Quantum field theory is a <i>framework</i> for building models. You can choose a largely arbitrary symmetry group structure and a largely arbitrary collection of matter fields in representations of that group (subject to a handful of mutual-consistency conditions), and wham: a possible universe. The Standard Model in particular is based on a not-very-elegant collection of symmetries and particles: SU(3)xSU(2)xU(1), with a weird (but miraculously self-consistent) grab bag of matter particles that inexplicably shows up copied three times.<p>Extending the underlying quantum mechanical formalism of QFT to be consistent with general relativity would be <i>fantastic</i>, no matter how it&#x27;s done. But it&#x27;s entirely possible that you&#x27;d still be left with an equally broad framework, and that the Standard Model would look just as weird and arbitrary as it does today. My impression is that something like this is the goal of most loop quantum gravity researchers, and proudly so: they&#x27;re trying to solve one incredibly hard and incredibly important problem, so why borrow trouble by muddying the waters with more complications?<p>The ideal &quot;theory of everything&quot;, if such a thing turns out to exist for our universe, would not just be a framework, but would also tell you the unique set of specific details that describes our universe: something that looks like our familiar Standard Model under ordinary conditions. As I said, I don&#x27;t have the impression that most LQG researchers have ever considered that to be a likely outcome of their work: it&#x27;s just not the business that they&#x27;re in (perhaps by deliberate choice).<p>String theory has at various times in its history aspired to be precisely such a &quot;theory of everything.&quot; (I&#x27;m not sure what fraction of folks in the field today would still claim that as a realistic expectation.) Because so many details of string theory are dynamical variables rather than God-given constants of nature, there&#x27;s at least the possibility that there is a unique &quot;lowest energy state&quot; of all those variables that might turn out to be equivalent to the Standard Model. (Even almost philosophical questions like &quot;How many dimensions of space do we perceive?&quot; could in principle have a unique stable answer within string theory.)<p>Now, in practice, the way we generally analyze string theory today does <i>not</i> point us toward a unique answer, but rather something like 10^500 equally valid answers. Maybe there&#x27;s some deeper principle that will select a unique one of those as &quot;truth&quot; (which we&#x27;d then eagerly compare against the Standard Model as a test of the theory). I&#x27;ve done a bit of work looking at such possibilities, and mostly my conclusion is &quot;this is ridiculously complicated&quot;. Or maybe string theory is also merely a &quot;framework&quot; in the same sense that quantum field theory is. (But a very nice framework: one that <i>does</i> unify quantum mechanics and gravity in an elegant way, along with whatever approved collection of symmetries and matter you happen to stick in as its background.)