How (un)usual is changing fields?

Question

For a long time I thought that when I start my PhD, my field of research is fixed for the rest of my academic career. However, I've encountered multiple people who have a PhD in space science or particle physics, and have later moved to atmospheric science or remote sensing — one of them even after already having tenure, starting an entirely new topic while remaining at the same institute. How common or uncommon is it to change to an unrelated field within natural science? How much chance would one have of a post-doc if the newly graduated PhD has no experience with the actual topic whatsoever? Is it expected that a Postdoc spends the first 3–6 months getting into the field, or that he/she can dive into the depth right away? Of course, a lot of scientifically relevant skills (data analysis, critical thinking, programming, statistics, etc.) are in common between different fields, but how important is the content of ones experience, really?

Related but different question: How might changing topic affect a career in academia? (different because from e.g. particle physics to climate science is more than just changing topic)

Answer 1

Most successful career researchers choose their field fairly early on in their career. This is often due to their approach to research; they have a fundamental question they're attempting to answer, and they spend years attacking different parts of the question through various projects. Pursuing research in this manner allows for flexibility in the research and can lead to some very interesting breakthroughs.

From what I've seen, those who do change areas of interest often do so within a single field, so that the majority of their expertise is still relevant. Yes, data analysis skills can transfer, but much of a researcher's expertise is in the form of a deep understanding of what the past and current state of the field; knowing important (and less important) papers, what different lab groups are researching, what's been tried and what hasn't. Since such a knowledge base can take many years to gain, people are often reluctant to switch.

I would venture that it's more common for a field to shift than for a single researcher to shift; i.e., some new technology or methodology allows a whole group of researchers in a given field to investigate something new or different.

Answer 2

I think that a lot of this depends on what you define by "change fields". In my observation, there is generally a lot of commonality even in a change, when the change is successful.

For example, somebody might have a mathematical toolkit of skills that they are very good at, and discover that it is useful in an application area that they didn't originate in. As they work in that application area, it exposes them to new problems that they find they need to solve to make progress, which leads to developing new skills and interests. From those one might move again, and so on.

The researchers whose work I respect most have often been through several of these types of transitions over the course of their careers. There are always uniting themes, but the topics, techniques, and intersecting communities may well change over time.

Answer 3

As someone who has changed fields completely, I wanted to chip in. In my experience, changing between fields (rather than within) is extremely uncommon. I have only met one other person in the last 10 years who has also done so; this is all in Europe, mind you.

The entire system of getting a PhD is about (aside from becoming a researcher) gaining very specific knowledge in a specific area- after having gained all this skill and knowledge, it is very costly to then leave the field to something that does not build on those skills nor the knowledge.

My advice would thus be to focus on transferable skills (such as the ones you mentioned) if you know that you want to switch. I knew before I started my PhD that I would never end up in the field- thus, I focused heavily on those and less so on expanding topic-wise. When applying for my post-docs, knowledge wasn't even considered- it was all about my technical skills. It all depends on the post-doc and the field, of course. As a personal note, while I don't regret switching, it was (and still is) a lot of work making up for essentially missing education in the area you work in.