Amy Bug does research in the field of computational condensed matter physics. She is the president-elect of the Division of Computational Physics of the American Physical Society and has written a book, Forces and Motion (2008), for middle-to-early high school students. Her courses at Swarthmore include classical mechanics, statistical physics, quantum mechanics, and computational physics. She also teaches a seminar on gender and physical science. Write to her at abug1@swarthmore.edu

The following is adapted from a recent issue of Physics World.

What will our soldiers think when they return to the university and find that they are expected to learn at the feet of a woman?" - a University of Göttingen faculty member, describing the German-born mathematician Emmy Noether, circa 1915.

Physics is phenomenally successful at taking data on sexless, raceless objects such as photons and transforming that information into mathematical laws with highly accurate predictive power. To be a physicist is to love working in a field where this is possible. So why should there be a paucity of women in physics, at all professional levels and in virtually all industrialized nations?

There are many theories to explain this phenomenon, and it is a tenet of gender studies that one should avoid attributing complicated effects to a single cause. Gender studies is a field guaranteed to annoy the physicist - where data not only stubbornly confound our ability to write laws but also where unifying principles, when they exist at all, offer much less in the way of accurate predictive power.

"Over the 20-plus years I've been teaching, I've known excellent people who didn't get good evaluations, who told me, 'I try so hard,'" Bug says. "I just started to feel something odd was going on. So I read the literature in sociology, where it's boringly obvious that who you are very much influences how good you are perceived to be."

With a grant from the Mellon Foundation I, together with my colleagues Kris Lui and Etsuko Hoshino-Browne, recently explored one cause that could explain the paucity of women in physics: a double standard of professional evaluation for men and women in the sciences. We conducted a study to determine how male and female physicists are evaluated in the classroom and used videotaped lectures in which professional actors - two male and two female - played the role of a physics professor. They each gave a 10-minute physics lecture to a class of students that included blackboard work, a demonstration, and a question-and-answer session. None of the actors were trained in physics but all received the same preparation and memorized the same script.

We then showed each of 126 physics students the lecture by one (chosen at random) of the four "professors" and got them to fill out a survey in which they rated various aspects of the lecture using a five-point scale. The students supplied some personal information but not their own gender, which was noted covertly by the person collecting the surveys.

Caught on Camera

Our study resembles those in which subjects are asked to assign certain qualities, such as competence or leadership, merely by looking at a photograph of a person. However, one would hope that viewing a lecture would produce a more meaningful evaluation - at least that is the hope of those of us who use student evaluations to decide on hiring, promotion, and salaries.

Responses to 17 survey questions were combined to create a single score. We found that, on average, the male professors received higher scores than the female professors. But while female students gave slightly higher marks to the female professors than they did to the men, male students rated male professors vastly better - a result that is reminiscent of studies of science-teacher evaluations from colleges and secondary schools.

"Social psychologists know that how you are raised, your life's journey, who you meet along the way, are all significant," Bug says. "It shouldn't rock your world that this happens."

We also considered the students' responses to questions that looked at gender-stereotypical attributes, such as if the lecturer had a "solid grasp of the material," if they were "knowledgeable," or "good with equipment." These questions yielded a distinct gender bias, in that both male and female students rated male professors as better. (Female students were, however, more equivocal - the gender gap in their ratings was not significant, as it was for male students.) On the other hand, a group of questions asking whether the professor "teaches in a way that really helps students learn," is "well organized" and "interacts well" with students produced quite a different effect. Here, there was a clear own-gender bias, with female students rating the female professors as superior and the male students giving higher marks to the male professors.

We concluded that not only can the gender of the physics professor make a difference to how a lecture is received by students, and in what sorts of strengths and weaknesses students perceive, but also that student gender can play a role. So the male soldiers of Göttingen would, on average, prefer to learn physics at the feet of a man - not at those of a woman speaking the same words, writing the same equations on the board, and giving the same answers to questions that the soldiers pose. Were there any female soldiers, their preference would be less clear cut.

A little bias goes a long way

"If I were a physicist who didn't like men, I'd be the biggest masochist in the world," Bug says. "Moreover, I wouldn't embark on this study if I didn't think the data could help. If you don't recognize the issue, there's little hope of addressing it. So my attitude is, let's confront this, let's learn from it and figure out a way to ameliorate the problem."

The results we found are consistent with the theory that people have implicit beliefs that associate different genders with different aptitudes and predilections. Even people who consciously believe in gender equality cannot suppress these automatic associations. Indeed, an online test reveals that I, too, have a moderate, innate tendency to associate men with science.

A set of associations forms a "schema," which is understandably useful to our survival as a species. However, schemas of gender, race, and disability also seep into our professional interactions and judgments. Psychologists like Virginia Valian have argued that an identity that violates such schemas - for example, a female physicist or a male nurse - has a negative consequence in terms of the individual's evaluation and perception.

"There's so much hope," Bug says. "That's why I did this. One commenter on a site where my study was discussed initially said, 'This study is invalid.' After I responded to him with a careful response and an explanation of our methods and results, he wrote back, 'Keep up the good work.' That made my week."

The good news is that in physics in the U.S., we have gone from a "leaky pipeline" at all career stages, overt discrimination, and tolerance of harassment to a much better situation: double-digit percentages of women on faculties, hiring, and promotion at equitable rates and gender bias that is usually quite subtle, like the implicit bias that the online test might reveal. The less-good news is that even small disadvantages such as an inferior teaching evaluation or a smaller start-up grant can accumulate over time - so that the cumulative effect has sizeable consequences on a career.

Today the big issues are acknowledging and correcting for implicit bias, reforming workplace-policy, bringing in students from under-represented minorities, retaining girls between school and college, and seeking equity in the developing world. I believe that progress will continue, as long as good people are willing to act - to recognize that effort is required not only to progress, but to maintain the gains we've made and resist backlash or backsliding. We also require continued effort by educational institutions, funding agencies, and professional organizations, so many of which have engaged in difficult introspection and institutional change. Hopefully, leaders in academia, government, and industry will continue to fund research and disseminate results and recommendations - so that eventually women will not need to "swim against the tide" in the physical sciences.