You are a doctor of philosopy. You have defended your thesis, you have got your degree. Now what do you do?
If you would like to cling to the academic world at least a little bit longer, perhaps with the goal of eventually becoming a professor or something like that, you are normally expected to go to another university or institute for a period (or two, or more) as a postdoc.
On our travel expense forms I'm a PDF. Not a portable document format, but a postdoctoral fellow. Usually I forget that this is the official title. In my experience people in general don't know what a postdoc is. It's something at the university. "So do you teach or something?" they ask. Or: "what classes are you taking then?" Nowadays, if I'm among normal people or even undergraduate students, I just say that I'm an apprentice researcher. That makes sense to most.
The postdoctoral years often seem to have a romantic shimmer around them in retrospect. Professors talk about it as the happiest time in their careers. It really is good in many ways. You are free from the pressures of thesis writing, you have few if any teaching responsibilities, and you can spend almost all of your time doing research. You also get to go to new places, learn new things, maybe experience a different culture. You try your wings and your initiative.
On the other hand it's a very insecure position. The job is temporary, and you will have to move one or more times within the next few years but you probably don't know where you will end up. You know that in front of you is The Bottleneck, the competition for faculty positions, and you need to produce results and publish now to prove that you are good enough to come into consideration. If you choose to go to industry instead, you will have to make new contacts and learn to navigate a new world.
I talked to two other postdocs the other day, telling them how I'm planning to go back to Sweden to resume my life: family, friends and all of that. They both shook their heads, and said that this connection to a certain place and social circle is something they haven't had for a long time. That's one of the drawbacks of this kind of career. Janna Levin depicted the problems of moving around as a postdoc in her book How the Universe Got Its Spots, a book I enjoyed very much for exactly those personal (and in extension sociological) aspects.
For me personally I have to say that this is really a happy time. I enjoy my job, I have no real financial problems at the moment, and having my family with me cures most of the attacks of homesickness. Still, I really have no idea what the future will bring. I'm not worrying, but sometimes I think about the future. I'm hopeful, but I have questions.
I want to move back to Uppsala and stay at least relatively close to there. But what kind of job will I find? Will I be able to live a mostly unstressful life with relatively mild and few depressions? Will I have at least enough money not to worry about it? (I've been through some of that, and with kids it's worse.)
Yes, I am a physicist. Now, what do I do with my life?