Dear All, Currently I am enrolled in a major American research university in the mathematics PhD program. I just finished my first year. I also hold a Bachelors and a Masters degree in statistics. However I have always want to do research in physics. So at this point I am very seriously considering to shift to a physics program. I would like to have advice on the following topics: 1. Which universities I should apply to? I do not have much physics background per se(I have taken undergraduate courses on CM, QM, EM and thermodynamics). However my math background is quite good and I have a number of advanced graduate level math courses under my belt. I also have quite high grades throughout my academic career. So what are my chances in some top notch physics department? I want to do research in theoretical high energy physics.(I should also mention that I have done no experiments after high school.) 2. Do I need to take the physics GRE? I have already taken the math GRE. 3. How should I phrase the statement of purpose? In particular, how should I explain my decision of moving from math to physics? And any thoughts on how to portray my strength in math as an advantage? I want to do research on theoretical high energy physics. So it would be very helpful if someone can provide a link to the statement of a similar applicant. 4. What about European universities? I don't know much about the application procedure there. 5. My current university has a quite good physics program. Is it possible to transition within the university without all the hassles of a new application procedure? I have heard stories of many people who have changed departments in gradschool(Witten himself). How does that work? Should I just email some professors in the physics department and rest my case to them? 6. This is a tricky question. If all my efforts come to naught and I fail to secure admission in any of the places I apply I would like to complete my current PhD in math. However I plan to ask some of my current professors to write letters for me. So they would know that I was planning to go away. Would that have some repercussions in future? Waiting eagerly for your replies. Thanks in advance.