A Yale University professor is teaching students around the world how science can help them lead a happier life. Laurie Santos started the class "Psychology and the Good Life" back in January. Nearly one-quarter of Yale's undergraduates enrolled, making it the most popular course in the school's more than 300-year history. Now, over 138,000 people around the world have registered for the class online.

Santos appeared "CBS This Morning" Thursday to talk about the class and what exactly people can do to lead a happier life. The first step, she says, is realizing you don't need all the things you think will make you happy.

"In the class, I talk to students about how our minds lie to us," Santos said. "They tell us if I want to be happy, I need to change my circumstances, I need a new job, or a better salary or I need to move. Really you just have to change your mindset. Your circumstances are fine. It's kind of how you react to them."

Santos said the best way to change your mindset is to "rewire the way you think about things."

"Re-wire the way you behave," she said. "One simple one is just to make more social connections with other people. What the research suggests is that very happy people spend lots of time with people. The people they like, they're loved ones, but also they just talk to the barista."

And those social connections shouldn't only be on your phone.

"We're scrolling through our Instagram feed and we feel like that's social, but it's not," Santos said. "We just need one-on-one live conversation with a human."

How you unwind and spend "me-time" makes a difference too.

"If I'm having a bad day, I'm going to treat myself," Santos said. "I'm going out for a manicure, me, me, me. But it turns out that helping others actually bumps up our happiness more than we think."

Instead of regular homework, students in Santos' class see requirements on their syllabus to experience gratitude and talk to someone. Santos also implores people not to dwell on negatives, as difficult as that may be.

"This is really hard for me," Santos said. "When I go out for a glass of wine with my girlfriend, I don't want to talk about the wonderful things. I want to complain. But it turns out that that's just another spot where the mind is lying to us. It's just wrong."

At the beginning of Santos' course, she has her students take an "authentic happiness inventory" to see how happy they really are. You can take that test here.

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