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Smolin's Loops 07 talk is up (slides and audio), looks like a biggie

  1. Aug 15, 2007 #1

    marcus

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    http://www.matmor.unam.mx/eventos/loops07/talks/PL5/Smolin.pdf

    http://www.matmor.unam.mx/eventos/loops07/talks/PL5/Smolin.mp3

    The Loops 07 website continues gradually posting the slides and audio of the talks and several very interesting new ones are now online as of 14 August.

    I just listened to the Smolin talk while scrolling along thru the slides and was impressed by how much progress Smolin's braidy gang has made even in the brief time since the telephone seminar.

    braidy particle physics suddenly is looking more real

    it is also very much on the spinfoam side AFAICS rather than the canonical LQG (hamiltonian etc.) side. also very much on the embedded side of things.

    like so much of the exciting new work that has come out there is no dependence AFAICS on a discrete volume spectrum (which some people have been worrying about recently) Please explain if I am wrong, but this seems to be a completely different picture of space, of spacetime, and the tangles in it we call matter----completely different from 1990s canonical LQG.
     
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  3. Aug 15, 2007 #2

    marcus

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    Bianca Dittrich Loops 07 talk is also online now

    The Loops 07 website has also now got Bianca's audio up too. I just listened to it: definitely one to hear.

    http://www.matmor.unam.mx/eventos/loops07/talks/1B/Dittrich.pdf
    http://www.matmor.unam.mx/eventos/loops07/talks/1B/Dittrich.mp3

    I'm a longtime fan of Bianca Dittrich, since hearing a seminar talk she gave at Penn State in 2005, I think it was.
    She is sure of what she says. you can bank on it.
    I like her recent work with Johannes Tambornino on partial and complete observables for General Relativity---getting relational observables for GR right, and set up for perturbation expansion.

    what she has now is a machine that can be used to address a lot of issues.
    a very powerful tool that she can apply to one thing after another---this recent thing with the geometric operators is only ONE application. there are sure to be several more.
     
    Last edited: Aug 15, 2007
  4. Aug 15, 2007 #3

    Kea

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    Last edited: Aug 15, 2007
  5. Aug 15, 2007 #4

    marcus

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    Bee Hossenfelder's is up as well

    the more complete they get the conference on line the more exciting it gets!

    a month ago when i summarized what slides and audio were up they didn't yet have Sabine Hossenfelder audio, but that's up now too

    http://www.matmor.unam.mx/eventos/loops07/talks/PL5/Hossenfelder.pdf
    http://www.matmor.unam.mx/eventos/loops07/talks/PL5/Hossenfelder.mp3

    this thread has a summary of which Loops 07 talks are available:
    https://www.physicsforums.com/showthread.php?t=177096
     
    Last edited: Aug 15, 2007
  6. Aug 15, 2007 #5

    CarlB

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    Kea, I guess I don't quite see the direct relation to what I'm messing around with. The basic difference is that they are assuming that the known fermions are each some topological object. I'm assuming that the known fermions are linear superpositions of objects. You could relate my version of reality to a topology, but it wouldn't be the one they're using because the linear superposition is too important.

    The reason I'm fairly sure that I'm doing this right and they've got it wrong is that everything in the standard model is built from complicated linear superpositions of things that look simple. I think that linear superposition is a principle that should go all the way down. For example, the proton is not a uud, but instead is a linear combination uud+udu+duu. This assumption makes the generations show up naturally because when you combine three distinct preons, you naturally end up with three orthogonal linear combinations, hence exactly three generations. (This is why the structure of the excitations of the uds spin-3/2 baryons can be an exact analogue to the generation structure of the charged fermions.)

    If you look at the chiral fermions, we assume that they are massless and therefore travel at speed c, and according to the usual relativity, that gives a reason why linear superposition should not be needed for the chiral fermions. And in this sense their way of doing things is internally consistent with the rest of physics. Light speed things need to be made from components that are frozen and do not interact with each other, hence must be elementary.

    But as you know, I don't believe in the usual relativity, so for me linear superposition is still possible for light speed objects. My version of reality is also internally consistent in its own way. The problem is that its internal consistencies are almost all incompatible with the internal consistencies of the standard view. The number of incompatible assumptions is about two dozen and they self reinforce in amazingly beautiful and complicated ways.

    Getting back to the Smolin paper, in previous stuff by these guys there was some speculation on where the weak hypercharge and or weak isospin numbers come from in terms of braids. I didn't see that repeated here. I thought the original version was kind of stretched.

    The generation structure comes up in slide 47 not 38. Maybe it's my failing eyesight, but it seems to me that they only got the first two generations, the electron and muon are included, but nothing from the tau generation. And then they admit to having fractionally charged states that are not observed. It's hard for me to pass judgement on this with a straight face.

    Carl
     
  7. Aug 15, 2007 #6

    Kea

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    Oh, don't worry, you're clearly more correct (they have Dark Energy?! Huh!) although personally I don't favour the superposition interpretation exactly (but that's only because I like the prospect of doing all this with higher topos theory, in particular 3-logic, and think about ribbons the way Grothendieck did). But the slides make it clear that they are at least heading in the right direction at last. And since only a handful of people are listening to you, that's a start, albeit a slow one. Some young people may begin to see the similarities here and perhaps start reading your work.

    BTW, it's the numbering scheme that gets mentioned on slide 38.
     
    Last edited: Aug 15, 2007
  8. Aug 15, 2007 #7

    CarlB

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    Okay, Kea, I see what you mean. The quantum numbers (a,b,c) arise from sums over parts of graphs. That's sort of equivalent to how I combine two primitive idempotents to make a "snuark". The quantum numbers also fall in the following cases:

    +1+1 == +1
    +1_1 == 0
    -1+1 == 0
    -1-1 == -1

    But they assume that the two center conditions are identical so they only have three cases.

    It's probably worthwhile to type up how this works out. It gives a good illustration of how algebraic ways of playing with preons works out differently as compared to topological ways.

    My way: First choose a direction, for instance, going in the +z direction. That gives a factor (1-zt)/2, which the rest of the world writes (more or less) as [tex](1-\gamma^3\gamma^0)/2[/tex]. All the primitive idempotents share the zt quantum number -1. I say "more or less", because I'm using Clifford algebra (4,1), and the gamma matrices are in the Clifford algebra (3,1). The extra guy I call "s", and is sort of like a [tex]\gamma^4[/tex] that is independent of the four other gammas. The x,y,z,s,t are just like the gamma matrices, but there's an extra one. That is, they anticommute, and I'm using east coast metric so x^2 = y^2 = z^2 = s^2 = 1, t^2 = -1. If you want west coast metric, multiply by a factor of i for each symbol. This notation greatly eases calculation in that it makes stuff shorter. And when one does QFT on qubits, one has no spatial dependence so there's no need to be confused about what "z" means, [tex]\gamma^3[/tex] or a spatial coordinate.

    By the way, as I mentioned above, Smolin etal are making the assumption required by special relativity that the chiral fermions are speed c and frozen. I also make a similar assumption, but at one stage deeper. I'm assuming that the primitive idempotents are "speed c" and therefore frozen and not subject to linear superposition, but I don't assume that the chiral fermions are so restricted.

    Choosing two more quantum numbers that commute with zt, we use ixy and s. There are therefore four primitive idempotents to choose between:
    [tex]\begin{array}{c}
    (1-zt)(1-ixy)(1-s)/8,\\
    (1-zt)(1-ixy)(1+s)/8,\\
    (1-zt)(1+ixy)(1-s)/8,\\
    (1-zt)(1+ixy)(1+s)/8,
    \end{array}[/tex]

    Writing out an idempotent, and ignoring the common factor (1-z)/8, their components are:
    [tex]\begin{array}{ccccc}
    A = &+1 & -ixy & -s & +ixys\\
    B = &+1 & -ixy & +s & -ixys\\
    C = &+1 & +ixy & -s & -ixys\\
    D = &+1 & +ixy & +s & +ixys\end{array}[/tex]

    Assume that the highest energy is associated with the largest number of reflections (in geometric algebra, each vector is interpreted as a reflection in that direction. For example, x is a reflection in the x direction. That's parly why xx = 1. See http://modelingnts.la.asu.edu/pdf/crystalsymmetry.pdf for a description of how geometric algebra is used in the practical problem of classifying the crystal symmetries.) Therefore, of the above four terms, 1, ixy, s, ixys, the one with the highest energy is ixys.

    To cancel off the very high ixys energy, we have to combine the primitive idempotents in pairs. There are four possible pairs, A+B, A+C, B+D, C+D. With the ixys quantum number cancelled and the 1 quantum number not distinguishing anything from anything else, there are two quantum numbers left, ixy and s. The sums on these come out as:

    [tex]\begin{array}{lcc}
    \textrm{Snuark}& ixy & s\\
    A+B=&-2&0\\
    A+C=&0&-2\\
    B+D=&0&+2\\
    C+D=&+2&0\end{array}[/tex]

    The (+2,-2) are interpreted as a sort of weak isospin doublet, and the (0,0) are two weak isospin singlets. These are the snuarks, roughly equivalent to the ribbons of the helot theory.

    So here's the difference between my snuarks and their ribbons. I have four snuarks with quantum charges of +2, 0, 0, -2. They have three ribbons, which carry charges of +1, 0, -1. I've got an extra 0 state, which makes my neutrino be a Dirac particle, and there is an overall factor of two difference, which means nothing.

    Carl
     
  9. Aug 16, 2007 #8

    marcus

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    On slide 38, where they appear, those quantum numbers (a,b,c) are called Kauffman numbers. In the 1990s the eponymous Kauffman coauthored a couple of papers with Crane. And then some 10 years later Kea co-authored a couple of papers with Crane.
    Small world, yes?
    Here are Louis Kauffman's papers
    http://arxiv.org/find/grp_physics/1/au:+Kauffman_L/0/1/0/all/0/1
    his interest in braiding and spin networks seems to go back a ways.
     
  10. Aug 17, 2007 #9

    marcus

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    Getting back to the Loops 07 talks, the website continues posting more of the audio and slides. As of yesterday the talk of Tambornino was available.

    http://www.matmor.unam.mx/eventos/loops07/talks/1B/Tambornino.pdf
    http://www.matmor.unam.mx/eventos/loops07/talks/1B/Tambornino.mp3

    He is a former student of Bianca Dittrich who is now one of her main collaborators. In this talk Tambornino does part of the exposition. Bianca gave a plenary talk the day before, presenting a part of the results, and in his parallel session talk he was presenting the rest.

    Both of them are very good.
    Tambornino is based at Aachen, where Bojowald started out (and where Hans Kastrup, one of Heisenberg's students, is the quantum gravity elder).

    what Dittrich and Tambornino are offering is a NEW WAY to do quantum cosmology that could supplement and potentially improve on the way that Bojowald and Kastrup started in 1999-2000 and has been carried out by Bojowald and his collaborators.

    it is a perturbation method where you perturb around a dynamically determined background (a symmetry-reduced sector) rather than around a fixed background. they use the full theory rather than working in a minisuperspace. It looks like they are able to calculate, but at the same time handle more in the way of anisotropy and inhomogeneity.

    Bojowald has also been moving more to the full theory rather than minisuperspace lately. His most recent paper on arxiv also used a CONTINUOUS model rather than discrete time difference equations.
    Quantum cosmology is moving rapidly.

    Maybe in case someone wants to listen to all three talks I will put the links to Bojowald's as well
    http://www.matmor.unam.mx/eventos/loops07/talks/PL4/Bojowald.pdf
    http://www.matmor.unam.mx/eventos/loops07/talks/PL4/Bojowald.mp3

    by odd coincidence I think all three of these speakers have association with Aachen and may have been guided at some point in career by Kastrup (so they are Heisenberg grandchildren :smile:)
     
    Last edited: Aug 17, 2007
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