# Extra Dimentions

1. Apr 17, 2004

### protonman

If there are six extra dimentions where are they?

2. Apr 18, 2004

Staff Emeritus
The standard explanation is that they are "compacted" - curled up into tiny closed shapes. So in every tiny region of spacetime - close to the planck length - there is one of these little manifolds. The size is much much smaller than we can probe with our biggest accelerators, or with any device we can imagine building. So we can't detect them. So it is said.

3. Apr 18, 2004

### marcus

I keep mine in my sock drawer

4. Apr 18, 2004

### protonman

How can they be compacted and never cross into one of the existing three dimentions?

5. Apr 18, 2004

### marcus

in a universe with enough dementions things you wouldnt expect can happen

think of rolling up a sheet of paper (in our everyday 3D world)

in that case one of the two dementions of the paper is being rolled up
while the other is left extended
and this doesnt interfere
noting crosses into something else
because intuitively there is enough room

protonman I am not saying this is how it is in our universe but only that
it is possible for some dementions to get rolled up without interfering with the rest. mathematically or geometrically possible
(not talking about the physics end of it)

6. Apr 18, 2004

### protonman

If you have a sheet of paper and roll it up it must be rolled into one of the three existing dimentions. If an object is extended in space it must be rolled up and occupying one of the three space dimentions.

7. Apr 20, 2004

### wolram

protonman I am not saying this is how it is in our universe but only that
it is possible for some dementions to get rolled up without interfering with the rest. mathematically or geometrically possible
(not talking about the physics end of it)
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and Bonnie and Clyde died an Honorable death

8. Apr 20, 2004

### marcus

and Bonnie and Clyde died an Honorable death
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LOL

9. Apr 21, 2004

### GRQC

Actually, that's a rather "old" description. More modern theories suggest that there are large extra dimensions (LED). which, while still compactified, could have radii of a few fractions of a millimeter. Gravity can propagate through all spacetime dimensions, but the other gauge fields are restricted to what we know as 4-dimensional spacetime (our brane).

Kaluza-Klein gravitons can propagate into the "bulk" (i.e. the extra dimensions) and due to the nature of the compactification, they can have any number of possible wavelengths (or ultimately masses).

These large extra dimensions can in theory be detected by simple Cavendish-type experiments, since if the dimensions are large enough classical Newtonian gravity would break down at the sub-millimeter scales (i.e. deviation from inverse-square). They are also potentially observable in accelerator experiments as "missing energy" from collisions. The predicted Kaluza-Klein gravitons would be analogous to neutrinos (i.e. used to explain missing angular momentum).

Theories of LEDs are quite elegant, and in fact solve a number of problems such as the hierarchy problem. They shrink the "energy desert" between electroweak and Planck scales, making the Planck scale accessible at the high GeV / low TeV level.

However, your final statement is still somewhat accurate. They essentially solve the problems by pushing the physics into these other dimensions, sort of like brushing the dirt under the carpet. So far, no deviations have been observed in the Cavendish experiments (placing upper limits on the possible size of dimenions, now down to a few micrometers). Same for accelerator experiments. These current limits suggest the number of large extra dimensions must be at least 2.

If correct, though, these theories stand to be the quantum revolution of the 21st century.

Last edited: Apr 21, 2004
10. Apr 21, 2004

### Mike2

So in theory if this Calabi-Yau manifold exists everywhere, can information travel through these curled up dimensions from here to the other side of the universe by going through a small distance? In other words, if all of large space also shares the small dimensions, then it seems possible to send information from one side of the universe to the other through a very short distance of one of these curled up dimensions?

11. Apr 21, 2004

### GRQC

Some of the large extra dimension theories suggest that our spacetime brane is folded on itself (similar to folding a piece of paper in half). The two "folds" are essentially separated by the bulk of the extra dimensions. The consequence of this is that objects which are distant (vis-a-vis the light cone) may in fact be only millimeters away from us through these extra dimensions!

I suppose you could "communicate" if you could tune the gravitons accordingly, but this would be such a weak effect that it would probably be useless.

Again, gravitons are the only particles able to penetrate the bulk, so in principle large gravitational events far away could be "felt" here. However, the only way to test this would be to detect some kind of gravitational anomaly, estiamte how far away the "kink" in the brane is, and hope to see an event (e.g. supernova) at some time in the future.

12. Apr 21, 2004

### Haelfix

(placing upper limits on the possible size of dimenions, now down to a few micrometers).

Actually the millimeter scale is pretty much ruled out with some pretty good confidence ratings, modern experiments are hovering in the 100s of micro meters.

Unfortunately, we are about an order of magnitude away from the experimental limit to how far you can take these.

I agree that its elegant, but im not holding my breath about LED, I have the nagging feeling if they do exist they're going to be firmly out of our range.

Here's to precision astronomy finding an anomalous Newtons constant.

13. Apr 22, 2004

### GRQC

I did say sub-millimeter -- i.e. fractions of a millimeter, which is the same as 100s of micrometers.

Anyway, I also agree with your statement that LED is a potential "fad". In fact, I went to school with Nima Arkani-Hamed, and I recall his propensity for "toy models" which were incredibly mathematically intricate, but at the end of the day were just that. This is certainly one big toy, but as more experiment goes on, it drives the limits further away.

14. Jun 10, 2004

### setAI

if the universe is in some fundemental way a "digital computer" an infinitude of extra/other "dimensions"/states could exist anywhere but are merely not directly entangled in this universe's computation- or the process/structures which emerged as this spacetime formed a 4-dimensional structure do to their topology- with other n-dimensional structures merely weakly/subtly interacting with it-

any dimension/state/structure/process that weakly/rarely interacts with the causality of our world MUST be invisible and oblivious to us because there would have been no selection pressure to evolve our senses and semiotics to detect extra/other dimensions or even be aware of them-

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/:set\AI transmedia laboratories

http://setai-transmedia.com [Broken]

Last edited by a moderator: May 1, 2017
15. Jun 10, 2004

### sol2

Last edited by a moderator: May 1, 2017