Physics Can I Switch to Theoretical Physics? A PhD Student's Confusion

[puregauge]

Hi. I'm currently a 4th year phd student in astrophysics, studying compact stars. I'm from China and am now an exchange student in US.

What I'm asking is: if I really have more interest in theoretical physics, do I still have a chance of entering the field?

I'm now in a very confusing stage: I have some knowledge in theoretical physics but still lacking basic research training in the field so I don't think I can do a very good job entering the field as a postdoc (also, it's unlikely postdoc position will be given to someone completely new to the field I suppose) So I suppose the only choice is a 2nd phd
But I have also read a lot of posts dissuading people to take a 2nd phd... So I'm currently extremely confused about what to do next.

Please help me out! Your advices can save my life! Thanks :)

PS: My undergrad major is "space physics", but I managed to finish all the courses needed for a theoretical/particle grad student (quantum mech, quantum statistics, QFT, gauge theory, GR, group theory etc) and have also taken a minor in math (called "double major" in my university but has less requirement than math major) plus some further math courses (topology, real analysis, functional analysis, homological algebra), some of these are taken during grad years.

As grad student my field is kind of interdisciplinary and have strong relation with particle physics and theoretical physics. But during my (not-very-successful) research, I had to keep inhibiting my true interest in theoretical physics and mathematical physics, like things beyond standard model (string, SUSY, extra dimension, quantum gravity, etc) because my field is still largely astrophysical.

 

[cristo]

But during my (not-very-successful) research

This is the most worrying thing that you say. Why was your research unsuccessful? What would make an employer think that you would be more successful undertaking research in a slightly different area?

 

[eri]

It's very unlikely any program will admit you for a PhD in physics with a PhD in astrophysics. They are simply too closely related. How about just working with someone in the physics department or a theoretician in your own department for your PhD instead? You can change topics for your PhD, it might just take an extra year or two (much less time than doing another PhD).

 

[A. Neumaier]

if I really have more interest in theoretical physics, do I still have a chance of entering the field? [...] So I suppose the only choice is a 2nd phd [...] I had to keep inhibiting my true interest in theoretical physics and mathematical physics, like things beyond standard model (string, SUSY, extra dimension, quantum gravity, etc) because my field is still largely astrophysical.

A second phd is pointless. The PhD just signifies that you can stick to a long term task and complete it successfully. To have this shown twice is not much of a plus. Thus finish you PhD - but learn & practice along the way the really interesting stuff in your spare time. Not only textbook stuff - handle it as if you were pursuing there a thesis! Maybe set yourself the goal to write a survey paper about a topic you find interesting (and you want to work later on) but where there is not yet a good overview in the literature. And try to get to know the people you'd like to work with later, or at least their work!

When you apply for a postdoc position you can say that you want to change to something more theoretical and that you already have the background needed. This of course you need to have - but in the form of knowledge and working practice, not in the form of official certificates.

 

[Choppy]

My experience has been the post-doctoral work is rarely the same as graduate work. I suppose it's usually in the same field, but not always. What I've seen happen for the most part is that post-docs are selected more for the skills they can bring to the position rather than the exact topic of their graduate research. Also, people will generally choose positions based on what's available at the time. Most people can't just sit around for 2 years waiting for the perfect post-doctoral project to come up.

My understanding is that theoretical physics post-doctoral positions are rather competative too. So even if your PhD was in exactly the same field you'd find yourself competing for a limited number of positions with perhaps only a slightly greater advantage. Doing a second PhD is probably not a great idea, if it's even possible.

But why not branch out from your current project? Why can't you have a side-project that's more in-line with your true passion? Use your main stream of work as your 'bread and butter' but then put aside some time to work on your passion. True, it will take away from time on your main project and you likely won't make as much progress as you would if you worked on it full time, but it has the major advantage of diversifying your skill set.

 

[puregauge]

It's very unlikely any program will admit you for a PhD in physics with a PhD in astrophysics. They are simply too closely related. How about just working with someone in the physics department or a theoretician in your own department for your PhD instead? You can change topics for your PhD, it might just take an extra year or two (much less time than doing another PhD).

Thanks a lot! I haven't thought about this before.
My worry is it might be too late for me to change topic and my university back in China probably won't let me. On the other hand maybe I can find someone here in US to work with on some small side-project? What do your suggest?

 

[puregauge]

This is the most worrying thing that you say. Why was your research unsuccessful? What would make an employer think that you would be more successful undertaking research in a slightly different area?

It is a little complicated to explain. I should probably do this in the original post but it'll make it too long to read...
My professor works in the field of neutron star study, he's a pure astrophysicist but he also advocates bold conjectures that are really particle/nuclear physics assertions (He's absolutely rare among his colleagues). I was first told to work on observation and have already done a paper before I requested to change for a more theoretical topic.
But because he wasn't really familiar about the theoretical part, I found out after a lot of literature reading that the topic is too bold and not really doable. Later I found this chance of exchange program and he agreed to send me here to collaborate with US professor on a slightly changed topic (still theoretical).

With (1) some amount of time devoted to learning more about the topic I'm truly interested in
(2) time wasted on observation topic
(3) time (somehow wasted) on literature reading/ background study only to find out something is not doable
I had only 2 publications (on nearly completely unrelated topic) and appeared very unsuccessful.

I know it all sounds like a hopeless mess, that's why I'm very very eager to have a new start with a clean slate.

 

[twofish-quant]

But because he wasn't really familiar about the theoretical part, I found out after a lot of literature reading that the topic is too bold and not really doable.

That's typical for Ph.D. dissertations. What you need to do is to work with your adviser and dissertation committee to figure out how you can turn what you have into a doable dissertation topic.

With (1) some amount of time devoted to learning more about the topic I'm truly interested in
(2) time wasted on observation topic
(3) time (somehow wasted) on literature reading/ background study only to find out something is not doable

3) is not a waste. Finding out that something doesn't work is progress since it gets you to something that does.

I know it all sounds like a hopeless mess, that's why I'm very very eager to have a new start with a clean slate.

It's not a hopeless mess. Finding out midway through your dissertation that your original topic was something that just won't work is normal and standard. If you start over with a clean slate, then you'll spend another three years before figuring out that your new idea just won't work.

You need to talk with your dissertation adviser and committee and other people in the field, and then change your topic to something that can be done. It is interesting that what is proposed can not be done. Sometimes the field is such that a dissertation that says something *can't* work is interesting. Can you generalize the argument? Do the mathematical techniques that you've learned work in another field?

You'll find that coming up with the right answers is easy, it's coming up with the right question that's much harder.

 

[twofish-quant]

What I'm asking is: if I really have more interest in theoretical physics, do I still have a chance of entering the field?

You are in the field. Look in the mirror and say to yourself, "I am a theoretical physicist" because you are.

I have some knowledge in theoretical physics but still lacking basic research training in the field

You'll learn this as you are doing your dissertation. The Ph.D. is rather unusual. In other degrees, someone tells you want you need to do. With the Ph.D., you need to figure out for yourself what needs to be done.

As grad student my field is kind of interdisciplinary and have strong relation with particle physics and theoretical physics. But during my (not-very-successful) research, I had to keep inhibiting my true interest in theoretical physics and mathematical physics, like things beyond standard model (string, SUSY, extra dimension, quantum gravity, etc) because my field is still largely astrophysical.

What you are doing much more theoretical physics and mathematical physics than what you want to change do. Trying to turn your dissertation into something that you are interested in, that's part of the thing that you have to teach yourself in order to be a researcher. If you can figure out how to use graded Lie Algebras to calculate nuclear equations of state because you happen to be interested in graded Lie Algebras, that's part of research.

 

[petergreat]

PS: My undergrad major is "space physics", but I managed to finish all the courses needed for a theoretical/particle grad student (quantum mech, quantum statistics, QFT, gauge theory, GR, group theory etc) and have also taken a minor in math (called "double major" in my university but has less requirement than math major) plus some further math courses (topology, real analysis, functional analysis, homological algebra), some of these are taken during grad years.

As grad student my field is kind of interdisciplinary and have strong relation with particle physics and theoretical physics. But during my (not-very-successful) research, I had to keep inhibiting my true interest in theoretical physics and mathematical physics, like things beyond standard model (string, SUSY, extra dimension, quantum gravity, etc) because my field is still largely astrophysical.

Look on the bright side. By the time you finish your PhD, LHC may already have wrecked hopes of seeing supersymmetry and large extra dimensions. Then you can watch the string theory boys not getting jobs! Not completely joking.
You have a very strong academic background to switch to more theoretical areas. The trick might be finding a "bridge". For example, I know some people with PhDs in string theory managed to get into condensed matter theory for postdoc, due to their knowledge in topological methods, strongly coupled gauge theory etc. And some people with PhDs in cosmology switched to more "stringy" areas during their postdoc period, by working on brane inflation, cosmic strings etc.