Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Large Extra Dimensions (?)

  1. May 10, 2004 #1
    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
     
    Last edited: May 11, 2004
  2. jcsd
  3. May 11, 2004 #2
    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?
     
  4. May 11, 2004 #3

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    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).
     
  5. May 11, 2004 #4
    Your right.. it was my first post here, i should have looked better :frown:

    So maybe there are no large extra dimensions :mad:
    But there is still hope..
     
  6. May 11, 2004 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    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!
     
  7. May 14, 2004 #6

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    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.
     
  8. May 14, 2004 #7
    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.
     
  9. May 14, 2004 #8

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    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.
     
  10. May 14, 2004 #9

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    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
     
  11. May 14, 2004 #10

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    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).
     
    Last edited: May 14, 2004
  12. May 14, 2004 #11

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    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]
     
    Last edited: May 14, 2004
  13. Jun 28, 2004 #12
    No... the deviataions are large already at micrometer scales!!
     
  14. Jun 28, 2004 #13

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    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.
     
  15. Jun 29, 2004 #14
    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.
     
  16. Jun 29, 2004 #15

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    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.
     
  17. Jun 30, 2004 #16
    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:
    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.
     

    Attached Files:

    Last edited: Jun 30, 2004
  18. Jun 30, 2004 #17
    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.
     
    Last edited: Jun 30, 2004
  19. Jul 3, 2004 #18
    Since the compactification scale was considered to be o(Planck) before, even a femtometer would be considered "large".


    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.
     
  20. Jul 3, 2004 #19

    Stingray

    User Avatar
    Science Advisor

    How is that? Does it get rid of the GZK cutoff?
     
  21. Jul 4, 2004 #20
    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Large Extra Dimensions (?)
  1. Extra Dimensions (Replies: 13)

  2. Extra dimension (Replies: 16)

Loading...