Physicists have a natural reluctance against deduced theories. Usually they require experimental verification of any physical statement. On the other hand not all physical concepts are observable. The deeper one dives into the foundation of physics the more often the possibility of experimental verification is violated. As a compensation a fully deduced physical model must be based on a solid foundation and that base must be extended by trustworthy mathematical methods.

So, in this realm, the first question that must be answered is:
"Can such model be built?"
The second question is:
"What suits as a solid foundation?"
Or equivalently:
"Are such solid foundations available?"

The third question is: 
"What mathematical methods are trustworthy?"