Once we’ve formed those kinds of stereotypes, for both mental and social reasons it’s hard to undo them. Psychologist George Kelly observed that our beliefs are like pairs of reality goggles. We use them to make sense of the world and navigate our surroundings. A threat to our opinions cracks our goggles, leaving our vision blurred. It’s only natural to put up our guard in response—and Kelly noticed that we become especially hostile when trying to defend opinions that we know, deep down, are false. Rather than trying on a different pair of goggles, we become mental contortionists, twisting and turning until we find an angle of vision that keeps our current views intact.

Socially, there’s another reason stereotypes are so sticky. We tend to interact with people who share them, which makes them even more extreme. This phenomenon is called group polarization, and it’s been demonstrated in hundreds of experiments. Juries with authoritarian beliefs recommend harsher punishments after deliberating together. Corporate boards are more likely to support paying outlandish premiums for companies after group discussions. Citizens who start out with a clear belief on affirmative action and gay marriage develop more extreme views on these issues after talking with a few others who share their stance. Their preaching and prosecuting move in the direction of their politics. Polarization is reinforced by conformity: peripheral members fit in and gain status by following the lead of the most prototypical member of the group, who often holds the most intense views.

Grow up in a family of Red Sox fans and you’re bound to hear some unpleasant things about Yankees fans. Start making regular trips to a ballpark packed with people who share your loathing, and it’s only a matter of time before your contempt intensifies and calcifies. Once that happens, you’re motivated to see the best in your team and the worst in your opponent. Evidence shows that when teams try to downplay a rivalry by reminding fans that it’s just a game, it backfires. Fans feel their identity is being devalued and actually become more aggressive. My first idea for disrupting this pattern came from outer space.

HYPOTHESIS 1: NOT IN A LEAGUE OF THEIR OWN

If you ever leave the planet Earth, you’ll probably end up rethinking some of your feelings about other human beings. A team of psychologists has studied the effects of outer space on inner space, assessing the changes in more than a hundred astronauts and cosmonauts through interviews, surveys, and analyses of autobiographies. Upon returning from space, astronauts are less focused on individual achievements and personal happiness, and more concerned about the collective good. “You develop an instant global consciousness . . . an intense dissatisfaction with the state of the world, and a compulsion to do something about it,” Apollo 14 astronaut Edgar Mitchell reflected. “From out there on the moon, international politics looks so petty. You want to grab a politician by the scruff of the neck and drag him a quarter of a million miles out and say, ‘Look at that, you son of a b*tch.’”

This reaction is known as the overview effect. The astronaut who described it most vividly to me is space shuttle commander Jeff Ashby. He recalled that the first time he looked back at the Earth from outer space, it changed him forever:

On Earth, astronauts look to the stars—most of us are star fanatics—but in space, the stars look the same as they do on Earth. What is so different is the planet—the perspective that it gives you. My first glimpse of the Earth from space was about fifteen minutes into my first flight, when I looked up from my checklist and suddenly we were over the lit part of the Earth with our windows facing down. Below me was the continent of Africa, and it was moving by much as a city would move by from an airline seat. Circling the entire planet in ninety minutes, you see that thin blue arc of the atmosphere. Seeing how fragile the little layer is in which all of humankind exists, you can easily from space see the connection between someone on one side of the planet to someone on the other—and there are no borders evident. So it appears as just this one common layer that we all exist in.

When you get to see an overview of the Earth from outer space, you realize you share a common identity with all human beings. I wanted to create a version of the overview effect for baseball fans.

There’s some evidence that common identity can build bridges between rivals. In one experiment, psychologists randomly assigned Manchester United soccer fans a short writing task. They then staged an emergency in which a passing runner slipped and fell, screaming in pain as he held his ankle. He was wearing the T-shirt of their biggest rival, and the question was whether they would stop to help him. If the soccer fans had just written about why they loved their team, only 30 percent helped. If they had written about what they had in common with other soccer fans, 70 percent helped.

When Tim and I tried to get Red Sox and Yankees fans to reflect on their common identity as baseball fans, it didn’t work. They didn’t end up with more positive views of one another or a greater willingness to help one another outside emergency situations. Shared identity doesn’t stick in every circumstance. If a rival fan has just had an accident, thinking about a common identity might motivate us to help. If he’s not in danger or dire need, though, it’s too easy to dismiss him as just another jerk—or not our responsibility. “We both love baseball,” one Red Sox supporter commented. “The Yankees fans just like the wrong team.” Another stated that their shared love of baseball had no effect on his opinions: “The Yankees suck, and their fans are annoying.”

HYPOTHESIS 2: FEELING FOR OUR FOES

I next turned to the psychology of peace. Years ago the pioneering psychologist and Holocaust survivor Herb Kelman set out to challenge some of the stereotypes behind the Israel-Palestine conflict by teaching the two sides to understand and empathize with one another. He designed interactive problem-solving workshops in which influential Israeli and Palestinian leaders talked off the record about paths to peace. For years, they came together to share their own experiences and perspectives, address one another’s needs and fears, and explore novel solutions to the conflict. Over time, the workshops didn’t just shatter stereotypes—some of the participants ended up forming lifelong friendships.

Humanizing the other side should be much easier in sports, because the stakes are lower and the playing field is more level. I started with another of the biggest rivalries in sports: UNC-Duke. I asked Shane Battier, who led Duke to an NCAA basketball championship in 2001, what it would take for him to root for UNC. His immediate reply: “If they were playing the Taliban.” I had no idea so many people fantasized about crushing terrorists in their favorite sport. I wondered whether humanizing a Duke student would change UNC students’ stereotypes of the group.

In an experiment with my colleagues Alison Fragale and Karren Knowlton, we asked UNC students to help improve the job application of a peer. If we mentioned that he went to Duke rather than UNC, as long as he was facing significant financial need, participants spent extra time helping him. Once they felt empathy for his plight, they saw him as a unique individual deserving of assistance and liked him more. Yet when we measured their views of Duke students in general, the UNC students were just as likely to see them as their rivals, to say that it felt like a personal compliment if they heard someone criticize Duke, and to take it as a personal insult if they heard Duke praised. We had succeeded in changing their attitudes toward the student, but failed in changing their stereotypes of the group.

Something similar happened when Tim and I tried to humanize a Yankees fan. We had Red Sox fans read a story written by a baseball buff who had learned the game as a child with his grandfather and had fond memories of playing catch with his mom. At the very end of the piece he mentioned that he was a die-hard supporter of the Yankees. “I think this person is very authentic and is a rare Yankee fan,” one Red Sox supporter commented. “This person gets it and is not your typical Yankee fan,” a second observed. “Ugh, I really liked this text until I got to the part about them being a Yankees fan,” a third fan lamented, but “I think this particular person I would have more in common with than the typical, stereotypical Yankees fan. This person is okay.”