What do you mean? It's not "out of date", as Kepler's laws or the ideal gas law or whatever is not out of date. It's just incomplete. Also, "modern physics" is

What do you mean? It's not "out of date", as Kepler's laws or the ideal gas law or whatever is not out of date. It's just incomplete. Also, "modern physics" is a term of art, vs "classical physics".