Gang of four--Lisi, Loll, Reuter, Rovelli--make trouble for stringery String thinking has been described as a framework for constructing theories---although one which has not as yet produced mature testable theory. As such there are some assumptions which serve as justification---assumptions about the NEED for and about the GOALS of the stringy way. As far as I can tell there are two main string-related big news stories going on at present A. the string research effort in USA is dwindling due to internal reasons. Citations of recent work are down. Cutbacks are planned. The researchers themselves seem less motivated and productive than, say, 5-10 years ago. B. the justifying assumptions are being challenged. This is causing occasional outbursts of reaction which are instructive to watch. ============= I think you can learn a lot from watching academic turmoil---key points that you might otherwise miss---what issues the hulabaloo and outrage seem to center around. Also it is just interesting. So I've chosen four researchers whom I see CHALLENGING those justifying assumptions---whether about the need for stringery or its goals. In most cases the name I give is just one standing for many. There are substantial groups in these cases so that I should really put "et al." after the names. These are people that we should be alert to reaction against them, because their work creates some form of cognitive dissonance. 1. Loll makes spacetime emerge from a deeper description. In recent years at conference talks, David Gross has been saying "We don't know what string theory is." And he usually continues by saying something like "We are missing some essential idea. Perhaps space and time are not fundamental realities, but appearances which emerge from some more fundamental [descriptive] degrees of freedom." Loll et al have discovered fundamental dynamical degrees of freedom from which a spacetime emerges whose very dimensionality is a quantum observable and varies with the scale at which it is measured. At macroscopic scale the emergent spacetime has the expected 4D dimensionality. A theory is a human artifact. If you don't know what it is, then it does not exist. Loll's theory is not the dream of a theory, it is a theory. And like any real scientific theory is testable (=falsifiable). It predicts that LHC will not see evidence of extra spatial dimensions. If such dimensions are demonstrated, Loll's theory is wrong. 2. Lisi proposes a Theory of Everything with 18 new particles and no free parameters The importance of the Lisi E8 theory now taking shape is not merely that it challenges the "only game in town" assumption. The challenge to stringy mindset is only a side issue. But that side issue is what this thread is about! I want to point out that various developments ARE creating a stir by challenging assumptions basic to that mindset, so we can better understand the reaction. E8 theory is predictive (that is to say falsifiable) because it has no free parameters to adjust. It will say what it will say---and if that is shown to be wrong, then the theory's wrong. As development proceeds changes might be made to the action and to the way E8 symmetry is broken, but a good many features are already locked in as unalterable predictions. Like the 18 new particles---which might serve to resolve the astrophysical dark---or might serve to trip the theory up! I don't see how E8 theory could accommodate extra spatial dimensions. So I believe it too would be falsified if such were discovered at LHC. In that sense also it is predictive. (When you make a prediction you have to specify the energy. The string framework does not predict that extra dimensions will be seen at LHC and it does not predict that they will NOT be seen---it is not at risk either way and is therefore not predictive regarding this.) E8 theory predicts what reactions are allowed for both the new and the already observed standard particles. So even though it is just taking shape the theory is already offering the prospect of something experimentalists can look for. Traditionally this is what hep-th is supposed to do. An unidentified moderator at ArXiv has removed Lisi's paper from the arxiv hep-th section. 3. Reuter presents evidence that quantum gravity is renormalizable after all Reuter et al are accumulating an increasing weight of evidence that gravity has a renorm group fixed point at high energy and thus can be SAFELY TREATED BY ORDINARY QUANTUM FIELD THEORY. This contradicts a major justification which has been assumed by string thinkers and others. It has been assumed that there is some NEED to take drastic steps and invent novel structures. The perceived need was based on the idea going back to at least 1970s that Einstein gravity was not renormalizable, could not be extended to high energies, was therefore not fundamental and would therefore be replaced by a more fundamental theory of gravity possibly arrived at by unification with other forces---hence the HOPE and faith placed in stringy approaches was based in large part on the imagined non-renormalizability. So Reuter et al challenge a major premise. Reuter can certainly turn out to be WRONG but so far the evidence continues to mount up. The approach is also predictive in the obvious sense that it would be falsified if extra spatial dimensions were exhibited. Interestingly, Reuter's approach converges with that of Loll in what it says about dimensionality at very small scale. Both theories predict scale-dependent dimensionality---4D at large scale declining to around 2D at small. Reuter's approach is (metric) background independent. i.e. does not depend on prior choice of geometric background. Reuter's approach has been subjected to scathing attack. 4. Rovelli et al progress on the dynamics and large scale limit front As a challenge this is lower key and longer term than the others. Speakers for the "only game in town" point of view have typically dismissed possibility that LQG would achieve a successful dynamics with correct largescale (Newtonian or classical GR) limit. The point is Rovelli et al are making visible progress! The essential in LQG has always been that it focuses on a manifold CONNECTION. In LQG proper, the geometry of an underlying manifold is always seen and described by a connection (rather than a metric or simplex triangulation, as in other approaches.) The configuration space of the quantum theory, on which quantum states are defined, has always been a space of connections. How you define the quantum states and their evolution (say by spinnetworks spinfoams or some other means) is secondary, as I see it, to the main goal of arriving at at background independent quantum dynamics of connections. One thing that Lisi's work does is confirm what has always been suspected namely that this goal is worth pursuing. To unite matter with geometry, Lisi's program is to have a quantum "connectio-dynamics" where the connection has a larger gauge group than just for gravity. It should be an E8 connection instead of just a deSitter connection or whatever. Do LQG but with a much larger Lie-algebra. Well Rovelli et al, which is a lot of people not necessarily all at Marseille or all collaborators, are doing is basically working out the details of "connectio-dynamics". Correct me if you think I'm wrong, but that's what I think the main idea of their work is. This year there have been a lot of papers about the "new LQG vertex" which is basically a way to do a PATH INTEGRAL QUANTIZATION of how the quantum state of the connection evolves dynamically. Loll and Reuter each show a different face of gravity---Reuter uses the 1915 einstein metric to describe geometry and Loll uses a triangulation with identical blocks---these are both very interesting and show stuff about how spacetime could actually emerge, but they don't have the valences to bond with Lisi. He wants a connection to be in the picture, and that is what Rovelli et al have. I should say what a connection is, as a technical idea---a mathematical construct in differential geometry. But this post is already long so I'll put it off till next.