How important is the "major" of the PhD?

Question

For sake of argument, let's say I obtain a bachelor's degree in physics, a master's degree in physics, and then a PhD in physical chemistry but from a department of chemistry. Can I then go on to be a physics professor? Or would I be confined to teaching chemistry?

One can imagine equivalent situations for other fields. Say, for example, a bachelor's in computer science, master's in computer science, and then a PhD in computational physics from a department of physics. Could that individual then become a computer science professor?

Answer 1

It depends more on the aspect of your research. If you have a physical chemistry degree but do research more in the realm of physics, it is possible that you could be hired in physics or chemistry, even hold a joint position in both.

The limiting factor that your PhD major will be in that it is the general area where you are more trained in, that is, you can probably teach courses in your major better than those in the other department. Sometimes hiring decisions do take this into account.

Answer 2

The answer is very field specific. In many departments all that matters is your research. Does your dissertation and publications fit the department's vision for what it means to do research in field X, regardless of the field of your degree.

However, in some fields it is really hard to get in the door without a degree in that field. The example I am thinking of is Mathematics. Theoretical biologists, economists, social scientists etc. with degrees in the field of application tend not to end up in math departments even if nearly 100% of their research is proving theorems. This isn't to say it can't be done, but it seems as though it is much easier to move in the opposite direction from a math department to a science department. For example if you work on pure problems in probability but your degree is in economics, it is hard to get a job in a math department.

Disclaimer 1: it is unclear how much of this is due to selection bias by the job candidate vs. discrimination in the math department against people without math degrees.

Disclaimer 2: this is based on anecdotal evidence and faculty listings on department websites that show where mathematicians from science departments end up after their degree. I have not sat on a hiring committee.