Are Large Extra Dimensions still acceptable?

[skowalcz]

are Large Extra Dimensions still acceptable

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]

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]

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]

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]

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]

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]

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:

http://gene.science.uva.nl/~skowalcz/Constraints%20on%20Large%20Extra%20Dimensions.pdf

It's from June 2003.

 

[ZapperZ]

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:

http://gene.science.uva.nl/~skowalcz/Constraints%20on%20Large%20Extra%20Dimensions.pdf

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]

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]

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]

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]

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]

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]

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]

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]

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" which 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. http://gene.science.uva.nl/~skowalcz/Constraints%20on%20Large%20Extra%20Dimensions.pdf it is again.

 

[skowalcz]

It the previous post I wanted to copy page 8,9 and 10 from this work.. However it didn't work, so you'll have to check the source itself.

The result of the calculations is plotted in figure 6, which shows the deviation from the inverse square law. On the vertical axis you have the error. On the horizontal axis the r/R. The resulting graph is an exponential function with a negative exponent. So a smaller R (compactification radius) results in a smaller error is you measure the gravitatinal force between two masses separated by a distance r.

 

[GRQC]

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"!

Since the compactification scale was considered to be o(Planck) before, even a femtometer would be considered "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.
Zz.

Not exactly true. The ADD paper placed an *upper limit* of a millimetre scale for the radius of the dimensions. Specifically, their paper had two "free parameters" -- radius and number of dimensions. They showed that the lagrest dimension you could have was a few hundered micrometers, and the number had to be two (lest Newton's law break down over astronomical unit-sized distances!). It is perfectly consistent to have a greater number of smaller dimensions. For example, cosmic ray experiment data suggest that there must be at least 4 extra dimensions of sub-micron scale.

 

[Stingray]

For example, cosmic ray experiment data suggest that there must be at least 4 extra dimensions of sub-micron scale.

How is that? Does it get rid of the GZK cutoff?

 

[GRQC]

How is that? Does it get rid of the GZK cutoff?

No, LED effects manifest themselves at much smaller energies (in the case of ADD, the electroweak unification scale, i.e. TeV eneries). Extra dimensions were used as an explanation for the 'knee' in the CR energy spectrum, which conveniently occurs at about a TeV.

 

[selfAdjoint]

GRQC, this is very interesting. Do you have a cite for the explanation?

 

[marcus]

GRQC, this is very interesting. Do you have a cite for the explanation?

It is remotely possible that GRQC could be referring to a short paper published in
Modern Physics Letters
or, if not, perhaps the references in this paper might hopefully help us
find something more substantial


hep-ph/0405280

"The Interplay of Ultrahigh-Energy Cosmic Rays and Extra Dimensions"
Je-An Gu
Contribution to 2003 International Symposium on Cosmology and Particle Astrophysics (CosPA 2003), Taipei, Taiwan, 13-15 Nov 2003


I have seen at least one paper which IIRC proposed using UHECR data to actually constrain extra dimensions, i.e. to rule them out above some scale. Unfortunately I didnt keep track of it, so the above is all I can suggest

 

[marcus]

here is another paper by the same author

http://arxiv.org/abs/astro-ph/0305523

I regret to say that although these two papers are recent (2003 and 2004)
they do not appear very helpful

this one in particular speculates about KK mechanisms which
might contribute to air-showers and thus be observable
but it does not appear to analyze data in such a way as to
draw any conclusions

some terminology such as "KKonium" and "KK bursts"
is evocative

 

[sol2]

http://www.nature.com/nature/journal/v411/n6841/images/411986af.0.jpg

There are no doubts when it comes to the ideas of measuring dimension, but becuase we weere easily lead to measure such distances we had to consider other things.

http://www.esi-topics.com/brane/interviews/DrLisaRandall.jpg

What exactly is the hierarchy problem?


The gist of it is that the universe seems to have two entirely different mass scales, and we don't understand why they are so different. There's what's called the Planck scale, which is associated with gravitational interactions. It's a huge mass scale, but because gravitational forces are proportional to one over the mass squared, that means gravity is a very weak interaction. In units of GeV [billions of electron volts], which is how we measure masses, the Planck scale is 10 to the 19th GeV. Then there's the electroweak scale, which sets the masses for the W and Z bosons. These are particles that are similar to the photons of electromagnetism and which we have observed and studied well. They have a mass of about 100 GeV. So the hierarchy problem, in its simplest manifestation, is how can you have these particles be so light when the other scale is so big.

http://www.esi-topics.com/brane/interviews/DrLisaRandall.html

Imagine then that such attempts are being forced to consider the nature of Quantum geometry in such a field of consideration? How many different discriptions do we have?

http://www.math.columbia.edu/~woit/mt/mt-comments.cgi?entry_id=48[/URL]

 

[GRQC]

The Randall-Sundrum LED theory is distinct from ADD. The former does not require compactified (KK) dimensions. Instead, they place severe constraints ("warp factors") on how much gravitational fields can leak into the EDs.

 

[GRQC]

GRQC, this is very interesting. Do you have a cite for the explanation?

The papers I was referencing are:

http://www.arxiv.org/abs/hep-ph/0109287 ("Cosmic Rays as Probes of Large Extra Dimensions and TeV Gravity")

http://www.arxiv.org/abs/hep-ph/0109247 ("Cosmic Rays and Large Extra Dimensions")

It's been a while since I read them, but I believe the first is the one that discusses the constraints.

 

[sol2]

First time I seen the topic of Glast spoke to directly.

Experimental tests of LQG in 2007-2010 timeframe

LQG may make hypotheses that can be experimentally testable in the near future.

The path taken by a photon through a discrete spacetime geometry would be different from the path taken by the same photon through continuous spacetime. Normally, such differences should be insignificant, but Giovanni Amelino-Camelia points out that photons which have traveled from distant galaxies may reveal the structure of spacetime. LQG predicts that more energetic photons should travel ever so slightly faster than less energetic photons. This effect would be too small to observe within our galaxy. However, light reaching us from gamma ray bursts in other galaxies should manifest a varying spectral shift over time. In other words, distant gamma ray bursts should appear to start off more bluish and end more reddish. Alternatively, highly energetic photons from gamma ray bursts should arrive a split second sooner than less energetic photons. LQG physicists eagerly await results from space-based gamma-ray spectrometry experiments -- a mission set to launch in February, 2007.

2007 will see the launch of GLAST, and the completion and operation of LHC. The results of these experiments will profoundly develop the course of QG. These experiments may establish spontaneously broken supersymmetry, higgs boson and higgs field, additional dimensions, and/or violations of lorentz invariance.

If the LHC discovers the higgs boson, supersymmetric particles, and/or additional dimensions, LQG can be modified to incorporate these experimental results, what Lee Smolin called "Loop Quantum Gravity II".

If GLAST detects violations of lorentz invariance in the form of energy-dependent photons velocity, in agreement with theoretical calculations, such observations and such agreement would strongly support LQG. It would also represent a severe problem for string/m-theory, as string theory in its current formulation presupposes lorentz invariance is an exact symmetry of nature, valid at all scales.

Astronomers are currently attempting to better understand both dark matter and dark energy, which should impact the theoretical structure of quantum gravity.

http://en.wikipedia.org/wiki/Loop_quantum_gravity

In bold quote would someone care to elaborate more?

 

[Haelfix]

The thing is, you can fine tune things well enough to get LED at just about any length scale, experiment just sets an upper limit. So the theory is sadly not predictive enough to be falsified.

Its still perfectly plausible, but I think its safe to say millimeter scale LED is out (which incidently falsifies a simple textbook parametrization).

 

[GRQC]

The thing is, you can fine tune things well enough to get LED at just about any length scale, experiment just sets an upper limit. So the theory is sadly not predictive enough to be falsified.

This is true -- the notion of extra dimensions isn't new, of course, but the idea that they could be larger than Planck scale was a novelty with some interesting observational consequences (deviations from Newton's law, anomalous cooling in supernovae, black hole pair production at TeV colliders, etc...). *Not* seeing these consequences is interpreted not as a failure of the theory, but instead as a new "upper bound" on the possible sizes. If you think about it, we could theoretically push the bounds back down to the Planck length! At what point does a theory of LEDs simply revert to the classic one of EDs (string theory and KK)?

Its still perfectly plausible, but I think its safe to say millimeter scale LED is out (which incidently falsifies a simple textbook parametrization).

What parameterization is that?

 

[sol2]

Is there not a universal position from which all attempts to explain quantum geometry, and the relationship dimension has in decribing a method, by which LQG, strings, twister theory would have been given support? They were attempts to describe this quantum geometry?

Comments: Revising the Landscape

I wanted to add this as well.

"Quantum gravity is the field devoted to finding the microstructure of spacetime. Is space continuous? Does spacetime geometry make sense near the initial singularity? Deep inside a black hole? These are the sort of questions a theory of quantum gravity is expected to answer. The root of our search for the theory is a exploration of the quantum foundations of spacetime. At the very least, quantum gravity ought to describe physics on the smallest possible scales - expected to be 10-35 meters. (Easy to find with dimensional analysis: Build a quantity with the dimensions of length using the speed of light, Planck's constant, and Newton's constant.) Whether quantum gravity will yield a revolutionary shift in quantum theory, general relativity, or both remains to be seen."

http://academics.hamilton.edu/physics/smajor/quantgrav.html

http://www.math.columbia.edu/~woit/mt/mt-comments.cgi?entry_id=48

The Elegant Universe, by Brian Greene, pg 231 and Pg 232

"But now, almost a century after Einstein's tour-de-force, string theory gives us a quantum-mechanical discription of gravity that, by necessity, modifies general relativity when distances involved become as short as the Planck length. Since Reinmannian geometry is the mathetical core of general relativity, this means that it too must be modified in order to reflect faithfully the new short distance physics of string theory. Whereas general relativity asserts that the curved properties of the universe are described by Reinmannian geometry, string theory asserts this is true only if we examine the fabric of the universe on large enough scales. On scales as small as Planck length a new kind of geometry must emerge, one that aligns with the new physics of string theory. This new geometry is called, quantum geometry."

You were right to point this out and from a common perspective, as a starting point .

But these discription were not limited to string theory alone as we have come to witness from the participants of LQG or dynamical traingulations of quantum gravity(quantum geometry).

Again you were right to point out the many facets of the attempts here, including Penrose and his twistors.

I am trying to find a common bound between them all, as we all are Some of my perspectives are being revealled on physicsforum, and the imput back to me, is pointing towards the usage of Glast as a possible discriptor of the metric.

All speculation of course.

Posted by sol at July 3, 2004 02:22 PM

Fedja Hadrovich

Twistor Primer

Introduction


In the past 30 years a lot of work has been done on developing twistor theory. Its creator, Roger Penrose, was first led to the concept of twistors in his investigation of the structure of spacetime and it was he who first saw the wide range of applications for this new mathematical construct. Yet 30 years later, twistors remain relatively unknown even in the mathematical physics community. The reason for this may be the air of mystery that seems to surround the subject even though it provides a very elegant formalism for both general relativity and quantum theory. These notes are based on a graduate lecture course given by R. Penrose in Mathematical Institute, Oxford, in 1997 and should give a brief introduction to the basic definitions. Let us begin with the building blocks: spinors.
http://users.ox.ac.uk/~tweb/00004/index.shtml

 

[GRQC]

Sol2, your posts have nothing to do with large extra dimensions. I don't understand the point you're trying to make. There are lots of theories which require extra dimensions. That's not new. Large extra dimensions are a very specific area.

Are you confusing LED and LQG?

 

[sol2]

Would we have not considered one end of the dimension and its strength in terms of energy, and not have considered the weak measure of gravity, as the other?

Are you confusing LED and LQG?

I am looking geometrical consistancy in the quantum world that connects to the world we understand around us. That one would call it discrete and one continuos , is part and parcel of their own distinctions. But they all began from the attempt to describe what?

it turns out that within string theory ... there is actually an identification, we believe, between the very tiny and the very huge. So it turns out that if you, for instance, take a dimension - imagine its in a circle, imagine its really huge - and then you make it smaller and smaller and smaller, the equations tell us that if you make it smaller than a certain length (its about 10-33 centimeters, the so called 'Planck Length') ... its exactly identical, from the point of view of physical properties, as making the circle larger. So you're trying to squeeze it smaller, but actually in reality your efforts are being turned around by the theory and you're actually making the dimension larger. So in some sense, if you try to squeeze it all the way down to zero size, it would be the same as making it infinitely big. ... (CSPAN Archives Videotape #125054)

I am looking for something more. Where each of these theories began. They had to all start from a fundamental principal? What is "that" which joins them all? Then these theories branch out into their respective differences.

Building that basis is important for me, and really, that the dimension would have some sort of scale was Quite intriguing once you considered the interaction of the graviton and the photon.

But as was pointed out there are respective differences where this would work with LQG and not with strings becuase of its continuous nature. But in respect of dimension, and what that graviton represents, how the heck could we have enter into the realm of GR and QM without considering a way in which to satisfy what this dimension could mean.

To strings it was specific that the approach of glast was not functionable to the Lorentz invariance as a exact symmetry in nature to strings?

Look deep, Deep into Nature, and Then You will Understand Everything Better--Albert Einstein

 

[Quantum_gravity]

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).

Actually, there have been several experiments, including mine, that have set limits on compactified extra dimensions.
Fir a list of most of the current experiments, check out my paper at:
http://www.phys.lsu.edu/mog/mog22/node9.html

I have a question about your avitar. It is hard to see, but is it an ARPES scan of bi-layer splitting in a cuperate?

Regards,
Mike

 

[sol2]

http://www.nature.com/nature/journal/v411/n6841/images/411986af.0.jpg

Eric Adelberger and Blayne Heckel of the University of Washington in Seattle are no strangers to difficult gravity experiments. In the 1980s, they led one of a number of groups that investigated the existence of a postulated fifth force, which would show up as a gravitational anomaly over distances of up to 100 metres. Their findings helped to kill the idea.

http://www.nature.com/nature/journal/v411/n6841/box/411986a0_bx1.html

http://www.physics.harvard.edu/nimaphoto.jpg[/URL]

[QUOTE][B]What got you started on the research in large extra dimensions, for which you're so highly cited? [/B]

Well, I had just obtained my degree from UC Berkeley and had just started my post-doc at the Stanford Linear Accelerator Center (SLAC). As a Ph.D. student, I had been working on what was a mature field. It was supersymmetry at low energies: the point was that everyone expects some sort of new physics to come in at a distance around 10-17 centimeters, and what we can see at accelerators today goes up to 10-16 centimeters. For 20 years, the dominant view has been that a new symmetry of nature will be revealed, called supersymmetry, and it will manifest itself in a variety of new particles with very distinctive properties. But this framework has been around for 20 years, and it may still very well be right, and it's what I spent my time exploring as a graduate student, but by the time I got to my post-doc I was definitely getting restless, wondering if there was some completely different framework for what might be happening at the 10-17 centimeter scale.

When I arrived at SLAC, I immediately started talking to Savas Dimopoulos, who's one of the people responsible for inventing this old paradigm of supersymmetry. We quickly realized we were both on the same page as far as wanting to think about something completely different. Gia Dvali was also interested in thinking that way. So the three of us started thinking about whether we could make sense of some older ideas about extra dimensions that might be large compared with what people normally thought about extra dimensions.

[url]http://www.esi-topics.com/brane/interviews/DrNimaArkani-Hamed.html[/url]

[/QUOTE]

[PLAIN]http://www.sciencewatch.com/may-june2001/savas-dimopoulos-big.jpg[/URL]


[QUOTE]In 1981 Savas Dimopoulos of Stanford University and Howard Georgi of Harvard University proposed the supersymmetric extension to the standard model. Revolutionary at the time, it is now accepted by many physicists. Dimopoulos has been strongly driven in his research by a desire to understand what lies beyond the standard model. His contributions have included work on grand unified theories of baryogenesis, which would provide an explanation of the origin of matter. Jointly with Stanford colleague Nima Arkani-Hamed and Gia Dvali of ICTP, Trieste, Italy, he has proposed an audacious solution to the problem of explaining the weakness of the gravitational force. [B]The proposal invokes new large dimensions accessible to the graviton. Among the extraordinary implications of this thinking is the notion that our entire universe is a single point in space of extra dimensions, and is but one of innumerable parallel universes.[/B] Thanks to this work, Dimopoulos has recently been a mainstay of the Physics Top Ten—one of the trio's papers on this subject has ranked among physics's most cited for more than a year (see table on next page, paper #3).

[PLAIN]http://www.sciencewatch.com/may-june2001/sw_may-june2001_page3.htm[/URL]
[/QUOTE]

 

[sol2]

http://www.nature.com/nature/journal/v411/n6841/images/411986af.0.jpg

http://physics.nyu.edu/people/dvali.georgi.jpg

http://www.physics.harvard.edu/nimaphoto.jpg[/URL]



[PLAIN]http://www.sciencewatch.com/may-june2001/savas-dimopoulos-big.jpg[/URL][/QUOTE]

When you see them together you learn to [PLAIN]http://wc0.worldcrossing.com/WebX?14@66.eO6PctewETX.5@.1ddf4a5f/123[/URL] where I am headed



[QUOTE=sol2][URL=https://www.physicsforums.com/showpost.php?p=303482&postcount=17][So I'll finish this post to prepare for others to follow. If you do not follow this history, you will never understand what Nima Arkani-Hamed, Sava Dimopoulos, and Gia Dvali been doing with extra dimensions. There is a conceptual feature here that I have spoken too in regards to gravity that few understand.[/URL] [/QUOTE]



I resurrected this post for those who had a hard time understanding what was going on here in terms of the what the measures mean and considered ,although many links were supplied for consideration, was something taken from this discussion?