Your field of interest absolutely affects your chances of getting into a program. Funding has a large part to do with it, as well as distributions of preferences within the applicant pool. Regarding the former reason, there is certainly more money floating around in some subfields of physics more than others (more money in experiment than theory, more in condensed matter and bio than gravitation and string theory because of stronger industry/gov't interest, plus the relative fractions of funding allocated to the various subfields in the NSF/NIH/DoE budgets, etc etc), while every school will also have research groups in many subfields varying substantially in size, which is a reflection of both the available funding in the field as well as the strength and reputation of the program at each particular institution (arrow of causality is not clear in this case). Recycling rates for grad students is higher in experimental programs with many small experiments, slower in programs with only a couple large experiments (fusion and high energy are good examples).
Regarding the spread of interests in the graduate applicant pool, there are certainly a few fields that attract far more applicants than there are positions. High energy theory is a quintessential example, as just about everyone with an affinity for theoretical physics considers doing it at some point. The most reputable programs typically only anticipate a small handful of students entering high energy theory for any given year, and indicating a strong preference for this field can have pretty stark implications for your chances of getting into grad school at the very top programs. When I was visiting Caltech, about 10 people attended the information session for high energy theory out of a pool of roughly 60 or so accepted students, but there was no way all 10 of those students would wind up being able to do string theory/QFT for their graduate pursuit, as the department only has a few full time faculty (though they are prolific faculty). Most likely only 2-4 would make the cut for high energy and secure a faculty advisor. Despite my having very good test scores/grades/letters/physics research, I was rejected from Stanford, Harvard, and Berkeley (my applications to these programs stated a strong preference for high energy theory). Caltech was the only "top" high energy theory program I was accepted to, while my success in plasma theory programs was much better, as plasma doesn't have quite the rock-star status that high energy does! And from looking around at the incoming class at Princeton, almost all of the foreign students here to do theoretical physics (high energy, CM, and cosmology) have masters degrees and a significant amount of in-field research already, and there's only a handful of American first-year theory students here as well, many of whom have done great research or have graduate-level academic experience going into the program. So seeing this, it's no surprise to me why I didn't get into most high energy theory programs I applied to...there's very few spots at each school, and way too many overqualified applicants vying for those spots; the competition is fierce. Now this shouldn't scare you away from applying, but it should help give you some perspective into the situation--you are competing against a world full of students for one of a VERY finite number of slots at each school, so apply to several schools and be realistic with how you choose the *majority* of the schools (though everyone should apply to at least one of their dream schools, especially if there is a strong, relevant reason to do so, ie they do research that builds on research you did as an undergrad and you really want to stay in-field, etc).
Last edited by schmit.paul
on Sun Nov 18, 2007 10:03 pm, edited 1 time in total.