“All my life, I have been fascinated by the big questions that face us, and have tried to find scientific answers to them. If, like me, you have looked at the stars, and tried to make sense of what you see, you too have started to wonder what makes the universe exist.  The questions are clear, and deceptively simple. But the answers have always seemed well beyond our reach. Until now.

“The ideas which had grown over two thousand years of observation have had to be radically revised.  In less than a hundred years, we have found a new way to think of ourselves.  From sitting at the center of the universe, we now find ourselves orbiting an average-sized sun, which is just one of millions of stars in our own Milky Way galaxy. And our galaxy itself is just one of billions of galaxies, in a universe that is infinite and expanding. But this is far from the end of a long history of inquiry.  Huge questions remain to be answered, before we can hope to have a complete picture of the universe we live in.

“I want you to share my excitement at the discoveries, past and present, which have revolutionized the way we think. From the Big Bang to black holes, from dark matter to a possible Big Crunch, our image of the universe today is full of strange sounding ideas, and remarkable truths. The story of how we arrived at this picture is the story of learning to understand what we see.” 

Strange Stuff Explained
What in the world (or in the universe) are quarks and quasars, nebulae and neutrinos? How can time be imaginary? Is a wormhole anything like an anthill? For definitions and descriptions of the tricky terminology of the universe, this is where the strange stuff becomes a little less so. 

Cosmological Stars
History will, no doubt, recognize many of today’s theorists and scientists for their astonishing collective and personal contributions to our future understanding of the universe. Here we recognize some—though certainly not all—of those whose ideas or discoveries have, over time, shaped human understanding of the stars and beyond. 

Universes
Hundreds of years ago, everyone believed that the Earth was at the center of the universe. Today we know better, but a complete picture of the universe remains elusive. From the ancient notion of a flat Earth to today’s theories on the very shape of past and future history, ideals of the universe have evolved with the help of scientific discovery and the eternal human imagination.

Unsolved Mysteries
Leading cosmologists address the questions even they have yet to answer. 

MARCELO GLEISER: Where Does Matter Come From?

MICHIO KAKU: Is Time Travel Possible?

CARLOS FRENK: Where Is the Missing Matter?

ALAN GUTH: An Eternity of Bubbles? 

SETH SHOSTAK: An Inhabited Universe? 

MICHIO KAKU:  Is There a Theory of Everything?

LEE SMOLIN: What Is the Future of Cosmology?

Things To Do In the Dark
Some Web sites present fascinating photographs from galaxies millions of light-years away, while others feature online discussions among today’s leading cosmologists. But where to look first? Our resources list describes and links to great spots on the Web, as well as books and magazines, for the cosmology enthusiast.

Teacher’s Guide
Our free downloadable Teacher’s Guide, in PDF format, is also available here.

About Stephen Hawking

Ask the Experts
Submit your own questions about the universe to prominent cosmologists.

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