Some Rishonim [medieval authorities] like the Ramban [Nahmanides] would hold that to learn practical professions for the sake of making a living is OK. He himself was a doctor. It was just that this group of rishonim would not hold that learning Physics and Metaphysics are a part of learning Torah.
You only see the opinion that Physics and Metaphysics are are part of Torah in Saadia Gaon, Ibn Pakuda [author of the Hovot Levavot], Binyamin the Doctor, the Rambam.
Words of the Rishonim are thought to be valid even when they argue.אלו ואלו דברי אלקים חיים. But I tend to go with the opinions based on Saadia Gaon.
But even if you go with Saadia Gaon, still how can one do physics which is hard? My suggestion is the idea of the Gemara לעלם לגרס איניש ואחר כך ליסבר אף על גב דמשכח ואף על גב דלא ידע מאי קאמר
Always one should just say the words in order and go on ["girsa"] and after that to go back and explain, even though he forgets and even though he does not know what he is saying.
