But it is not obvious that a theory can be expressed by a program. I am prepared to believe that there are fields in mathematics or genetics or something where

But it is not obvious that a theory can be expressed by a program. I am prepared to believe that there are fields in mathematics or genetics or something where this is not problematic. In physics, theories often describe a world which is both infinite and continuous, which is hard to encode in a form suitable for computation; typically finite-volume and discretisation approximations (at the very least) are made. In these situations the theory represented in code isn't the same as the theory you started with. One has to work quite hard to demonstrate that the differences are quantitatively understood and under control, and that the domain of applicability is understood.