Unless you misunderstood your professor, what they said is entirely and utterly wrong. Calculus of variations is one of the guiding principles of modern physics

Unless you misunderstood your professor, what they said is entirely and utterly wrong. Calculus of variations is one of the guiding principles of modern physics. Pull out any textbook on quantum field theory or general relativity and there will be a section dedicated to using calculus of variations to derive the equations of motion. Heck, for a lot of theories, writing down the action and deriving the equations of motion from the Euler-Lagrange equations is the first thing you do. Plus calculus of variations is closely related to differential geometry, which is a massive field. Same with control theory, another massive field with close ties to differential geometry and calculus of variations. I have no idea what point your professor was trying to make.