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Prospective grand unifying theory?

  1. String theory (includes M theory and superstrings)

    8 vote(s)
    23.5%
  2. quantum loop gravity

    6 vote(s)
    17.6%
  3. E8 (248 dimensional shape representing each particle)

    3 vote(s)
    8.8%
  4. other (please specify. i'm interested

    17 vote(s)
    50.0%
  1. Jul 3, 2011 #1
    prospective grand unifying theory??

    dunno if it belongs in this section but there are a handful of theories out there that try and describe our universe at a fundamental level. i just wanted to get everyone's opinion on two things: which GUT is most likely to become a theory of everything?
    do you think looking at stuff at a fundamental level is the right way to go about the process?
     
  2. jcsd
  3. Jul 3, 2011 #2
    Re: prospective grand unifying theory??

    just to add. in my opinion, i support string/m theory in coming to an eventual theory of everything because it fully explains how gravity works at a fundamental level and explains why gravity is a relatively weak force. dimensions are a new interesting way of looking at things.
     
  4. Jul 3, 2011 #3
    Re: prospective grand unifying theory??

    i don't really understand how quantum loop gravity works, would anyone be able to explain it to me? also, are there any other contenders for "theory of everything" (TOE) other than the ones i've mentioned.
     
  5. Jul 3, 2011 #4
    Re: prospective grand unifying theory??

    Since QT and GR are based on observations, they require further explanations themselves. So any theory based on them does not explain everything and so is not a theory of everything.
     
  6. Jul 3, 2011 #5
    Re: prospective grand unifying theory??

    but it could be a prospective theory of everything
     
  7. Jul 3, 2011 #6
    Re: prospective grand unifying theory??

    if there are calculations that yield experimental proofs which are proven true?
     
  8. Jul 3, 2011 #7

    marcus

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    Re: prospective grand unifying theory??

    Miba, if you are interested in the realistic prospects for unification you may have started out on the wrong foot, so to speak. I would suggest you watch the first 25 minutes of this talk

    http://media.medfarm.uu.se/flvplayer/strings2011/video24

    It is by a Nobel laureate, one of the authors of an important part of the Standard Model, who is still comparatively young and active in research. He is often invited to give overview talks about the state of particle physics and what he sees as the possible future developments.

    After some 5 minutes of introduction he starts talking about quantitative unification to be accomplished in the next few years based on observations from the LHC and cosmology.

    If you listen to Wilczek's talk about what he sees as the future of physics, especially in unification, you will learn about other things besides String and Loop and it will not be about Horava or CDT either.

    The reason Wilczek is so young compared with other authors of the Standard Model is that he was only a 21-year-old graduate student when he took part in the work for which three people were later awarded the Nobel prize. This was in 1972-1973. It was about the "strong nuclear force" part of the Standard Model picture, which came together in the 1970s.

    In his talk he is speaking to other physicists, trying to give an honest realistic picture. So it is not a popularization such as you might get from Kaku or Brian Greene. They paint romantic pictures to stimulate the popular imagination. Beware! :biggrin:

    I think Wilczek's perspective on practical quantitative unification is invaluable because he combines the wisdom of experience of top level involvement in the 1970s with still-youthful involvement in today's front line.

    I hope you watch the video. (Just the first 40% is enough). It could be 25 minutes well spent.
     
    Last edited: Jul 3, 2011
  9. Jul 3, 2011 #8
    Re: prospective grand unifying theory??

    okay then will do - actually i just wanted to hear everyone's feeling on each of the would be TOE's
     
  10. Jul 3, 2011 #9

    tom.stoer

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    Re: prospective grand unifying theory??

    String theory is the only program which could be seen as a candidate for a ToE.

    Loop Quantum Gravity isn't (strictly speaking) b/c the quantized gravitational field and other fields are treated on the same footing but are not unified (at least up to know).

    E8 (248 dimensional shape representing each particle) by Lisi has been proven (by Distler) to be incapable to contain the standard model; perhaps you have a chance to ask Garret Lisi who is from time to time active here in this forum.
     
  11. Jul 3, 2011 #10

    garrett

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    Re: prospective grand unifying theory??

    Hi Tom,
    You shouldn't just take my word for it, but what Distler actually proved is that when one embeds gravity and the standard model in E8 in the most direct way, there are also mirror fermions. Since many were misled regarding this point, I wrote this paper to make the issue clear:
    http://arxiv.org/abs/1006.4908
    and described it in this SciAm post:
    http://www.scientificamerican.com/blog/post.cfm?id=garrett-lisi-responds-to-criticisms-2011-05-04
    Personally, I'm using this embedding as a starting point, and now working on how to describe the three generations and mixing.
    Best,
    Garrett
     
  12. Jul 3, 2011 #11

    MTd2

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    Re: prospective grand unifying theory??

    LQG is not an unifying theory. And the way people fight over vanities right now is an indication that we are hopeless.
     
  13. Jul 3, 2011 #12

    martinbn

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    Re: prospective grand unifying theory??

    In my opinion none of the listed and not listed current contenders is going to be the TOE, because none of them looks mathematically sexy enough.
     
  14. Jul 4, 2011 #13

    MTd2

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    Re: prospective grand unifying theory??

    Oh, damn. I am becoming bored again.
     
  15. Jul 4, 2011 #14

    tom.stoer

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    Re: prospective grand unifying theory??

    Correct.

    Nobody ever claimed that it is; read Rovelli's papers, he explicitly states that the LQG research program was not started and never meant to be an unification approach.
     
  16. Jul 4, 2011 #15

    MTd2

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    Re: prospective grand unifying theory??

    That statement is my overall feeling about the whole theoretical community, it was not related to the first statement.

    I am bored.
     
  17. Jul 4, 2011 #16
    Re: prospective grand unifying theory??

    you're right, but surely finding a way to "quantise" gravity would be the closest yet we are to a unifying theory - more possibly a theory of everything. Just my opinion.
    i still think string theory rules though :)
     
  18. Jul 4, 2011 #17
    Re: prospective grand unifying theory??

    that's a shame. i watched the TED talk that Lisi gave and it seemed quite awesome - though i'd add that i barley understood it (it would be helpful if i had some kind of link to a simple explanation of all the mathematics behind the E8 model). the theory seemed to be a theory of everything because (kind of like string theory) it tells us that all the fundamental particles in our universe are different manifestations of the same "particle". Am I right?
     
  19. Jul 4, 2011 #18
    Re: prospective grand unifying theory??

    wasn't the whole idea of the Lisi's E8 model that the standard model was incomplete because of the symmetries that exist in the various dimensions rotated in different ways. the standard model simply groups particles that we already know of. if there were many more fundamental particles, wouldn't the standard model be kind of wrong anyway?
     
  20. Jul 4, 2011 #19

    qsa

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    Re: prospective grand unifying theory??

    Lets say you manage the three generations, would your theory answer these questions anytime soon.


    1. all couplings values and their relations and origin. That includes computing the behavior at all energies (and distances-up to edge of the universe if there is one(CC)). and if there is a physical cut-off or not.

    2. the theory must predict particles with their masses explained.Inculding light and its clear interaction picture with matter.

    3. What is charge exactly and how does the value come about.

    4. the origin of Spin and entanglment.

    5. how do particles behave in flight, like the double slit experiment.

    6. The real source of the effect of relativity. That is of course includes what is Space and time. and what is vacuum made of.

    7. the relation between all of the above.

    8. the origin and the fate of the universe or(universes)

    But Most of all what is existance made of, if not a mathematical imperative.
     
  21. Jul 4, 2011 #20

    garrett

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    Re: prospective grand unifying theory??

    mibaokula: Yes, more or less. Although the sm also includes some kind of Higgs mechanism, beyond the particles we strictly know of.

    qsa: Yes, potentially. But that is a big presumption you're making. However, I'm already very happy with how E8 theory describes the charges and spin.
     
  22. Jul 4, 2011 #21
    Re: prospective grand unifying theory??

    What is the difference between the graviton and the Higgs boson in terms of how they are percieved in nature

    If I'm right, the higgs boson gives certain particles mass limiting their range and velocity and the graviton mediates gravitational force. These properties seem quite related to me
     
  23. Jul 4, 2011 #22
    With your E8 theory, is the universe one giant E8 shape or does the E8 represent each fundamental particle - much like strings represent each fundamental particle in string theory?
     
  24. Jul 4, 2011 #23
    Re: prospective grand unifying theory??

    A grand unifying theory is not really a theory of everything it is just a theory that unites the Standard Model with GR.

    A theory of everything has to go quite a bit further, in particular it should explain QM. The type of theory qsa is always going on about ( :wink: ) has been proposed by Holger Bech Nielsen , a respected (former?) string theorist, namely random dynamics.

    (eg see the essay by Nielsen et al in proceedings What Comes Beyond the Standard Model 2007 Slovenia, or the articles by Kleppe in 2004 and 2009 conferences)

    Actually I would think QM is a theory of everything, just that we haven't understood it correctly yet.
     
    Last edited: Jul 4, 2011
  25. Jul 4, 2011 #24

    marcus

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    Re: prospective grand unifying theory??

    That's odd. There seemed to me to be a confusion at the very start of this thread because I thought that by grand unifying theory, he meant a Grand Unified Theory (GUT).

    A GUT is normally understood NOT to involve gravity. It is the "quantitative unification" that Wilczek was describing and foreseeing in his talk. Unify the three forces. Make the Standard Model nice and neat, better understood, less arbitrary clutter.

    It's worth getting clear about what we mean, I think. GUT is not the same as TOE.

    BTW Unusualname, thanks for your idea about downloading the talk file. I may get someone to help me and try to do it.
     
  26. Jul 4, 2011 #25

    garrett

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    Re: prospective grand unifying theory??

    mibaokula: The geometric setup of E8 theory is that of a principal bundle. Basically, at every point over our four dimensional base manifold there is a copy of the 248 dimensional E8 Lie group. The connection field at each point describes how this Lie group twists over the base manifold, with each of the 248 different possibilities corresponding to a different kind of elementary particle existing at that point. Sixteen of these correspond to the four gravitational frame fields (one time and three space directions) times the four standard model Higgs field components. In this way, gravity and Higgs are directly partnered, and via symmetry breaking the Higgs field and gravitational frame both take on a non-zero background value.

    unusualname, marcus: Yes, ToE = GUT + GR.
     
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