So you want to do science for a living. Some scientists work for companies, developing new products. Some work for governments. But if you want to do “pure science”, science just to learn about the world, then you’ll likely work at a university, as part of what we call academia.
The first step towards academia is graduate school. In the US, this means getting a PhD.
(Master’s degrees, at least in the US, have a different purpose. Most are “terminal Master’s”, designed to be your last degree. With a terminal Master’s, you can be a technician in a lab, but you won’t get farther down this path. In the US you don’t need a Master’s before you apply for a PhD program, and having one is usually a waste of time: PhD programs will make you re-take most of the same classes.)
Once you have a PhD, it’s time to get a job! Often, your first job after graduate school is a postdoc. Postdocs are short-term jobs, usually one to three years long. Some people are lucky enough to go to the next stage quickly, others have more postdoc jobs first. These jobs will take you all over the world, everywhere people with your specialty work. Sometimes these jobs involve teaching, but more often you just do scientific research.
In the US system, If everything goes well, eventually you get a tenure-track job. These jobs involve both teaching and research. You get to train PhD students, hire postdocs, and in general start acting like a proper professor. This stage lasts around seven years, while the university evaluates you. If they decide you’re not worth it then typically you’ll have to leave to apply for another job in another university. If they like you though, you get tenure.
Tenure is the first time as an academic scientist that you aren’t on a short-term contract. Your job is more permanent than most, you have extra protection from being fired that most people don’t. While you can’t just let everything slide, you have freedom to make more of your own decisions.
A tenured job can last until retirement, when you become an emeritus professor. Emeritus professors are retired but still do some of the work they did as professors. They’re paid out of their pension instead of a university salary, but they still sometimes teach or do research, and they usually still have an office. The university can hire someone new, and the cycle continues.
This isn’t the only path scientists take. Some work in a national lab instead. These don’t usually involve teaching duties, and the path to a permanent job is a bit different. Some get teaching jobs instead of research professorships. These teaching jobs are usually not permanent, instead universities are hiring more and more adjunct faculty who have to string together temporary contracts to make a precarious living.
I’ve mostly focused on the US system here. Europe is a bit different: Master’s degrees are a real part of the system, tenure-track doesn’t really exist, and adjunct faculty don’t always either. Some particular countries, like Germany, have their own quite complicated systems, other countries fall in between.
4 gravitons 
The nuances I would add for the U.S. system, is that there are a significant number of non-tenure track teaching positions as assistant professors who aren’t adjunct faculty (typically with the title “instructor”) on fixed one to three year contracts. Adjunct faculty are typically hired on a course by course basis at very low wages competing with high school teachers, industry physicists and stay at home mom physicists looking for a class or two a year to teach mostly as a paid hobby for variety who can work for less, while non-tenure track assistant professors have a salary based compensation and benefits, and work loads, similar to tenure track assistant professors, but without the expectation that they’ll be considered for tenure or the allowance of time and resources needed to publish or do research (or an expectation that research will advance you in your current position).
It is also worth noting that academic graduate students are really more apprentices than they are pure students. Generally speaking, anyone who has a seriously shot of completing a PhD and then become a career academic will receive either a research assistantship or a teaching assistantship (or an alternating mix of the two from year to year), that comes with a tuition waiver and a modest salary accompanied by research assistant or teaching assistant responsibilities, for the duration of their studies, usually not actually running their own experiments or classes, but instead serving as support staff to tenured professors who do. This, plus work with a dissertation advisor, means that PhDs have significant on the job training and an academic sub-disciplinary specialty when they get their lamb’s skin diplomas. Universities take on PhD students without a teaching or research assistantship pretty much to soak up their tuition money even though the institution has no faith that they have futures as academic scientists – they are the dumb money of academia. The role of a PhD student’s dissertation advisor looms large, as both a mentor and often also as an unfair tyrant.
Also, in addition to national laboratories, there are some basically academic physicists in the U.S. who work either as civil servants in government agencies (like the NSA or DARPA or NASA), or as employees of non-profit institutions that don’t have teaching as a primary missions (like the Perimeter Institute or Sante Fe Institute), but whose research oriented work and career path is still pretty much the same as for one working for a national laboratory that you describe.
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Another big cultural event that distinguishes working towards an undergraduate major in a field and graduate school is the nature of the institutions and the make up of the students. Lots of undergraduate colleges and universities offer majors in academic sciences and the student bodies are predominantly although not exclusively domestic. At the PhD level, while a significant number of institutions have PhD programs, the vast majority of PhD students are in one of several dozen highly selective national universities and the student body is frequently 50%+ non-U.S. born, with many having never studied as full time undergraduate students in the U.S. The U.S. is still the dominant source of graduate education in the sciences globally, even though it is not the only advanced country participating in this market. For many students who attended less prestigious undergraduate institutions with mostly domestic student bodies, this is a huge cultural shift and is also a major identity forming moment.
Also, while the vast majority of undergrads are single, lots of graduate students in PhD programs are married or have found a partner that they plan to marry, which also influences the career decision making process and social scene.
PhD programs in STEM are also very different from those in the humanities and social sciences. STEM PhDs typically graduate in a pretty swift and orderly fashion, often in three to five years, and a dissertation, while it is a major project, is often a natural component of a larger research program already set in place by a dissertation advisor and there isn’t the same premium on making original groundbreaking novel insights as there is in the humanities or social sciences. Original, groundbreaking dissertation work certain does put you in the creme de la creme for top posts after your PhD, but it isn’t necessary for a career as an academic. In contrast, non-STEM PhDs are lonely affairs, place inordinate premiums on trying to be original and groundbreaking (despite the fact that they often aren’t), involve less advisor participation and advise on dissertation research, and frequently involve 7-9 years in the program, and the stakes are higher for a dissertation which is a key job application component since a much smaller proportion of non-STEM PhDs than STEM PhDs will be able to land academic careers if that is what they are looking for. Non-STEM PhD entry level positions typically have 100-200 PhD bearing applicants per job posting.
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I’m not sure about the statement that lots of graduate students in PhD programs are married or have found a long-term partner. There were certainly a few in my cohort, but not obviously a much higher percentage than in undergrad.
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Maybe Millennials have grown more relationship shy over the years. Good to know.
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For grad students, I’ve got a more extensive post that goes into that, but yes it’s worth stating here too. (Part of the point of this post is a rough draft of a dedicated page to serve as a “part two” to this one.)
Thanks for the comments! I’d offer a minor correction regarding Perimeter, professors there are also professors at another university so they aren’t really an exception.
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Re Emeritus professors, like my late father, some of the big benefits in addition to an office are use of the recreational facilities of the university at a faculty price (like the rec centers), tuition waivers for younger children attending the university (faculty tend to have kids late in life), an edu email address, free access to library paid subscription services in your field, and invitations to faculty social and university governance functions and commencements that make you feel like you are still part of the community. Often you are called upon to give little lunchtime lectures to majors, grad students and faculty in your field, and you also often get called upon to give memorial minutes (or whatever it is called at your institution) which are short speeches to fellow members of a department or school or university honoring deceased colleagues in a professional informed and years of interaction enriched manner. Few lines of work try so hard to keep retired senior employees as continuing members of their community and it’s really a very nice gig for those who attain it.
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