Time. We waste it, save it, kill it, make it. The world runs on it. Yet ask physicists what time actually is, and the answer might shock you: They have no idea. Even more surprising, the deep sense we have of time passing from present to past may be nothing more than an illusion. How can our understanding of something so familiar be so wrong?

Scientists want to know if methane gas on Mars is a product of biological processes or a result of geologic activity. To find out, NASA is sending a robotic rover called Curiosity to Mars. This video clip from NOVA's program Finding Life Beyond Earth explores the questions that drive the scientists and the implications of possible findings.

Take a spectacular trip to distant realms of our solar system to discover where secret forms of life may lie hidden. Combining the latest telescope images with dazzling animation, this program immerses audiences in the sights and sounds of alien worlds, while top astrobiologists explain how these places are changing how we think about the potential for life in our solar system.

Learn how to find signs of extraterrestrial life in our galaxy without leaving home.

Gripping personal stories from Japan offer lessons on how to act in the face of a life-threatening disaster. Airs September 28, 2011 on PBS.

Designing and building One World Trade Center and the National September 11 Memorial & Museum Premiering September 7, 2011 at 9pm on PBS

At PBS' recent Annual Meeting, physicist and acclaimed author Brian Greene discusses his return to NOVA with "The Fabric of the Cosmos," coming to PBS Wednesdays, November 2-23, 2011, at 9:00 p.m. ET. The four-part miniseries takes us to the frontiers of physics to see how scientists are piecing together the most complete picture yet of space, time, and the universe.

Are we finally on the brink of a clean energy revolution? Airs April 20, 2011 on PBS

See neuroscientist Oliver Sacks's brain respond differently to music by Bach & Beethoven.

See why an explosion three miles above Earth would act like a hot tornado on the surface.

Explore a new generation of ingenious materials, from clothes that monitor your mood to real-life invisibility cloaks. 8/28/2013

Vision as we know it remains elusive for machines. But as this video short shows, they are starting to get the picture.

Jeopardy! challenges even the best human minds. Can a computer win the game?

Can innovative materials help solve the energy crisis and lead to a sustainable future? David Pogue investigates.

Future technologies will depend on tiny stuff -- from new kinds of silicon chips to micro-robots that probe the human body. 8/21/2013

David Pogue tests his mettle against the world's strongest stuff, from steel and Kevlar to bioengineered silk. 8/21/2013

Technology reporter David Pogue hosts a 4-part special series exploring the materials that will shape our future. Wednesdays starting January 19, 2011

David Pogue visits DuPont to get a closer look at fireproof clothing.

"Absolute Zero" presents the epic story of humanity's struggle to master extreme cold. This NOVA special re-creates groundbreaking discoveries across four centuries that expanded our knowledge of low temperatures and led ultimately to today's cutting edge "cold technologies."

They've transformed our cities and our lives, but how safe are they?