Getting into new field after tech career / PhD in STEM, should i start a new degree as undergrad or at postgrad level I have an undergrad and PhD in a STEM field (engineering), and a few publications in some decent journals. since passing my PhD, i've been working in a management position in a tech company for the last few years, but needing some mental stimulation / diversification, started doing some papers in economics and philosophy after hours. I've done pretty well and i'd like to continue diversifying. After many years of self guided research, being back in the teaching environment as a student has actually been very cathartic and enjoyable and it turns out social sciences / humanities seem to come more naturally to me than i had thought previously.
My question relates to whether it would be wiser to start in a new field 'from the bottom up' (ie undergrad) or try to get into things at a higher level. I dont want to be bored but i also enjoy the rigour of starting at undergrad level. I'd like to get some opinions on this since most of the academics i know  tend to stay in their research fields. I should note i never intended to do a PhD but was promoted from a masters after my field year. I also seem to believe that education is not only about specialisation as is more common in the modern era, but more in tune with academics who covered many fields during their careers for instance Liebniz (law, mathematics etc)
Are their any PhD's out there who have diversified effectively into a completely new field? What is your advice? Did you end up 'starting again' ?
I don't see any reason to formally do another undergraduate degree. And you may not even need a credential at a higher level if you already have a doctorate and some publications in your new field.
My perspective is the US, where an undergraduate degree has a lot of things not related to the &quot;major&quot; subject. That is different elsewhere, of course.
But there may be some gaps in your education. If you are at a university, there is little reason why you can't ask a professor in some other field if you can &quot;sit in&quot; on one of their courses. I've done this, actually. The professor even agreed to give me ordinary student feedback (but no posted grade) on the homework assignments and exams. It was all informal and just let me &quot;scratch an itch&quot; in his field.
Once you think you have the knowledge gaps plugged you can, if you need the credential, apply for some higher level degree. You probably need to ask for special treatment in the admissions process, I suppose, but can probably justify it.