For reference, the poorly named "standard model" which is the quantum theory of all forces except gravity, cannot really be called equations in the usual sense. This is because the kind of mathematical model that would describe the standard model (nonperturbative QFT) can't currently be done rigorously. It can only be done for simpler models in lower dimensions. The standard model is a very complex sort of approximation to a theory that is assumed to exist.

This might be a mere detail to some but to me it is a sign that physics is complex in all kinds of ways, and can't really be described as "choosing the right equations". Even if you think that this is what physics is fundamentally, I think you would have to admit that it wasn't possible to describe what the meaning of "equation" was before qft was developed, and the same may be true about future theories that unify the standard model and gravity.