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

Garrett Lisi bid to join Std. Model w/ gravity

  1. Nov 21, 2005 #1

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Garrett, occasional visitor here, posted this today:

    http://arxiv.org/abs/gr-qc/0511120
    Clifford bundle formulation of BF gravity generalized to the standard model
    A. Garrett Lisi
    24 pages
    "The structure and dynamics of the standard model and gravity are described by a Clifford valued connection and its curvature."

    congratulations.
     
  2. jcsd
  3. Nov 21, 2005 #2

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    several of us here took an interest in the Freidel/Starodubtsev paper
    which IIRC we had a thread on, and which also John Baez was excited about

    this Lisi paper builds on that, or more generally on the BF model

    I dont know how successfully---need time to think and hope to hear other people's comments----but it makes sense as something to try. the BF model looked like a very promising way to treat gravity, so makes sense to see how the Std Mdl might be welded onto it.

    for convenience, here is the Freidel/Staro paper
    http://arxiv.org/abs/hep-th/0501191
    Quantum gravity in terms of topological observables

    here are some of Freidel other papers to see what he is doing by way of joining matter to gravity
    http://arxiv.org/find/grp_physics/1/au:+Freidel/0/1/0/all/0/

    Lisi's handle on the Standard Model comes from some 1999 work by Greg Trayling
    http://arxiv.org/hep-th/9912231
    A geometric approach to the standard model
    Here is Garrett's conclusions paragraph giving a descriptive overview of what he has accomplished:
    "This paper has progressed in small steps to construct a complete picture of gravity and the standard model from the bottom up using basic elements with as few mathematical abstractions as possible. It began and ended with the description of a Clifford algebra as a graded Lie algebra, which became the fiber over a four dimensional base manifold. The connection and curvature of this bundle, along with an appropriately restricted BF action, provided a complete description of General Relativity in terms of Lie algebra valued differential forms, without use of a metric. This “trick” is equivalent to the MacDowell-Mansouri method of getting GR from an so(5) valued connection. Hamiltonian dynamics were discussed, providing a possible connecting point with the canonical approach to quantum gravity. Further tools and mathematical elements were described just before they were needed. The matrix representation of Clifford algebras was developed, as well as how spinor fields fit in with these representations. The relevant BRST method produced spinor fields with gauge operators acting on the left and right. These pieces all came together, forming a complete picture of gravity and the standard model as a single BRST extended connection. If this final picture seems very simple, it has succeeded. As a coherent picture, this work does have weaknesses. Everything takes place purely on the level of “classical” fields – but with an eye towards their use in a QFT via the methods of quantum gravity, which must be applied in a truly complete model. The BRST approach to deriving fermions from gauge symmetries, although a straightforward application of standard techniques, may be hard to swallow. If this method is unpalatable, it is perfectly acceptable to begin instead with the picture of a fundamental fermionic field as a Clifford element with gauge fields acting from the left and right in an appropriate action. The model conjectured at the very end, based on the related u(4) GUT, is yet untested and should be treated with great skepticism until further investigated. In a somewhat ironic twist, after arguing in the beginning for the more natural description of the MM bivector so(5) model in terms of mixed grade Cl1,3 vectors and bivectors, this conjectured model is composed purely of bivector gauge fields. Although the model stands on its own as a straightforward Cl8 fiber bundle construction over four dimensional base, there are many other compatible geometric descriptions. One alternative is to interpret ⇁ ̃A as the connection for a Cartan geometry with Lie group G – with a Lie subgroup, H, formed by the generators of elements other than ⇁e, and the spacetime “base” formed by G/H. Another particularly appealing interpretation is the Kaluza-Klein construction, with four compact dimensions implied by the Higgs vector, φ = −φ ψΓ ψ, and a corresponding translation of the components of ⇁ ̃A into parts of a vielbein including this higher dimensional space. The model may also be extended to encompass more traditional unification schemes, such as using a ten dimensional Clifford algebra in a so(10) GUT. All of these geometric ideas should be developed further in the context of the model described here, as they may provide valuable insights. In conclusion, and in defense of its existence, this work has concentrated on producing a clear and coherent unified picture rather than introducing novel ideas in particular areas. The answer to the question of what here is really “new” is: “as little as possible.” Rather, several standard and non-standard pieces have been brought together to form a unified whole describing the conventional standard model and gravity as simply as possible."
     
    Last edited: Nov 21, 2005
  4. Nov 21, 2005 #3

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    just as additional context
    here is Not Even Wrong blog from earlier this year where John Baez comments and mentions Garrett in connection with the work by Greg Trayling that this paper draws on

    http://www.math.columbia.edu/~woit/wordpress/?p=173
     
  5. Nov 21, 2005 #4

    garrett

    User Avatar
    Gold Member

    Hey Marcus, thanks for mentioning my work. Everything went down just as you said -- I was playing around with the MacDowell-Mansouri idea recently revived by Freidel et al, and I was amazed to find all the other pieces coming together and fitting more or less perfectly. Thus the paper.
     
  6. Nov 22, 2005 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Hey thanks for visiting us. We should make a list of recent ventures at putting gravity together with Std Mdl. maybe they have underground tunnels connecting them

    I can think of yours and of the preon-spinnetwork approach. Can you suggest others?
     
    Last edited: Nov 23, 2005
  7. Nov 22, 2005 #6

    garrett

    User Avatar
    Gold Member

    Well, the best attempts, IMO, are all old. The Kaluza-Klein idea is probably the best overall. But it has problems with chiral spinors, and more problems with "towers" of states. And the KK idea had a rebirth in the 80's with supergravity, and again with string theory. But I think the attempts to get the standard model out of string theory are pretty bad -- way too many unjustified assumptions.

    Trayling's model, and mine the addition of gravity to his, is really just the Kaluza-Klein idea wearing Clifford robes.

    In the "final" theory, if there is one, I think everything is going to have to come together at once. It's a lot to tackle, which is why most contemporary physicists don't want to touch it. There's also the taboo subject of trying to "derive" quantum mechanics from something. This whole field is also chalk full with crackpots, so it's damn near academic suicide to enter it. It also doesn't help that you probably can't, or shouldn't, be publishing a paper a month when you're working on the big questions.
     
  8. Nov 23, 2005 #7

    selfAdjoint

    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    This is not quite that, but it is an interesting venture in combining matter into GR; sources of matter arise as changes of differentiable structure!

    Differential Structures - the Geometrization of Quantum Mechanics

    Torsten Asselmeyer-Maluga, Helge Rose'

    Abstract:
    The usual quantization of a classical space-time field does not touch the non-geometrical character of quantum mechanics. We believe that the deep problems of unification of general relativity and quantum mechanics are rooted in this poor understanding of the geometrical character of quantum mechanics. In Einstein's theory gravitation is expressed by geometry of space-time, and the solutions of the field equation are invariant w.r.t. a certain equivalence class of reference frames. This class can be characterized by the differential structure of space-time. We will show that matter is the transition between reference frames that belong to different differential structures, that the set of transitions of the differential structure is given by a Temperley-Lieb algebra which is extensible to a $C^{*}$-algebra comprising the field operator algebra of quantum mechanics and that the state space of quantum mechanics is the linear space of the differential structures. Furthermore we are able to explain the appearance of the complex numbers in quantum theory. The strong relation to Loop Quantum Gravity is discussed in conclusion.
     
    Last edited: Nov 23, 2005
  9. Nov 23, 2005 #8

    garrett

    User Avatar
    Gold Member

    Hey SA, that does look interesting. I'll give it a read. Here's the arxiv link for it:
    http://arxiv.org/abs/gr-qc/0511089
    I also liked this paper by Ashtekar and Schilling:
    Geometrical Formulation of Quantum Mechanics
    http://arxiv.org/abs/gr-qc/9706069
    Though it was more conservative.
    I do think quantum field theory is going to have to get a geometric description eventually. It's hard though. And there are a lot of wild and crazy ideas out there too. One of the wackier approaches is to try to do Bohmian quantum mechanics, with an objective reality and pilot waves, applied to field theory -- usually capitalizing on some scalar field.
     
  10. Nov 23, 2005 #9

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    http://arxiv.org/abs/gr-qc/0511124
    Spin Gauge Theory of Gravity in Clifford Space
    Matej Pavsic
    9 pages, talk presented at the QG05 conference, 12-16 September 2005, Cala Gonone, Italy
    "A theory in which 16-dimensional curved Clifford space (C-space) provides a realization of Kaluza-Klein theory is investigated. No extra dimensions of spacetime are needed: "extra dimensions" are in C-space. We explore the spin gauge theory in C-space and show that the generalized spin connection contains the usual 4-dimensional gravity and Yang-Mills fields of the U(1)xSU(2)xSU(3) gauge group. The representation space for the latter group is provided by 16-component generalized spinors composed of four usual 4-component spinors, defined geometrically as the members of four independent minimal left ideals of Clifford algebra."

    garrett, is this someone you might want to get in touch with?

    EDIT since time hasnt run out and I can still edit, I will reply to your next post here!
    Garrett, glad to here you have ALREADY been in touch with Pavsic, whose work although different has some similar directions. the way it looks to me as (fairly naive) outsider is that it is good to have potential allies who can help each other get a hearing for their work. I was interested by this QG '05 conference held just this past September in SARDINIA. several people whose names I recognized were there, and also Pavsic whom I didnt know of until now.
     
    Last edited: Nov 23, 2005
  11. Nov 23, 2005 #10

    garrett

    User Avatar
    Gold Member

    Hey Marcus,
    Yes, I've read Matej Pavsic's papers and corresponded with him. And our work shares many common lines. But I came to the conclusion after playing with it a bit that the standard model just doesn't naturally fit in Cl_{1,3}. This isn't to say I don't think his work is good, and he never says it does fit -- he just says "it might." But, most of the stuff I've laid out in my paper are independent of the dimension and signature of what Clifford algebra you want to work in. It's a fairly compact introduction to model building with Clifford valued forms. I just picked Trayling's model as the one that looks by far the best in the end, especially when joined with gravity.
     
  12. Nov 25, 2005 #11
    How is he defining a "topology change" as opposed to the a change in geometry? Thanks.
     
  13. Nov 25, 2005 #12

    selfAdjoint

    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed


    A geometry change in this paper is a curvature change. The authors show that unlike a diffeomorphism itself, a change of differential structure introduces an extra term in the connection, and hence a change in curvature of the manifold. They identify this with sources of matter.

    A topologocical change would be something like the appearance of a new hole or handle on the manifold. The authors show that in spite of using radical topological surgery, cutting out tori and sewing them back in twisted or knotted, they do NOT introduce topology change.
     
  14. Nov 25, 2005 #13

    garrett

    User Avatar
    Gold Member

    SA,
    The differential structures idea is very interesting. Unfortunately, I only have a poor physicist's understanding of the topic. I know a differential structure is an equivalence class of atlases, and an atlas is a collection of maps from a manifold to R^4 and transition functions. But I don't get how to enumerate the various differential structures, or why there are an infinite number of them for four dimensional manifolds, and one or a finite number for many others. Although I see it is directly related to the number of smooth structures over n dimensional spheres. But I don't understand that well either. Do you know of any introductory description of this stuff, preferably online?

    This would integrate very well with the paper I wrote if it works like they seem to be saying it does. My paper lays everything out, the standard model and gravity, as a single connection over a four dimensional base manifold. The differential structures idea could give a natural explanation for the quantization of such a connection.
     
  15. Nov 26, 2005 #14
    Hi garrett, thanks for your interest in our paper.
    In the physical point of view an atlas is set of reference frames which are needed to describe measurements at different space-time regions. With Einstein all reference frames are physically equal if the charts can be transformed by diffeomorphisms - the charts are compatible.
    In 1,2,3 dimensions all charts (reference frames) are compatible. In 4 dimensions you can find one set S1 of charts which are compatible with all other charts in this set. But you can also find a further set S2, were all charts compatible in S2 but with no chart in S1. S1 and S2 are two different representants of two atlases. S1 and S2 belong to two different differential structures.
    In mathematics the differential structures are called exotic smooth strctures. It can be shown that for a manifold (e.g. Dim=7 like Milnor) atlases exist which are not compatible (transfromable by diffeomorphisms). It is also known that for a compact 4-manifold the number of non-compatible altlases are countable infinite. But the structure of the set of differential structures was unknown. We have shown that the set of the changes of a differential structure is a Temperley-Lieb algebra and the set of differential structures is a Hilbert-space (Dim H = inf). This is a mathematical fact like: "the number of integers is countable infinite". Torsten is writing a book about Exotic Structures and Physics: Differential Topology and Spacetime Models
    At the mean time you may looking for the mathematical papers about "Exotic Structures", but this is hard to cover.
    This is very interesting, please sent me a copy: rose@first.fhg.de
     
    Last edited: Nov 26, 2005
  16. Nov 26, 2005 #15
    Do you have more info on this book, such as a table of contents?

    Secondly, what are they talking about when they mention singularities? Is this supposed to be a topological entity, or is this a scalar function defined on a manifold whose value goes to infinity at various points on the manifold? Thanks.
     
  17. Nov 27, 2005 #16
    For the table ask Torsten (torsten@first.fhg.de).
    In our paper the term singular has the usual mathematical meaning in the context of maps:
    The map f: M -> N is singular at points were its differential
    df: T_x M -> T_f(x) N
    is vanishing. We do not mean poles etc. and it is not a topological entity (M,N are homeomorph). The map f is smooth but because of the singular points f^-1 does not exists (Like: a curve with a self intersection). f is a map between 4-manifolds, the set of singular points is 3-dimensional. We mean this singular 3d-set of map f when we use the term singularity - it is a 3d-region in the 4d space-time, like a particle. This singular set determines a 1-form -> the connection change between M, N -> differential structure change. Thus a 3d-set determines the transition of DS of a 4-MF.
     
    Last edited: Nov 27, 2005
  18. Nov 27, 2005 #17

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    thanks for the extra explanation. it is appreciated. sometimes just saying the same thing over (repeating what you already said in the paper with maybe a few more words) can be very helpful

    it looks like we need to refer to Brans papers
    I will try to find arxiv numbers

    http://arxiv.org/abs/gr-qc/9604048
    Exotic Smoothness on Spacetime

    http://arxiv.org/abs/gr-qc/9405010
    Exotic Smoothness and Physics*

    http://arxiv.org/abs/gr-qc/9404003
    Localized Exotic Smoothness*

    http://arxiv.org/abs/gr-qc/9212003
    Exotic Differentiable Structures and General Relativity*

    *these are cited in the recent paper

    we also need to be able to check out some Sladowski papers
    I am getting sleepy, and also I am worried now that this approach could be crazy. It looks too good. maybe I had better go to bed and try to understand some more tomorrow. thanks for your help so far Helge
     
    Last edited: Nov 27, 2005
  19. Nov 27, 2005 #18
    I appreciate the help, of course.

    So as I understand it, you've made a "connection" between 3D particles and 4D geometry, right? So that if we have means of determining the QFT of the vacuum, then we can connect this via differential structures to the background metric, is this right? It sounds like this effort might be getting close to figuring out the quantum geometry of the background (read quantum gravity) from QFT. Or is this saying that the same ZPE of QFT exists for any amount of curved space (the operator algebra is the same in all curvatures)? Thanks
     
  20. Nov 27, 2005 #19
    Yes, the singular 3d-support of the 1-form determines the change of connection of the 4-MF and thus the differential structure (DS). But note the DS is not the only structure which influences the geometry of the 4-MF . You have also the freedom to choose the metric and by this you can modify the geometry but the DS is fixed.
    if you mean the metric is fixed by the DS - no! I do not know how strong metric and DS are independent, but there is no one-to-one connection.
    And note in our model is no background metric: Also for a fixed DS the metric is dynamical - determined by Einsteins eq.
    As I can see, this can not answered yet. In any case the quantum geomety will be dynamical and we need to better understand the dynamics, i.e. the field eq. of DS - but we don't know.
     
  21. Nov 27, 2005 #20

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Helge, thanks for the explanation you have given so far!
    Do you have any suggestions of papers to read as preparation for your paper with Torsten?

    So far I just see the citations to papers by Brans and by Sladowski (including one that Torsten co-authored with Brans)
    are these the best to read or are there also others you might suggest?

    I know this is a very hard question to answer since we here are totally miscellaneous----some of us are self-taught, others are, or used to be, engineers and mathematicians. So it is a total mystery what information would help us to understand. But go ahead and take a chance. If you have anything to recommend, please do.

    this whole subject is incredibly interesting.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?