I would probably decide prior to graduate school about whether I wanted to pursue experimental or theoretical physics because you will tend to specialize in one particular field. However, I would imagine its possible to get a doctorate in theoretical physics and perhaps still have (even if they are slim) opportunities to work in experimental physics afterwards.
I'll let some of the more experienced and knowledgeable members provide you with a more in-depth and specific set of responses.
It depends what you mean here. Not all physicists are theorists... At least in the US the differentiation between experimentalists and theorists occurs in graduate school.
I'm assuming that this question is asking 'can I get a PhD in physics and then go find an industry job somewhere doing physics'. The answer to this is yes, if you choose a research area for your PhD which has applications in industry or at the very least if you develop skills that are useful in industry. I know plenty of people who did experimental condensed matter physics who now work in the semiconductor manufacturing industry. I also know several that did work on photovoltaics in grad school who are now working on them in industry.
Now if you mean can you get a PhD focusing on say string theory or cosmology and then transition afterwards to doing condensed matter experiment, then the answer is that you probably could not. If you were doing mostly computational physics (which is actually fairly common in theory), then transition to into some other area of physics doing computational stuff might be possible.
There are many different sub-fields of physics (astrophysics, biophysics, condensed matter physics, geophysics, medical physics, particle physics, optics, sociophysics, etc.) and within those sub-fields people tend to gravitate towards their strengths - either the theoretical or experimental side. Some people will work on both sides over their career, depending on their intereststs, and the opportunities available.
In my own field, medical physics, the work very heavily application-based.
I recall hearing from professors that 50% of physics students want to be theoreticians, and only 5% of the jobs are in theoretical physics. So no, absolutely not. Theoretical physics doesn't have immediate practical use (though in the long term it may have enormous uses once it gets applied.) So there isn't a lot of money for it, the way there is money to get useful and desired things built that people will pay for. I think 50% of physicists are in academia and the other 50% are in industry. Anyone want to improve my numbers?
I recall hearing from professors that 50% of physics students want to be theoreticians, and only 5% of the jobs are in theoretical physics. So no, absolutely not. Theoretical physics doesn't have immediate practical use (though in the long term it may have enormous uses once it gets applied.) So there isn't a lot of money for it, the way there is money to get useful and desired things built that people will pay for. I think 50% of physicists are in academia and the other 50% are in industry. Anyone want to improve my numbers?
I am not sure about industry or in national labs, but in academic there is not a 5/95 split of theoreticians to experimentalists. My guess is perhaps 40/60 or 45/55.
