Yup, but the computer isn't _learning_ it, it's already enforced by the fact that what the computer is learning is a time-independent Lagrangian. (I suppose it

Yup, but the computer isn't _learning_ it, it's already enforced by the fact that what the computer is learning is a time-independent Lagrangian. (I suppose it's learning a symmetry in the following sense: just _what_ is conserved depends on what the Lagrangian is, and so as it's learning the dynamics it's also learning what the energy is that it should be conserving. But at every point in the training process, there's _some_ thing, which we might as well call "energy", which its model conserves.)