Professor Laura Carstensen. Credit: Andrew Brodhead/Stanford University

As 100-year lives become increasingly common, Stanford psychologist Laura Carstensen is working to understand the implications—and to ensure we can make the most of our extra years. The following are the researchers' own words, edited and condensed for clarity.

I got interested in aging following a car accident I was in when I was 21 years old. I broke 20-plus bones, and I ended up in an orthopedic ward for four months. It turns out, orthopedic wards have a bimodal age distribution with young people recovering from motor vehicle accidents and older people healing from broken hips and knees or other surgeries. After I recovered from the worst of it, the nurses decided to give me an assignment to talk with the older patients so they would stay alert and oriented—in hindsight, the nurses were trying to help me.

I got to know a lot of older women, and at 21, I found we had so much in common: All of us had been lifted out of our worlds and were completely dependent on other people. A shared experience emerged from the struggles we faced together. But when it came to the care we received, there was a huge disparity. I started to see that because of my age, I was treated differently. To the doctors, my youth signaled optimism—I had an entire future ahead of me—and during rounds, they would discuss different ways to help my recovery. But the older women in my ward were brushed aside.

It made me wonder about aging, and specifically, how much of aging, which is a biological process, is also shaped by the social world.

When I left the hospital, I wanted to examine this question. I didn't know what discipline would provide me with the best answers, and after taking courses in different disciplines, I settled on psychology. Psychology is a discipline that considers individuals, at the cellular level, all the way to larger, societal influences that shape and give meaning to who we are.

I trained as a clinical psychologist, and for many years I saw patients at a clinic established to serve older adults with limited resources. I came to know hundreds of people in ways I never would have as part of a research study. What impressed me the most was their emotional resilience. I would leave in the evenings feeling inspired, and I wanted to understand better how older people facing enormous challenges displayed such remarkable emotional strength.

What I discovered in my research was consistent with my clinical observations: Study after study suggested that emotionally, older people fare much better than middle-aged and younger people. At this point, there is general consensus in the field that emotional well-being improves with age.

In my classes at Stanford, my favorite talk is on emotion and aging. I tell students these are not the best years of their lives. Young people don't know that. Instead, they are told the opposite.

But according to my research, that's just not true. Late adolescence and early adulthood are the worst years for emotional well-being, and it gets better over time.

The theory my students and I formulated and tested over the years has to do with future time horizons—the perception of how much time is left in life. Humans are unique in our ability to appreciate mortality throughout our lives. We're constantly taking account of where we are in our life course.

When time horizons are vast and open-ended, people focus on learning and exploration over emotional well-being and satisfaction. But this can be hard because learning, by definition, is difficult. It's a process of trial and error. We fail, and with each failure, we learn.

As a species, we are pretty good at adaptation. But what we are really bad at is ambiguity. It's hard emotionally when you do not know what is going to happen: Will I meet my soulmate? Will I get into the university I want to go to? What if I don't get the job I want? What if these things don't happen?

When time horizons are vast like this, there is a lot of uncertainty.

Starting from the mid-20s, people gradually experience fewer negative emotions as they get older. While there's no change in the frequency or intensity of positive emotions, emotional balance improves with age.

In one study, when we induced a sense of endings in younger people, they experienced a mix of emotions that did not make them less happy. We also identified a phenomenon where people attend more to positive information than negative information as they grow older. For years in social psychology, people believed that humans look at negative stimuli more than positive. But we started looking at it in middle-aged and older people, and found that the effect is gone by middle age. By old age, it's flipped: Positive stimuli are what people attend to more than negative stimuli.

Emotionally speaking, life gets better as we get older, and it seems to have a lot to do with how we view future time. When we're reminded of our mortality, we shift cognitively to look on the bright side.

As life expectancies approach the century mark, my hope is that we come to appreciate each stage of life while we're in—from what's good to what's challenging—and that we can look forward to being older and more emotionally balanced. Just like no day in life is perfect, no stage in life is perfect either. If we can come to appreciate the good things about the stage we're in, we'll be happier about all the stages.

When you learn that older people are more pro-social, more likely to give to others, more emotionally even-handed, more likely to forgive, have fewer negative emotions, are slower to anger, and have accumulated knowledge and experience, it's an incredible resource that we've never had in human history.

Appreciating longevity has never been more important.

For most of human evolution, the average life expectancy was between 18 and 20 years old. Thanks to advances in science, technology, and culture, we've created a world where people live to be much longer. In the United States and beyond, 100-year lives are increasingly common.

Old age is new, and we've never had such age diversity in human history.

That poses a whole set of challenges that people 200 years ago didn't have to think about.

But the problem is that people are born into a world that was largely built by and for young people, and that model doesn't work for century-long lives. We need a "New Map of Life."

Longevity is going to change almost all aspects of our lives. It will change education, how we work, when we get married, financial planning and security, when we retire, how many jobs we go in and out of, where we live, our health, and our happiness.

We need to very quickly create an environment that supports longer life spans. That's the goal of the Center on Longevity, a research center I co-founded with Tom Rando and a number of other faculty at Stanford in 2007 to make the most of the 100-year opportunity we've been given.

But we need to start rethinking how we approach everything from health and well-being to education, work, retirement, and financial planning. We need research and technology more than ever to help us be healthy and engaged productively for decades longer than we have ever lived in the past. Without that, we will actually have a crisis on our hands.

What we try to do is ensure that a longer lifespan is a good thing and not a bad thing. My hope is that we come to appreciate each stage in life while we're in it, and that we can look forward to growing up and growing old in an age-diversified world.