Not so much begging the question, but making an assertion that I don't have space to prove. How could I prove that modern physics is correct to someone who had

Not so much begging the question, but making an assertion that I don't have space to prove. How could I prove that modern physics is correct to someone who had perused a physics textbook and concluded it wasn't worth serious consideration? >Since modern economics is focussed on greed and selfishness... is shallow