Modern Physics vs Classical Physics

After at chat with ChatGPT I have learned that the essential difference between modern and classical physics is that the postulates of modern physics, the postulates of relativity theory and quantum mechanics, are not directly testable experimentally, while this is a key requirement of classical mechanics. 

It seems to be more constructive to discuss physics with GPT than with a living modern physicist typically taking a very defensive position admitting nothing. 

Now, a physical theory based on postulates about facts of physics, which cannot be directly tested experimentally, and thus cannot be directly falsified, runs the risk of being a self-fulfilling prophecy without real value. This may well be the case concerning relativity theory based on postulates of (i) general principle of equivalence of gravitational and inertial mass and (ii) general covariance of physical laws, which cannot be tested experimentally. 

Laws or Postulates of classical mechanics, such as Hooke's Law, Coulomb's Law, Fourier''s Law  and Newton's Law of Gravitation, can all be tested and verified experimentally. A theory based on postulates of basic laws of physics express logical consequences of these laws. If the postulates can be verified, then the theory is valid. If not, the theory lacks factual basis and has no value.

In modern physics the fundamental principle of testability of basic postulates, has been given up and so may reduce to free speculation. A return to classical physics with testable postulates is necessary. There is no reason to start with postulates which cannot be directly tested. Unless you want to invent a new theory based on speculations possibly without factual basis, and so become a modern physicist of reputation.  Your choice!