Philosopher Stephen Cave wants to know: Why is humanity so obsessed with living forever?

Stephen Petranek untangles emerging technologies to predict which will become fixtures of our future lives -- and which could potentially save them.

Stephen Ritz teaches at-risk kids in the South Bronx.

Stephen Coleman studies applied ethics, particularly the ethics of military and police force, and their application to human rights.

Stephen Wolfram is the creator of Mathematica and Wolfram|Alpha, the author of A New Kind of Science, and the founder and CEO of Wolfram Research.

In his influential poetry criticism, Stephen Burt links the contemporary with the classical, pinpoints new poetry movements, and promotes outstanding little-known poets.

Stephen Lawler and the Virtual Earth team have created an addictively interactive 3D world that is poised to reinvent our view of advertising, gaming, weather/traffic reporting, instant messaging and more.

Stephen DeBerry uses the economy and culture to build a more just and joyful society.

Stephen Webb is a science fiction fan who's passionately interested in what the future might hold for our species.

Stephen Palumbi studies the way humanity and ocean life interact and intertwine. His insights into our codependence offer ideas for protecting both the ocean and ourselves.

Inspired by open-source software models, Sage Bionetworks co-founder Stephen Friend builds tools that facilitate research sharing on a massive and revolutionary scale.

Stephen Hawking's scientific investigations shed light on the origins of the cosmos, the nature of time and the ultimate fate of the universe. His bestselling books for a general audience have given an appreciation of physics to millions.

By blending up to 100 still photographs into a seamless composite that captures the transition from day to night, Stephen Wilkes reveals the stories hidden in familiar locations.

Steven Levitt's eye-opening Freakonomics took economic theory into the real world of suburban parenting and urban drug gangs, turning conventional wisdom upside-down.

Steven Addis is a father and photography buff who, by day, harnesses the power of branding for social change.

Michael Stevens is the creator and host of Vsauce, an educational YouTube channel that addresses scientific oddities, like "Is Your Red the Same as My Red?"

Bryan Stevenson is the founder and executive director of the Equal Justice Initiative, fighting poverty and challenging racial discrimination in the criminal justice system.

Steven Cowley directs the UK's leading fusion research center. Soon he'll helm new experiments that may make cheap fusion energy real on a commercial scale.

When MIT-trained mechanical engineer Jamie Heywood discovered that his younger brother was diagnosed with the terminal illness ALS, he focused all his energy on founding revolutionary healthcare initiatives to help his brother and others like him.

A doctor by training, Stefan Larsson of BCG researches how transparency of medical outcomes and costs could radically transform the healthcare industry.

By challenging long-held legal notions of “personhood”, Steven Wise seeks to grant cognitively advanced animals access to a full spectrum of fundamental rights.

Stefana Broadbent watches us while we communicate, work and go about our daily lives. She is one of a new class of ethnographers who study the way our social habits and relationships function and mutate in the digital age.

Stefon Harris plays the vibraphone -- and leads a jazz ensemble with a collaborative sound built on collective inspiration.

Leonard Susskind works on string theory, quantum field theory, quantum statistical mechanics and quantum cosmology at Stanford.

John Bohannon is a scientist and writer who runs the annual Dance Your Ph.D. contest.

John Lloyd helps make some of the cleverest television in the UK.

Renowned for album covers, posters and his recent book of life lessons, designer Stefan Sagmeister invariably has a slightly different way of looking at things.

Alex Steffen explores our planet's future, telling powerful, inspiring stories about the hard choices facing humanity ... and our opportunity to create a much better tomorrow.

In his work in applied mathematics, Steven Strogatz studies the way math and biology intersect.

Stefano Mancuso is a founder of the study of plant neurobiology, which explores signaling and communication at all levels of biological organization, from genetics to molecules, cells and ecological communities.