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Force unification

  1. Oct 14, 2008 #1
    Is it currently being researched as to how the four fundamental forces we know of can somehow just be one greater force working differently. Didnt einstein try to figure this out. Im not sure if this is the right section for this kind of question.
  2. jcsd
  3. Oct 15, 2008 #2


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    Einstein spent the better part of the last thirty years of his life trying to unify gravity (general relativity) with the electromagnetic force. The strong and weak nuclear forces had not yet been discovered. In any case, he was unsuccessful.
  4. Oct 15, 2008 #3
    has any progress on unifying all four of them or even just two of them been made since then?
  5. Oct 16, 2008 #4


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    Electromagnetic and weak forces have been unified.

    String theory is supposed to be the unfication of all four. However, no experiments have been made to verify any of it. Furthermore the theory is so complicated that very few testable deductions have come out of it.
  6. Oct 16, 2008 #5
    wow this is very interesting, is string theory the only one, it seems like the only one ive heard for the theory of everything.
  7. Oct 17, 2008 #6


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    There is at least one alternative. It is called "loop quantum gravity". This forum (Beyond the Standard Model) is supposed to be all about these questions.
  8. Oct 30, 2008 #7
    Inasmuch as I understand things, this isn't entirely true.

    Loop Quantum Gravity will tell you how to quantize gravity, but I don't see how one gets the other three forces out of the whole framework. (Marcos, I'm sure, will link me to papers from the arXiv that I won't read.) In string theory, there are ways to get the forces and particles we see in one unified framework. The alternative programs seem to be much less successful in this regard.

    So when it comes to "unifying the four forces", I think string theory is the only way to go. If you only care about understanding quantum gravity, then there are alternatives.

    It just comes down to what you want out of your theory of everything.
  9. Oct 30, 2008 #8


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    I hope that we can see more alternatives that just those two as well. As I see it, alternatives aren't static, they are constructed by science and thus the evolutionary perspective is important. So the generation of novel hypothesis continues to be important.

    For a fair comparasion string theory is I think soon 50 years old (since it's original formulation as a tentative theory for the strong force which was later abandonded in favour of QCD) and LQG is I think only around 20 years? and I'm not sure how the investments in each approach compare to the 5/2 ratio.

    Yet there might be yet undiscovered or VERY young alternatives that fits in neithere string nor loop classifcations that might well outgrow the old players in the future.

    I think it's fair to say that noone knows yet, and to say that this and that alternative is the only possible one, seems risky at best. I remember one of my old teachers who is now a string theory professor told me that the future of theoretical physics is string theory and if you like to research theoretical physics you better adapt to string theory. I think such statements are somewhat irresponsible and abuse of position towards young students coming into the field.

    I think string theory should be researched, but to say it as the only alternative in the sense that we need to look no further, doesn't sound right.

  10. Oct 30, 2008 #9
    Supersymmetry SUSY...

    According to Brian Cox at CERN, the Standard Model forces do not unify simultaneously into a 'superforce' at the same energy.

    The theory of supersymmetry (SUSY), doubles the number of fundamental particles in the Standard Model from 17 to 34. The new particles are known as superpartners. According to this model, all the forces unify nearly simultaneously at nearly the same energy, except gravity.

    SUSY is simulated by determining the Lagrangian for supersymmetry (SUSY).

    SUSY has 17 superpartners and according to the Garrett Lisi E(8) model there are 20 new fundamental particles, including 2 superweak neutrinos.

    Does this mean that these new Garrett Lisi E(8) model particles are superpartners?

    Is a superweak neutrino a superpartner of a neutrino?

    The Garrett Lisi E(8) model does not include for 17 antimatter superpartners?

    Is a infinite dimensional M-Theory Element E(11) really capable of breaking symmetry into a subset Gosset polytope Garrett Lisi Element E(8) TOE model?

    Reference 5: left Gosset E(8) with Vertices, right Garrett Lisi E(8) with new particles.
    Attachment: left Standard Model, right SUSY.

    Supersymmetry - Wikipedia
    TED - Brian Cox - CERN
    Standard Model equation - Brian Cox - CERN
    TED - Garrett Lisi - TOE E(8)
    Garrett Lisi E(8) model
    Lie Groups - Orion1
    M-theory - Wikipedia

    Attached Files:

    Last edited: Oct 30, 2008
  11. Oct 31, 2008 #10
    I'm not sure why people are still talking about Garrett Lisi's E8 model, as I'm pretty sure that even Garrett himself has admitted that one can't get chiral matter (i.e. anything that looks like the real world) out of the framework.

    We can always remain hopeful for a new and interesting alternative, but as it stands, string theory offers the only hope for unifying the four forces. This is not something that LQG can do, in most cases. The only attempt at getting matter out of LQG that I have seen recently (and, to be fair, I don't normally pay attention to the field) is Lee Smolin's last paper, where he predicts four generations of neutrinos---this prediction is highly unlikely, and most people don't take the idea of another generation seriously.
  12. Nov 10, 2008 #11
    Be careful though.String theory is a candidate to unify all forces and far from having done this already.
  13. Nov 10, 2008 #12
    I work in string theory because I at least see the potential for a unified theory. The other approaches to quantizing gravity are far from convincing, in this respect. There is an active community of people working on "string phenomenology", and we're working at the level of trying to get particle masses right. The other LQG approaches are still trying to get the standard model out in the first place.
  14. Nov 10, 2008 #13


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    How about thus 10^500 number that pops in the popular media all the time? I'm a biologist and fudge my models all the time, but even that sounds too much. :confused:
  15. Nov 11, 2008 #14
    Hi Ben!I also work in theoretical high energy physics!I agree with you (although there are far fewer people working in LPG and reasonably their progress is slower).Since the forum is read by non physicists as well i just wanted to mention that they shouldn't think string theory as a complete theory in a sense that there are still open subjects.But i have to admit that is the most promising one(unfortunately it gives much more than we originally asked)...
  16. Nov 11, 2008 #15


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    Lisi gets the SM, however, it comes with aditional particles for each of the 3 generaltions within it. That is, the Standard Model is not a subgroup of his theory, but it is subset of his E8, and those particles are called by Jacques Distler calls "spurious particles".

    The chiral problem happens when one tries to find the standard model in such a representation that should give SM as we know it today, that is, without aditional particles. And the lack of chirality is not the only problem to this approach, the other one it is that in this case, one can only get on generation.

    So, I really don't see any problem with Garrett's model yet, considering that these aditional particles were not yet studied properly in his model.

    Also, grand unifying theories, like SU(5), contrary to popular belief are not falsified yet, since the proton decay half life was ruled out until 10^(34) years. But given that the upper threshold for proton decays in several GUTs are around 10^(38) years to 10^(42)years.

    Nevermind that the works with Wan's brainding might (already did, but didnt bring the picture together yet) bring Standard Model, and possibly all redundancy of string theory, to LQG. For these reason, I would rather study LQG for the sake of introducing a new mathematical theory, that is might works with the real world, as I believe it will, than sticking with a string monoculture. Indeed, the progress is slow, but it is getting faster lately, as more people want to see something different.

    Note that here, I don't refer to strings as a topological study of cobordisms and smoothness. It gives rise to a lot of general mathematical statements, and in this sense, those common superstrings works awsomely well as toy models for mathematical structures. But it's nice to look for other approaches, IMHO.
  17. Nov 11, 2008 #16


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    That's because string theory is a mathematical framework that embed a lot of "realistic" physical theories. But it doesnt meant that it reflects a "fundamental reality" nor that something will be found that rules out all of them. It just that, with everything that we've found so far, we can't find a way to say none of them will work out. String Theories is like killing terrorists, for every person killed, 10 more shows up, and 100 more are recruited the more you piss them off.
  18. Nov 11, 2008 #17


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    I really think that LQG will be soon be just one more generic terrorist field like string theory. There will be others. I can see that Connes Geometry will soon follow this path, for example But at least, we've got more teams to have fun!!!! :eek: (unfortunantely, i really think they will be soon, that is, in less than 200 years, to be proven all horribly wrong)
  19. Nov 11, 2008 #18


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    Alain Connes hasn't given up his theory. After a few weeks his theory was ruled out, he came up with something new and even will release a new book on this... Wow, without experiments, high energy physics will become literaly feudal properties.
  20. Nov 11, 2008 #19
    I like the example you gave...i also like string theory.I think we can gain a lot from studies of both theories.but i also strongly believe that physics is an experimental science(although i am a theorist).If we don't see any of these things in the ''lab'' it will remain unclear what is the real picture.It's always been this way.a lot of theories from the past have been forgotten because they were not the case.that is my point and that's way i originally wrote that string theory (and LPG) are just nice candidates.
  21. Nov 11, 2008 #20
    This is the number of possible string models that one can build, many of them having nothing to do with the real world.

    How many possible models could you build, as a biologist, if you weren't concerned with matching data? (An ACTUAL count isn't necessary, just ballpark it :) ).

    There are lots of problems with Lisi's model. The biggest one is chirality---the SM is chiral, and it doesn't look like Lisi can get chiral fermions out. If that is the case, then it is just wrong. I am no expert in his work, though, and will stand corrected.

    Secondly, Lisi doesn't quantize gravity. Lisi gets an SO(4) out of E8, which is different from actually quantizing gravity. So Lisi's theory shows how to embed SM x GR into E8. While this is beautiful and impressive, it is different from quantizing gravity.

    The minimal models are all dead, for various reasons. One has to dress the models up with large higgs representations, which are ugly and poorly motivated. See these papers: http://xxx.lanl.gov/abs/hep-ph/0108104, http://xxx.lanl.gov/abs/hep-ph/0007213

    Also note that most of the people who started working on Grand Unified Theories in the 1980's now work on string theory.

    If you're talking about Smolin's last paper, he predicts, pretty clearly, a fourth SM generation, which is ruled out by observation.

    Either way, this seems engineered. There are several ways that chiral matter and non-Abelian gauge symmetries appear in string theory, "for free". Take Type II string theories. You build a theory of open strings, and you realize that these open string endpoint have to live on hypersurfaces called D-branes, which are required for the consistency of the theory. Then you examine configurations of D branes and find that you can stack them on top of each other and get a U(N) theory out. So there you go---a non-Abelian gauge theory for free, given by things that are already appearing in the theory in the first place.

    Alain Connes predicted a higgs a 160-170 GeV, and Fermi Lab ruled a higgs out at that mass earlier this year. But, it's always possible to fix your model by adding stuff.
    Last edited by a moderator: Apr 23, 2017
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