The Universe On A String

In clear, nontechnical language, string theorist Brian Greene explains how our understanding of the universe has evolved from Einstein's notions of gravity and space-time to superstring theory, where minuscule strands of energy vibrating in 11 dimensions create every particle and force in the universe. (This mind-bending theory may soon be put to the test at the Large Hadron Collider in Geneva.)

A Call To Arms from Biologist Richard Dawkins

The session was titled "The Design of Life," and the TED audience was probably expecting remarks about evolution's role in our history from biologist Richard Dawkins. Instead, he launched into a full-on appeal for atheists to make public their beliefs and to aggressively fight the incursion of religion into politics and education (quoting Douglas Adams in the bargain). Scientists and intellectuals hold very different beliefs about God from the American public, he says, yet they are cowed by the overall political environment. Dawkins' scornful tone drew strongly mixed reactions from the audience; some stood and applauded his courage. Others wondered whether his strident approach could do more harm than good. Dawkins went on to publish The God Delusion and become perhaps the world's best-known atheist.

Earth's Final Century? - Part 2

In a taut soliloquy that takes us from the origins of the universe to the last days of a dying sun 6 billion years later, renowned cosmologist Sir Martin Rees explains why the 21st century is a pivotal moment in the history of humanity: the first time in history when we can materially change ourselves and our planet. Stunning imagery of cosmological wonders show us the universe as we know it now. Speaking as "a concerned member of the human race," Rees harkens to the wisdom of Einstein, calling for scientists to act as moral compasses, confronting the coming developments and ensuring our role in "the immense future."

Earth's Final Century? - Part 1

Professor Stephen Hawking asks some Big Questions about our universe -- How did the universe begin? How did life begin? Are we alone? -- and discusses how we might go about answering them.

Professor Hawking also sounds a dire warning: because of the exponential increases in world population and the consumption of Earth's finite natural resources, this century could be our last.