Is there an easy (aka intuitive) way to understand that the conserved quantity from time translation symmetry is just what we call energy? In other words, we use two definitions of energy. One is ...
My physics instructor told the class, when lecturing about energy, and that it can't be created or destroyed. Why is that? Is there a theory or scientific evidence that proves his statement true or ...
Written in a book I read that the "total energy is not preserved when the potential depends explicitly on time", i.e. $U=U(x,t)$. Is there any proof or explanation for this?