I'm not currently a grad student, just a prospective looking around. Some schools I've looked at emphasis that they only enroll or will fully fund students who plan on pursuing a PhD, not just a masters. Some grad students I've talked to said enrolling as a PhD student isn't that bad, because if you realize getting a doctorate in physics is too much for you, you can walk away from the university with at least a masters. However this seem counter intuitive to me. How can a school let you walk away from the program with a masters and the money they invested in you without some sort of consequence? Is a master in physics just not worth a lot compared to a doctorate? How do they keep students that only want a masters from getting a free ride? High admission requirements?