Our culture is obsessed with happiness, but what if there's a more fulfilling path? Happiness comes and goes, says writer Emily Esfahani Smith, but having meaning in life -- serving something beyond yourself and developing the best within you -- gives you something to hold onto. Learn more about the difference between being happy and having meaning as Esfahani Smith offers four pillars of a meaningful life.

Underneath every shiny new megacity, there's often a story of communities displaced. In this moving, poetic talk, OluTimehin Adegbeye details how government land grabs are destroying the lives of thousands who live in the coastal communities of Lagos, Nigeria, to make way for a "new Dubai." She compels us to hold our governments and ourselves accountable for keeping our cities safe for everyone. "The only cities worth building, indeed the only futures worth dreaming of, are those that include all of us, no matter who we are or how we make homes for ourselves," she says.

In a mind-bending talk that blurs the line between science and art, Tomás Saraceno exhibits a series of air-inspired sculptures and installations designed to usher in a new era of sustainability, the "Aerocene." From giant, cloud-like playgrounds suspended 22 meters in the air to a balloon sculpture that travels the world without burning a single drop of fossil fuel, Saraceno's work invites us to explore the bounds of our fragile human and terrestrial ecosystems. (In Spanish with English subtitles.)

Terrorists and extremists aren't all naturally violent sociopaths -- they're deliberately recruited and radicalized in a process that doesn't fit into a neat pattern. Erin Marie Saltman discusses the push and pull factors that cause people to join extremist groups and explains innovative ways of preventing and countering radicalization.