What is the optimal value of the ratio R between the numbers of experimentalists (NE) and theorists (NT) in a physics department faculty ? Is there such a thing as an optimal ratio ? If so, is it something like two or greater (i.e., two or more experimentalists for each theorist), as I often hear in conversation (almost invariably experimentalists are the ones to make this claim) ?
Several arguments are typically invoked to explain/justify the preponderance of experimentalists in the make-up of a physics faculty. The most popular seem to be the following:
1) Physics is an experimental science.
2) More students will do experimental than theoretical work.
3) Students who are trained as experimentalists are more likely to find employment.
The above arguments vary in validity; 1) is true but its connection with R is not immediate; 2) may or not be true, I have never seen the numbers; it is true that there are more students doing experiment than theory, but this in and of itself may be merely a reflection of there being more faculty doing experiment; and 3), well, that’s sheer nonsense.
There are also other factors at play, which may become increasingly important in the years to come. For example, the difficulty of carrying out experiments in-house in certain research areas (such as high-energy physics or cosmology), as well as the increasing cost of experimental research across the spectrum, may significantly affect the average value of R in the years to come.
So, leaving aside the difficult question of what the optimal R should be, what is R on average now ? I have looked up NE and NT for the top 25 physics departments, based on US and News and World Report rankings of graduate programs. It seems reasonable to take this sample as representative of current trends in physics.
The numbers reported in the table below are taken from departmental web pages .
I have restricted myself to my own research area, namely condensed matter physics, not only to simplify my task, but also because a) it is by far the largest in terms of membership, and b) it is one in which, for the most part, experiments are carried out in-house, i.e., in a laboratory at the institution of affiliation of the faculty .
The average value of R is 1.5; however, because of its large standard deviation (0.5) this number is not particularly telling. More interesting is the information contained in the distribution itself. In particular, 68% of the departments in this sample have a ratio R of 1.5 or less. Moreover, over half of the departments with R greater than 1.5 feature relatively small condensed matter theory groups (i.e., four faculty or less) . Finally, it is also worth noting that there is a moderate at best correlation between the value of R and the ranking of the department.
These data clearly show that, “ideology” aside, the notion of “two experimentalists for every theorist” clashes with reality. A good “rule of thumb” these days seems closer to three experimentalists for every two theorists (I don’t like chopping people in half… although, come to think of it, we are talking experimentalists… kidding !). It would be interesting to know what the situation was, say, thirty years ago.
(Thanks in advance to those who will provide more accurate numbers. Also, my apologies if a similar or equivalent study has already been published by some other nerd, er, blogger)
 Information contained in departmental web pages has been assumed reliable and up-to-date, even though in many cases it must be carefully analyzed and “re-interpreted”, given the tendency of places to make themselves look bigger and better than they are. The most widely adopted technique is that of listing the same person several times under different labels, such as “condensed matter” and “nanoscience”; also popular is neglecting to update the page to reflect faculty departures and/or retirements, as well the listing of individuals whose actual affiliation to the department can be defined tenuous at best. There is therefore a (hopefully small) degree of subjectiveness on my part, in the way data from web pages are collected.
Excluded from the count are retired, emeriti (including “research professors”), adjunct (“affiliate”) faculty, lecturers, as well as cross-appointed faculty whose primary affiliation is not with the physics department. Individuals have been excluded from the count only if their status (e.g., emeritus) is explicitly mentioned in the departmental web page (no assumption has been made on the basis of age). All cases of joint appointment in which the primary departmental affiliation could not be determined have been included in the count. I have not attempted to exclude those individuals who have ostensibly taken on major administrative duties (e.g., provost) and may therefore not be active in research at this time.
In those cases in which conflicting data can be found on different pages (e.g., the main departmental web page and that of the condensed matter group, web pages of different departments listing the same person, etc.), the conflict has been resolved by looking up recent information from other web sources.
 I have restricted my statistics to faculty identified as “condensed matter theorists” or “condensed matter experimentalists”.
 Data for the first 50 departments have been compiled and are available here. Results for the larger sample mimic those shown above.