The universe is incredibly old, astoundingly vast and populated by trillions of planets -- so where are all the aliens? Astronomer Stephen Webb has an explanation: we're alone in the universe. In a mind-expanding talk, he spells out the remarkable barriers a planet would need to clear in order to host an extraterrestrial civilization -- and makes a case for the beauty of our potential cosmic loneliness. "The silence of the universe is shouting, 'We're the creatures who got lucky,'" Webb says.

Where are all the aliens? | Stephen Webb

Some of the world's greatest scientists, doctors and medical researchers share their discoveries and visions onstage at the TED conference, TEDx events and partner events around the world. You can also download these and many other videos free on TED.com, with an interactive English transcript and subtitles in up to 80 languages. TED is a nonprofit devoted to Ideas Worth Spreading.

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Medicine

Could the next wonder drug be somewhere in Canada's snowy north? Take a trip to this beautiful, frigid landscape as chemist Normand Voyer explores the mysterious molecular treasures found in plants thriving in the cold. These scarcely investigated organisms could hold immense medical promise, he says – so long as we work quickly enough to discover them.

Are life-saving medicines hiding in the world's coldest places? | Normand Voyer

As Arctic ice melts, polar bears are being forced on land -- and they're hungry. With the apex predators frequently turning to human junkyards for a snack, northern towns have had to get creative in order to keep both their people and wildlife safe. Biologist and conservationist Alysa McCall shares lessons from the field on how to safely navigate contact with these magnificent animals and plan for a future where climate change forces us all a little closer.

What to do when there's a polar bear in your backyard | Alysa McCall

Meet the fantastically colorful and astonishingly adaptable sea slugs that found a way to photosynthesize (or create energy from sunlight) like plants. Diving deep into these often overlooked creatures, invertebrate zoologist Michael Middlebrooks introduces the solar-powered slugs that lost their shells -- but gained the ability to directly harness the power of the sun.

The fantastically weird world of photosynthetic sea slugs | Michael Middlebrooks

Our memories and bodies give us clues about who we are, but what happens when this guidance shifts? In this mind-bending talk, science writer Anil Ananthaswamy shares how the experiences of "altered selves" -- resulting from schizophrenia, Alzheimer's, foreign limb syndrome or other conditions -- shed light on the constructed nature of identity. He breaks down where our sense of self comes from and invites us to challenge our assumptions about who we are, with the aim of building a better you and a better world.

Where does your sense of self come from? A scientific look | Anil Ananthaswamy

Farming is the worst thing humanity has ever done to the planet, says journalist George Monbiot. What's more: the global food system could be heading toward collapse. Detailing the technological solutions we need to radically reshape food production -- from lab-grown, protein-rich foods to crops that don't require plowing -- Monbiot shares a future-focused vision of how humanity could feed itself without destroying the planet.

Where are all the aliens? | Stephen Webb

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