Four Reasons Why I like String Theory

It is exactly one year since I started this blog, so to celebrate I will give my four top reasons for liking string theory.

This is partly a response to a recent survey on Cosmic Variance which included a question about what likelihood people gave to string theory being correct. With about 170 people responding, about half of them gave string theory 10% or less, many said 1% or even 0%. Now, science isn’t settled by democratic votes especially by a random sample of commenters on one particular blog. Nevertheless it is a revealing outcome and there are plenty of other physicists who think the same. The reasons people gave were roughly along the lines of “It has not had any experimental success after a long time” or “it is unfalsifiable”. I dont agree that these are real issues but instead of talking about that I want to review why I think it is still a theory worthy of being excited about.

(1) My top reason for thinking that string theory is a correct approach to unifying physics is that it provides a consistent perturbative description of particle physics with the inclusion of gravitons, and there is no known alternative. Gravity is a very weak force and spacetime is nearly flat on small scales. There must be some perturbative description of the quantized interaction of particles with gravity as a series of approximations. A direct quantisation of GR cannot do this, but string theory can. Furthermore it achieves this in a way that did not have to work, but it does because of surprising cancellations. There are five consistent string theories in 10 dimensions which are all related by non-perturbative dualities. The reductions to 4 spacetime dimensions is a consistent process which is now reasonably well understood, except we dont know the correct compactification manifold. The only alternative way to get a consistent perturbative theory is possibly from supergravity, but by now we understand that supergravity too is just another  limiting case of string theory. Some physicists have suggested that there may be a chance of finding other non-perturbative solutions to the quantum gravity problem, but no complete solution of that type has been found yet. Until it has, this reason alone is a very strong indication that string theory is on the right path.

(2) Supersymmetry! There are many ways that string theory can reduce to low energy particle physics and not all of them would result in observable supersymmetry. On the other hand, supersymmetry is a natural byproduct of string theory and if it does exist in nature at scales currently being probed by the LHC then it can explain several mysteries. These include the hierarchy problem, dark matter, a light Higgs and the convergence of the running coupling constants at the GUT scale where SUSY says they all have a value of around 1/24. In the last few weeks we have seen the exclusion limits for SUSY greatly extended by CMS and ATLAS. They say that if you throw a frog into hot water it will quickly jump out, but if you put it in cold water and gradually heat the water up it will stay there until it is boiled to death. You should not try this experiment at home but it seems like nature is trying it on physicists who like supersymmetry. In the 1980s we thought that supersymmetric partners would have light masses to avoid fine tuning. If this was right they would have been seen at LEP or the Tevatron. Now the LHC has pushed the minimum masses to uncomfortably high values implying quite a lot of fine tuning. The water is heating up but we will stay put because we now know that the multiverse allows for such fine tuning provided it is in the best interests of our existence. Perhaps the higher masses were needed to allow dark matter to form galaxies or some such.

(3) My third best reason for supporting string theory is that it provides a solution to the black hole information paradox via the holographic principle. This is a much more theoretical argument but it is still quite convincing, I find. Although there may never be any evidence for Hawking radiation from black holes, we know theoretically that it has to be there. Some reasoning using semiclassical quantum gravity tells us the laws of entropy for a black hole, and this should remain correct for any complete theory of quantum gravity such as string theory. Further arguments also tell us that the rules of thermodynamics must obey a holographic principle to avoid the paradox of thermodynamic information being lost inside a black hole. Again, any theory of quantum gravity worth its salt has to comply. It is therefore a triumph for string theory that the AdS/CFT correspondence shows that string theory does (or can) realize the holographic principle.  It is another indication that string theory is on the right track.

(4) My final reason for liking string theory is that it comes with a multiverse. For some people this is the favourite reason for not liking string theory and my reasoning for thinking otherwise is partly philosophical, so only people with similar philosophical leanings will agree with me. Ten years ago I did not favour anthropic reasoning. That was because the anthropic principle requires a range of theories that the universe can choose from so that one customised for intelligent life can be selected. I am comfortable with the platonic view that all mathematically consistent universes exist and we just inhabit some part of that realm, but in order to explain the symmetries that govern the laws of physics I think you need to invoke a further principle. For me that principle is universality in the sense of universal behavior seen in complex dynamical systems such as those seen in critical phenomena. I think there is a universal behavior of some type in the realm of complex mathematical systems which overwealms all other possible laws of physics so that only one unique possibility complete with all its beautiful symmetries can be what we experience. You can see that this does not fit well with the anthropic principle. However, there are good indications that the laws of physics are somehow selected to promote intelligent life in a way that would not be consistent with a single unique set of physical laws, contradiction! Luckily the multiverse comes to the rescue in the form of the string landscape. It turns out that string theory does indeed follow from some unique over-arching M-theory, but it can be realized in many forms in lower dimensions by a choice of vacuum determined by the compactification manifold. A wide range of these vacua are stable and there could be as many as 10^500 of them, plenty enough to account for anthropic reasoning. In my view it is the perfect outcome.

So those are my four best reasons for liking string theory. This does not mean that I don’t value other approaches to quantum gravity. We still need to find its complete non-perturbative formulation andIi am sure that such a thing must exist even if string theory has nothing to do with the laws of physics. Other theories such as Loop Quantum Gravity, Non-Cummutative Geometry or Group Field Theory lead to rich mathematical concepts. I see this as a sign that they are telling us something about our world, but I think you have to look for what it says about possibilities for non-perturbative string theory. For example, Loop Quantum Gravity tells us that knot polynomials and spin networks should be important. I like the fact that recently Witten has explored implications of  high dimensional generalisation of the knot polynomials (Khovanov homology) to branes from M-theory. This is the kind of outcome I expect from alternative approaches.

So what of the problems people say are issues for string theory? I see the multiverse landscape as an asset, not a problem. It means that string theory cannot tell us much about low energy physics so we will have to look for Planck scale effects instead. Such predicted effects may not be known until the non-perturbative side of string theory is understood, and after that it may be a long time before technology allows us to test them. That I am afraid is the nature of the game. We have no automatic right to expect nature to be kind to us and provide an easy test of any theory of quantum gravity. We are suddenly in a position where almost anything we can observe seems to be  covered by the standard model + general relativity so it should be no surprise that testing string theory is very difficult. Any other theory of quantum gravity is likely to have the same problem.

63 Responses to Four Reasons Why I like String Theory

  1. Kea says:

    OMG, you can’t be serious. There are no gravitons, SUSYs or stringy multiverses! If you want to keep on supporting string theory, at least like it for its strong points: arithmetic structure, information theoretic dualities etc. In other words, ditch stringy ‘physics’. If it doesn’t agree with experiment, as Feynman put it, IT’S WRONG.

    • Philip Gibbs says:

      Hi Kea, I do like its mathematical properties too. As a mathematician I might be interested in it purely for those reasons, but as a physicist I like it because of the ways it corresponds to reality.

      Of course I agree that string theory has to agree with experiment. If it disagreed with experiment I would give it up as a unified theory and so would every other physicist. I would also give it up if there was another theory that solved the same problems while providing more information about e.g. low energy particle physics, but there isn’t.

    • Lawrence B. Crowell says:

      This is a problem I have with your agenda. Your ideas about braids and discrete topological structures are interesting, but physics is more that topology. Homology implies usually curvature on a bundle or space, which puts one back into the territory of geometry. Yet it appears that you reject so much of physics that is developed that you have painted yourself into a corner — and off the game board.

      String theory is vast, with lots of structure. It is too big to be completely false. It of course might be too big to all be correct as well. Besides, if you get into it some you find it is rather interesting.

      • Kea says:

        Of course string theory is not completely false. I openly support dualities, information theoretic M theory, the arithmetic aspects, and much more. But that is MATHS, not physics. If the stringers are wrong about the PHYSICS of susy, multiverses, fairy fields, and just about everything else, then they are WRONG. Plain and simple. And if they are decent physicists, they will admit it. You don’t seem to understand that we are in the business of DERIVING string theory, so saying that all I have a few discrete knots just shows your ignorance of this approach.

  2. Leonard Otto says:


    I like this presentation I found on Kea’s blog.

    You might see my post today as relevant at least from the philosophy of it all. Not sure if it is an alternate theory needing experiment or not as a way to settle things. (I think Kea is on the right tract).

    I suggest that we do need a balance of existentialism and pragmatism, for such a balance would raise the deeper paradox of Abbagano’s synthesis: “There are no necessary realities.”

    The PeSla

    • Philip Gibbs says:

      Leonard, it is good to see you over here.
      I don’t know if Kea is one the right tract or the right track 🙂 but I also like a lot of the things she posts.

      “There are no necessary realities.” I like the sound of that but I have no idea what it means. Feel free to explain.

  3. mark a. thomas says:

    Here is another reason to believe in string theory: exp^2(pi*sqrt163) 70^2 = 337736875876935471466319632506024463200.00000080231935662524957710441240659… , which is almost equivalent to the closed physics form hc/piGm^2 = 3.37700(34) x 10^38 (dimensionless) where m = neutron mass and all physics values are Codata 2006. If you invert this value and divide by 2 you have the weak gravity value 5.9…x 10^-39. Looking at the forms you have: exp^2(pi*sqrt163) 70^2 ~ hc/piGm^2 where hc/piGm^2 = (Planck mass/neutron mass)^2 and it is less likely to appear coincidence because of its quadratic form R^2 70^2 = (Planck mass/neutron mass)^2 where R = Ramanujan constant and 70^2 is the null vector construction of the hyperbolic Leech lattice (relating the 26d bosonic string). Further considerations of this not to be coincidental are a factorization integer square form 256 x 9 x 25 x 49 x 109390588060032031^2 = 337736875876935471466319632507953926400 which is very near to the above number as (640320^3 +744) is to e^(pi sqrt163). Also, Bekenstein Hawking entropies can be calculated using the number theory form in very good agreement with the physics form. Last I have to say that it is hard to prove from a math rigor that something like this is not a mathematical coincidence and that goes without saying but the relation is razor sharp.

    • Lawrence B. Crowell says:

      These relationships we discussed last month at some depth. These seem enticing in some ways. I also have to wonder whether these are not accidents of sorts as well.

      Cheers LC

      • mark a. thomas says:

        Hi Lawrence, yes it could be coincidence. There is a utility that works very well with this though and that is Bekenstein-Hawking entropies can be calculated that agree very well with the regular semiclassical entropy calculation. The calculation is S_bh = 8pi (#degrees of freedom)^2 (e^(2pi sqrt163) 70^2)^-1 That is if you designate number of degrees of freedom as number of degenerate neutronic bags at or on the event horizon. In addition the quadratic form R^2 70^2 = (planck mass/neutron mass)^2 makes it appear less arbritrary also. I will make a prediction here. When the new Codata appears I am thinking that the closed physics form calculation will converge even more onto the mathematic structure. That is if experimeters get a good handle on the worst actor that being Newton’s G.

        Hope you are progressing in your work. mark

      • Lawrence B. Crowell says:

        Unfortunately this month I have been really sick with pneumonia. It has pretty much knocked me flat, so I have not gotten that much done of late.

        Newton’s G is in natural units an area. The area of a black hole event horizon is composed of Planck areas Għ/c^3 which contain string modes. The number of string modes which define a black hole horizon area is then effectively an integer partition, which has been commented on here. It would be of some interest to know what the relationship is between that and

        S_bh = 8π(#deg)^2 (e^(2π sqrt163) 70^2)^{-1}

        Cheers LC

  4. Kea says:

    Mark, that’s not string theory. The 70 is recovered from the 24 dimensional bosonic space of the Leech lattice, which is accounted for by the quantum numbers of the standard model plus some CPT violation, and NO stringy physics. This is the maths of VOAs, which are operads, and if you knew any maths you would know that this has nothing to do with string theory. In fact, quantum gravity DERIVES string theory from something far more elegant, using higher dimensional operads. Check your facts.

  5. Kea says:

    To prove my point: antineutrons and neutrons have distinct masses, as do neutrinos and antineutrinos. The neutron sector mass difference is about 9 x 10^(-5), as a fraction of m. You have just specified this difference with your two figures, but it was not predicted by string theory.

  6. Kea says:

    That is, take exp(2.pi.sqrt(163)/3). Then take the inverse of the non integer part, and take the square root to get a mass number. You will get 9 x 10^(-5). Since the antineutron is lighter (yes?) it has the integer mass.

  7. Kea says:

    Oops, no, the cubed root should only be applied to the error fraction …

  8. Kea says:

    Mark, I cannot download your vixra paper … ??

    • mark a. thomas says:

      Kea, I removed it because of concerns that it was not up to par with what is expected of genuine scientific discourse. In a note I am not a physicist or mathematician and my technical writing is quite bad so I am not pursuing this or anything else. However, I did find that e^(2pi sqrt163) 70^2 ~ hc/piGm^2 (m= neutron mass) and although one could consider that I was lucky to have found this I wonder about that too as to whether it was just luck only. Sometimes observations of disparate stuctures being related goes a long way to reconciling things (unifying concepts). I could be happy for just finding this only if it is not coincidental. I disagree with you that this is not related to string physics as per the Dedkind eta function relation with the Leech lattice and bosonic string theory. In additon Richard Borcherds proved the monstrous moonshine conjectures using the 26D string theory and yes it incudes pretty much of everything you say above. As to e^(2pi sqrt163) 70^2 = hc/piGm^2 intepretation is open and it does not necessarily have to include string physics although that would be my layman’s guess. See Munafo’s analysis (not explanation) of this relation .It will be interesting to see what Phil says about the 24 cell and qubits and all. By the way I do enjoy your blog.

      • Kea says:

        No, Mark. The 26D theory does NOT include all the underlying categorical mathematics of operads. Most stringy predictions, if they can even be called that, hinge on SUSY theories, not the 26D bosonic theory. These predictions are wrong. I have been looking for physics in String Theory for about 30 years, and I don’t see much.

    • Alejandro Rivero says:

      Hey, I didn’t know this equation, I regret you have removed it from Vixra because I like to have a chronological assessment of when each of these numerical relationships are conjectured. Did you notice it recently?

  9. kneemo says:

    Great post. I would add a fifth reason: string/M-theory is still work in progress. Another great reason is that string/M-theory is forced to exist in certain dimensions, e.g. bosonic string theory in D=26, M-theory in D=11, superstring theory in D=10. This seems surprising at first, but in pure mathematics, this kind of dimensionality restriction also occurs with certain structures such as the exceptional groups, composition algebras, Hopf fibrations, densest lattice packings, etc. So considering M-theory as a mathematical theory in progress, it behooves us to investigate and discover the deeper geometric and algebraic structures behind it.

  10. Kea says:

    Yeah, kneemo, go on. Keep supporting them in public and admitting their failure in private. Very courageous of you.

  11. Lawrence B. Crowell says:

    Another reason is the gravitational modes or degrees of freedom are determined by quantum fields on a boundary or horizon. This reduces the estimated entropy of the world.


  12. One should avoid taking the attitudes to string theory and super-symmetry as an emotional yes-no questions.

    Super-conformal invariance implying also space-time super-symmetry -but very probably not realized in the same manner as in MSSM and in string models- is something very beautiful and I believe that it is matter of time when SUSY is discovered in its correct form. LHC is just now taking care of this and this is a fascinating intellectual adventure for all involved. I am happy to participate this adventure this and this).

    TGD framework provides a new view about SUSY which seems to conform nicely with the intuitive picture: essential new elements are p-adic length scale hierarchy and the breakdown of R-symmetry by mixing of right-handed neutrino with left-handed one. Again one starts from experimental problem as good physics must always start. What is the physical role of mysterious right handed neutrino in physics? This is the question. CP_2 geometry provides this role as generator of super-symmetry. Supersymmetry breaking follows automatically when space-times are regarded as surfaces and is due to the special properties of induced spinor structure: string people still have failed to discover it: to me this looks incredible!

    The basic reason for the failure of string theory as a physical theory is the belief that fundamental objects are strings.There is no need to assume this. In TGD framework very stringy physics emerges for 4-D fundamental objects with the generalization of conformal invariance from 2-D context to 3-D light-like surfaces. Space-time dimension D=4 is completely unique. String like objects emerge naturally and also the slicing of space-time surfaces by string world sheets as also preferred string world sheets so that AdS/CFT correspondence is replaced with much simpler one. Amusingly, holography appears in the form we are accustomed to in our everyday experience.

    Spontaneous compactification and landscape catastrophe can be avoided when basic objects are 4-D space-time surfaces and imbedding space is fixed by mathematically consistency and symmetries as well as number theoretical arguments.

    My prediction is that within few years twistor program with replace string approach and string like objects will be reduced to bound states of massless particles. This means also a new view about perturbation theory.

    • kneemo says:

      Matti, M-theory on CP^2 has been investigated by Vafa et al in hep-th/0111068. Using toric geometry, it was argued that M2-branes are mapped to lines in CP^2, while M5-branes correspond to quadrics.

  13. Thank you for the link kneemo. It would be interesting to see how they get CP_2. Physical interpretation must be totally different as compared to that in TGD framework. I admit that brane I do not have any intuitive grasp to thinking in terms of branes.

    What I should have also emphasized is that massivation and breaking of SUSY and R-symmetry are the most fundamental poorly understood problems of string models and QFT.

    Here the notion of induced spinor structure is the key concept. The simplest version means defining induced gamma matrices as projections of imbedding space gammas: this works for volume action in the sense that super currents and fermion currents are conserved.

    More refined versions replaced induced gammas with contractions of canonical momentum densities with imbedding space gammas. The mixing of M^4 and CP_2 type gammas implies M^4 chirality mixing serving as a signature of massivation and breaking of supersymmetry and R-symmetry. In well-define sense this is essentially gravitational effect.

    It is sad this message is not received and people are fighting to make sense of such desperately ugly symmetry breaking mechanisms. I was really disappointed when I learned that mSUGRA is on such shaky grounds.

  14. Dear kneemo,

    I looked the article very sketchily and understood nothing-absolutely nothing;-)! I was not even able to find CP_2 anywhere-just P^2-maybe it denoted CP_2.

    • kneemo says:

      Matti, yes P^2 is CP^2 in the paper. Study the constructions in section 2.5 carefully and take note of figure 13, as well as tables on pgs. 25 and 27. The point of the paper is that once one understands CP^2 well, one can geometrically classify objects in compactified M-theory and string theory, by merely blowing up k generic points of CP^2 to construct del Pezzo surfaces, B_k.

      M-theory in D=11 is mapped to CP^2, while M-theory on tori T^k in D=11-k corresponds to M-theory on the del Pezzo B_k. The U-duality group of M-theory on T^k is given by the Weyl group of E_k (for compactifications with no C-field vevs), which is mapped to a subgroup of the global diffeomorphisms of the del Pezzo B_k.

      For M-theory on T^k, where k=4,5,6,7,8, one recovers E_4=SU(5), E_5=SO(10), E_6, E_7, E_8, and on page 27 the representations of these groups are identified with curves in the corresponding del Pezzos. For example, the M2-brane is the 5 of SU(5), while the M5-brane is the 15.

      • Lawrence B. Crowell says:

        This looks to be a type of moduli construction for classes of curves over the E_k’s.

        Cheers LC

  15. Luboš Motl says:

    Dear Phil, good thoughts (and given the composition of your readers, you have balls haha). Don’t you want this to be reposted on TRF? A factor of 25 increase in readers.

    • Philip Gibbs says:

      viXra Log has a very mixed readership with a wide range of opinions which makes the discussions very interesting. If you want to repost on TRF please go ahead. It would be nice to have more comments from there.

  16. Philip Gibbs says:

    Nice to see so many comments appear while I have been sleeping.

    Of course I like all this fun numerology stuff and the lovely mathematics of string theory too, but if I tell people that my reasons for liking string theory are to do with its math I wont sound very convincing. I need to tell them about the physics related reasons instead.

    To make up for it I will do a fun post about the 24-cell, four qubits, and everything, stay tuned.

  17. Ulla says:

    Could not M-theory be seen as a top-bottom theory, and that would explain its difficulties?

    Theories with few dimensions, starting from the common 3+1, doubled in TGD, would be the bottom-up, as also Keas theory would be?

    These cannot be discussed on a line then?

    • Philip Gibbs says:

      It’s hard to show that two approaches are incompatible because ideas that look completely different can turn out to be dual versions of the same thing. Until they say things about physics that can be seen to be inconsistent we should assume that different paths could converge at their ends even if they look very different at the start, especially if they all have features that make them seem promising in complementary ways. I think this opinion makes me a relative optimist. Most physicists seem to take a more narrow point of view.

  18. Physicsphile says:

    Nice post. I will have to add your blog to my list. I like string theory for all the reasons you mentioned. Although I prefer working on things a little bit closer to observations, myself. I think string theory may never be observationally testable, but I think its obviously worth trying to find a way, because as you say there is no other game in town at the moment.

    • Philip Gibbs says:

      Physicsphile, thanks, however I tend to avoid this expression that string theory is the only game in town. There are other ways to tackle quantum gravity as I mentioned and people should certainly study them. They may help to understand non-perturbative string theory, or they may even lead to a better alternative. I dont think the latter will happen but I would be less confident of that if physicists were not trying.

      String theory is the only solution to solving the weak field limit perturbatively which I suppose is what you are referring to. It is a crucial observation.

      • Physicsphile says:

        Yes I agree. I’ve been reading some of your previous posts and I’m really impressed. I think its very wrong if someone with your level of understanding has trouble putting preprints on the arxiv.

      • Philip Gibbs says:

        Funny you should mention that. I submitted a paper to arXiv:hep-th recently with the help of an endorser. It was moved to general mathematics which is one of the categories they use so that serious physicists or mathematicians don’t have to waste their time reading it. Normally you cant even cross-list from these categories and they are not indexed in any of the scientific catalogues. Even after some appeals they would not move it back despite two good citations in hep-th. Reasons are never given so it is hard to dispute them. Finally they made the concession of allowing the paper to be cross-listed to hep-th. The paper’s listing on viXra is probably doing a better job of getting the work noticed.

      • Physicsphile says:

        Well done on preserving and getting it cross listed in the end. Rightly or wrongly I think it does make a difference in how seriously people take a paper.
        Another fairly arbitrary convention that rightly or wrongly makes a difference is that its worth writing the paper in LaTeX as its such a convention now that when people see a non-LaTeX paper they just dismiss it out of hand.

      • Philip Gibbs says:

        I actually deliberately write them in Word now to filter out the superficial readers who are not likely to make anything of it 🙂

  19. Nigel says:

    On first point, gravitons. The gravitons included by string theory are spin-2 gravitons, which are an error by Pauli and Fierz

    The groupthink behind spin-2 gravitons begins with the assumption that there are just two masses in the universe. Sure, if that were true gravitons must be spin-2 to cause attraction.

    But it isn’t. Then you get the nice claim that rank-1 tensors (vectors) are used in Maxwell’s equations and they work by spin-1 virtual photons, while rank-2 tensors are used on GR, apparently proving the need for spin-2 bosons.

    The groupthink here is the false claim that you need to represent electromagnetic forces by Faraday’s field lines. If you draw field lines, the gradients and curls (differences between gradients of the field in perpendicular directions) are first order (rank-1) because you have chosen this field line description as the basis for the mathematical model! In GR a completely different basis, spacetime curvature (i.e. accelerations), is used, not field lines. So the mathematics of GR is automatically different because it’s modelling not field lines but spacetime curvature.

    Put another way, you can use rank-2 tensors for electromagnetism if you give up Faraday/Maxwell field lines and instead express electromagnetism in terms of spacetime curvature. You can also express gravitation in terms of rank-1 tensors if you choose a model based on gravitational field lines (which Einstein didn’t). There is thus a convenient but ad hoc and arbitrary inconsistency between the modelling of fields in electromagnetism and gravitation, and this is causing confusion.

    Regarding the second point, the alleged unification of fundamental interactions at high energy in supersymmetry, it’s also physically shallow and mathematically messy. I.e. the cancellations of infinities by SUSY is not possible to prove; there is an infinite number of terms in a perturbative expansion, and the fact that SUSY seems to work for the first couple which are relatively simple doesn’t prove it works for all infinite number of increasingly complex terms. So you can’t ever prove that SUSY works mathematically, even in principle.

    Then you have the problem of what is physically occurring as you approach unification energy. Any discussion of physical mechanisms for the conservation of energy density in fundamental fields that are shielded by vacuum polarization (which transfers field energy to off-shell fermions, that are moved apart and thus last longer before annihilation back into off-shell bosons) is heretical and sneeringly referred to as “heuristic physics”. Trial and error has been a heresy in quantum field theory promulgation since Dirac tried to reintroduce the aether in an article in Nature (1951), and so physics has now gone into obfuscation in a big way. contains an excerpt from Irving L. Janis, “Victims of Groupthink,” 1972; Houghton Mifflin Company; ISBN: 0-395-14044-7 (pp. 197-204)

    • Lawrence B. Crowell says:

      The graviton is usually modelled as s = 2 because the weak gravity wave has two helicity states.

      Cheers LC

      • Nigel Cook says:

        Hi Laurence,

        ‘In the particular case of spin 2, rest-mass zero, the equations agree in the force-free case with Einstein’s equations for gravitational waves in general relativity in first approximation …’

        – Conclusion of the paper by M. Fierz and W. Pauli, ‘On relativistic wave equations for particles of arbitrary spin in an electromagnetic field’, Proc. Roy. Soc. London., v. A173, pp. 211-232 (1939).

        That’s from the Jan 2010 blog post I cited. What happens is that someone takes a false classical theory (GR), predicts some classical wave phenomenon from it, labels it a “spin-2 graviton”, then spends decades building a theory which is compatible with that assumed fact! Problem is, when you look at the Pauli-Fierz paper, while it’s perfectly good speculation from the classical GR standpoint, GR is not a good framework point for QG.

        First, GR only works at all when the stress-energy tensor is set up with a continuous (not discrete) distribution of matter. So to get smooth curvature, you have to artificially get rid of particles by smoothing out the distribution of mass and energy causing the “curvature”. The whole process is fine for large scale approximations, but it’s as fake as possible at the quantum level.

  20. ervin goldfain says:


    When experiments do not provide enough information and/or fail to point in a definitive direction, it is only natural to “jump the gun” on what lies behind “effective” theories such as SM and GR. As the list of open questions continues to grow by the day, it seems reasonable to step back and take an unbiased look at what some observational evidence is hinting at.

    I kindly ask Phil to allow opening an informal poll. To this end, I urge all participants to focus and reply on three recent findings that, in my opinion, are particularly relevant to what lies ahead:

    1) no direct evidence for gravitational waves (LIGO).
    2) no evidence for large extra-dimensions and physics beyond SM (early LHC).
    3) placing SUSY breaking scale around 1 TeV, an order of magnitude higher than the EW scale of about 200 GeV (early LHC).

    When formulating your answers, please attempt to distance yourself from ANY preconceived views you had prior to the release of these findings.


    Ervin Goldfain

    • Philip Gibbs says:

      My attempts at polls have not been very useful because the number of readers here is not very large. People can add their responses in reply to your message if they wish.

      My responses would be that

      1) Failure to detect gravitational waves so far is disappointing but not a fundamental problem. It is just because the LIGO physicists were over optimistic about the number and strengths of suitable sources when they applied for the original funding. I hope they are not still being optimistic with what they are saying about prospects after the next upgrade.

      2) Very few people expect extra large dimensions to show up at the LHC so it is not a problem if they are not there. Data so far is not sufficient to draw any conclusions

      3) The SUSY breaking scale should be much higher but I think you mean the scale of the lightest particles. I already gave my reaction which is that it is uncomfortable that SUSY has not shown up yet but we need to see what does turn up before we can form a reaction.

      • ervin goldfain says:

        Thanks Phil. Please elaborate on these follow-up questions:

        1) “Failure to detect gravitational waves so far is disappointing but not a fundamental problem.” How about gravitons? Are they real?

        2) “Very few people expect extra large dimensions to show up at the LHC so it is not a problem if they are not there.” What are the implications for the reality/stability of extra-dimensional space-time?



      • Philip Gibbs says:

        Gravitational waves will be quantised as gravitons but they will never be detected as individual quanta. The scale is too high.

        If there are no gravitational waves detected when the instruments get very sensitive then classical GR is wrong, so we would have to step back much further than any theory of quantum gravity.

        If extra dimensions exist they would most likely be seen at the Planck scale or at least the GUT scale. If they are not seen at the LHC little will change because the LHC energy is much less.

    • Kea says:

      Sheesh. I have been saying for years that these things will never be seen – with reasons.

    • Bill K says:

      1) no direct evidence for gravitational waves (LIGO).
      Gravitational wave experiments have been scandalously overoptimistic since the days of Joe Weber. This is the way they get their funding! Just a little bit more money and we’ll find ’em for sure.

      2) no evidence for large extra-dimensions and physics beyond SM (early LHC).
      Resolutely opposed to extra dimensions, large or small. Enough trouble as it is, trying to explain the first four.

      3) placing SUSY breaking scale around 1 TeV, an order of magnitude higher than the EW scale of about 200 GeV (early LHC).
      Not a rabid SUSY enthusiast, nevertheless I’m hoping that the LHC will yet see it. Like many other theories, SUSY looks simple at first, but then opens the gates to enormous complexity when you try to describe how it is broken. Isn’t there a theory that lies somewhere between a desert and a total mob scene?

      • Lawrence B. Crowell says:

        Always keep in mind the Hulst-Taylor result, which showed the frequency change in the orbit of two pulsars perfectly fits the predictions of gravity waves in the PPN approach of general relativity. So we already have indirect evidence for gravity waves. The LIGO machines will detect gravity waves from the collision of two 10 solar mass black holes within 50 million ly. We have to wait it out and keep increasing the sensitivity of the apparatus.

      • Kea says:

        What the H-T result shows is that GR is an excellent means of describing the LOCAL pulsar system. It says NOTHING about the propagation of grav waves across large astrophysical distances, and NOTHING about the particulate nature of said waves.

      • Lawrence B. Crowell says:

        The inspiral of the two neutron stars is predicted by the production of gravitational radiation. This makes G-waves a necessary condition though it is not sufficient.

        Gravity waves in the O(G^3) terms in the PPN result from equations that are formally identical to Maxwell’s equation. In the weak limit gravity waves exist for the same reason Maxwell proposed his displacement current.

        Of course for various reasons you reject a whole range of physics, from Higgs field to SUSY to gravity waves, and God knows what else. That puts you not only far out in right field, but frankly out of the ball field and stadium.

      • Kea says:

        Out of the stadium? For rejecting things that have not been observed? Using ideas that make actual concrete numerical predictions in line with experiment? Perhaps you should hold the stringers to the same standards.

      • Lawrence B. Crowell says:

        Atoms were proposed by Democritus and Lucretius 2400 and 1900 years before they were observed. Boltzmann proposed an atomic basis for his statistical mechanics. The pillory he received for this drove him to suicide. There is a pretty decent history of time lags between prediction and observation.

        Cheers LC

      • Kea says:

        Indeed. I learned that as a toddler. But a scientist is supposed to discriminate between all possible observations. You may also have heard of a few null results, like Michelson-Morley.

  21. ervin goldfain says:

    Kea, Bill K., Lawrence,

    Thanks for your feedback.


    Do you have an opinion on my second and third questions?


    • Lawrence B. Crowell says:

      I really hold out hope for SUSY. That should show in the 10 Tev range. As for extra-large dimensions I am a bit less sanguine on that. I think these things are certainly possible. We might get some signatures of this sort of physics.

      I really think the post LHC future of particle physics is with cosmic rays. I have this idea of placing detectors on heliostats that hover at various altitudes in the atmosphere. We then have a target mass in orbit, which might be fairly substantial. Cosmic rays slam into this and produce secondary particles. We then use the Earth’s atmosphere as a sort of scintillation counter. Various teams could then have their balloon based detectors arrays at different places and we then work that way. Cosmic rays start out at the 20TeV range, and those are the low energy ones. If we are clever enough and get the statistics on this well enough understood we might be able to look at 100-1000TeV physics.

      The question is with track finding, and I imagine the target as a disk of solid material in a cylinder. The secondary particles pass through a grid at the end with elements that detect the motion of these particles through the Hall effect. These are then used in track finding with the scintillation data recorded in the atmosphere. It is a rough idea, but the LHC looks to be the final accelerator.

  22. Kea says:

    And your last reply does not address the points I raised. We already agreed that GR (or some approximation thereof) is correct in determining the energy loss in the pulsar system.

    • Nigel says:

      The relationship between gravitational wave radiation and gravitons in GR is similar to the relationship between Maxwell’s electromagnetic radiation and the photon, in the sense that the classical model is misleading on small scales, although it works fine for large scales.

      The photon deduced from Maxwell’s model is incompatible with quantum field theory, as Feynman shows in his 1985 book “QED”. Feynman shows that the double slit experiment is explained by the “photon” taking an infinite variety of different paths, with those of large actions cancelling one another out. Thus, there is no wavefunction collapse: part of the photon goes through one slit and part through the other, and the recombination (not the observer) produces the diffraction pattern on the screen. Maxwell’s theory is only valid for the path of least action, or zero action when dealing with a photon. You can expect the same limitations in GR: it will be fine for geodesics that obey the principle of least action! But nature in QFT doesn’t obey the principle of least action, but must include contributions from all paths including those of larger actions which often (but not always) cancel one another out.

      Just as Hertz’s radio waves were touted as “proof” of Maxwell’s classical (non-quantum!) theory of light waves, so the Hulst-Taylor pulsar data is touted as “proof” of Einstein’s classical (non-quantum!) theory of gravitational waves. Caveat emptor!

  23. To Lawrence:

    The crucial assumption making the lower limits for squark masses so high is R-parity invariance.

    If R-parity is broken situation changes and in TGD this is the case due to the breaking of R-symmetry caused by the mixing of right handed neutrino with left handed one making possible decays sP –> P+nu. This allows to sparticle masses and SUSY parameters consistent with g-2 anomaly of muon requiring low value of m_SUSY: it would be most naturally given by weak p-adic mass scale 105 GeV in TGD framework.

    If Higgs is eaten by photon to give it small mass, also the little hierarchy problem disappears.

    TGD leads to precise predictions for SUSY parameters since p-adic mass scale hypothesis allows the option in which super partners obey same mass formula as partners apart from the different choice of p-adic mass scale. This also fixes the value of beta angle to tan(beta)=1 and the mass matrices of weak gaugino-Higgssino pairs are fixed to high degree since the sum of diagonal elements must vanish.

    SUSY parameters are extremely tightly fixed and the checking of TGD predictions could begin anytime. From TGD point of view the recent view emerging from LHC is totally misguided. Don’t blame me after ten years that I did not tell!;-). I have tried to do this again and again.

    For a concise summary see my blog postings

    and .

  24. Whether the failure to detect gravitational waves is already now a real problem is not quite clear to me. Hulse-Taylor implies that gravitational radiation is emitted so that one might try to imagine possible mechanisms explaining why they are not detected. My imagination is limited to TGD framework;-).

    a) Gravitons with large hbar would decay to bunches of ordinary gravitons instead of a continuous flow. The bunches would be very probably interpreted as a noise by experimenter knowing nothing about TGD;-).

    b) TGD suggests (might be more honest but not diplomatically clever to confess “predicts” ) that also all gauge bosons and also gravitons develop a small mass. This does not mean loss of general coordinate invariance nor gauge invariance. All particles -even virtual ones- consist are at fundamental wormhole throat level of massless particles able to have also negative sign of energy. In GRT massive gravitons are highly problematic.

    Massivation would reduce the intensity of gravitational radiation from distant objects: large value of hbar_gr however scales up the Compton length
    dramatically so that the effect would disappear. A widening of the arrival time distribution for photons from pulsars based on surfing of photons on wave crests of gravitational waves has been proposed:if the mechanism indeed works it puts the rather mild lower bound of 1 pc to the Compton length of graviton. Much stronger bounds follow if one believes on naive modification of gravitational potential.

    For details see the posting .

  25. Alejandro Rivero says:

    SUSY is a great reason, but my own opinion is that it points to the QCD string or to a close cousin of it, see references in, which I uploaded five days ago 🙂 After five years, I am still undecided, but if it were QCD, it would imply that the LHC is going to discover only the gauginos, because we have already discovered all the scalars. On other hand, the SO(2^5) symmetry of strings could have associated some “classical” SU(5) –via a mechanism near to Marcus-Sagnotti, remember SO(8192) — and the similitude to three generations of QCD quarks could be just a coincidence. But something keeps going on, there in the structure of the standard model itself.

  26. Lawrence B. Crowell says:

    I am not sure whether p-adic number systems tell us much about gravity waves. They do turn out to be important for density of black holes microstates in Eisenstein series.

    The reason we have not found gravity waves is that we have not been lucky. Current detectors require a black hole collision within 50 million light years. Gravity is very weak and getting higher order effects like waves is tough.

    There is nothing about believing things. Working in or having an interest in string theory is not about believing in it. It is more about exploring some of these structures to see what it can lead to. Some of these structures or putative results are sufficiently compelling to make one think they most likely do exist. This holds in particular for gravity waves. The universe just literally makes no sense if they do not exist.

    Cheers LC

%d bloggers like this: