Hello. Is it hard to achieve a PhD in, for example, physics? What do you have to do/study beforehand, like in school? Is a PhD like a first published paper/research? How do you achieve a PhD is things like physics and mathematics, which are so theoretical? If I want a PhD in physics or chemistry, what do I need to study in school and what subjects to choose? (A bit of an off topic question...) Thank you for considering all these questions.