With more than half of the world population living in cities, one thing is undeniable: we are an urban species. Part game, part urban planning sketching tool, "Cities: Skylines" encourages people to use their creativity and self-expression to rethink the cities of tomorrow. Designer Karoliina Korppoo takes us on a tour through some extraordinary places users have created, from futuristic fantasy cities to remarkably realistic landscapes. What does your dream city look like?

How can a super-thin 3-inch disk levitate something 70,000 times its own weight? In a riveting demonstration, Boaz Almog shows how a phenomenon known as quantum locking allows a superconductor disk to float over a magnetic rail -- completely frictionlessly and with zero energy loss. Experiment: Prof. Guy Deutscher, Mishael Azoulay, Boaz Almog, of the High Tc Superconductivity Group, School of Physics and Astronomy, Tel Aviv University.

David Lang is a maker who taught himself to become an amateur oceanographer -- or, he taught a robot to be one for him. In a charming talk Lang, a TED Fellow, shows how he and a network of ocean lovers teamed up to build open-sourced, low-cost underwater explorers.

By dissecting a cockroach ... yes, live on stage ... TED Fellow and neuroscientist Greg Gage shows how brains receive and deliver electric impulses -- and how legs can respond. This talk comes from the TED-Ed project.

What if we could use existing technologies to provide Internet access to the more than 4 billion people living in places where the infrastructure can't support it? Using off-the-shelf LEDs and solar cells, Harald Haas and his team have pioneered a new technology that transmits data using light, and it may just be the key to bridging the digital divide. Take a look at what the future of the Internet could look like.

The constant thud underneath your feet. The constrained space. The monotony of going nowhere fast. Running on a treadmill can certainly feel like torture, but did you know it was originally used for that very purpose? Conor Heffernan details the dark and twisted history of the treadmill. [Directed by Yukai Du, narrated by Addison Anderson, music by WORKPLAYWORK and Cem Misirlioglu].

Reuse of syringes, all too common in under-funded clinics, kills 1.3 million each year. Marc Koska clues us in to this devastating global problem with facts, photos and hidden-camera footage. He shares his solution: a low-cost syringe that can't be used twice.

Singer/guitarist Raúl Midón performs "All the Answers" in a world premiere at TED2007, followed by the sprightly "Tembererana."

Shereen El Feki shows how some Arab cultures are borrowing trademarks of Western pop culture -- music videos, comics, even Barbie -- and adding a culturally appropriate twist. The hybridized media shows how two civilizations, rather than dividing, can dovetail.

Ecologist Eric Berlow doesn't feel overwhelmed when faced with complex systems. He knows that more information can lead to a better, simpler solution. Illustrating the tips and tricks for breaking down big issues, he distills an overwhelming infographic on U.S. strategy in Afghanistan to a few elementary points.