Large Extra Dimensions (?)

**skowalcz** · May10-04, 10:21 AM

Hi folks,

a couple of years ago [in 1998] some people (Arkani-Hamed, Dimopoulos, and Dvali [ADD]) proposed a scenario which uses a string inspired brane world hypothesis. In this model the world that we see is a 3-dimensional brane in a higher dimensional world.
Light and matter are confined to the brane. Gravity is allowed to propagate throuh te bulk.
This scenario allows for much larger dimensions than the Planck lenght. This because gravity, the only force affected, has only been tested down to scaled of a millimeter orso. This was the case some time ago. Has there been any improvement in testing gravity on submillimeter scales? What is the general opinion on this ADD-model? I wonder whether after some years after it's invention it's still acceptable.

- Stefan

**skowalcz** · May11-04, 10:55 AM

I wonder whether after some years after it's invention it's still acceptable.

Was this weird scenario back in 1998 acceptable? Are there many physics profs working on this idea, or is this idea of Large (=much larger radius than the Planck scale) Extra Dimensions just very speculative?

**ZapperZ** · May11-04, 11:03 AM

Originally Posted by skowalcz

Hi folks,

a couple of years ago [in 1998] some people (Arkani-Hamed, Dimopoulos, and Dvali [ADD]) proposed a scenario which uses a string inspired brane world hypothesis. In this model the world that we see is a 3-dimensional brane in a higher dimensional world.
Light and matter are confined to the brane. Gravity is allowed to propagate throuh te bulk.
This scenario allows for much larger dimensions than the Planck lenght. This because gravity, the only force affected, has only been tested down to scaled of a millimeter orso. This was the case some time ago. Has there been any improvement in testing gravity on submillimeter scales? What is the general opinion on this ADD-model? I wonder whether after some years after it's invention it's still acceptable.

- Stefan

Not sure why you would ask this in this section of PF since there clearly is a String/Brane/etc section.

The Arkani-Hamed conclusion that one can detect deviation to Newtonian law of gravity at the millimeter scale is having some problems. There have been TWO (count 'em) experimental measurements within the past 3 years that have measured G up to sub-millimeter scale, and have found no such deviations.[1,2]

So draw your own conclusions from that.

Zz.

[1] C.D. Hoyle et al., PRL v.86, p.1418 (2001).
[2] J.C. Long et al., Nature v.421, p.922 (2003).

**skowalcz** · May11-04, 11:24 AM

Originally Posted by ZapperZ

Not sure why you would ask this in this section of PF since there clearly is a String/Brane/etc section.

Your right.. it was my first post here, i should have looked better

So draw your own conclusions from that.

So maybe there are no large extra dimensions

But there is still hope..

**marcus** · May11-04, 11:32 AM

Originally Posted by ZapperZ

Not sure why you would ask this in this section of PF since there clearly is a String/Brane/etc section...
...
[1] C.D. Hoyle et al., PRL v.86, p.1418 (2001).
[2] J.C. Long et al., Nature v.421, p.922 (2003).

In case anyone wants to look online at the Hoyle et al article which Zapper mentioned, the preprint is

http://arxiv.org/hep-ph/0011014
Sub-millimeter tests of the gravitational inverse-square law: A search for "large" extra dimensions
C. D. Hoyle, U. Schmidt, B. R. Heckel, E. G. Adelberger, J. H. Gundlach, D. J. Kapner, H. E. Swanson
4 pages, 5 figures
Phys.Rev.Lett. 86 (2001) 1418-1421

a preprint version of the Long et al article which Zz cited is
http://arxiv.org/hep-ph/0210004
New Experimental Limits on Macroscopic Forces Below 100 Microns
Joshua C. Long, Hilton W. Chan, Allison B. Churnside, Eric A. Gulbis, Michael C. M. Varney, John C. Price
25 Pages, 7 Figures
Letter version published in Nature 421, 922-925 (2003)

thanks for these references!

**ZapperZ** · May14-04, 08:04 AM

We can add more woes to the Arkani-Hamed et al. predictions.

At the recent APS April meeting, a team from University of Mainz, Germany reported an even finer measurement of the gravitational law by dropping.... get this.... NEUTRONS. They measure the bounce height of cold neutrons onto a surface, and the deviation from the expected height of the bounce will indicate a deviation from the inverse square law of Newtonian gravity [the caveat here being that since a neutron is a quantum particle, it's bounce height is "quantized", but still governed by the gravitational potential].

This group found no significant deviation from the Newtonian gravitational law, up to the nanometer scale length! I'm guessing this result is being prepared or in the process for peer-review publication since there are no citation yet. I will fully admit that as an experimentalist, I get an extra "glee" out of something like this. :)

Zz.

**skowalcz** · May14-04, 08:43 AM

Really cool, Neutron bouncing!

My interested for these large extra dimension came from
some meetings with some other students and Prof. R. Dijkgraaf
(Chair of Mathematical physics; Univ. of Amsterdam)
[ps. was he one of the inventers of matrix string theory?]

But the article we wrote on this subject (half theory/half experiments)
was written by us, not by him, but still it might be interesting to someone:

Constraints on Large Extra Dimensions

It's from June 2003.

**ZapperZ** · May14-04, 08:52 AM

Originally Posted by skowalcz

Really cool, Neutron bouncing!

My interested for these large extra dimension came from
some meetings with some other students and Prof. R. Dijkgraaf
(Chair of Mathematical physics; Univ. of Amsterdam)
[ps. was he one of the inventers of matrix string theory?]

But the article we wrote on this subject (half theory/half experiments)
was written by us, not by him, but still it might be interesting to someone:

Constraints on Large Extra Dimensions

It's from June 2003.

Ah. Then it appears that from your model, you will only get deviations from the inverse square law at the Planck length scale, no? This then is the continuing predicament of String theory - lack of experimental evidence. In fact, in many instances, there is also the lack of the physical possibility of producing an experimentally measurable evidence. In our history of science, has there ever been such a singular field of study in physics that has gain such notoriety, such popularity, such large following, over such length of time, and yet lack even a single shred of supporting experimental evidence?

Zz.

**marcus** · May14-04, 09:56 AM

Originally Posted by ZapperZ

We can add more woes to the Arkani-Hamed et al. predictions.

At the recent APS April meeting, a team from University of Mainz, Germany reported an even finer measurement of the gravitational law by dropping.... get this.... NEUTRONS. They measure the bounce height of cold neutrons onto a surface, and the deviation from the expected height of the bounce will indicate a deviation from the inverse square law of Newtonian gravity [the caveat here being that since a neutron is a quantum particle, it's bounce height is "quantized", but still governed by the gravitational potential].

This group found no significant deviation from the Newtonian gravitational law, up to the nanometer scale length! I'm guessing this result is being prepared or in the process for peer-review publication since there are no citation yet. I will fully admit that as an experimentalist, I get an extra "glee" out of something like this. :)

Zz.

this sounds like a similar apparatus to one constructed in 2002 in Grenoble
for a neutron-bouncing experiment reported in Phys Rev D in 2003
http://arxiv.org./hep-ph/0306198
also reported earlier in a 2-page note in Nature
one of the team that did the neutron dropping experiment at Grenoble
was S. Baessler, who is from Mainz
it seems likely there is a connection

**ZapperZ** · May14-04, 10:18 AM

Originally Posted by marcus

this sounds like a similar apparatus to one constructed in 2002 in Grenoble
for a neutron-bouncing experiment reported in Phys Rev D in 2003
http://arxiv.org./hep-ph/0306198
also reported earlier in a 2-page note in Nature
one of the team that did the neutron dropping experiment at Grenoble
was S. Baessler, who is from Mainz
it seems likely there is a connection

Thanks very much for the citation. I must have somehow missed that one. The only neutron "drop" experiment that I'm aware of was from several years ago that showed that gravitational potential is also quantized like other potentials.[1] This recent work appears to make use of that.

Zz.

Er.. after looking at the preprint that you gave, even though the title is slightly different, I think we are citing the identical paper. I think the report given at the recent APS meeting isn't on that one. They did use the same technique, however, in determining the bounce height of the neutrons.

So phew! I didn't miss that one after all! I would have never forgiven myself if I missed something this significant! :)

[1] V.V. Nesvizhevsky et al., Nature v.415, p.297 (2002).

**marcus** · May14-04, 10:36 AM

I will keep a lookout for news of what you told about
from the April 2004 APS meeting

If you find a preprint or anything online please let me know
I would appreciate hearing

the new work does seem related to the 2002 Grenoble experiment
but I'm unclear how as yet

[edit: PS I just found another good article about that
experiment
http://arxiv.org/hep-ph/0301145
"Quantum states of neutrons in the gravitational field and limits for non-Newtonian interaction in the range between 1 µm and 10 µm"

googled with the name of the Mainz guy---Stefan Baessler
this article is more graphic and clear about some things
like the neutron mirror, and how the Ultracold Neutrons are
produced, fascinating stuff

this article was published by Springer in a collection
called Aspects of Quantum Gravity (2003)
edited by Laemmerzahl]

**skowalcz** · Jun28-04, 10:29 AM

Originally Posted by ZapperZ

Ah. Then it appears that from your model, you will only get deviations from the inverse square law at the Planck length scale, no?

No... the deviataions are large already at micrometer scales!!

**ZapperZ** · Jun28-04, 10:32 AM

Originally Posted by skowalcz

No... the deviataions are large already at micrometer scales!!

If this is true, then you have a serious problem. All experiments done up to micrometer scale have shown NO deviation from Newtonian gravitational laws.

Zz.

**skowalcz** · Jun29-04, 03:20 AM

No we have no problem. These experiments just place constraints on the radii of the 'large' extra dimensions. Having measured no deviation up to micrometer scales means that the compactification radius < 10^-6 m, but still the possibility exists that for example R=10^-11 m and that we don't know about it yet.

**ZapperZ** · Jun29-04, 07:34 AM

Originally Posted by skowalcz

No we have no problem. These experiments just place constraints on the radii of the 'large' extra dimensions. Having measured no deviation up to micrometer scales means that the compactification radius < 10^-6 m, but still the possibility exists that for example R=10^-11 m and that we don't know about it yet.

If that is the case, then you just contradicted yourself when you said "...the deviataions are large already at micrometer scales!!" If the compactification is LESS than 10^-6, then I certainly would NOT say that any deviation here is "large"!

Besides, aren't we really playing retract-the-boundaries-here? The Arkani-Hamed postulate clearly indicated a millimeter (or even sub millimeter) scales of deviation. Are we talking about some OTHER predictions that was published since that one that are now making a different length scales? Can you give me the reference?

Zz.

**skowalcz** · Jun30-04, 06:14 AM

Originally Posted by ZapperZ

If that is the case, then you just contradicted yourself when you said "...the deviataions are large already at micrometer scales!!" If the compactification is LESS than 10^-6, then I certainly would NOT say that any deviation here is "large"!

Ok. You are right. I should have said: "The deviations CAN be large already on micrometer scales. It depends on the compactification radius. So yes, what we are doing is exactly:

playing retract-the-boundaries-here

The Arkani-Hamed postulate clearly indicated a millimeter (or even sub millimeter) scales of deviation. Are we talking about some OTHER predictions that was published since that one that are now making a different length scales? Can you give me the reference?

Zz.

Maybe you are right that what I am talking about is not really what Arkani-Hamed was talking about.. I thought that in their stuff there was also a free parameter "R" wich could be adjusted. By the way the title of the work that I took the above from was "Constraints on Large Extra Dimensions" (sorry not a 'real' refrence from the arXiv. It was written by me and 5 fellow students.)

I already gave the link. Here it is again.