Langer came to believe that one way to enhance well-being was to use all sorts of placebos. Placebos aren’t just sugar pills disguised as medicine, though that’s the literal definition; they are any intervention, benign but believed by the recipient to be potent, that produces measurable physiological changes. Placebo effects are a striking phenomenon and still not all that well understood. Entire fields like psychoneuroimmunology and psychoendocrinology have emerged to investigate the relationship between psychological and physiological processes. Neuroscientists are charting what’s going on in the brain when expectations alone reduce pain or relieve Parkinson’s symptoms. More traditionally minded health researchers acknowledge the role of placebo effects and account for them in their experiments. But Langer goes well beyond that. She thinks they’re huge — so huge that in many cases they may actually be the main factor producing the results.

As an example, she points to a study she conducted in a hair salon in 2009. She got the idea from a study undertaken nearly a decade earlier by three scientists who looked at more than 4,000 subjects over two decades and found that men who were bald when they joined the study were more likely to develop prostate cancer than men who kept their hair. The researchers couldn’t be sure what explained the link, though they suspected that androgens (male hormones including testosterone) could be affecting both scalp and prostate. Langer had another theory: “Baldness is a cue for old age,” she says. “Therefore, men who go bald early in life may perceive themselves as older and may consequently be expected to age more quickly.” And those expectations may actually lead them to experience the effects of aging. To explore this relationship between expectations of aging and physiological signs of health, Langer and her colleagues designed the hair-salon study. They had research assistants approach 47 women, ranging in age from 27 to 83, who were about to have their hair cut, colored or both. They took blood-pressure readings. After the subjects’ hair was done, they filled out a questionnaire about how they felt they looked, and their blood pressure was taken again. In a paper published in 2010 in the journal Perspectives on Psychological Science, they reported that the subjects who perceived themselves as looking younger after the makeover experienced a drop in blood pressure.

A few years earlier, Langer and one of her students, Alia Crum, conducted a study, published in the journal Psychological Science, involving 84 hotel chambermaids. The maids had mostly reported that they didn’t get much exercise in a typical week. The researchers primed the experimental group to think differently about their work by informing them that cleaning rooms was fairly serious exercise — as much if not more than the surgeon general recommends. Once their expectations were shifted, those maids lost weight, relative to a control group (and also improved on other measures like body mass index and hip-to-waist ratio). All other factors were held constant. The only difference was the change in mind-set.

Critics hunted for other explanations — statistical errors or subtle behavior changes in the weight-loss group that Langer hadn’t accounted for. Otherwise the outcome seemed to defy physics. “To which I would say, ‘There’s no discipline that is complete,’ ” Langer responds. “If current-day physics can’t explain these things, maybe there are changes that need to be made in physics.”

In the course of her career, Langer says, she has written or co-written more than 200 studies, and she continues to churn out research at a striking pace. Just before winter break, in her final meeting with two dozen or so students and postdocs, Langer went around the table checking the progress of nearly 30 experiments, all of which manipulated subjects’ perceptions. Some used a special clock that could be set to run at half-speed or double-speed. In one study, sleeping subjects were fooled, upon awakening, into thinking they had more or less sleep than they actually did. She posits that the scores on measures of short-term memory and reaction time will vary accordingly, regardless of how long the subjects actually slept. In a yet-to-be-published diabetes study, Langer wondered whether the biochemistry of Type 2 diabetics could be manipulated by the same psychological intervention — the subjects’ perception of how much time had passed. Her theory was that the diabetics’ blood-glucose levels would follow perceived time rather than actual time; in other words, they would spike and dip when the subjects expected them to. And that’s what her data revealed. When a student emailed her with the results this fall, she could barely contain her excitement. “This is the beginning of a psychological cure for diabetes!” she told me.

Some of the new experiments rely on variables that change self-perception. In a study using avatars, scheduled to take place at the popular gaming facility Second Life, subjects will watch a digital version of themselves playing tennis and gradually getting thinner from the exertion. Langer is exploring whether watching an avatar will have a physiological effect on the real person. “You see yourself, you’re playing tennis,” Langer said. “The question is: Will people lose weight? We’ll see.”