But most important, you're 20 years younger. How do you feel? Well, if you're at all like the subjects in a provocative experiment by Harvard psychologist Ellen Langer, you actually feel as if your body clock has been turned back two decades. Langer did a study like this with a group of elderly men some years ago, retrofitting an isolated old New England hotel so that every visible sign said it was 20 years earlier. The men—in their late 70s and early 80s—were told not to reminisce about the past, but to actually act as if they had traveled back in time. The idea was to see if changing the men's mindset about their own age might lead to actual changes in health and fitness.