Thirty-five years ago I was seeking advice for University and I remember the Provost at the university of South Carolina, Dr. Daniel Antion telling me that all the university education anyone needed was enough to allow them to do what they wanted to do. He said B.S. was bull, M.S. was More and a PhD was Piled higher and deeper. I have always remembered that advice. He felt that you got the basics for what you wanted to do, and then get out in the industry and get experience. It is still applicable today, but if you are really wanting to work in science, that means a post graduate degree!
This is because science has become very fragmented and specialized, and to be successful one need to be as knowledgeable in their specific field as possible. Physics was at one time just physics, now it is Quantum Physics and Biophysics and atomic physics and such, and to get ahead you literally need a degree in that specific section of physics, and if it is not a postgraduate degree, you will be tuning up electrical generators.
Even high school teachers are now required to have a postgraduate degree. Does it make then a better teacher in their field of science? Not always, but it does show a willingness and dedication to learning the specialty. In science it is two things that will get you ahead, an inherent level of intelligence and dedication to the field of study. One cannot alter their intelligence, but the postgraduate degree does allow you to exercise and develop it more, and it demonstrates the dedication to the subject.
This means that the postgraduate education may not be essential if you just want to work in an area, but it is if you want to succeed and advance in the sciences. Even as a teacher, you will only be allowed to advance so far at a school without that advanced degree. You could be training Nobel Prize winners and it matters not without a certificate to hang on the wall!
It should be noted that the reason why it is essential is because society has made it essential. Many of the famous scientists in the past had no advanced degrees at all and yet made discoveries that are still important today. Where would the world be today without Benjamin Franklin or Michael Faraday? They didn’t have any degrees!