# Why is Standard Model + Loop Quantum Gravity usually not listed as a theory of everything

I have often seeen statements on physics.SE such as,

The only consistent theory of everything which we know of to date (2013) is string theory.

Why exactly is this so? Adding the Loop Quantum Gravity Lagrangian Density (the Einstein-Hilbert-Palatini-Ashtekar lagrangian density) to the Standard Model Lagrnagian Density should be able to describe all the interactions and fermions, in my opinion. Maybe it isn't as elegant as string theory since it doesn't really unify all the forces/interactions and fermions but it is still a complet description, right? Because once the Lagrangian Densities are added, one obtains the following "Complete Lagrangian Density": $${{{\cal L}}_{\operatorname{complete}}} = - \frac{1}{4}{H^{\mu \nu \rho }}{H_{\mu \nu \rho }} + i\hbar {c_0}\bar \psi \not \nabla \psi + {c_0}\bar \psi \phi \psi + \operatorname{h.c.} + {\left\| {\not \nabla \phi } \right\|^2} - U\left( \phi \right){\rm{ }}+\Re \left( {\frac{1}{{4\kappa }}\mbox{}^ \pm\Sigma _{IJ}^\mu {{\rm{ }}^ \pm }F_{IJ}^\mu} \right)$$

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I a not a theorist so can only comment that my impression is that LQG does not respect Lorenz invariance in local spaces. I do not know whether this is evident in the lagrangian you have written. Lets hope somebody in the know will reply to you. Have a look at motls.blogspot.gr/2009/08/… – anna v Jun 6 '13 at 4:22
The arguments on either side are just going to be propaganda and cheerleading. Neither LQG nor ST has made a prediction that can be tested with any known or foreseeable technology, which means that neither is actually a theory yet. Since they're not theories of anything, they're not theories of everything. I'm pretty sure it's false that you can add all the particles of the SM into LQG just by adding Lagrangians; AFAIK this is an unsolved problem in LQG. – Ben Crowell Jun 6 '13 at 4:35
Because the "theory" you write down doesn't exist. It's just an incoherent mixing of apples and oranges. You can't construct a theory by simply throwing random pieces of Lagrangians from different theories as if you throw different things to the trash bin. LQG is inconsistent by itself, for millions of reasons, but even if it weren't, it has many properties that make it incompatible with the SM, for example its Lorentz symmetry violation. And even if these incompatible properties weren't there, adding up several disconnected Lagrangians just isn't a unified theory of anything. – Luboš Motl Jun 6 '13 at 4:47
@Luboš that should be an answer – David Z Jun 6 '13 at 6:20
In my opinion a necessary condition for any theory of everything is the demonstrated ability to embed the Standard Model without contradictions.The SM is the mathematical shorthand for thousands of experimental data. That is the first step that a TOE has to fulfill. I think that string theories have many possibilities of embedding the SM . Falsifieable predictions from a TOE would be great, but if it does not even explain the existing data it has lost at the start, imo. – anna v Jun 6 '13 at 6:36