.org/wgbh/nova/elegant/program.html

[jordan]

Yeah, I guess I did know that. I'm just really tired right now.

 

Your last question, Phi for All:

I guess we would have to get a good handle on what the dimesions are, other than the math, to understand how they relate to one another. Basicly, they are there to discribe the motion of "stings". Therefore, they are the building blocks for the other dimensions to be built around.

[Phi for All]

Oh yah... whats the last dimension in M Theory

The last dimension in M-theory was to account for the need for a full ten spatial dimensions plus one temporal, but I think Witten placed time as the familiar fourth dimension. If I'm not mistaken (and I often am), the final dimension was added to account for gravitons crossing multiple parallel universes to account for its relatively weak force when compared to the other three forces. I've even heard that many physicists are starting to believe the electromagnetic and the weak nuclear forces are one and the same due to the similarities between the wave functions of EM and radiation.

[Phi for All]

Here's an interesting article in Science News, http://www.sciencenews.org/articles/20000219/bob1.asp, a few years old though, suggesting that the higher dimensions may not all be at Planck's length. Could navigation of the universes be accomplished using these dimensions? Are they why gravity appears so weak compared to other forces.

[bloodhound]

first of all, can u define what u mean by dimension.

[Phi for All]

first of all, can u define what u mean by dimension.

The first three spatial dimensions are length, width and height. We can only see in three dimensions. Length and width alone are invisible to us. We need height for light to illuminate an object so we can see it. Even a flat piece of paper has a measurable height, as would pencil markings on the piece of paper.

 

String theory states that there are probably seven other spatial dimensions that give further perspective to to the first three. I would assume that you can't have a fourth dimension without the first three, a fifth without the first four, and so on.

 

My question is why are so many perspectives necessary? Do the higher dimensions have another function besides perspective?

[bloodhound]

u still havent defined it. u just gave some examples.

 

edit: i could give u the definition of dimension that i have studied

[J'Dona]

I don't know enough about basic string theory yet to really make a comment, but why couldn't there be multiple time dimensions?

 

The reason I think this is that it might explain something about parallel universes. Imagine everything is travelling through time normally at a constant rate (assuming no relativity effects due to near light speed travel). It would have a constant rate of travel in the x-direction of time. But maybe every time there is a probability of some sort, every time someone in one dimension does one thing and their twin in another does something else, they're moving differently in the y-direction or the z-direction. How this would occur I've no idea, these are just unfounded ideas.

 

If this were the case though, it might resolve the causality problems with travelling back in time (and before anyone rolls their eyes, I didn't come up with all this for some science fiction story idea, I had it during a physics seminar at Leeds university). If you had certain (x, y, z) co-ordinates and you travelled back in time, to a point where your universe was at different (x, y, z) co-ordinates to your own, then unless you could control the particular aspects of the time dimensions that you travelled through you could quite possible miss your past and end up in someone else's. Alternatively, if you did make it back to your past, then any changes you made (which you would make simply from being there) wouldn't affect your future, because you would split that dimension off onto another direction through time and the future from which you came would be unaffected, because by going back to the past in which you weren't originally there, by being there the universe must split off onto different (x, y, z) co-ordinates, because it's different.

 

Okay, most of that was probably rubbish, but mostly I'm just wondering why there can't be multiple time dimensions. How do the current theories explain the idea of parallel universes now with one time dimension? I'm not challenging current science, particularly as I don't yet understand it, and if someone could tell me how current theory precludes the need for multiple time dimensions, I'll breathe a sigh of relief and leave it at that.

[swansont]

I don't know enough about basic string theory yet to really make a comment' date=' but why couldn't there be multiple time dimensions?

[/quote']

 

It would have to be orthogonal to the existing one to qualify as a "new dimension," thus the two could not affect each other.

[timo]

wow, so many replies and noone knew an answer and just randomly quoted some things one reads into newspapers, sci-fi pages and popular scientific books. I don´t know the answer myself -in fact I never even read one page of a scientific paper of theories using more than four dimensions- but I´d guess you introduce new dimension to imbed your 4D-curved space into a flat one like you can imbed your 2D surface of the earth into 3D by maping it on a sphere.

Just a rough guess, like I said. ´

[Martin]

Jan Ambjorn (copenhagen U) and Renate Loll (utrecht U)

 

"We present evidence that a macroscopic four-dimensional world emerges from this theory dynamically."

 

http://arxiv.org/hep-th/0404156

 

 

they construct a quantum model of spacetime where the development of spacetime geometry follows a quantum version of einstein's GR and they implement this quantum model in a computer-----four dimensional worlds result.

 

Ambjorn and Loll began their collaboration when they were both at the MPI Potsdam.

they (and Jurkiewicz) have taken a step towards explaining why D = 4

 

the paper is called

"Emergence of a 4D world from causal Quantum Gravity"

[Martin]

this thread raises a good issue

why are there just this number of dimensions?

 

Does anyone know of any evidence that there are more than 4 dimensions?

 

(various theories require more than four in order to work, but as far as I know there is no experimental confirmation of any of those theories)

 

a theory of how spacetime arises should probably be able to explain

why it appears to be 4D

 

and it looks like the Ambjorn paper, with their computer simulation of the universe where 4D emerges dynamically, is making a start

[Martin]

Are the higher spatial dimensions there simply to...?

 

first question would be "Are they there?"

the theories (string...) that need D > 4 to work have not made predictions allowing them to be checked empirically

no evidence they're right and growing indications they aren't

field in something of a muddle right now around the

huge number of possible vacuum states and the "anthropic principle"

 

So it's probably safest to assume the world is just plain 4D.

 

A satisfactory theory of gravity (gravity = geometry of spacetime)

should predict, among other things, this four-dimensionality.

 

You should be able to put the equations of the model

into a computer and run a simulation of (at least the broad outlines of ) the universe and have that dimensionality emerge from the model.

 

this was done for the first time this year.

 

the work is still very new.

 

(it has no relation to string theory but it does relate to some other approaches to quantum gravity which people are researching)

 

two of the people working on this are Jan Ambjorn and Renate Loll

 

http://arxiv.org/hep-th/0404156

[jana]

first question would be "Are they there?"

the theories (string...) that need D > 4 to work have not made predictions allowing them to be checked empirically

no evidence they're right and growing indications they aren't

field in something of a muddle right now around the

huge number of possible vacuum states and the "anthropic principle"

 

So it's probably safest to assume the world is just plain 4D.

 

A satisfactory theory of gravity (gravity = geometry of spacetime)

should predict' date=' among other things, this four-dimensionality.

 

You should be able to put the equations of the model

into a computer and run a simulation of (at least the broad outlines of ) the universe and have that dimensionality emerge from the model.

 

this was done for the first time this year.

 

the work is still very new.

 

(it has no relation to string theory but it does relate to some other approaches to quantum gravity which people are researching)

 

two of the people working on this are Jan Ambjorn and Renate Loll

 

http://arxiv.org/hep-th/0404156[/quote']

 

My understanding is that these sort of reggeesque theories are deficient in a number of ways. Here are a few:

 

1) Since spacetime dimension is dynamical in them, the associated fundamental degrees of freedom are not fixed in number and so these theories ultimately can't be unitary.

 

2) The most important thing we've learned about about quantum gravity (in fact GR all by itself apparently suggests this too, but I don't understand how) is that any quantum gravity theory must be holographic so they must not have fundamental degrees of freedom that are volume like.

 

3) They can't really explain the emergence of GR since the hilbert action is used as input.

 

4) Since they euclideanize to calculate the path-integrals, amplitudes reflect the microconfigurations that dominate the path-integral. So the reason that something that looks like 4d spacetime emerges isn't some deep heretofore unknown reason, but just that they only allow microconfigurations that look like the macroscopic configurations they want to result. Also, it is known in euclidean quantum gravity that when you "fine tune" the path integral this way, the theory in addition to seeming naive, usually ends up being nonunitary.

 

4) They predict new nonperturbative effects which must have descriptions at the semiclassical level and so must appear at energies below the planck energy. But this would require the theory give us a new constant of nature associated with this energy, but these theories never do which makes them seem more like toy models that have nothing to do with the physical universe.

 

5) Since as already mentioned, these theories quantize GR directly, they leave out the almost certain to be true possiblity that GR the hilbert action is just the lowest energy part of an action that contains other interactions that are suppressed at higher energies.

 

I don't think we should assume that spacetime is four dimensional. Instead, a quantum gravity theory should predict how many dimensions there are and then explain why if there are more than four dimensions, why we only see four of them. I think that String theory to some extent does both since it automatically imposes einsteins equations on the vacuum fields which determines the number of dimensions and also allows the idea that higher dimensions are either curled up too tightly to detect or interact only gravitationally as in braneworld scenarios. If we assume that all spacetime dimensions began life compactified, the question is why did only four of them decompactify. From what I understand string theory offers a large number of possible explanations for this, but I don't know any off hand.

 

Regards,

Jana

[YT2095]

I always thought there were only 10 Dimensions?

 

Height, width and depth, all 3 of these exist in the Past, the Pressent and the Future. making 9 dimensions, the Present 3 converge to make the NOW, being the Tenth (where we reside).

 

it always seemed to make sense to me?

[jordan]

Wow, YT.