The standard model isn&#x27;t the same thing as quantum theory.  It&#x27;s possible to make a quantum theory of gravity that for one reason or another isn&#x27;t compatible with the standard model.<p>More specifically, the SM is a theory of a bunch of <i>fields</i> plus a bunch of parameters describing how they interact with each other.  Quantum mechanics is much more basic.  There is an analogy (from Scott Aaronson I think) that quantum mechanics and classical mechanics are like two different operating systems, and the dynamical theories of physics (e.g. field theories) are programs that run on those operating systems.  There are rules of thumb for porting programs from one OS to the other, but they aren&#x27;t guaranteed to work.