[tescocles]

I get exactly the same pang of sadness. I even distinctly remember learning perturbation theory. But I use so little of what I learnt, and it's so long ago, that at lunch table discussions I can't even be the "ex-physicist that'll know the answer to that" any more. It fills me with great sadness.

It's not even that I feel that time was wasted - I like my field and I don't think I was suited for the path I didn't take. But it's such a rich and interesting field (physics, maths, chemistry, the lot) it's so fun to talk about. And with that training at least I could engage meaningfully in those discussions when I was fresh out of uni.

Now, not so much. My amateur astronomer colleague knows more about cosmology than I do at this point.

[jabl]

Same. Although I had long ago decided that an academic career wasn't for me, I was always thinking that after I finish my PhD (computational condensed matter physics), I would somewhat keep up with my field just for fun. But between kids, work, other hobbies etc. I never really had the time nor energy to do that. So while I'm somewhat confident I could relatively quickly relearn much of what I have forgotten, it also feels that world is slipping further and further away for each moment. Not that I really dwell over it, there's a lot of interesting things in life and so little time, you can't just do everything.

I don't really miss lunch table discussions though. Typically if it's by members of the general public, they're sprouting some misunderstanding based on some magazine article they read, written by some journalist who didn't really grok the topic either, and I can't just be arsed to start lecturing people how it's not that simple and their understanding is all wrong. More agreeable to just talk about football, beer, or the weather. Or if it's a lunch table discussion between experts, then it's usually about some minute detail of their particular expertise and you need to be pretty knowledgeable about that particular subtopic in order to be able to contribute.

[Escapado]

I’m kind of relieved to know I’m not alone. Got my masters 4 years ago and immediately became a web dev after. I am greatful for the time and I think a lot of the resilience, logical thinking and general problem solving skills transferred well to my current work. Yet some part of me wishes I had stayed and gotten a PhD but I also remember I was overworked and had significantly higher imposter syndrome although my grades indicated that I was doing really well.

To get back on the topic of perturbation theory I remember how the mathematical physicists in our lectures always complained that the systems the professors would use it for were not well suited to use it in the first place but often times the results were kinda nice so they used it anyway. Not that I remember any details but I was so fascinated when I found perturbation theory used again in QFT and it really dawned on my how powerful of a tool it is.

[admissionsguy]

I'd felt the same and decided I actually could not live without it. So I am now 34 and studying for an undergraduate degree in life sciences (just finished the notoriously challenging organic chemistry 1&2) while adding some graduate-level physics classes on top. Really, really refreshing and good experience so far, though I don't know if I have the stomach to try going for a PhD again (would rather become independently wealthy and fund my own research, heh).

[nathan_compton]

I encourage you both to do this if you are interested. It isn't that hard and, in fact, many universities have put their entire quantum mechanics courses online if you want a refresher.

Since finishing grad school I've taught myself the basics of General Relativity and Quantum Field Theory. You can do it too.