When you think of health, what do you picture? A hospital? A doctor? This week on How to Change the World we're out to change your perception on what it really means to be "healthy". 

We sit down with Dr. Sandro Galea, dean and professor at the Boston University School of Public Health, to talk about what it means to be healthy. Dr. Galea, one of Time Magazine's top scientific minds, brings together the social, economic and environmental conditions that lead to health in our conversation and in his new book Well: What we need to talk about when we talk about health.